Yashwantrao Chavan
Maharashtra Open University
Digital Art
B. Sc. in Media Graphics and Animation
BMG 103: Color Theory
YASHWANTRAO
CHAVAN
MAHARASHTRA
OPEN
UNIVERSITY
T97:B.Sc. in Media Graphics and Animation [B.Sc. (MGA)]
2010 Pattern: Course code: BMG103
COLOUR THEORY
YASHWANTRAO CHAVAN MAHARASHTRA OPEN UNIVERSITY
Dnyangangotri, Near Gangapur Dam, Nashik 422 222, Maharshtra
YASHWANTRAO CHAVAN MAHARASHTRA OPEN UNIVERSITY
Vice-Chancellor : Prof. (Dr.) E. Vayunandan
School of Continuing Education School Council
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School of Continuing Education
School of Agriculture Science
YCMOU, Nashik
YCMOU, Nashik
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Professor
Assistant Professor
School of Continuing Education
School of Computer Science
YCMOU, Nashik
YCMOU, Nashik
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Dr Latika Ajbani
Assistant Professor
Assistant Professor
School of Continuing Education
School of Commerce & Mgt
YCMOU, Nashik
YCMOU, Nashik
Shri Ram Thakar
Dr Sunanda More
Assistant Professor
Assistant Professor
School of Continuing Education
School of Science & Tech.
YCMOU, Nashik
YCMOU, Nashik
Smt Jyoti Shetty.
Principal
S.P. More College, Panwel
Dr Abhay Patil
Assistant Professor
School of Health Science
YCMOU, Nashik
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Associate Professor
FTII Pune
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Dy District Voc Education &
Training Officer,
DVET, Nashik
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Wow Fafctors Ind Pvt Ltd, Delhi
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School of Continuing Education
Effect Design and Arts
Effect Design and Arts
Pune
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Y.C.M.O. U.
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Manager, Print Production Centre, YCMOU, Nashik
© 2017, Yashwantrao Chavan Maharashtra Open Univesity, Nashik
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First Publication
Publication No.
Typesetting
Printer
Published by
: June 2017
:
:
:
: Dr. Dinesh Bhonde, Registrar, Y. C. M. Open University, Nashik - 422 222.
B-16-17-93 (BTH331)
BMG 103: Colour Theory
Credit 1
UNIT 1 COLOUR THEORY: OVERVIEW
Credit 2
UNIT 2 COLOUR BASICS
Credit 3
UNIT 3 COLOUR HARMONY
UNIT 4 COLOUR MEANINGS
Credit 4
UNIT 5 COLOUR MODEL
UNIT 6 PSYCHOLOGY OF COLOUR
Contents
UNIT 1: COLOUR THEORY: OVERVIEW
8
1.0 INTRODUCTION
8
1.1 UNIT OBJECTIVES
9
1.2 COLOUR BALANCE AND CHROMATIC COLOURS
9
1.3 COLOUR SCHEME
10
1.4 TRADITIONAL COLOUR THEORY
13
1.4.1 Warm and cool colours
14
1.4.2 Achromatic colors
14
1.4.3 Complementary colors
15
1.4.4 Tints and shades
15
1.4.5 Split Primary Colours
16
1.5 Historical background
17
1.6 COLOUR HARMONY AND COLOUR MEANINGS
19
1.7 EMOTIONAL RESPONSE TO COLOURS
21
1.8 PHYSIOLOGICAL PRINCIPLE FOR EFFECTIVE USE OF COLOUR
24
1.8.1 Mechanism of dichromatic color vision
25
1.8.2 Human Visual System
26
1.8.3 Phototransduction
27
1.8.5 Difference between Rods and Cones
27
1.8.6 Function
28
1.8.7 Signaling
29
1.8.8 Ganglion cell
29
1.9 Lens
1.9.1 Position, size, and shape
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31
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1.9.2 Lens Structure and Function
31
1.9.3 Accommodation: changing the power of the lens
32
1.9.4 Crystallins and Transparency
32
1.10 Retina
33
1.11 Human Brain
36
1.12 Effective use of colours
37
1.14 SUMMARY
38
1.15 END QUESTIONS
39
UNIT 2: COLOUR BASICS
41
2.0 INTRODUCTION
41
2.1 UNIT OBJECTIVES
41
2.2 COLOUR SYSTEMS
41
2.3 WORKING WITH COLOUR SYSTEMS
45
2.3.1 Subtractive colour scheme
45
2.3.2 Additive colour scheme
46
2.3.3 Working with systems
47
2.4 COLOUR WHEEL
47
2.4.1 COLOR RELATIONSHIPS
48
2.4.2 Color wheels and paint color mixing
48
2.4.3 Color wheel software
49
2.4.4 Colour Scheme
49
2.5 COLOUR RELATIONSHIP
52
2.5.1 Complementary Colours
53
2.5.2 Perceptual Opposites
56
2.5.3 Color Combinations
56
2.6 COLOUR CONTRAST
BMG 103: Color Theory
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2.7 ITTEN'S COLOUR CONTRAST
59
2.8 PROPORTION AND INTENSITY
62
2.9 CONTRAST AND DOMINANCE
64
2.10 COLOUR SHADES AND TINTS
66
2.11 COLOUR STUDIES OF COMPLEMENTARY RELATIONSHIPS
67
2.12 SUMMARY
72
2.13 KEY TERMS
72
2.14 END QUESTIONS
73
UNIT 3: COLOUR HARMONY
74
3.0 INTRODUCTION
74
3.1 UNIT OBJECTIVES
74
3.2 SOME FORMULAS FOR COLOUR HARMONY
74
3.2.2 Colour Scheme Based on Analogous Colours
74
3.2.3 Colour scheme based on complementary colour
75
3.2.4 Colour Scheme Based on Nature
75
3.3 COLOUR CONTEXT
3.4 Different readings of the same colour
3.5 classic colour schemes
76
76
77
3.5.1 Monochromatic colors
77
3.5.2 Complementary colors
78
3.5.3 Split-Complementary
78
3.5.4 Triadic colors
78
3.5.5 Tetradic colors
79
Rectangle
79
Square
79
3.6 summary
BMG 103: Color Theory
79
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3.7 KEY TERMS
80
3.8 END QUESTIONS
80
UNIT 4: COLOUR MEANINGS
81
4.0 INTRODUCTION
81
4.1 UNIT OBJECTIVES
81
4.2 colour meanings and colours that go together
81
4.3 cool colours
86
4.4 warm colours the colours of excitement
86
4.5 mixed warm and cool colour scheme
87
4.6 neutral colours
87
4.7 more about colours
88
4.8 summary
92
4.9 KEY TERMS
93
4.10 END QUESTIONS
93
UNIT 5 COLOUR MODEL
94
5.0 INTRODUCTION
94
5.1 UNIT OBJECTIVES
94
5.2 OVERVIEW OF COLOUR MODEL
94
5.2.1 Tristimulus color space
94
5.2.2 CIE XYZ color space
95
5.2.3 RGB color model
97
5.2.4 HSV and HSL representations
97
5.2.5 CMYK color model
99
5.2.6 Color systems
100
5.2.7 Other uses of "color model"
101
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5.2.7 Vertebrate evolution of color vision
5.3 LIGHT
101
101
5.3.1 Electromagnetic spectrum and visible light
102
5.3.2 Speed of light
103
5.3.3 Light sources
104
5.3.4 Units and measures
105
5.3.5 Historical theories about light, in chronological order
106
5.4 CIE CHROMATICITY DIAGRAM(CIE 1931 color space)
112
5.4.1 Tristimulus values
113
5.4.2 Meaning of X, Y and Z
114
5.4.3 CIE standard observer
115
5.4.4 Computing XYZ From Spectral Data
116
5.4.5 CIE xy chromaticity diagram and the CIE xyY color space
116
5.4.6 Definition of the CIE XYZ color space
119
5.5 RGB color model
125
5.6 CMYK Model
133
5.6.1 Halftoning
135
5.6.2 Benefits of using black ink
136
5.6.3 Other printer color models
139
5.6.5 Conversion
140
5.7 Hue
142
5.7.1 Computing hue
142
5.7.2 Hue vs. dominant wavelength
144
5.7.3 Hue difference:
145
5.7.4 Names and other notations for hues
145
5.8 Saturation
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5.9 Value Color Model
147
5.10 Intuitive Color Concept
156
5.11 SUMMARY
159
5.12 KEY TERMS
160
5.13 END QUESTIONS
161
5.14 REFERENCES
162
UNIT 6 PSYCHOLOGY OF COLOUR
163
6.0 INTRODUCTION
163
6.1 UNIT OBJECTIVES
163
6.2 COLOUR PSYCHOLOGY: AN OVERVIEW
163
6.2.1 Influence of color on perception
164
6.2.2 Color preference and associations between color and mood
164
6.2.3 General model
165
6.2.4 Specific color meaning
167
6.2.5 Individual differences
170
6.2.6 Color and sports performance
172
6.2.7 Color and time perception
173
6.3 UTILIZING PSYCHOLOGICAL EFFECTS IN PAINTING
174
6.4 HOW TO JUDGE YOUR COLOUR SELECTION
182
6.5 CHARACTERISTIC COLOUR COMBINATIONS
182
6.6 COLOURS IN PHOTOGRAPHY VERSUS COLOURS IN PAINTING
183
6.7 COLOURS IN PAINTING VERSUS COLOURS IN A ROOM
184
6.8 SUMMARY
185
6.9 KEY TERMS
185
6.10 END QUESTIONS
186
6.11 REFERENCES
186
BMG 103: Color Theory
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BMG 103: Color Theory
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UNIT 1: COLOUR THEORY: OVERVIEW
1.0 INTRODUCTION
The foundations of pre-20th-century color theory were built around "pure" or ideal colors,
characterized by sensory experiences rather than attributes of the physical world. This has led to a
number of inaccuracies in traditional color theory principles that are not always remedied in modern
formulations.
The most important problem has been a confusion between the behavior of light mixtures, called
additive color, and the behavior of paint, ink, dye, or pigment mixtures, called subtractive color. This
problem arises because the absorption of light by material substances follows different rules from the
perception of light by the eye.
A second problem has been the failure to describe the very important effects of strong luminance
(lightness) contrasts in the appearance of colors reflected from a surface (such as paints or inks) as
opposed to colors of light; "colors" such as browns or ochres cannot appear in mixtures of light. Thus,
a strong lightness contrast between a mid-valued yellow paint and a surrounding bright white makes
the yellow appear to be green or brown, while a strong brightness contrast between a rainbow and the
surrounding sky makes the yellow in a rainbow appear to be a fainter yellow, or white.
A third problem has been the tendency to describe color effects holistically or categorically, for
example as a contrast between "yellow" and "blue" conceived as generic colors, when most color
effects are due to contrasts on three relative attributes that define all colors:
lightness (light vs. dark, or white vs. black),
saturation (intense vs. dull), and
hue (e.g. red, orange, yellow, green, blue or purple).
Thus, the visual impact of "yellow" vs. "blue" hues in visual design depends on the relative
lightness and saturation of the hues.
These confusions are partly historical, and arose in scientific uncertainty about color perception
that was not resolved until the late 19th century, when the artistic notions were already entrenched.
However, they also arise from the attempt to describe the highly contextual and flexible behavior of
color perception in terms of abstract color sensations that can be generated equivalently by any
visual media. Many historical "color theorists" have assumed that three "pure" primary colors can mix
all possible colors, and that any failure of specific paints or inks to match this ideal performance is
due to the impurity or imperfection of the colorants. In reality, only imaginary "primary colors" used
in colorimetry can "mix" or quantify all visible (perceptually possible) colors; but to do this, these
imaginary primaries are defined as lying outside the range of visible colors; i.e., they cannot be seen.
Any three real "primary" colors of light, paint or ink can mix only a limited range of colors, called a
BMG 103: Color Theory
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gamut, which is always smaller (contains fewer colors) than the full range of colors humans can
perceive.
Understanding of color theory is extremely important for you as a student and as a professional in
media, graphics and animation. Which color to choose for a graphic, animation or photograph is of
crucial importance. You will decide on the basis of the demand of the project, which color schemes to
chose. The topics covered under this course will help you understand various concepts covered in all
other courses like photoshop, illustrator, 3Ds max or Maya animation courses which you will study as
part of your study in BSc(MGA).
1.1 UNIT OBJECTIVES
After going through this unit, you will be able to:
•
•
•
•
Elaborate colour balance and chromatic colours
Explain the different colour schemes
Explain the traditional colour theory
Explain the effects of colours on retina, lens and brain
1.2 COLOUR BALANCE AND CHROMATIC COLOURS
In photography and image processing, color balance is the global adjustment of the
intensities of the colors (typically red, green, and blue primary colors). An important goal of
this adjustment is to render specific colors – particularly neutral colors – correctly. Hence, the
general method is sometimes called gray balance, neutral balance, or white balance. Color
balance changes the overall mixture of colors in an image and is used for color correction.
Generalized versions of color balance are used to correct colors other than neutrals or to
deliberately change them for effect.
Image data acquired by sensors – either film or electronic image sensors – must be
transformed from the acquired values to new values that are appropriate for color
reproduction or display. Several aspects of the acquisition and display process make such
color correction essential – including the fact that the acquisition sensors do not match the
sensors in the human eye, that the properties of the display medium must be accounted for,
and that the ambient viewing conditions of the acquisition differ from the display viewing
conditions. The color balance operations in popular image editing applications usually
operate directly on the red, green, and blue channel pixel values, without respect to any color
sensing or reproduction model. In film photography, color balance is typically achieved by
using color correction filters over the lights or on the camera lens.
Color balancing an image affects not only the neutrals, but other colors as well. An image
that is not color balanced is said to have a color cast, as everything in the image appears to
BMG 103: Color Theory
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have been shifted towards one color. Color balancing may be thought in terms of removing
this color cast.
Color balance is also related to color constancy. Algorithms and techniques used to attain
color constancy are frequently used for color balancing, as well. Color constancy is, in turn,
related to chromatic adaptation. Conceptually, color balancing consists of two steps: first,
determining the illuminant under which an image was captured; and second, scaling the
components (e.g., R, G, and B) of the image or otherwise transforming the components so
they conform to the viewing illuminant.
Viggiano found that white balancing in the camera's native RGB color model tended to
produce less color inconstancy (i.e., less distortion of the colors) than in monitor RGB for
over 4000 hypothetical sets of camera sensitivities. This difference typically amounted to a
factor of more than two in favor of camera RGB. This means that it is advantageous to get
color balance right at the time an image is captured, rather than edit later on a monitor. If one
must color balance later, balancing the raw image data will tend to produce less distortion of
chromatic colors than balancing in monitor RGB.
CHECK YOUR PROGRESS
Explain the concept of Color Balancing.
Elaborate the importance of Color Balancing.
1.3 COLOUR SCHEME
In color theory, a color scheme is the choice of colors used in design for a range of
media. For example, the "Achromatic" use of a white background with black text is an
example of a basic and commonly default color scheme in web design.
Color schemes are used to create style and appeal. Colors that create an aesthetic feeling
when used together will commonly accompany each other in color schemes. A basic color
scheme will use two colors that look appealing together. More advanced color schemes
involve several related colors in "Analogous" combination, for example, text with such colors
as red, yellow, and orange arranged together on a black background in a magazine article.
The addition of light blue creates an "Accented Analogous" color scheme.
Color schemes can contain different "Monochromatic" shades of a single color; for
example, a color scheme that mixes different shades of green, ranging from very light
(white), to very neutral (gray), to very dark (black). Use of the phrase color scheme may also
BMG 103: Color Theory
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and commonly does refer to choice and use of colors used outside typical aesthetic media and
context, although may still be used for purely aesthetic effect as well as for purely practical
reasons. This most typically refers to color patterns and designs as seen on vehicles,
particularly those used in the military when concerning color patterns and designs used for
identification of friend or foe, identification of specific military units, or as camouflage.
A color scheme in marketing is referred to as a trade dress and can be sometimes be
copyrighted, as is the pink color of Owens-Corning fiberglass.
Monochromatic colors are all the colors (tints, tones, and shades) of a single hue.
Monochromatic color schemes are derived from a single base hue, and extended using its
shades, tones and tints (that is, a hue modified by the addition of black, gray (black + white)
and white. As a result, the energy is more subtle and peaceful due to a lack of contrast of hue.
Complementary color scheme Colors that are opposite each other on the color wheel are
considered to be complementary colors (example: red and green). The high contrast of
complementary colors creates a vibrant look especially when used at full saturation. This
color scheme must be managed well so it is not jarring. Complementary color schemes are
tricky to use in large doses, but work well when you want something to stand out.
Complementary colors are really bad for text.
Analogous color scheme Analogous color schemes use colors that are next to each other
on the color wheel. They usually match well and create serene and comfortable designs.
Analogous color schemes are often found in nature and are harmonious and pleasing to the
eye. Make sure you have enough contrast when choosing an analogous color scheme. Choose
one color to dominate, a second to support. The third color is used (along with black, white or
gray) as an accent.
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Triadic color scheme A triadic color scheme uses colors that are evenly spaced around
the color wheel. Triadic color schemes tend to be quite vibrant, even if you use pale or
unsaturated versions of your hues. To use a triadic harmony successfully, the colors should
be carefully balanced - let one color dominate and use the two others for accent.
Split-Complementary color scheme The split-complementary color scheme is a
variation of the complementary color scheme. In addition to the base color, it uses the two
colors adjacent to its complement. This color scheme has the same strong visual contrast as
the complementary color scheme, but has less tension. The split-complimentary color scheme
is often a good choice for beginners, because it is difficult to mess up.
Rectangle (tetradic) color scheme The rectangle or tetradic color scheme uses four
colors arranged into two complementary pairs. This rich color scheme offers plenty of
possibilities for variation. Tetradic color schemes works best if you let one color be
dominant. You should also pay attention to the balance between warm and cool colors in
your design.
The following are some examples of media where colour schemes are used :
Graphic design
Product packaging
Logo designing
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Advertising
Graphical user interface
Window managers such as GNOME, KDE and Blackbox
Irix 4dwm's GUI uses more colour schemes, where information is stored in files named
base colour palette
The world wide web
Cascading style sheet allow easily-editable colour scheme that may be applied to HTML
webpage
Publishing- The utilization of a range of colours in text and imagery of a magazine tends
not to adapt to a special set of colours all around the magazine
Interior designing
Video games
Art
CHECK YOUR PROGRESS
Explain the concept of Color Scheme.
Elaborate the importance of Color Scheme.
Explain the idea of Complementary color scheme.
Explain the idea of Complementary color scheme.
Explain the idea of Analogous color scheme.
Explain the idea of Triadic color scheme.
Explain the idea of Split-Complementary color scheme.
Explain the idea of Rectangle (tetradic) color scheme.
List the various areas where designers give importance to color schemes.
1.4 TRADITIONAL COLOUR THEORY
For the mixing of colored light, Isaac Newton's color wheel is often used to describe
complementary colors, which are colors which cancel each other's hue to produce an
achromatic (white, gray or black) light mixture. Newton offered as a conjecture that colors
exactly opposite one another on the hue circle cancel out each other's hue; this concept was
demonstrated more thoroughly in the 19th century.
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A key assumption in Newton's hue circle was that the "fiery" or maximum saturated hues
are located on the outer circumference of the circle, while achromatic white is at the center.
Then the saturation of the mixture of two sp
spectral
ectral hues was predicted by the straight line
between them; the mixture of three colors was predicted by the "center of gravity" or centroid
of three triangle points, and so on. Primary, secondary, and tertiary colors of the RYB color
model
According to traditional
raditional color theory based on subtractive primary colors and the RYB
color model, which is derived from paint mixtures, yellow mixed with violet, orange mixed
with blue, or red mixed with green produces an equivalent gray and are the painter's
complementary
tary colors. These contrasts form the basis of Chevreul's law of color contrast:
colors that appear together will be altered as if mixed with the complementary color of the
other color. Thus, a piece of yellow fabric placed on a blue background will appear tinted
orange, because orange is the complementary color to blue.
1.4.1 Warm and cool colours
The distinction between "warm" and "cool" colors has been important since at least the
late 18th century. The contrast, as traced by etymologies in the Oxford English
English Dictionary,
seems related to the observed contrast in landscape light, between the "warm" colors
associated with daylight or sunset, and the "cool" colors associated with a gray or overcast
day. Warm colors are often said to be hues from red through yellow, browns and tans
included; cool colors are often said to be the hues from blue green through blue violet, most
grays included. There is historical disagreement about the colors that anchor the polarity, but
19th-century
century sources put the peak contras
contrastt between red orange and greenish blue.
Color theory has described perceptual and psychological effects to this contrast. Warm
colors are said to advance or appear more active in a painting, while cool colors tend to
recede; used in interior design or fa
fashion,
shion, warm colors are said to arouse or stimulate the
viewer, while cool colors calm and relax. Most of these effects, to the extent they are real,
can be attributed to the higher saturation and lighter value of warm pigments in contrast to
cool pigments. Thus, brown is a dark, unsaturated warm color that few people think of as
visually active or psychologically arousing. Contrast the traditional warm
warm–cool
cool association of
color with the color temperature of a theoretical radiating black body, where the asso
association
of color with temperature is reversed. For instance, the hottest stars radiate blue light (i.e.,
with shorter wavelength and higher frequency), and the coolest radiate red.
1.4.2 Achromatic colors
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Any color that lacks strong chromatic content is said to be unsaturated, achromatic, near
neutral, or neutral. Near neutrals include browns, tans, pastels and darker colors. Near
neutrals can be of any hue or lightness. Pure achromatic, or neutral colors include black,
white and all grays. Near neutrals are obtained by mixing pure colors with white, black or
grey, or by mixing two complementary colors. In color theory, neutral colors are easily
modified by adjacent more saturated colors and they appear to take on the hue
complementary to the saturated color; e.g.: next to a bright red couch, a gray wall will appear
distinctly greenish. Black and white have long been known to combine "well" with almost
any other colors; black decreases the apparent saturation or brightness of colors paired with
it, and white shows off all hues to equal effect.
1.4.3 Complementary colors
when complementary colors are chosen based on definition by light mixture, they are not
the same as the artists' primary colors. This discrepancy becomes important when color
theory is applied across media. Digital color management uses a hue circle defined according
to additive primary colors (the RGB color model), as the colors in a computer monitor are
additive mixtures of light, not subtractive mixtures of paints.
One reason the artist's primary colors work at all is that the imperfect pigments being
used have sloped absorption curves, and thus change color with concentration. A pigment
that is pure red at high concentrations can behave more like magenta at low concentrations.
This allows it to make purples that would otherwise be impossible. Likewise, a blue that is
ultramarine at high concentrations appears cyan at low concentrations, allowing it to be used
to mix green. Chromium red pigments can appear orange, and then yellow, as the
concentration is reduced. It is even possible to mix very low concentrations of the blue
mentioned and the chromium red to get a greenish color. This works much better with oil
colors than it does with watercolors and dyes.
1.4.4 Tints and shades
Mixing colored light (additive color models), the achromatic mixture of spectrally
balanced red, green and blue (RGB) is always white, not gray or black. When we mix
colorants, such as the pigments in paint mixtures, a color is produced which is always darker
and lower in chroma, or saturation, than the parent colors. This moves the mixed color
toward a neutral color—a gray or near-black. Lights are made brighter or dimmer by
adjusting their brightness, or energy level; in painting, lightness is adjusted through mixture
with white, black or a color's complement.
It is common among some painters to darken a paint color by adding black paint—
producing colors called shades—or lighten a color by adding white—producing colors called
tints. However it is not always the best way for representational painting, as an unfortunate
result is for colors to also shift in hue. For instance, darkening a color by adding black can
BMG 103: Color Theory
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cause colors such as yellows, reds and oranges, to shift toward the greenish or bluish part of
the spectrum. Lightening a color by adding white can cause a shift towards blue when mixed
with reds and oranges. Another practice when darkening a color is to use its opposite, or
complementary, color (e.g. purplish-red added to yellowish-green) in order to neutralize it
without a shift in hue, and darken it if the additive color is darker than the parent color. When
lightening a color this hue shift can be corrected with the addition of a small amount of an
adjacent color to bring the hue of the mixture back in line with the parent color (e.g. adding a
small amount of orange to a mixture of red and white will correct the tendency of this
mixture to shift slightly towards the blue end of the spectrum).
1.4.5 Split Primary Colours
If you learn the split-primary color-mixing system, you'll never make mud again, unless
you intend to! It's really quite simple. You use just six colors, including two of each primary
hue. The trick is in choosing the right colors and then combining them correctly to get the
optimum result. The illustration shows you a bright, high-intensity color wheel mixed with
split primaries. Here's how it works:
Make a circle with a three-legged figure in the center, like a clock with three hands. At
the top of the circle (12 o'clock) to the right of the line, place Winsor Lemon or Cadmium
Lemon (or another color that looks similarly cool and lemony, but not Lemon Yellow Nickel
Titanate. Place New Gamboge, Cadmium Yellow or Indian Yellow to the left of the line.
Next, going clockwise around the circle to four o'clock, place Winsor Blue (Green Shade or
Red Shade) or Phthalo Blue above the line and French Ultramarine below the line.
Continuing clockwise to eight o'clock, place Alizarin Crimson or Permanent Rose below the
line and Winsor Red, Permanent Red, Scarlet Lake or Cadmium Red above the line.
CHECK YOUR PROGRESS
Explain the concept of traditional color theory.
Elaborate the importance of warm and cool colors.
Discuss the idea of warm and cool colors.
Explain the concepts of Achromatic colors.
Elaborate the concepts of Tints and shades.
Descibe the idea of Split Primary Colors.
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1.5 HISTORICAL BACKGROUND
Issac Newton (1642 - 1727) : A pioneer in the field of colour, Isaac Newton in 1672,
published his first, controversial paper on colour, and forty years later, his work 'Opticks'.
Newton passed a beam of sunlight through a prism. When the light came out of the prism
is was not white but was of seven different colours: Red, Orange, Yellow, Green, Blue,
Indigo and Violet. The spreading into rays was called dispersion by Newton and he called the
different coloured rays the spectrum.
He learnt that when the light rays were passed again through a prism the rays turned back
into white light. If only one ray was passed through the prism it would come out the same
colour as it went in. Newton concluded that white light was made up of seven different
coloured rays.
Color theory was originally formulated in terms of three "primary" or "primitive"
colors—red, yellow and blue (RYB)—because these colors were believed capable of mixing
all other colors. This color mixing behavior had long been known to printers, dyers and
painters, but these trades preferred pure pigments to primary color mixtures, because the
mixtures were too dull (unsaturated).
The RYB primary colors became the foundation of 18th century theories of color vision,
as the fundamental sensory qualities that are blended in the perception of all physical colors
and equally in the physical mixture of pigments or dyes. These theories were enhanced by
18th-century investigations of a variety of purely psychological color effects, in particular the
contrast between "complementary" or opposing hues that are produced by color afterimages
and in the contrasting shadows in colored light. These ideas and many personal color
observations were summarized in two founding documents in color theory: the Theory of
Colours (1810) by the German poet and government minister Johann Wolfgang von Goethe,
and The Law of Simultaneous Color Contrast (1839) by the French industrial chemist Michel
Eugène Chevreul. Charles Hayter published A New Practical Treatise on the Three Primitive
Colours Assumed as a Perfect System of Rudimentary Information (London 1826), in which
he described how all colours could be obtained from just three.
Subsequently, German and English scientists established in the late 19th century that
color perception is best described in terms of a different set of primary colors—red, green
and blue violet (RGB)—modeled through the additive mixture of three monochromatic
lights. Subsequent research anchored these primary colors in the differing responses to light
by three types of color receptors or cones in the retina (trichromacy). On this basis the
quantitative description of color mixture or colorimetry developed in the early 20th century,
along with a series of increasingly sophisticated models of color space and color perception,
such as the opponent process theory.
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Across the same period, industrial chemistry radically expanded the color range of
lightfast synthetic pigments,
igments, allowing for substantially improved saturation in color mixtures
of dyes, paints and inks. It also created the dyes and chemical processes necessary for color
photography. As a result, three-color
color printing became aesthetically and economically fea
feasible
in mass printed media, and the artists' color theory was adapted to primary colors most
effective in inks or photographic dyes: cyan, magenta, and yellow (CMY). (In printing, dark
colors are supplemented by a black ink, known as the CMYK system; in both
both printing and
photography, white is provided by the color of the paper.) These CMY primary colors were
reconciled with the RGB primaries, and subtractive color mixing with additive color mixing,
by defining the CMY primaries as substances that absorbed only one of the retinal primary
colors: cyan absorbs only red (−R+G+B),
−R+G+B), magenta only green (+R−G+B), and yellow only
blue violet (+R+G−B).
−B). It is important to add that the CMYK, or process, color printing is
meant as an economical way of producing a wide range
range of colors for printing, but is deficient
in reproducing certain colors, notably orange and slightly deficient in reproducing purples. A
wider range of color can be obtained with the addition of other colors to the printing process,
such as in Pantone's Hexachrome printing ink system (six colors), among others.
Fig 1.01: Munsell's color system represented as a three
three-dimensional
dimensional solid showing all
three color making attributes: lightness, saturation and hue.
For much of the 19th century artistic color theory
theory either lagged behind scientific
understanding or was augmented by science books written for the lay public, in particular
Modern Chromatics (1879) by the American physicist Ogden Rood, and early color atlases
developed by Albert Munsell (Munsell Book of Color, 1915, see Munsell color system) and
Wilhelm Ostwald (Color Atlas, 1919). Major advances were made in the early 20th century
by artists teaching or associated with the German Bauhaus, in particular Wassily Kandinsky,
Johannes Itten, Faber Birren and
nd Josef Albers, whose writings mix speculation with an
empirical or demonstration-based
based study of color design principles.
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1.6 COLOUR HARMONY AND COLOUR MEANINGS
(Source: http://www.sensationalcolor.com/understanding-color/theory/colorrelationships-creating-color-harmony-1849#.WdOxIsZx3IU)
Harmony is nature’s way of saying that two or more things together make sense. Color
harmony represents a satisfying balance or unity of colors. Combinations of colors that exist
in harmony are pleasing to the eye. The human brain distinguishes the visual interest and the
sense of order created by the harmony and forms a dynamic equilibrium.
Experts have specific ideas based on the principles of color theory and color psychology
of color combinations that are aesthetically appealing and pleasant. The color wheel becomes
the designer’s tool for creating the harmonies. Just keep in mind, as you learned in “Get to
Know the Color Wheel” that it is color relationship reference tool not color selection tool.
Once you have a harmony in mind you will then use your a fanguide, chip rack or online tool
that shows the hundreds or maybe even thousands of colors you have to chose from.
Creating Color Harmony
The basic formulas for creating harmony are described and illustrated on the designer’s
color wheel. This section focuses on understanding color relationships and how to develop a
finished palette that is pleasing to the eye. Successful color schemes rely on your knowledge
of hue, value and chroma. We have all heard someone say “those colors clash” or ‘don’t
work together.’
What follows are examples of the color harmonies found on the color wheel that all begin
with the color yellow as the common color however you could create these harmonies with
any of the twelve hues on our color wheel
Color Harmonies
Monochromatic harmony uses various values (tints, tones, and shades) within the same color
family.
Analogous harmonies are based on three or more colors that sit side-by-side on the color wheel.
Complementary colors (or Direct Complementary) are those that appear opposite each other on
the color wheel.
A split-complementary color arrangement results from one color paired with two colors on
either side of the original color’s direct complement creating a scheme containing three colors.
Double complement harmonies include two sets of complementary colors that sit next to and
across from each other on the color wheel forming an X.
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Use color harmonies along with hue, value, and chroma to develop your color schemes. Color can
come first or last in the design process. Some designers prefer to choose each color, identifying the
color harmony and color description, then find the other elements for their design. Other designers
will do just the opposite and create their color plan by responding to an inspiration or another element
of design.
Besides taking into consideration color theory: hue, value, chroma, and color harmony, you also
need to understand how people might react to the palette on a psychological basis. Learning the
meanings and associations of the different colors can assist you in finding just the right colors.
Meanings of colours
Red is the color of energy, passion, action, ambition and determination. It is also the color of
anger and sexual passion.
Orange is the color of social communication and optimism. From a negative color meaning it is
also a sign of pessimism and superficiality.
Yellow is the color of the mind and the intellect. It is optimistic and cheerful. However it can also
suggest impatience, criticism and cowardice.
Green is the color of balance and growth. It can mean both self-reliance as a positive and
possessiveness as a negative, among many other meanings.
Blue is the color of trust and peace. It can suggest loyalty and integrity as well as conservatism
and frigidity.
Indigo is the color of intuition. In the meaning of colors it can mean idealism and structure as
well as ritualistic and addictive.
Purple is the color of the imagination. It can be creative and individual or immature and
impractical.
Brown is a friendly yet serious, down-to-earth color that relates to security, protection, comfort
and material wealth.
Gray is the color of compromise - being neither black nor white, it is the transition between two
non-colors. It is unemotional and detached and can be indecisive.
Silver has a feminine energy; it is related to the moon and the ebb and flow of the tides - it is
fluid, emotional, sensitive and mysterious.
Gold is the color of success, achievement and triumph. Associated with abundance and
prosperity, luxury and quality, prestige and sophistication, value and elegance, the color psychology
of gold implies affluence, material wealth and extravagance.
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White is color at its most complete and pure, the color of perfection. The color meaning of white
is purity, innocence, wholeness and completion.
Black is the color of the hidden, the secretive and the unknown, creating an air of mystery. It
keeps things bottled up inside, hidden from the world.
CHECK YOUR PROGRESS
Explain the concept of color harmony.
Elaborate the importance of creating color harmony.
Explain the idea of meaning attached to colors.
Explain the meaning attached to golden, purple, black, white, indigo, brown, gray, silver and blue
colors.
1.7 EMOTIONAL RESPONSE TO COLOURS
RED: Physical
Positive: Physical courage, strength, warmth, energy, basic survival, 'fight or flight',
stimulation, masculinity, excitement.
Negative: Defiance, aggression, visual impact, strain.
Being the longest wavelength, red is a powerful colour. Although not technically the most
visible, it has the property of appearing to be nearer than it is and therefore it grabs our
attention first. Hence its effectiveness in traffic lights the world over. Its effect is physical; it
stimulates us and raises the pulse rate, giving the impression that time is passing faster than it
is. It relates to the masculine principle and can activate the "fight or flight" instinct. Red is
strong, and very basic. Pure red is the simplest colour, with no subtlety. It is stimulating and
lively, very friendly. At the same time, it can be perceived as demanding and aggressive.
BLUE. Intellectual.
Positive: Intelligence, communication, trust, efficiency, serenity, duty, logic, coolness,
reflection, calm.
Negative: Coldness, aloofness, lack of emotion, unfriendliness.
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Blue is the colour of the mind and is essentially soothing; it affects us mentally, rather
than the physical reaction we have to red. Strong blues will stimulate clear thought and
lighter, soft blues will calm the mind and aid concentration. Consequently it is serene and
mentally calming. It is the colour of clear communication. Blue objects do not appear to be as
close to us as red ones. Time and again in research, blue is the world's favourite colour.
However, it can be perceived as cold, unemotional and unfriendly.
YELLOW. Emotional
Positive: Optimism, confidence, self-esteem, extraversion, emotional strength,
friendliness, creativity.
Negative: Irrationality, fear, emotional fragility, depression, anxiety, suicide.
The yellow wavelength is relatively long and essentially stimulating. In this case the
stimulus is emotional, therefore yellow is the strongest colour, psychologically. The right
yellow will lift our spirits and our self-esteem; it is the colour of confidence and optimism.
Too much of it, or the wrong tone in relation to the other tones in a colour scheme, can cause
self-esteem to plummet, giving rise to fear and anxiety. Our "yellow streak" can surface.
GREEN. Balance
Positive: Harmony, balance, refreshment, universal love, rest, restoration, reassurance,
environmental awareness, equilibrium, peace.
Negative: Boredom, stagnation, blandness, enervation.
Green strikes the eye in such a way as to require no adjustment whatever and is,
therefore, restful. Being in the centre of the spectrum, it is the colour of balance - a more
important concept than many people realise. When the world about us contains plenty of
green, this indicates the presence of water, and little danger of famine, so we are reassured by
green, on a primitive level. Negatively, it can indicate stagnation and, incorrectly used, will
be perceived as being too bland.
VIOLET. Spiritual
Positive: Spiritual awareness, containment, vision, luxury, authenticity, truth, quality.
Negative: Introversion, decadence, suppression, inferiority.
The shortest wavelength is violet, often described as purple. It takes awareness to a
higher level of thought, even into the realms of spiritual values. It is highly introvertive and
encourages deep contemplation, or meditation. It has associations with royalty and usually
communicates the finest possible quality. Being the last visible wavelength before the ultraviolet ray, it has associations with time and space and the cosmos. Excessive use of purple
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can bring about too much introspection and the wrong tone of it communicates something
cheap and nasty, faster than any other colour.
ORANGE.
Positive: Physical comfort, food, warmth, security, sensuality, passion, abundance, fun.
Negative: Deprivation, frustration, frivolity, immaturity.
Since it is a combination of red and yellow, orange is stimulating and reaction to it is a
combination of the physical and the emotional. It focuses our minds on issues of physical
comfort - food, warmth, shelter etc. - and sensuality. It is a 'fun' colour. Negatively, it might
focus on the exact opposite - deprivation. This is particularly likely when warm orange is
used with black. Equally, too much orange suggests frivolity and a lack of serious intellectual
values.
PINK.
Positive: Physical tranquillity, nurture, warmth, femininity, love, sexuality, survival of
the species.
Negative: Inhibition, emotional claustrophobia, emasculation, physical weakness.
Being a tint of red, pink also affects us physically, but it soothes, rather than stimulates.
(Interestingly, red is the only colour that has an entirely separate name for its tints. Tints of
blue, green, yellow, etc. are simply called light blue, light greenetc.) Pink is a powerful
colour, psychologically. It represents the feminine principle, and survival of the species; it is
nurturing and physically soothing. Too much pink is physically draining and can be
somewhat emasculating.
GREY.
Positive: Psychological neutrality.
Negative: Lack of confidence, dampness, depression, hibernation, lack of energy.
Pure grey is the only colour that has no direct psychological properties. It is, however,
quite suppressive. A virtual absence of colour is depressing and when the world turns grey
we are instinctively conditioned to draw in and prepare for hibernation. Unless the precise
tone is right, grey has a dampening effect on other colours used with it. Heavy use of grey
usually indicates a lack of confidence and fear of exposure.
BLACK.
Positive: Sophistication, glamour, security, emotional safety, efficiency, substance.
Negative: Oppression, coldness, menace, heaviness.
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Black is all colours, totally absorbed. The psychological implications of that are
considerable. It creates protective barriers, as it absorbs all the energy coming towards you,
and it enshrouds the personality. Black is essentially an absence of light, since no
wavelengths are reflected and it can, therefore be menacing; many people are afraid of the
dark. Positively, it communicates absolute clarity, with no fine nuances. It communicates
sophistication and uncompromising excellence and it works particularly well with white.
Black creates a perception of weight and seriousness. It is a myth that black clothes are
slimming:
WHITE.
Positive: Hygiene, sterility, clarity, purity, cleanness, simplicity, sophistication,
efficiency. Negative: Sterility, coldness, barriers, unfriendliness, elitism.
Just as black is total absorption, so white is total reflection. In effect, it reflects the full
force of the spectrum into our eyes. Thus it also creates barriers, but differently from black,
and it is often a strain to look at. It communicates, "Touch me not!" White is purity and, like
black, uncompromising; it is clean, hygienic, and sterile. The concept of sterility can also be
negative. Visually, white gives a heightened perception of space. The negative effect of white
on warm colours is to make them look and feel garish.
BROWN.
Positive: Seriousness, warmth, Nature, earthiness, reliability, support.
Negative: Lack of humour, heaviness, lack of sophistication.
Brown usually consists of red and yellow, with a large percentage of black.
Consequently, it has much of the same seriousness as black, but is warmer and softer. It has
elements of the red and yellow properties. Brown has associations with the earth and the
natural world. It is a solid, reliable colour and most people find it quietly supportive - more
positively than the ever-popular black, which is suppressive, rather than supportive.
1.8 PHYSIOLOGICAL PRINCIPLE FOR EFFECTIVE USE
OF COLOUR
Perception of color begins with specialized retinal cells containing pigments with
different spectral sensitivities, known as cone cells. In humans, there are three types of cones
sensitive to three different spectra, resulting in trichromatic color vision.
Each individual cone contains pigments composed of opsin apoprotein, which is
covalently linked to either 11-cis-hydroretinal or more rarely 11-cis-dehydroretinal.
The cones are conventionally labeled according to the ordering of the wavelengths of the
peaks of their spectral sensitivities: short (S), medium (M), and long (L) cone types. These
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three types do not correspond well to particular colors as we know them. Rather, the
perception of color is achieved by a complex process that starts with the differential output of
these cells in the retina and it will be finalized in the visual cortex and associative areas of the
brain. For example, while the L cones have been referred to simply as red receptors,
microspectrophotometry has shown that their peak sensitivity is in the greenish-yellow
yellow region
of the spectrum. Similarly, the S-- and M-cones
cones do not directly correspond to blue and green,
although they are often described as such. The RGB color model, therefore, is a convenient
means for representing color, but is not directly
directly based on the types of cones in the human
eye.The peak response of human cone cells varies, even among individuals with so
so-called
normal color vision; in some non
non-human
human species this polymorphic variation is even greater,
and it may well be adaptive
1.8.1 Mechanism of dichromatic color vision
Trichromatic color vision is the ability of humans and some other animals to see different
colors, mediated by interactions among three types of color-sensing
color sensing cone cells. The
trichromatic color theory began in the 18th century, when Thomas Young proposed that color
vision was a result of three different photoreceptor cells. Hermann von Helmholtz later
expanded on Young's ideas using color
color-matching
matching experiments which showed that people with
normal vision needed three wavelengths to create the normal range of colors. Physiological
evidence for trichromatic theory was later given by Gunnar Svaetichin (1956).
Fig 1.02: Normalised responsivity spectra of human cone cells
Each of the three types of cones in the retina of the eye contains a different type of
photosensitive pigment, which is composed of a transmembrane protein called opsin and a
light-sensitive
sensitive molecule called 11
11-cis
cis retinal. Each different pigment is especially sensitive to
a certain wavelength of light (that
at is, the pigment is most likely to produce a cellular response
when it is hit by a photon with the specific wavelength to which that pigment is most
sensitive). The three types of cones are L, M, and S, which have pigments that respond best
to light of long
ong (especially 560 nm), medium (530 nm), and short (420 nm) wavelengths
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respectively. Since the likelihood of response of a given cone varies not only with the
wavelength of the light that hits it but also with its intensity, the brain would not be able to
discriminate different colors if it had input from only one type of cone. Thus, interaction
between at least two types of cone is necessary to produce the ability to perceive color. With
at least two types of cones, the brain can compare the signals from each type and determine
both the intensity and color of the light. For example, moderate stimulation of a mediumwavelength cone cell could mean that it is being stimulated by very bright red (longwavelength) light, or by not very intense yellowish-green light. But very bright red light
would produce a stronger response from L cones than from M cones, while not very intense
yellowish light would produce a stronger response from M cones than from other cones. Thus
trichromatic color vision is accomplished by using combinations of cell responses.
It is estimated that the average human can distinguish up to seven million different colors
1.8.2 Human Visual System
Solving the problem of converting light into ideas, of visually understanding features and
objects in the world, is a complex task far beyond the abilities of the world's most powerful
computers. Vision requires distilling foreground from background, recognizing objects
presented in a wide range of orientations, and accurately interpreting spatial cues. The neural
mechanisms of visual perception offer rich insight into how the brain handles such
computationally complex situations.
Visual perception begins as soon as the eye focuses light onto the retina, where it is
absorbed by a layer of photoreceptor cells. These cells convert light into electrochemical
signals, and are divided into two types, rods and cones, named for their shape. Rod cells are
responsible for our night vision, and respond well to dim light. Rods are found mostly in the
peripheral regions of the retina, so most people will find that they can see better at night if
they focus their gaze just off to the side of whatever they are observing. Cone cells are
concentrated in a central region of the retina called the fovea; they are responsible for high
acuity tasks like reading, and also for color vision. Cones can be subcategorized into three
types, depending on how they respond to red, green, and blue light. In combination, these
three cone types enable us to perceive color.
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fovea : The fovea
ovea centralis (the term fovea comes from the Latin, meaning pit or pitfall)
is a small, central pit composed of closely packed cones in the eye. It is located in the center
of the macula lutea of the retina.
Blind Spot:: The area of the retina where the optic
optic nerve is attached is completely devoid
of photosensitive cells. This means that there is a “blind spot” in the field of vision for each
eye. Most of the time we are not aware of this deficit in our vision, but it is quite easy to
locate it.
1.8.3 Phototransduction
transduction
There is more than what can be see... Vision Signal Transduction Pathway Cell Signal
Transduction Pathway Eye Structure and Vision Pathway Rods signal tranduction pathway
Structure of Rods and Cones Retina Structure/Function Cornea: the trans
transparent
parent most outer
part of the eye, this is where mucles attached to move the eye. Iris: controls the light level
that enters the eye. Optic Nerve: carry signals from back of the eye to the brain. Focal Point:
Where it collects all the rays of light. Retina:
Retina: inner most layer, contains photoreceptors (rods
and cones) and neurons which the photoreceptors act upon. Crystalline lens: Refracts light to
be focus in the retina Ligand: ""the messenger" light travels through cornea > iris > lens >
focal point > retinaa > optic nerve > brain
1.8.5 Difference between Rods and Cones
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Properties of Rod and Cone Systems
Rods
Cones
More photopigment
Less photopigment
Slow response: long
integration time
Fast response: short
integration time
High amplification
Less amplification
Comment
Temporal integration
Single quantum detection
in rods (Hecht, Schlaer &
Pirenne)
The rods' response
saturates when only a small
amount of the pigment is
Saturating Response (by
Non-saturating response
bleached (the absorption of a
6% bleached)
(except S-cones)
photon by a pigment molecule
is known as bleaching the
pigment).
Not directionally
selective
Highly convergent
retinal pathways
High sensitivity
Low acuity
Directionally selective
Less convergent retinal
pathways
Stiles-Crawford effect (see
later this chapter)
Spatial integration
Lower absolute
sensitivity
High acuity
Achromatic: one type of
Chromatic: three types
pigment
of pigment
Results from degree of
spatial integration
Color vision results from
comparisons between cone
responses
1.8.6 Function
Photoreceptors do not signal color; they only signal the presence of light in the visual
field.
A given photoreceptor responds to both the wavelength and intensity of a light source.
For example, red light at a certain intensity can produce the same exact response in a
photoreceptor as green light of a different intensity. Therefore, the response of a single
photoreceptor is ambiguous when it comes to color. To determine color, the visual system
compares responses across a population of photoreceptors (specifically, the three different
cones with differing absorption spectra). To determine intensity, the visual system computes
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how many photoreceptors are responding. This is the mechanism that allows trichromatic
color vision in humans and some other animals.
1.8.7 Signaling
The rod and cone photoreceptors signal their absorption of photons via a decrease in the
release of the neurotransmitter glutamate to bipolar cells at its axon terminal. Since the
photoreceptor is depolarized in the dark, a high amount of glutamate is being released to
bipolar cells in the dark. Absorption of a photon will hyperpolarize the photoreceptor and
therefore result in the release of less glutamate at the presynaptic terminal to the bipolar cell.
Every rod or cone photoreceptor releases the same neurotransmitter, glutamate. However, the
effect of glutamate differs in the bipolar cells, depending upon the type of receptor imbedded
in that cell's membrane. When glutamate binds to an ionotropic receptor, the bipolar cell will
depolarize (and therefore will hyperpolarize with light as less glutamate is released). On the
other hand, binding of glutamate to a metabotropic receptor results in a hyperpolarization, so
this bipolar cell will depolarize to light as less glutamate is released. In essence, this property
allows for one population of bipolar cells that gets excited by light and another population
that gets inhibited by it, even though all photoreceptors show the same response to light. This
complexity becomes both important and necessary for detecting color, contrast, edges, etc.
Further complexity arises from the various interconnections among bipolar cells, horizontal
cells, and amacrine cells in the retina. The final result is differing populations of ganglion
cells in the retina, a sub-population of which is also intrinsically photosensitive, using the
photopigment melanopsin.
1.8.8 Ganglion cell
In humans the retinal ganglion cell photoreceptor contributes to conscious sight as well as
to non-image-forming functions like circadian rhythms, behaviour and pupil reactions. Since
these cells respond mostly to blue light, it has been suggested that they have a role in mesopic
vision. Zaidi and colleagues' work with rodless coneless human subjects hence also opened
the door into image-forming (visual) roles for the ganglion cell photoreceptor. It was
discovered that there are parallel pathways for vision – one classic rod and cone-based
pathway arising from the outer retina, and the other a rudimentary visual brightness detector
pathway arising from the inner retina, which seems to be activated by light before the other.
Classic photoreceptors also feed into the novel photoreceptor system, and colour constancy
may be an important role as suggested by Foster. The receptor could be instrumental in
understanding many diseases including major causes of blindness worldwide like glaucoma,
a disease that affects ganglion cells, and the study of the receptor offered potential as a new
avenue to explore in trying to find treatments for blindness. It is in these discoveries of the
novel photoreceptor in humans and in the receptors role in vision, rather than its non-imageforming functions, where the receptor may have the greatest impact on society as a whole,
though the impact of disturbed circadian rhythms is another area of relevance to clinical
medicine.
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Most work suggests that the peak spectral sensitivity of the receptor is between 460 and
482 nm. Steven Lockley et al. in 2003 showed that 460 nm wavelengths of light suppress
melatonin twice as much as longer 555 nm light. However, in more recent work by Farhan
Zaidi et al., using rodless coneless humans, it was found that what consciously led to light
perception was a very intense 481 nm stimulus; this means that the receptor, in visual terms,
enables some rudimentary vision maximally for blue light.
CHECK YOUR PROGRESS
Explain the physiological basis for color perception in humans.
Elaborate the importance of Mechanism of dichromatic and tri-chromatic color vision.
Explain the features of Human Visual System.
Describe the concept of Phototransduction
Discuss the difference between Rods and Cones.
Explain the functions of photoreceptors.
Explain the signaling mechanism of photoreceptors.
Explain the functions of Ganglion cell.
Explain the functions of photoreceptors.
1.9 LENS
The lens is a transparent, biconvex (lentil-shaped) structure in the eye that, along with the
cornea, helps to refract light to be focused on the retina. The lens, by changing shape,
functions to change the focal distance of the eye so that it can focus on objects at various
distances, thus allowing a sharp real image of the object of interest to be formed on the retina.
This adjustment of the lens is known as accommodation (see also Accommodation, below). It
is similar to the focusing of a photographic camera via movement of its lenses.
The lens is also known as the aquula (Latin, a little stream, dim. of aqua, water) or
crystalline lens. In humans, the refractive power of the lens in its natural environment is
approximately 18 dioptres, roughly one-third of the eye's total power.
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1.9.1 Position, size, and shape
The lens is located in the anterior segment of the eye. Anterior to the lens is the iris,
which regulates the amount of light entering the eye. The lens is suspended in place by the
zonular fibers, which attach to the lens near its equatorial line and connect the lens to the
ciliary body. Posterior to the lens is the vitreous body. The lens has an ellipsoid, biconvex
shape. In the adult, the lens is typically 10 mm in diameter and has an axial length of 4 mm,
though it is important to note that the size and shape can change due to accommodation and
because the lens continues to grow throughout a person’s lifetime.
1.9.2 Lens Structure and Function
The lens is comprised of three main parts: the lens capsule, the lens epithelium, and the
lens fibers. The lens capsule forms the outermost layer of the lens and the lens fibers form the
bulk of the interior of the lens. The cells of the lens epithelium, located between the lens
capsule and the outermost layer of lens fibers, are found only on the anterior side of the lens.
Lens Capsule
The lens capsule is a smooth, transparent basement membrane that completely surrounds
the lens. It is synthesized by the lens epithelium and its main components are Type IV
collagen and sulfated glycosaminoglycans (GAGs). The capsule is very elastic and so causes
the lens to assume a more globular shape when not under the tension of the zonular fibers,
which connect the lens capsule to the ciliary body. The capsule varies from 2-28 microns in
thickness, being thickest near the equator and thinnest near the posterior pole.
Lens Epithelium
The lens epithelium, located in the anterior portion of the lens between the lens capsule
and the lens fibers, is a simple cuboidal epithelium. The cells of the lens epithelium regulate
most of the homeostatic functions of the lens. As ions, nutrients, and liquid enter the lens
from the aqueous humor, Na+/K+ ATPase pumps in the lens epithelial cells pump ions out of
the lens to maintain appropriate lens osmolarity and volume, with equatorially positioned lens
epithelium cells contributing most to this current. The activity of the Na+/K+ ATPases keeps
water and current flowing through the lens from the poles and exiting through the equatorial
regions.
The cells of the lens epithelium also serve as the progenitors for new lens fibers.
Lens fibers
The lens fibers form the bulk of the lens. They are long, thin, transparent cells, with
diameters typically between 4-7 microns and lengths of up to 12 mm long. The lens fibers
stretch lengthwise from the posterior to the anterior poles and are arranged in concentric
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layers rather like the layers of an onion. These tightly packed layers of lens fibers are referred
to as laminae. The lens fibers are linked together via gap junctions and interdigitations of the
cells that resemble “ball and socket” forms.
The lens is split into regions depending on the age of the lens fibers of a particular layer.
Moving outwards from the central, oldest layer, the lens is split into an embryonic nucleus,
the fetal nucleus, the adult nucleus, and the outer cortex. New lens fibers, generated from the
lens epithelium, are added to the outer cortex. Mature lens fibers have no organelles or
nuclei.
1.9.3 Accommodation: changing the power of the lens
An image that is partially in focus, but mostly out of focus in varying degrees.
The lens is flexible and its curvature is controlled by ciliary muscles through the zonules.
By changing the curvature of the lens, one can focus the eye on objects at different distances
from it. This process is called accommodation. At short focal distance the ciliary muscles
contract, zonule fibers loosen, and the lens thickens, resulting in a rounder shape and thus
high refractive power. Changing focus to an object at a distance requires the stretching of the
lens by the ciliary muscles, which flattens the lens and thus increases the focal distance.
The refractive index of the lens varies from approximately 1.406 in the central layers
down to 1.386 in less dense cortex of the lens. This index gradient enhances the optical
power of the lens.
Aquatic animals must rely entirely on their lens for both focusing and to provide almost
the entire refractive power of the eye as the water-cornea interface does not have a large
enough difference in indices of refraction to provide significant refractive power. As such,
lenses in aquatic eyes tend to be much rounder and harder.
1.9.4 Crystallins and Transparency
Crystallins are water-soluble proteins that comprise over 90% of the protein within the
lens. The three main crystallin types found in the eye are α-, β-, and γ-crystallins. Crystallins
tend to form soluble, high-molecular weight aggregates that pack tightly in lens fibers, thus
increasing the index of refraction of the lens while maintaining its transparency. β and γ
crystallins are found primarily in the lens, while subunits of α -crystallin have been isolated
from other parts of the eye and the body. α-crystallin proteins belong to a larger superfamily
of molecular chaperone proteins, and so it is believed that the crystallin proteins were
evolutionarily recruited from chaperone proteins for optical purposes. The chaperone
functions of α -crystallin may also help maintain the lens proteins, which must last a human
for his/her entire lifetime.
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Another important factor in maintaining the transparency of the lens is the absence of
light-scattering organelles such as the nucleus, endoplasmic reticulum, and mitochondria
within the mature lens fibers. Lens fibers also have a very extensive cytoskeleton that
maintains the precise shape and packing of the lens fibers; disruptions/mutations in certain
cytoskeletal elements can lead to the loss of transparency.
CHECK YOUR PROGRESS
Explain the physiological aspects of lens in a human eye.
Elaborate the importance of position, size and shape of human eye lens.
Explain the Structure and Function of human lens.
Describe the concept of Lens Epithelium.
Discuss the Lens Capsule.
Explain the functions of Lens fibers.
Explain the accommodation mechanism of human lens.
Explain the functions of Crystallins and mechanism of maintaining Transparency in human lens.
1.10 RETINA
The retina is the third and inner coat of the eye which is a light-sensitive layer of tissue.
The optics of the eye create an image of the visual world on the retina (through the cornea
and lens), which serves much the same function as the film in a camera. Light striking the
retina initiates a cascade of chemical and electrical events that ultimately trigger nerve
impulses. These are sent to various visual centres of the brain through the fibres of the optic
nerve. Neural retina typically refers to three layers of neural cells (photo receptor cells,
bipolar cells, and ganglion cells) within the retina, while the entire retina refers to these three
layers plus a layer of pigmented epithelial cells.
In vertebrate embryonic development, the retina and the optic nerve originate as
outgrowths of the developing brain, specifically the embryonic diencephalon; thus, the retina
is considered part of the central nervous system (CNS) and is actually brain tissue. It is the
only part of the CNS that can be visualized non-invasively.
The retina is a layered structure with several layers of neurons interconnected by
synapses. The only neurons that are directly sensitive to light are the photoreceptor cells. For
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vision, these are of two types: the rods and cones. Rods function mainly in dim light and
provide black-and-white vision while cones support the perception of colour. A third type of
photoreceptor, the photosensitive ganglion cells, is important for entrainment and reflexive
responses to the brightness of light. Neural signals from the rods and cones undergo
processing by other neurons of the retina. The output takes the form of action potentials in
retinal ganglion cells whose axons form the optic nerve. Several important features of visual
perception can be traced to the retinal encoding and processing of light.
Structure
The vertebrate retina has ten distinct layers. From closest to farthest from the vitreous
body - that is, from closest to the front exterior of the head towards the interior and back of
the head:
Inner limiting membrane – basement membrane elaborated by Müller cells
Nerve fibre layer – axons of the ganglion cell nuclei (note that a thin layer of Müller cell
footplates exists between this layer and the inner limiting membrane)
Ganglion cell layer – contains nuclei of ganglion cells, the axons of which become the
optic nerve fibres for messages and some displaced amacrine cells
Inner plexiform layer – contains the synapse between the bipolar cell axons and the
dendrites of the ganglion and amacrine cells.
Inner nuclear layer – contains the nuclei and surrounding cell bodies (perikarya) of the
amacrine cells, bipolar cells and horizontal cells.
Outer plexiform layer – projections of rods and cones ending in the rod spherule and cone
pedicle, respectively. These make synapses with dendrites of bipolar cells. In the macular
region, this is known as the Fiber layer of Henle.
Outer nuclear layer – cell bodies of rods and cones
External limiting membrane – layer that separates the inner segment portions of the
photoreceptors from their cell nucleus
Layer of rods and cones – layer of rod cells and cone cells
Retinal pigment epithelium - single layer of cuboidal cells (with extrusions not shown in
diagram). This is closest to the choroid.
These can be simplified into 4 main processing stages: photoreception, transmission to
bipolar cells, transmission to ganglion cells which also contain photoreceptors, the
photosensitive ganglion cells, and transmission along the optic nerve. At each synaptic stage
there are also laterally connecting horizontal and amacrine cells.
Rods, cones and nerve layers in the retina. The front (anterior) of the eye is on the left.
Light (from the left) passes through several transparent nerve layers to reach the rods and
cones (far right). A chemical change in the rods and cones send a signal back to the nerves.
The signal goes first to the bipolar and horizontal cells (yellow layer), then to the amacrine
cells and ganglion cells (purple layer), then to the optic nerve fibres. The signals are
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processed in these layers. First, the signals start as raw outputs of points in the rod and cone
cells. Then the nerve layers identify simple shapes, such as bright points surrounded by dark
points, edges, and movement
Diseases and disorders of the eye
Retinitis Pigmentosa
: A group of inherited disorders of the retina (the light-sensitive
lining at the back of the eye), which cause poor night vision and a progressive loss of side
vision.
Macular Degeneration : An eye disease affecting the macula (the center of the lightsensitive retina at the back of the eye), causing loss of central vision.
Retinoblastoma : A rare type of eye cancer occurring in young children that develops in
the retina, the light-sensitive lining at the back of the eye.
Color Blindness : Color blindness is not actually blindness in the true sense but rather is
a color vision deficiency—people who are affected by it simply do not agree with most other
people about color matching.
Red–green color blindness : Protanopia, deuteranopia, protanomaly, and deuteranomaly
are commonly inherited forms of red–green color blindness which affect a substantial portion
of the human population. Those affected have difficulty with discriminating red and green
hues due to the absence or mutation of the red or green retinal photoreceptors.
Blue–yellow color blindness : Those with tritanopia and tritanomaly have difficulty
discriminating between bluish and greenish hues, as well as yellowish and reddish hues.
Color blindness involving the inactivation of the short-wavelength sensitive cone system
(whose absorption spectrum peaks in the bluish-violet) is called tritanopia or, loosely, blue–
yellow color blindness.
Total color blindness : Total color blindness is defined as the inability to see color.
Although the term may refer to acquired disorders such as cerebral achromatopsia also known
as color agnosia, it typically refers to congenital color vision disorders (i.e. more frequently
rod monochromacy and less frequently cone monochromacy)
CHECK YOUR PROGRESS
Explain the physiological aspects of retina in a human eye.
Elaborate the importance of position, size and shape of human retina.
Explain the diseases in human eyes.
Describe the concept of color blindness and their types.
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1.11 HUMAN BRAIN
The human brain is the command center for the human nervous system. It receives input
from the sensory organs and sends output to the muscles. The human brain has the same basic
structure as other mammal brains, but is larger in relation to body size than any other brains.
Facts about the human brain
The human brain is the largest brain of all vertebrates relative to body size
It weighs about 3.3 lbs. (1.5 kilograms)
The brain makes up about 2 percent of a human's body weight
The cerebrum makes up 85 percent of the brain's weight
It contains about 86 billion nerve cells (neurons) — the "gray matter"
It contains billions of nerve fibers (axons and dendrites) — the "white matter"
These neurons are connected by trillions of connections, or synapses
Parts of the brain
The brain is divided into three major regions - the hindbrain, the midbrain and the
forebrain. Each region is composed of different brain parts that work together to process the
information they receive.
Forebrain : The Forebrain is considered as the highest region of the brain because it
essentially differentiates us humans from the rest in the animal kingdom. This region is also
involved in processing complex information.
Midbrain :The Midbrain serves to relay information between the hindbrain and the
forebrain, particularly information coming from the eyes and the ears.
The reticular formation is involved with stereotypical patterns of behavior such as
walking, sleeping, and other reflexes. Parkinson's disease, a degenerative disease of the brain
that causes involuntary tremors on affected body parts, damages a section near the bottom of
the midbrain.
Hindbrain : It is involved in alertness and in monitoring basic survival functions such as
breathing, heartbeat, and blood pressure. It is also known as the "reptilian brain" because it is
considered the entire brain of reptiles.
Cerebral Cortex
The cerebral cortex is divided into two hemispheres - the left and the right hemispheres.
The left hemisphere is associated with verbal processing, such as speech and grammar, and
mathematics; while the right hemisphere is involved with nonverbal processing, such as
spatial perception, visual recognition and emotion. The left hemisphere processes information
coming from the right side of the body, while the right hemisphere processes information
coming from the left side of the body. The two hemispheres of the brain are connected with
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each other by a bundle of axons called the corpus callosum. This connection allows the left
and the right hemispheres to communicate and integrate information with each other.
CHECK YOUR PROGRESS
Explain the physiological aspects of human brain.
Elaborate the importance parts of human brain.
Explain the features of cerebral cortex.
1.12 EFFECTIVE USE OF COLOURS
I believe that effective use of colour is key to a successful and accessible website.
Communication and brand recognition is greatly aided by the use of a simple, relevant and
effective colour scheme throughout the site.
Optimising design for the screen based medium is something many print designers take a
while to get to grips with as designing for websites involves dealing with backlit
luminescence, which can vary from monitor to monitor and from platform to platform.
Colours are RGB not CMYK. Therefore effective and use of limited colour with emphasis on
contrast is very important. An understanding of how certain colours perform on screen
compared to when they are printed helps avoid communication and branding mistakes.
In general it's a good idea to restrict the number of colours used and isolating areas
involving large amount of colour variation i.e. colour-coded section dividers, navigation
elements and photography. Other points to note are that: large areas of text are more readable
on black on white than white on black. Sites can involve movement as well as clever use of
colour to emphasise important points and branding truths.
Understand your audience
Understand your site's message and brand
Choose colours that reinforce your message. For instance, if designing a site for a
financial institution hoping to convey stability, choose cool, muted colours such as blue, grey,
and green. In this case, using warm, vibrant hues would undermine the site's brand.
Cultural differences can lead to unexpected responses to colour. Additionally,
demographic segments and age groups respond to colours differently. Younger audiences
generally respond to more saturated hues that are less effective with older segments.
Use contrast for readability
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Colours similar in value do not provide enough contrast and hinder legibility and
accessibility. Black text on white backgrounds provides the highest degree of contrast.
CHECK YOUR PROGRESS
Explain the aspects of making effective use of colors.
Elaborate the importance of making effective use of colors.
Explain the importance of contrast and readability.
1.14 SUMMARY
• A basic knowledge of colour theory definitely helps in making a harmonious combination which
is pleasing to the eyes.
• With the basic knowledge of colour theory, one can easily understand how to make effective use
of colours in our daily life.
• For a person who belongs to art background, judgement about colours and their meaning is easy.
• For a lay man visualizing colours is not an easy task. A poor and undeveloped sense of colour
proves to be a great hindrance in making good colour decisions.
• In the visual arts, colour theory refers to the visual impact created by different types of colours,
both individually and in combination with each other.
• Colour balance refers to the use of congruous colours in a design.
• Colour scheme is the choice of colours used in a design for a range of media used in colour
theory. Colour schemes are basically used to create style and appeal
• Complementary colour scheme includes a combination of any two colours that me positioned
opposite to each other on the colour wheel Analogous colours appear non to each other on the colour
wheel
• Warm colours are bright and pleasing. They are generally associated with daylight and cool
colours with night .
• Colour theory helps us to understand the various possible combinations that would look
harmonious together.
• An organism's retina comprises three different types of colour receptors called cone cells with
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different absorption spectra
• Trichromatic colour vision is the natural aptitude of humans and some other animals to see
different co burs, interposed by interactions among three types of colour-sensing cone cells.
• A photoreceptor is a specialized type of nerve cell that is capable of phototransduction.
• Phototransduction is the composite process through which the energy of a photon is utilized to
alter the intrinsic membrane potential of the photoreceptor.
• Signals are conducted by polarization and depolarization of the neurons.
• One of the most important differences between rods and cones is that while rods are meant for
scotopic vision, while cones are responsible for photopic
• Corpus callosum: The thick band of fibres that connect the left and right brain hemispheres.
• Fissure of Sylvus: The parietal and temporal lobes of the cerebral cortex are separated by a deep
grove called the "Fissure of Sylvus"
• Colour blindness: An unnatural condition induced by the inability to distinguish clearly between
colours of the spectrum
• Monochromacy: Takes place when two or all three of the cone pigments are not present and
colour and light vision is decreased to one dimension.
• Rod monochromicy: A rare, non-progressive colour blindness whereby it is unable to
differentiate any colour as a result of absence of mini cones or non-functional retinal cones.
• Tritanopia: A generally rare colour vision disturbance in which there are only two cone
pigments present and the blue retinal receptors are totally absent,
• Tritanomaly: A rare type of hereditary colour Wildness where colour vision deficiency causes
blue yellow hue discrimination.
1.15 END QUESTIONS
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
Explain the concept of Color Balancing.
Elaborate the importance of Color Balancing.
Explain the concept of Color Scheme.
Elaborate the importance of Color Scheme.
Explain the idea of Complementary color scheme.
Explain the idea of Complementary color scheme.
Explain the idea of Analogous color scheme.
Explain the idea of Triadic color scheme.
Explain the idea of Split-Complementary color scheme.
Explain the idea of Rectangle (tetradic) color scheme.
List the various areas where designers give importance to color schemes
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12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
46.
47.
48.
Explain the concept of traditional color theory.
Elaborate the importance of warm and cool colors.
Discuss the idea of warm and cool colors.
Explain the concepts of Achromatic colors.
Elaborate the concepts of Tints and shades.
Descibe the idea of Split Primary Colors.
Explain the concept of color harmony.
Elaborate the importance of creating color harmony.
Explain the idea of meaning attached to colors.
Explain the meaning attached to golden, purple, black, white, indigo, brown, gray, silver and
blue colors.
Explain the physiological basis for color perception in humans.
Elaborate the importance of Mechanism of dichromatic and tri-chromatic color vision.
Explain the features of Human Visual System.
Describe the concept of Phototransduction
Discuss the difference between Rods and Cones.
Explain the functions of photoreceptors.
Explain the signaling mechanism of photoreceptors.
Explain the functions of Ganglion cell.
Explain the functions of photoreceptors.
Explain the physiological aspects of lens in a human eye.
Elaborate the importance of position, size and shape of human eye lens.
Explain the Structure and Function of human lens.
Describe the concept of Lens Epithelium.
Discuss the Lens Capsule.
Explain the functions of Lens fibers.
Explain the accommodation mechanism of human lens.
Explain the functions of Crystallins and mechanism of maintaining Transparency in human
lens.
Explain the physiological aspects of retina in a human eye.
Elaborate the importance of position, size and shape of human retina.
Explain the diseases in human eyes.
Describe the concept of color blindness and their types
Explain the physiological aspects of human brain.
Elaborate the importance parts of human brain.
Explain the features of cerebral cortex.
Explain the aspects of making effective use of colors.
Elaborate the importance of making effective use of colors.
Explain the importance of contrast and readability.
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UNIT 2: COLOUR BASICS
2.0 INTRODUCTION
With colors you can set a mood, attract attention, or make a statement. You can use color to
energize, or to cool down. By selecting the right color scheme, you can create an ambiance of
elegance, warmth or tranquility, or you can convey an image of playful youthfulness. Color can be
your most powerful design element if you learn to use it effectively. Colors affect us in numerous
ways, both mentally and physically. A strong red color has been shown to raise the blood pressure,
while a blue color has a calming effect.
Being able to use colors consciously and harmoniously can help you create spectacular results.
Understanding of color basics is extremely important for you as a student and as a professional in
media, graphics and animation. Which color to choose for a graphic, animation or photograph is of
crucial importance. You will decide on the basis of the demand of the project, which color schemes to
chose. The topics covered under this course will help you understand various concepts covered in all
other courses like photoshop, illustrator, 3Ds max or Maya animation courses which you will study as
part of your study in BSc(MGA).
2.1 UNIT OBJECTIVES
After going through this unit, you will be able to:
•
•
•
•
•
Elaborate the basic concepts of colour systems
Explain the history of colour wheel
Discuss how shades differ from tints
Describe perceptual opposites
Explain complementary relationships
2.2 COLOUR SYSTEMS
Three factors are important in describing a colour.
(i) name
(ii) The degree of saturation, i.e., how pure it is
(iii) Its value or lightness
Although pink., crimson and brick are all various shades rifted, each hue is unique and
discriminated by its intensity, saturation, chroma and value.
Intensity, saturation, chroma and luminance/value are mutually-related terms , Which describe
different aspects of colour.
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Chroma
Chroma, measured radially from the center of each slice, represents the “purity” of a color
(related to saturation), with lower chroma being less pure (more washed out, as in pastels). Note that
there is no intrinsic upper limit to chroma. Different areas of the color space have different maximal
chroma coordinates. For instance light yellow colors have considerably more potential chroma than
light purples, due to the nature of the eye and the ph
physics
ysics of color stimuli. This led to a wide range of
possible chroma levels—up
up to the high 30s for some hue
hue–value
value combinations (though it is difficult or
impossible to make physical objects in colors of such high chromas, and they cannot be reproduced
on current computer displays).
Saturation
Saturation scale (0% at bottom, corresponding to black and white).
Saturation is defined as the "colorfulness of an area judged in proportion
proportion to its brightness", which
in effect is the perceived freedom from whitishn
whitishness of the light coming from the area. A note
accompanying this definition in effect indicates that an object with a given spectral reflectance
exhibits approximately constant saturation for all levels of illumination, unless the brightness is very
high. Since
ince the chroma and lightness of an object are its colorfulness and brightness judged in
proportion to the same thing ("the brightness of a similarly illuminated area that appears white or
highly transmitting"), the saturation of the light coming from that object is in effect the chroma of the
object judged in proportion to its lightness. On a Munsell hue page, lines of uniform saturation thus
tend to radiate from near the black point, while lines of uniform chroma are vertical
vertical.
Intensity
Intensity refers to the purity of a hue. Intensity is also known as Chroma or Saturation. The
highest intensity or purity of a hue is the hue as it appears in the spectrum or on the color wheel. A
hue reduced in intensity is called a Tone. A tone is a hue with reduced or dulled
dulled strength.
Luminance
A certain color can be defined by hue (0° - 360°), saturation (0% - 100%) and lightness (0% 100%). Luminance on the other hand is a measure to describe the perceived brightness of a color
(Encyclopædia Britannica: "luminance, or
or visually perceived brightness"). You can lighten or darken
a colour by adjusting its lightness value, but lightness is not the only dimension to consider for
luminance. That is because each hue naturally has an individual luminance value.
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If luminance is dependent on hue, it's also dependent on saturation. Reducing the saturation level
of any pure hue to 0% results in a 50%-gray and a 50% value in luminance respectively. So for hues
with natural luminance above 50%, luminance decreases when the saturation level decreases. For
hues with natural luminance below 50%, luminance increases when the saturation level decreases.
Tints and Shades
In color theory, a tint is the mixture of a color with white, which increases lightness, and a shade
is the mixture of a color with black, which reduces lightness. A tone is produced either by the mixture
of a color with gray, or by both tinting and shading.
Tint is the term used to describe a hue that has been lighted in value from its normal value. Pink is
tint of red. Tints are achieved by mixing white with a pigment or by using a pigment in a dilute form
to allow for the white of the ground to show through.
Shade is the term used to describe a hue that has be darkened in value from its normal value.
Maroon is a shade of red. Shades are achieved by mixing black with a pigment.(This use of the term
shade is specific to color theory. In common usage a “shade” is usually a variation in color of a hue.
To say “your coat is a nice shade of blue” usually means that your coat is not true blue but some blend
of blue with other colors.)
Primary Colours
A set of primary colors is a small, arbitrary set of pigmented physical media, lights or purely
abstract elements of a mathematical colorspace model. Distinct colors from a larger gamut can be
specified in terms of a mixture of primary colors which facilitates technological applications such as
painting, electronic displays and printing. Any small set of pigments or lights are "imperfect" physical
primary colors in that they cannot be mixed to yield all possible colors that can be perceived by the
human color vision system. The abstract (or "imaginary") primaries X, Y and Z of the CIEXYZ
colorspace can be mathematically summed to specify essentially all colors that can be perceived but
these primaries cannot be physically realized due to the underlying structure and overlapping spectral
sensitivities of each of the human cone photoreceptors. The precise set of primary colors that are used
in a specific color application depend on gamut requirements as well as application-specific
constraints such as cost, power consumption, lightfastness, mixing behavior etc.
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In an additive set of colors, as in coincident projected lights or in electronic visual displays, the
primary colors normally used are red, green and blue (but the precise visible light spectra for each
color can vary significantly). In a subtractive set of colors, as in mixing of pigments or dyes for
printing, the colors magenta, yellow and cyan are normally used. See RGB color model, and CMYK
color model for more on these popular sets of primary colors.
Perceptually based colour models
A color model is an abstract mathematical model describing the way colors can be represented as
tuples of numbers, typically as three or four values or color components. When this model is
associated with a precise description of how the components are to be interpreted (viewing conditions,
etc.), the resulting set of colors is called color space. This section describes ways in which human
color vision can be modeled.
A color model is a system for creating a full range of colours from a small set of primary colors.
There are two types of colour models: additive and subtractive. Additive color models use light to
display color, while subtractive color models use printing inks. The most common color models that
graphic designers work with are the CMYK model for printing and the RGB model for computer
display.
HSV color model
HSV, which stands for hue, saturation and value, depicts three-dimensional color. HSV seeks to
depict relationships between colors, and improve upon the RGB color model. If you think about HSV
as a wheel, the center axis goes from white at the top to black at the bottom, with other neutral colors
in between. The angle from the axis depicts the hue, the distance from the axis depicts saturation, and
the distance along the axis depicts value.
HSL color model
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HSL, like HSV, is a 3-D representation of color. HSL stands for hue, saturation, and lightness.
The HSL color model has distinct advantages over the HSV model, in that the saturation and lightness
components span the entire range of values.
RGB color model (Device dependent color model)
Media that transmit light (such as television) use additive color mixing with primary colors of
red, green, and blue, each of which stimulates one of the three types of the eye's color receptors with
as little stimulation as possible of the other two. This is called "RGB" color space. Mixtures of light of
these primary colors cover a large part of the human color space and thus produce a large part of
human color experiences. This is why color television sets or color computer monitors need only
produce mixtures of red, green and blue light. See Additive color.
Other primary colors could in principle be used, but with red, green and blue the largest portion of
the human color space can be captured. Unfortunately there is no exact consensus as to what loci in
the chromaticity diagram the red, green, and blue colors should have, so the same RGB values can
give rise to slightly different colors on different screens.
CMYK color model
It is possible to achieve a large range of colors seen by humans by combining cyan, magenta, and
yellow transparent dyes/inks on a white substrate. These are the subtractive primary colors. Often a
fourth ink, black, is added to improve reproduction of some dark colors. This is called "CMY" or
"CMYK" color space.
It is frequently suggested that the ‘K’ in CMYK comes from the last letter in ‘black’ and was
chosen because B already refers to blue. However, this explanation is incorrect. The ‘K’ in CMYK
stands for ‘key’ since in four-color printing cyan, magenta, and yellow printing plates are carefully
keyed or aligned with the key of the black key plate. Black is used because the combination of the
three primary colors (CMY) doesn’t produce a fully saturated black.
2.3 WORKING WITH COLOUR SYSTEMS
Available color systems are dependent on the medium with which a designer is working. When
painting, an artist has a variety of paints to choose from, and mixed colors are achieved through the
subtractive color method. When a designer is utilizing the computer to generate digital media, colors
are achieved with the additive color method.
2.3.1 Subtractive colour scheme
A subtractive color model explains the mixing of a limited set of dyes, inks, paint pigments or
natural colorants to create a wider range of colors, each the result of partially or completely
subtracting (that is, absorbing) some wavelengths of light and not others. The color that a surface
displays depends on which parts of the visible spectrum are not absorbed and therefore remain visible.
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Subtractive color systems start with light, presumably white light. Colored inks, paints, or filters
between the watchers and the lightt source or reflective surface subtract wavelengths from the light,
giving it color. If the incident light is other than white, our visual mechanisms are able to compensate
well, but not perfectly, often giving a flawed impression of the "true" color of th
thee surface.
CHECK YOUR PROGRESS
Define colour
What is chroma?
What is HSV and HSL model ?
What is Substractive colour model ?
2.3.2 Additive colour scheme
Additive color is color created by mixing a number of different light colors, with shades of red,
green, and blue being the most common primary colors used in additive color system.
Additive color is in contrast to subtractive color, in which colors are created by subtracting
(absorbing) parts of the spectrum of light present in ordinary white light, by means of colored
pigments or dyes, such as those in paints, inks, and the three dye layers in typical color photographs
on film.
The combination of two of the standard three additive primary colors in equal proportions
produces an additive secondary color
or—cyan, magenta or yellow—which,
which, in the form of dyes or
pigments, are the standard primary colors in subtractive color systems. The subtractive system using
primaries that are the secondaries of the additive system can be viewed as an alternative approach to
reproducing a wide range of colors by controlling the relative amounts of red, green, and blue light
that reach the eye.
Computer monitors and televisions are the most common examples of additive color.
Examination with a sufficiently powerful magnifyi
magnifying
ng lens will reveal that each pixel in CRT, LCD
and most other types of color video displays is composed of red, green and blue sub
sub-pixels,
pixels, the light
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from which combines in various proportions to produce all the other colors as well as white and
shades of gray. The colored sub-pixels do not overlap on the screen, but when viewed from a normal
distance they overlap and blend on the eye's retina, producing the same result as external
superimposition.
Another example of additive color can be found in the overlapping projected colored lights often
used in theatrical lighting for plays, concerts, circus shows and night clubs
2.3.3 Working with systems
The Visible spectrum consists of billions of colors, a monitor can display millions, a high quality
printer is only capable of producing thousands, and older computer systems may be limited to 216
cross-platform colors. Reproducing color can be problematic with regard to printed, digital media,
because what we see is not what is possible to get. Although a monitor may be able to display 'true
color' (16,000,000 colors), millions of these colors are outside of the spectrum available to printers.
Since digital designs are generated using the RGB color system, colors used in those designs must be
part of the CMYK spectrum or they will not be reproduced with proper color rendering. Working
within the CMYK color system, or choosing colors from Pantone palettes insures proper color
rendering.
2.4 COLOUR WHEEL
A color wheel or colour circle is an abstract illustrative organization of color hues around a circle,
which shows the relationships between primary colors, secondary colors, tertiary colors etc. A color
wheel also referred to as a color circle is a visual representation of colors arranged according to their
chromatic relationship. Begin a color wheel by positioning primary hues equidistant from one
another, then create a bridge between primaries using secondary and tertiary colors. Some sources use
the terms color wheel and color circle interchangeably; however, one term or the other may be more
prevalent in certain fields or certain versions as mentioned above. For instance, some reserve the term
color wheel for mechanical rotating devices, such as color tops or filter wheels. Others classify
various color wheels as color disc, color chart, and color scale varieties.
As an illustrative model, artists typically use red, yellow, and blue primaries (RYB color model)
arranged at three equally spaced points around their color wheel. Printers and others who use modern
subtractive color methods and terminology use magenta, yellow, and cyan as subtractive primaries.
Intermediate and interior points of color wheels and circles represent color mixtures. In a paint or
subtractive color wheel, the "center of gravity" is usually (but not always) black, representing all
colors of light being absorbed; in a color circle, on the other hand, the center is white or gray,
indicating a mixture of different wavelengths of light (all wavelengths, or two complementary colors,
for example).
The original color circle of Isaac Newton.showed only the spectral hues and was provided to
illustrate a rule for the color of mixtures of lights, that these could be approximately predicted from
the center of gravity of the numbers of "rays" of each spectral color present (represented in his
diagram by small circles). The divisions of Newton's circle are of unequal size, being based on the
intervals of a Dorian musical scale. Most later color circles include the purples, however, between red
and violet, and have equal-sized hue divisions. Color scientists and psychologists often use the
additive primaries, red, green and blue; and often refer to their arrangement around a circle as a color
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circle as opposed to a color wheel.
2.4.1 COLOR RELATIONSHIPS
Color relationships may be displayed as a color wheel or a color triangle
The Painter's color triangle consists of colors we would often use in art class—those colors we
learn about as children. The primary hues are red, blue and yellow.
The Printers' color triangle is the set of colors used in the printing process. The primaries are
magenta, cyan, and yellow.
Nine-part harmonic triangle of Goethe begins with the printer's primaries; the secondaries formed
are the painter's primaries; and the resulting tertiaries formed are dark neutrals.
2.4.2 Color wheels and paint color mixing
There is no straight-line relationship between colors mixed in pigment, which vary from medium
to medium. With a psychophysical color circle, however, the resulting hue of any mixture of two
colored light sources can be determined simply by the relative brightness and wavelength of the two
lights. A similar calculation cannot be performed with two paints. As such, a painter's color wheel is
indicative rather than predictive, being used to compare existing colors rather than calculate exact
colors of mixtures. Because of differences relating to the medium, different color wheels can be
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created according to the type of paint or other medium used, and many artists make their own
individual color
or wheels. These often contain only blocks of color rather than the gradation between
tones that is characteristic of the color circle.
2.4.3 Color wheel software
A number of interactive color wheel applications are available both on the Internet and as de
desktop
applications. These programs are used by artists and designers for picking colors for a design.
The HSL and HSV color spaces are simple geometric transformations of the RGB cube into
cylindrical form. The outer top circle of the HSV cylinder – or the outer middle circle of the HSL
cylinder – can be thought of as a color wheel. There is no authoritative way of labeling the colors in
such a color wheel, but the six colors which fall at corners of the RGB cube are given names in the
X11 color list, andd are named keywords in HTML.
2.4.4 Colour Scheme
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Color schemes are logical combinations of colors on the color wheel.
Moses Harris, in his book The Natural System of Colours (1776), presented this color palette.
Complementary colors are two colors directly across from each other; for example, red and green are
complementary colors. Tetradic color palettes use four colors, a pair of complementary color pairs.
For example, one could use yellow, purple, red, and green. Tetrad colors can be found by putting a
square or rectangle on the color wheel.
In color theory, a color scheme is the choice of colors used in design for a range of media. For
example, the use of a white background with black text is an example of a common default color
scheme in web design.
Color schemes are used to create style and appeal. Colors that create an aesthetic feeling together
commonly appear together in color schemes. A basic color scheme uses two colors that look
appealing together. More advanced color schemes involve several colors in combination, usually
based around a single color—for example, text with such colors as red, yellow, orange and light blue
arranged together on a black background in a magazine article.
Ignaz Schiffermüller, Versuch eines Farbensystems (Vienna, 1772), plate I. Color wheels can be
used to create pleasing color schemes. An analogous color scheme is made up of colors next to each
other on the wheel. For example, red, orange, and yellow are analogous colors.
Color schemes can also contain different shades of a single color; for example, a color scheme
that mixes different shades of green, ranging from very light (almost white) to very dark. Analogous
colors are colors next to each other on the wheel. For example, yellow and green. Monochromic
colors are different shades of the same color. For example, light blue, indigo, and cyan blue.
Complimentary colors are colors across from each other on a color wheel. For example, blue and
orange. Triadic colors are colors that are evenly across from each other, in a triangle over the color
wheel. For example, the primary colors red, yellow, and blue are triadic colors.
Monochromatic Relationship Colors that are shade or tint variations of the same hue.
Monochromatic colors are all the colors (tints, tones, and shades) of a single hue. Monochromatic
color schemes are derived from a single base hue, and extended using its shades, tones and tints (that
is, a hue modified by the addition of black, gray (black + white) and white. As a result, the energy is
more subtle and peaceful due to a lack of contrast of hue.
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Complementary Relationship Those colors across from each other on a color wheel.
For the mixing of colored light, Newton's color wheel is often used to describe complementary
colors, which are colors which cancel each other's hue to produce an achromatic (white, gray or black)
light mixture. Newton offered as a conjecture that colors exactly opposite one another on the hue
circle cancel out each other's hue; this concept was demonstrated more thoroughly in the 19th century.
Split-Complementary Relationship One hue plus two others equally spaced from its
complement. The split-complementary (also called Compound Harmony) color scheme is a variation
of the complementary color scheme. In addition to the base color, it uses the two "Analogous" colors
adjacent to its complement. Split-complementary color scheme has the same strong visual contrast as
the complementary color scheme, but has less pressure.
Double-Complementary Relationship Two complementary color sets; the distance between
selected complementary pairs will effect the overall contrast of the final composition.
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Analogous Relationship Those colors located adjacent to each other on a color wheel. Analogous
colors (also called Dominance Harmony) color scheme are groups of colors that are adjacent to each
other on the color wheel, with one being the dominant color, which tends to be a primary or secondary
color, and two on either side complementing, which tend to be tertiary.
Triad Relationship Three hues equally positioned on a color wheel. The triadic color scheme uses
three colors equally spaced around the color wheel. The easiest way to place them on the wheel is by
using a triangle of equal sides. Triadic color schemes tend to be quite vibrant, even when using pale or
unsaturated versions of hues, offers a higher degree of contrast while at the same time retains the
color harmony. This scheme is very popular among artists because it offers strong visual contrast
while retaining balance, and color richness. The triadic scheme is not as contrasting as the
complementary scheme, but it is easier to accomplish balance and harmony with these colors.
2.5 COLOUR RELATIONSHIP
We are very familiar with the RGB colour model as . model is used in most computer
applications, digital cameras, monitor, etc. CMYK is a common colour model used in the print
industry. In computer applications, RGB and CMYK colour models can be utilized by using any
modem version of Adobe Photoshop.
By using only the .t letter of each of the RGB and CMKY colours, we can repmsent all of the
other supported colours in the maid. RGB model can represent 16.7 million coburs by employing red,
green and blue. while CMYK model uses cyan, magenta and yellow to nuke its cobur range. To fully
accomplish thc depth needed for some CMKY cobtus, a fourth colour 'black' is also added. The
technique is obsolete now.
It can be a link bit confusing, if you are not familiar with CMKY There is a bit of relation
between RGB and CMYK that becomes especially helpful to know when performing color correction.
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C M Y K if you know what colour the colour cast of the amp is, while color correcting an image,
you can easily correct it by adding the corresponding color from the other color model. For example,
adding red will help eradicate the cyan cast of an image. On the other hand, slowly adding magenta
will counterbalance the green, if your image is on the green side
The RGB colour space generally uses an additive process. So, each color adds to the earlier one.
Adding each primary color will give a white image. CMYK is a good example of a subtractive
process. In CMYK each color do. not allow light. In this Way, a mixture of all three colors will give
black.
CHECK YOUR PROGRESS
What is a colour wheel?
What is metaneric colour matching?
What arc color scheme?
2.5.1 Complementary Colours
Complementary colors are those pair of colors that are of opposite hue in some color model In
color theory, when two colours are mixed in the correct proportion. known as complementary colors,
they produce a neutral color such as grey, white or black. The neutral colours (white, grey and black )
lie along a central axis. in an approximate color model In the HSV colour space, for example color as
defined in HSV lie opposite to each other on any horizontal cross section.
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Whenever we discuss complementary colour, only fully saturated, bright colours are taken into
consideration. Brightness and saturation are also key factors in a formal definition of complementary
colours. Accord* to CIE 1931 colour space, a particular 'dominant' wavelength of a colour can be
combined with a particular amount of the 'complementary' wavelength to produce a neutral colour
(grey or white)
In the RGB colour model and also with obtained model such as HSV, primary and secondary
colours are paired accordingly as follows:
Red and Cyan
Green and Magenta
Blue and Yellow
When we look at a single colour (red for example) constantly fixed for a prolonged period of time
for about thirty seconds to a minute, and then look at a white surface, an after-image of the
complementary colour (in this case cyan) will appear. These after-effect are prepared according to the
psychology of visual view point which is generally signs of fatigue, in various parts of the human
visual system. The photo receptors for red light in the retina are fatigued in the above case, decreasing
their ability to transformation to the brain. When we see white light, the red part of the incident fight
which fall on our eye are not efficiently transmitted as the other wavelengths (or colours). This results
in an illusion of viewing the complementary colour. The illusion will gradually vanish as the photo
receptors are given time to rest. normally, the eye will reach an equilibrium because the receptors for
other fight coburs are also being fatigued.
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Various Cells in the Retina
Aesthetically, the use of complementary colours is very pleasing in the field of an and graphic
design. This is not only limited to art and design, but also extends to other fields such as demarcating
colours in logos and retail displays. If placed next to each other, complementary colours make each
other form brighter. An artistic colour wheel is a bit different, where complementary colours are
placed opposite to each other although these models are not accurate according to the scientific
definition By mixing two prim, colours in a subtractive system, a colour is produced using the
complement of each primary colour.
Blue complements (red+ yellow) = orange
Red complements (blue + yellow)
Green Yellow complements (red + blue) = purple
Grey is produced by mixing two complements.
Neurobiological reason
The difference between violet and blue as complements for yellow and the difference between
cyan and green as complements for red is an upward move in the spectrum. It is called the opponentBMG 103: Color Theory
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colour system as described by a colour viewpoint model. It is also a topic of controversy that
differentiating complementary colour from negative colour can be solved: blue for the negative with
violet for the complement of yellow; cyan for the negative with green for the complement of red.
Both complementary colours and negative colours are concerned with providing contrast that
activates retinal ganglion cells int., in a covered versus centre opponent process.
2.5.2 Perceptual Opposites
We have studied from the connections visualized by a color wheel that every color has an
opposite. Every color has both a color wheel opposite as well as a perceptual opposite. Due to a
special phenomenon of our eyes, it is possible to find the opposite of a colour without using a color
wheel. We all have our different perceptions towards color due to the physiological differences.
2.5.3 Color Combinations
Color combinations may proceed unnoticed when pleasing, yet outrage dramatically when
compositions seem to come into conflict. We always seek a successful use of color in the final form
or composition. We determine our success by decisively judging the visual balance and harmony of
the final composition. Balance and harmony are accomplished by the visual contrast that exists
between color combinations. The observation and judgement of color relationships is a key for
planning a successful color combination
2.6 COLOUR CONTRAST
Every visual presentation involves figure-ground relationships. This relationship between a
subject (or figure) and its surrounding field (ground) will evidence a level of contrast; the more an
object contrasts with its surrounds, the more visible it becomes. The difference in visual characteristic
that makes an object or its representation in an image distinct from other objects and the background
is called a contrast. Difference in the color and brightness of the object determines demarcation in t.
real world's visual viewpoint and other objects within . same field of view. This happens because the
human visual system is very sensitive to demarcate than absolute luminance. Regardless of the huge
changes in illumination over the day or from place to place, we can identify world.
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Contrast Sensitivity of Haman Eyes
A regular band-pass shape peaking at around 4 cycles per degree shown by t. human contrast
sensitivity, with sensitivity dropping off from either side of the peak. This discloses that the human
visual system is most sensitive in recognizing contrast differences taking place at 4 cycles per degree.
Humans can detect lower contrast differences at this spatial frequency, than at any other spatial
frequency.
One optical limitation of the visual system to be able to resolve detail is the high-frequency cutoff and is generally about 60 cycles per degree. The packing density of the retinal photo receptor cells
is related to the high-frequency cut-off
A typical ganglion cell of a retina shows a central area with either excitation or inhibition and a
surround region with the opposite sign. Due to lateral inhibition within the ganglion cells of the retina,
the low-frequency drop-off occurs. Lateral inhibition results because the bright bands, by using coarse
grating, fall on the inhibitory as well as the excitatory regions of the ganglion cell. This accounts for
the low-frequency drop-off of the human contrast sensitivity function.
The inhibition of blue in the confines, if blue light is displayed against white leads to a yellow
surrounding, is an experimental form. The yellow is obtained from the inhibition of blue on the
surroundings by the center. The reason is that white minus blue is red and green which combines to
become yellow, for example, in graphical computer displays, demarcation depends on two things;
one, the properties of the picture source or file, and two, the properties of the computer display,
including its variable settings. The angle between the screen surface and the observer's line of sight is
also an important way to present for some screens.
Contrast is also known as the difference between the colors. It is also the difference between
shading of the printed material on a document and the background on which it is printed. Optical
character recognition is one such example. There are various definitions of contrasts which are used in
different situations. Following is an example of luminance contrast. In different situations, the
definitions of contrast represent a rat, of the type:
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Luminance difference
Average luminance
This formula can be applied to other physical quantities.
The logical cause behind this is that if the average luminance is high, then a small difference is
negligible; if the average luminance is low, the same difference matters a lot.
Contrast sensitivity
Demarcation sensitivity is a measure of the ability to distinguish between luminance of different
levels in a static image. Demarcation sensitivity differs between individuals, reaching a maximum at
approximately twenty years of age, and also at spatial frequencies of about 2-5 cycles/degree. It can
drop down with age and also due to other conditions such as diabetic retinopathy and cataracts.
Improving contrast sensitivity
It was an old thought that demarcation sensitivity was relatively fixed and with age it becomes
worse. But new research has proved that playing video games can slightly improve demarcation
sensitivity.
The contrast ratio, can be explained as the ratio of the luminance of the bright. colour (white) to
that of the darkest colour (black) that the system is capable of producing. It is a measure of display
system. One of the aspects for any display is a high contrast ratio. Sometimes different measured
values can produce the same results, with various methods o f measurements for a system.
Different manufacturers provide contrast ratio ratings of display devices that are not necessarily
comparable to each other The reason is the differences in method of measurement, function and
unstated variables. Manufacturers have always preferred measurement process that quarantines the
device from the system, some designers have taken into account the effect of the room An ideal room
is the one, which absorbs all the light being reflected from a projection screen or emitted by a CRT. In
an ideal room, light would come only from the display device.. contrast ratio of the image would be
the same as the device in such a room In a realistic situation a real room reflects some of the light
back to the displayed image, which lowers the demarcation ratio seen in the image.
There are two types of contrast ratios:
(i) Static demarcation ratio: It is the ratio of the luminosity of the darkest and the brightest
colour the system is capable of producing concurrently at any instant of time.
(ii) Dynamic demarcation ratio: It is the ratio of the luminosity of the darkest and the brightest
colour the system is capable of producing over time.
Methods of measurement
The use of the full on/full off method of measurement is favoured by many display instruments.
The method cancels out the effect of the room arid produces an ideal ratio. As long as the room stays
the same, equal proportions of light will reflect from the display to the room and back in both 'black'
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and 'white' measurements. increase the light levels of both measurements proportionally, leaving the
black to white luminance ratio unaffected.
Some manufacturers have used different device parameters for the three test, even further
inflating the calculated demarcation ratio. Wah DLP projectors, one method to do this is to be able to
clear the sector of the colour filter wheel for the 'on. part and disable it for the 'off' part. This practice
is very doubtful as it will be impossible to reproduce such demarcation ratios with any useful image
content.
ANSI demarcation is another kind of measure, in which the measurement is done with a checker
board patterned test image where the luminosity values are measured concurrently. In fact, this is a
more realistic measure of system capability, • but it also includes the potential by taking into account
the effects of the room in the measurement. if the test is not performed in a room that is close to ideal.
One should note that the full on/full off method efficiently measures the dynamic demarcation
ratio of a display, while the ANSI demarcation measures the static demarcation ratio.
2.7 ITTEN'S COLOUR CONTRAST
Johannes Itten was one of the first people to define and identify strategies for successful color
combinations. Through his research he devised seven methodologies for coordinating colors utilizing
the hue's contrasting properties. These contrasts add other variations with respect to the intensity of
the respective hues; i.e. contrasts may be obtained due to light, moderate, or dark value.
The Contrast Of Saturation
The contrast is formed by the juxtaposition of light and dark values and their relative saturation.
The Contrast Of Light And Dark
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The contrast is formed by the juxtaposition of light and dark values. This could be a
monochromatic composition.
The Contrast Of Extension
Also known as the Contrast of Proportion. The contrast is formed by assigning proportional field
sizes in relation to the visual weight of a color.
The Contrast Of Complements
The contrast is formed by the juxtaposition of color wheel or perceptual opposites.
Simultaneous Contrast
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The contrast is formed when the boundaries between colors perceptually vibrate. Some interesting
illusions are accomplished with this contrast.
The Contrast Of Hue
The contrast is formed by the juxtaposition of different hues. The greater the distance between
hues on a color wheel, the greater the contrast.
The Contrast Of Hue - Primaries
The contrast is formed by the juxtaposition of primary hues.
The Contrast Of Warm And Cool
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The contrast is formed by the juxtaposition of hues considered 'warm' or 'cool.'
Design practitioners should understand the importance of Johannes Itten's work, who withed to
use contrast of colour to raise a desired reaction on those who look at his designs. We should know
that colour is one of the elements of design:
[it] can make designs more visually interesting and aesthetic. and can reinforce the organisation
and meaning of elements a design'- Lidwell, Holden, Butler, 2003.
Utilizing contrast is one of most effective ways to use colour. In designing, contrast demonstrates
an element in opposition.
Itten wished to create theories of contrast which incorporates objective perception of colour
harmony. While studying colour contrast, he developed a systematic oversight, commonly known as
Itten's seven contrasts. One must have the know-how of his twelve hue colour circle, called Farbkreis
to realize the contrasts system organized by Itten. It was a change of the colour wheel which was
developed by 18th century colour theorist Johann Wolfgang Goethe.
CHECK YOUR PROGRESS
What is a contrast?
Define 'Michelson's demarcation'.
What is an ideal room?
2.8 PROPORTION AND INTENSITY
When colors are juxtaposed, our eyes perceive a visual mix. This mix will differ depending on the
proportions of allocated areas.
The color with the largest proportional area is the dominant color (the ground).
Smaller areas are subdominant colors.
Accent colors are those with a small relative area, but offer a contrast because of a
variation in hue, intensity, or saturation (the figure).
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Placing small areas of light color on a dark background, or a small area of dark on a light
background will create an accent.
If large areas of a light hue are used, the whole area will appear light; conversely, if large
areas of dark values are used, the whole area appears dark.
Alternating color by intensity rather than proportion will also change the perceived visual
mix of color.
EXAMPLES OF PROPORTION
Dominant color
Sub-dominant colors
Accent
Dominant color
Sub-dominant colors
Accent
Dominant color
Sub-dominant colors
Accent
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Dominant color
Sub-dominant colors
Accent
2.9 CONTRAST AND DOMINANCE
When creating a composition—either something freeform, or a more text based layout, a
determination for the final impact of the whole presentation needs to be identified. Is your intent to
craft a vibrant, attention grabbing ad, or a presentation with a low, or more moderate level of contrast?
These decisions concern what is known as the dominant elements of the design.The dominant element
may be classified as either "contrast dominant" or "value dominant." Designs that evidence contrast
dominance or value dominance are then sub-divided into low, moderate, and high contrast, or light,
medium, and dark value categories. The choice of colors will enhance or minimize the overall
impact.It is easiest to understand the difference between dominant elements in the following
compositions from a distance, or by squinting your eyes a bit. If the proximity between the
neighboring hues is less apparent when you squint, the overall composition a displays lower contrast
level; if the overall composition appears light, it has a light value. Conversely, if distinctions between
hues are very apparent, the contrast is high, and if the overall composition appears dark, the value
level is dark. Understanding how the relationships between the colors of a chosen palette will affect
the final outcome of an overall composition is integral to mastering the use of color.
EXAMPLES OF CONTRAST DOMINANCE
In the examples below, the overall contrast level of a composition changes with the range of
luminosity between chosen hues.
Low contrast
Low contrast compositions use colors within a narrow range of luminosity or brightness levels.
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Moderate contrast
moderate contrast compositions use colors within a moderate range of luminosity or brightness
levels.
High contrast
High contrast compositions colors range from very light (high-luminosity) to very dark (low
luminosity).
EXAMPLES OF VALUE DOMINANCE
In the examples below, the overall value of each composition changes with the incorporated hues'
relative saturation.
Light value
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A composition made up of tints, displays an overall light value.
Medium value
A medium value composition is made up of a balance between tints, saturated hues, and shades.
Dark value
A dark value composition displays mostly shades.
2.10 COLOUR SHADES AND TINTS
Using a color wheel divided into various shades and tints is one method of identifying possible
options for color schemes. The split complementary relationship shown in this example presents many
possible combinations. By varying the saturation and experimenting with shades and tints within the
hue relationship, you can achieve quite a variety of palette options.
Moderately-high contrast, medium value, composition using fully saturated hues.
High contrast, medium value, composition using shades, tints & various saturation levels.
Moderately-low contrast, medium-light value, using tints & various saturation levels.
Moderate contrast, medium value, using shades, tints & various saturation levels.
Moderately-low contrast, medium-dark value, using shades & various saturation levels.
Low contrast, medium value, using shades, tints & various saturation levels.
Moderately-high contrast, medium value, using shades, tints & various saturation levels.
High contrast, light value, using shades, tints & various saturation levels.
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It is common among some artistic painters to darken a paint color by adding black paint—
producing colors called shades—or to lighten a color by adding white—producing colors called tints.
However, this is not always the best way for representational painting, since an unfortunate result is
for colors to also shift in their hues. For instance, darkening a color by adding black can cause colors
such as yellows, reds and oranges, to shift toward the greenish or bluish part of the spectrum.
Lightening a color by adding white can cause a shift towards blue when mixed with reds and oranges.
Another practice when darkening a color is to use its opposite, or complementary, color (e.g. violetpurple added to yellowish-green) in order to neutralize it without a shift in hue, and darken it if the
additive color is darker than the parent color. When lightening a color this hue shift can be corrected
with the addition of a small amount of an adjacent color to bring the hue of the mixture back in line
with the parent color (e.g. adding a small amount of orange to a mixture of red and white will correct
the tendency of this mixture to shift slightly towards the blue end of the spectrum).
2.11 COLOUR STUDIES OF COMPLEMENTARY
RELATIONSHIPS
COLORS OF A COMPLEMENTARY RELATIONSHIP.
Colors of a complementary relationship assigned equal proportion.
Colors reassigned with proportions allocated to dominant and subdominant areas.
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Color intensity and proportion modified. Using tints and shades of the original colors results in a
moderate level of contrast and medium value.
Colors applied to composition.
Color intensity and proportion modified - the whole area displays a moderately-high contrast and
medium value.
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Colors applied to composition.
COLORS OF A TRIAD RELATIONSHIP.
Colors of a triad relationship assigned equal proportion.
Colors reassigned with proportions allocated to dominant, subdominant, and accent areas.
Color intensity and saturation modified - the whole area displays a moderately-high contrast
level.
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Colors applied to composition.
Color intensity and saturation modified - the whole area displays a moderately low contrast level.
Colors applied to composition.
Color intensity and saturation modified - the whole area displays a medium/dark value.
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Colors applied to composition.
Color intensity and saturation modified - the whole area displays a light value,
Colors applied to composition.
Sir Isaac Newton propounded various hypotheses about the relationships of colours with musical
sounds in pursuit of discovering fundamental laws of colour harmony. It was Newton, work on
complement, colours which has the greatest influence in the history of painting. Sir Isaac Newton
worked extensively with light rather than with pigments. Brook Taylor (1685-1731), a great
mathematician, mentioned in his book New Principles of Linear Perspective (1719) that "the
knowledge of . [Newton's] theory may be of great use in painting'. Taylor explained in his book how
Newton, circle plays a vital role in the inking of paints. A key factor has been the confusion between
additive and subtractive mixing. That is the reason why there has been such a multiplication of
different colour wheels.
Complement, colour three different meanings:
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(i) Complementary co bur gives a chromatically neutral colour (known as subtractive
compliment) if we mix a pair of colours as paints or inks.
(ii) A pair of colours (essentially additive colour mixing) that spin to grey on Maxwell disks is
called an optical complement.
(iii) An after-image complement gives when a colour and its afterimage that gives if the colour is
stared at and then removed.
2.12 SUMMARY
Colour comes out from the spectrum of light, i.e., distribution of light energy against wavelength.
which interacts in our eye with the spectral sensitivities of the tight receptors.
Colour divisions and physical specifications of colour are also associated with object, materials,
light sources, etc.
The colour divisions and specifications are based on the physical properties such as light
absorption, reflection, or emission spectra.
Colours can be identified numerically by their coordinates by the definition of a colour space.
The important features of the composition °flight that are detectable by humans (wavelength
spectrum from 380 nm to 740 nm, roughly) are involved which relates the psychological phenomenon
of colour to its physical specification.
Colours maybe explained and determined by the degree to which they stimulate cone cells in the
retina, as a result, the perception of colour sprung up from varying sensitivity of the cells to different
parts of the spectrum. • New research has shown that playing video games can slightly improve
contrast sensitivity, compared to the older thought that contrast sensitivity is static and degrades with
age.
Likewise red-orange and blue-green are pa. of extreme cold-warm contrasts.
2.13 KEY TERMS
Achromatic: Colour lacking hue; neutral such . black. white or grey.
Additive mixture: When different colour tights are mixed, the light from each component of this
mixture reaches the eye an unmodified state known as additive mixture.
Brightness: A characteristic of visual perception according to which an area seems to en. more or
less light. The perceived amount of light comes from an area.
Chroma: A feature of a visual sensation that allows a judgement to be formed of the amounts of
pure chromatic colour present, irrespective of the amount of achromatic colour.
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Chromatic response function: A function from the wavelength of a stimulus to facets of
perceived colour.
CIE Standard Observer: A set of tri-stimulus values for spectral lights that is designed to allow a
standard and object. way of describing the colour matching properties of different lights
Electron-volt: The amount of energy required to move an electron across a potential change of
one volt, a common unit of energy . physics.
Colour space: A ,stem for ordering colours that respects the relationships of similarity among
them. There are varieties of different colour margins, but they are all three dimensional
Colorimetry: The science of measuring colour and colour appearance.
Ganglion cells: The output cell of the retina that gather inputs from the photoreceptors and send
their outputs to the brain.
Intensity: Intensity is the power/strength of light.
2.14 END QUESTIONS
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
Give the basic description of colour.
Define 'chrome'.
Differentiate between intensity and luminance.
Differentiate between shade and tint.
What arc subtractive colours?
What arc analogous colours?
Differentiate between dominant and sub-dominant coburs,
Define 'optical complement'.
Explain the basic concepts of colour system:.
What is a colour wheel? Highlight its importance in paint colour mixing.
What are complementary colours? Add a note on perceptual opposites.
Write Itten's colour contrasts.
Define colour
What is chroma?
What is HSV and HSL model ?
What is Substractive colour model ?
What is a colour wheel?
What is metaneric colour matching?
What arc color scheme?
What is a contrast?
Define 'Michelson's demarcation'.
What is an ideal room?
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UNIT 3: COLOUR HARMONY
3.0 INTRODUCTION
Harmony can be interpreted as a pleasing adaptation of parts in music, poetry, color. painting or
even food. Harmony is something that is pleasing to our eye in our visual experiences. It occupies the
viewer and creates an order of an inner sense which balances the visual experience. It is chaotic and
boring when something is not harmonious. In the utmost degree is a visual experience that is not so
stimulating, in this case. the viewer is not so occupied by the experience. The human brain is designed
in such a way that it will not recognize under-stimulating information. At the other extreme is a visual
experience which is so completely disordered that it leaves the viewer totally' unpleased. The human
brain does not recognize unorganized patterns and rejects what it cannot understand. A logical
structure is the basic requirement of the visual task.
Understanding of color harmony is extremely important for you as a student and as a professional
in media, graphics and animation. Which color schemes to choose for a graphic, animation or
photograph, is of crucial importance. You will decide on the basis of the demand of the project, which
color schemes to choose. The topics covered under this course will help you understand various
concepts covered in all other courses like photoshop, illustrator, 3Ds max or Maya animation courses
which you will study as part of your study in BSc(MGA).
3.1 UNIT OBJECTIVES
After going through this unit you will be able to:
•
•
Understand the essence of color harmony
Discuss the various color schemes
3.2 SOME FORMULAS FOR COLOUR HARMONY
The monochromatic colour (Refer to Figure C3) scheme is deduced from a single base colour. A
monochromatic colour is derived by using just a single hue. By using its shades and tints, this single
colour is stretched out; that is, a modified colour is produced by the addition of black and white. Due
to a deficiency of colour contrast, the energy which results is more delicate and peaceful.
Monochromatic colours present very little contrast and unless there is a variety within the design, they
may be considered mentally as boring.
Only though regulating saturation and tones, the composition of the painting or any. work is
achieved. Although monochrome colours are very limited they can be used as powerful tools.
3.2.2 Colour Scheme Based on Analogous Colours
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Analogous colors are groups of three colors that are next to each other on the color wheel, sharing
a common color, with one being the dominant color, which tends to be a primary or secondary color,
and a tertiary. Red, orange, and red-orange are examples.
The term analogous refers to having analogy, or corresponding to something in particular. An
analogous color scheme creates a rich, monochromatic look. It is best used with either warm or cool
colors, creating a look that has a certain temperature as well as proper color harmony. While this is
true, the scheme also lacks contrast and is less vibrant than complementary schemes. These color
schemes are most often seen in nature. For example, during the fall, one might often see the changing
leaves form an analogous sort of color scheme, progressively moving through the color wheel to
create a gradient in its natural pattern.
3.2.3 Colour scheme based on complementary colour
The complementary colour formula is commonly us. to increase co formula uses two colo
examples of opposites and are used appropriate in various proportions
3.2.4 Colour Scheme Based on Nature
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The nature colour scheme yields more ease in choosing coburs. The reason behind the freedom is
that you can use any colour combination which appears in natural environments. Red, yellow and
green always produce a harmonious design.
3.3 COLOUR CONTEXT
Red combines with green to produce yellow, green combines with blue to produce cyan and blue
combines with red to form magenta. In full intensity red, green and blue combines to produce white.
How colour acts with different shapes and in relation to other colours is quite a complex area of
colour theory, but for the same red square we can compare the contrast effects of different colour
backgrounds.
Red does not appear bright against 'Mike background, but a appears very bright against a black
background. It appears dull in contrast with orange; whereas, it shows brilliance in contrast with bluegreen. Observe that red square applies larger on black than on any other background colours.
3.4 Different readings of the same colour
(Source: https://www.color-meanings.com/)
Colors play a very important role in our lives, whether we realize it or not. They have the ability
to affect our emotions and moods in a way that few other things can.
This page describes color meanings importance for us as people, what they do to our emotions
and how color meaning through advertising can be used to influence our view of a product. You will
be surprised how much influence colors have in our everyday lives.
How does a yellow room make your feel? Does the blue color calm and relax you? Designers
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have already for a long time understood how color can affect moods and emotions in a big way. Color
is a very powerful tool for communicating and can be used to indicate an action, affect the mood and
cause reactions in peoples mind. Some colors can actually raise your blood pressure and increase
metabolism. They have even been known to cause eyestrain, if looked on long enough.
How color meanings change
Your own feelings about colors can of course also be very personal. Color meanings may have
something to do with your past, your experiences or your culture. For instance, while the color white
is often used in many Western countries to represent purity and innocence, it is seen as a symbol of
mourning in many Eastern European countries.
How significant is the meaning of colors and why do they play such a big role in our lives? What
impact do they have on our body and mind? Read on to explore color meanings, how they
are used, the effects they may have and some of the latest research on color psychology.
3.5 CLASSIC COLOUR SCHEMES
(Source: https://en.wikipedia.org/wiki/Color_scheme)
In color theory, a color scheme is the choice of colors used in design for a range of media. For
example, the "Achromatic" use of a white background with black text is an example of a basic and
commonly default color scheme in web design.
Color schemes are used to create style and appeal. Colors that create an aesthetic feeling when
used together will commonly accompany each other in color schemes. A basic color scheme will use
two colors that look appealing together. More advanced color schemes involve several related colors
in "Analogous" combination, for example, text with such colors as red, yellow, and orange arranged
together on a black background in a magazine article. The addition of light blue creates an "Accented
Analogous" color scheme.
3.5.1 Monochromatic colors
Monochromatic colors are all the colors (tints, tones, and shades) of a single hue.
Monochromatic color schemes are derived from a single base hue, and extended using its shades,
tones and tints (that is, a hue modified by the addition of black, gray (black + white) and white. As a
result, the energy is more subtle and peaceful due to a lack of contrast of hue.
Pros: The monochromatic scheme is easy to manage, and always looks balanced and visually
appealing.
Cons: This scheme lacks color contrast. It is not as vibrant as the complementary scheme.
Tips: 1. Use tints, shades, and tones of the key color to enhance the scheme.
2. Try the analogous scheme; it offers more nuances while retaining the simplicity and elegance
of the monochromatic scheme.
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3.5.2 Complementary colors
For the mixing of colored light, Newton's color wheel is often used to describe complementary
colors, which are colors which cancel each other's hue to produce an achromatic (white, gray or black)
light mixture. Newton offered as a conjecture that colors exactly opposite one another on the hue
circle cancel out each other's hue; this concept was demonstrated more thoroughly in the 19th century.
A key assumption in Newton's hue circle was that the "fiery" or maximum saturated hues are
located on the outer circumference of the circle, while achromatic white is at the center. Then the
saturation of the mixture of two spectral hues was predicted by the straight line between them; the
mixture of three colors was predicted by the "center of gravity" or centroid of three triangle points,
and so on.
Pros:The complementary color scheme offers stronger contrast than any other color scheme, and
draws maximum attention.
Cons:This scheme is harder to balance than monochromatic and analogous schemes, especially
when desaturated warm colors are used.
Tips:1. For best results, place cool colors against warm ones, for example, blue versus orange.
2. If you use a warm color (red or yellow) as an accent, you can desaturate the opposite cool
colors to put more emphasis on the warm colors.
3. Avoid using desaturated warm colors (e.g. browns or dull yellows).
4. Try the split complementary scheme; it is similar to the complementary scheme but offers more
variety.
3.5.3 Split-Complementary
The split-complementary (also called Compound Harmony) color scheme is a variation of the
complementary color scheme. In addition to the base color, it uses the two "Analogous" colors
adjacent to its complement. Split-complementary color scheme has the same strong visual contrast as
the complementary color scheme, but has less pressure.
Pros:The split complementary scheme offers more nuances than the complementary scheme while
retaining strong visual contrast.
Cons:The split complementary scheme is harder to balance than monochromatic and analogous
color schemes.
Tips:1. Use a single warm color against a range of cool colors to put an emphasis on the warm
color (red versus blues and blue-greens, or orange versus blues and blue-violets).
2. Avoid using desaturated warm colors (e.g. browns or dull yellows), because this may ruin the
scheme.
3.5.4 Triadic colors
The triadic color scheme uses three colors equally spaced around the color wheel. The easiest
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way to place them on the wheel is by using a triangle of equal sides. Triadic color schemes tend to be
quite vibrant, even when using pale or unsaturated versions of hues, offers a higher degree of contrast
while at the same time retains the color harmony. This scheme is very popular among artists because
it offers strong visual contrast while retaining balance, and color richness. The triadic scheme is not as
contrasting as the complementary scheme, but it is easier to accomplish balance and harmony with
these colors.
Pros:The triadic color scheme offers high contrast while retaining harmony.
Cons:The triadic color scheme is not as contrasting as the complementary scheme.
Tips:1. Choose one color to be used in larger amounts than others.
2. If the colors look gaudy, try to subdue them.
3.5.5 Tetradic colors
The tetradic (double complementary) colors scheme is the richest of all the schemes because it
uses four colors arranged into two complementary color pairs. This scheme is hard to harmonize and
requires a color to be dominant or subdue the colors.; if all four colors are used in equal amounts, the
scheme may look unbalanced.
Rectangle
The rectangle color scheme uses four colors arranged into two complementary pairs and offers
plenty of possibilities for variation. Rectangle color schemes work best when one color is dominant.
Square
The square color scheme is similar to the rectangle, but with all four colors spaced evenly around
the color circle. Square color schemes works best when all colors are evenly balanced.
Pros:The tetradic scheme offers more color variety than any other scheme.
Cons:This scheme is the hardest scheme to balance.
Tips:1. If the scheme looks unbalanced, try to subdue one or more colors.
2. Avoid using pure colors in equal amounts.
3.6 SUMMARY
Many prominent artists and scientists devoted their lives searching for the perfect laws of colour
harmony.
The nature of colour primaries, the circular nature of hue & concept of complementary colours
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are important for maintaining colour harmony
The predominant view intro literature of colour theory is that it is impossible to take out the
concept of art and design from the context of colour harmony
Thus, what we take into consideration as harmonious is to a great, extent subject to fashion,
personal preference and other cultural influences.
The complementary colour formula commonly used to increase colour contrast.
Two colours, adjacent to each other interact with each other and accordingly change our
perception The result of this interaction is called simulation contrast
The triadic colour scheme which uses three colours equally spaced around the colour wheel is
popular among antis. because it provides strong visual contrast. while keeping the balance intact, and
retaining colour riches as well.
The tetradic scheme which uses four colours efficiently arranged into two complementary colour
pairs, is the richest among all the schemes as it can offer more colour variety than any other scheme.
3.7 KEY TERMS
•
•
•
Monochromatic colour: Colour derived by using just a single hue.
Simultaneous contrast: The result of interaction of two adjacent colour which change our
perception.
Complementary colours: Pairs of colours set diametrically opposite on a colour circle
Triadic colour scheme: Uses three colours equally spaced around the colour wheel.
3.8 END QUESTIONS
1. Define colour harmony?
2. Differentiate between analogous and monochromatic colour scheme.
3. Name one colour scheme most preferred by artists.
4. Define nature colour scheme.
5. List the pros and cons of the complementary colour scheme.
6. Explain how colour harmony could be achieved?
7. Analyse the characteristics of the various colour schemes. Add a note on their pros and cons.
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UNIT 4: COLOUR MEANINGS
4.0 INTRODUCTION
All colors mean something on an emotional level and they can help add new visual layers to your
film. For example: warm colors (such as red, yellow, or orange) wake us up and get us moving while
cool colours (such as blue, green, white) have a calming effect on us.
It is also essential that you learn what colors mean to various cultures and traditions around the
world. For example: in Western culture, black is the color of death (mourning). In Eastern culture, the
color of mourning is white.
Understanding of color meaning is extremely important for you as a student and as a professional
in media, graphics and animation. Which color to choose for a graphic, animation or photograph is of
crucial importance. You will decide on the basis of the demand of the project, which color schemes to
chose. The topics covered under this course will help you understand various concepts covered in all
other courses like photoshop, illustrator, 3Ds max or Maya animation courses which you will study as
part of your study in BSc(MGA).
4.1 UNIT OBJECTIVES
After going through this unit, you will be able to:
•
•
•
Explain the meaning of colour in different cultures.
Differentiate between warm and cool colours.
Describe the concept of neutral colour.
4.2 COLOUR MEANINGS AND COLOURS THAT GO
TOGETHER
The meaning of colors can vary depending on culture and circumstances.
Each color has many aspects to it but you can easily learn the language of color by understanding
a few simple concepts.
Color is a form of non verbal communication. It is not a static energy and its meaning can change
from one day to the next with any individual - it all depends on what energy they are expressing at
that point in time.
For example, a person may choose to wear red on a particular day and this may indicate any one
or more of the psychological meanings of the color red, including the following:
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•
this is their favorite color, or
•
it may be that they are ready to take action in some way, or
•
they may be passionate about what they are going to be doing that day, or
•
it may mean that they are feeling angry that day, on either a conscious or
subconscious level.
All are among the traits of the color red.
Red is the color of fire and blood, so it is associated with energy, war, danger, strength, power,
determination as well as passion, desire, and love.
i) Red is a very emotionally intense color. It enhances human metabolism, increases respiration rate,
and raises blood pressure. It has very high visibility, which is why stop signs, stoplights, and fire
equipment are usually painted red. In heraldry, red is used to indicate courage. It is a color found in
many national flags.
Red brings text and images to the foreground. Use it as an accent color to stimulate people to
make quick decisions; it is a perfect color for 'Buy Now' or 'Click Here' buttons on Internet banners
and websites. In advertising, red is often used to evoke erotic feelings (red lips, red nails, red-light
districts, 'Lady in Red', etc). Red is widely used to indicate danger (high voltage signs, traffic lights).
This color is also commonly associated with energy, so you can use it when promoting energy drinks,
games, cars, items related to sports and high physical activity.
Light red represents joy, sexuality, passion, sensitivity, and love.
Pink signifies romance, love, and friendship. It denotes feminine qualities and passiveness.
Dark red is associated with vigor, willpower, rage, anger, leadership, courage, longing, malice,
and wrath.
Brown suggests stability and denotes masculine qualities.
Reddish-brown is associated with harvest and fall.
ii) Orange combines the energy of red and the happiness of yellow. It is associated with joy, sunshine,
and the tropics. Orange represents enthusiasm, fascination, happiness, creativity, determination,
attraction, success, encouragement, and stimulation.
To the human eye, orange is a very hot color, so it gives the sensation of heat. Nevertheless,
orange is not as aggressive as red. Orange increases oxygen supply to the brain, produces an
invigorating effect, and stimulates mental activity. It is highly accepted among young people. As a
citrus color, orange is associated with healthy food and stimulates appetite. Orange is the color of fall
and harvest. In heraldry, orange is symbolic of strength and endurance.
Orange has very high visibility, so you can use it to catch attention and highlight the most
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important elements of your design. Orange is very effective for promoting food products and toys.
Dark orange can mean deceit and distrust.
Red-orange corresponds to desire, sexual passion, pleasure, domination, aggression, and thirst
for action.
Gold evokes the feeling of prestige. The meaning of gold is illumination, wisdom, and wealth.
Gold often symbolizes high quality.
iii) Yellow is the color of sunshine. It's associated with joy, happiness, intellect, and energy.
Yellow produces a warming effect, arouses cheerfulness, stimulates mental activity, and
generates muscle energy. Yellow is often associated with food. Bright, pure yellow is an attention
getter, which is the reason taxicabs are painted this color. When overused, yellow may have a
disturbing effect; it is known that babies cry more in yellow rooms. Yellow is seen before other colors
when placed against black; this combination is often used to issue a warning. In heraldry, yellow
indicates honor and loyalty. Later the meaning of yellow was connected with cowardice.
Use yellow to evoke pleasant, cheerful feelings. You can choose yellow to promote children's
products and items related to leisure. Yellow is very effective for attracting attention, so use it to
highlight the most important elements of your design. Men usually perceive yellow as a very
lighthearted, 'childish' color, so it is not recommended to use yellow when selling prestigious,
expensive products to men – nobody will buy a yellow business suit or a yellow Mercedes. Yellow is
an unstable and spontaneous color, so avoid using yellow if you want to suggest stability and safety.
Light yellow tends to disappear into white, so it usually needs a dark color to highlight it. Shades of
yellow are visually unappealing because they loose cheerfulness and become dingy.
Dull (dingy) yellow represents caution, decay, sickness, and jealousy.
Light yellow is associated with intellect, freshness, and joy.
iv) Green is the color of nature. It symbolizes growth, harmony, freshness, and fertility. Green has
strong emotional correspondence with safety. Dark green is also commonly associated with money.
Green has great healing power. It is the most restful color for the human eye; it can improve
vision. Green suggests stability and endurance. Sometimes green denotes lack of experience; for
example, a 'greenhorn' is a novice. In heraldry, green indicates growth and hope. Green, as opposed to
red, means safety; it is the color of free passage in road traffic.
Use green to indicate safety when advertising drugs and medical products. Green is directly
related to nature, so you can use it to promote 'green' products. Dull, darker green is commonly
associated with money, the financial world, banking, and Wall Street.
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Dark green is associated with ambition, greed, and jealousy.
Yellow-green can indicate sickness, cowardice, discord, and jealousy.
Aqua is associated with emotional healing and protection.
Olive green is the traditional color of peace.
v) Blue is the color of the sky and sea. It is often associated with depth and stability. It symbolizes
trust, loyalty, wisdom, confidence, intelligence, faith, truth, and heaven.
Blue is considered beneficial to the mind and body. It slows human metabolism and produces a
calming effect. Blue is strongly associated with tranquility and calmness. In heraldry, blue is used to
symbolize piety and sincerity.
You can use blue to promote products and services related to cleanliness (water purification
filters, cleaning liquids, vodka), air and sky (airlines, airports, air conditioners), water and sea (sea
voyages, mineral water). As opposed to emotionally warm colors like red, orange, and yellow; blue is
linked to consciousness and intellect. Use blue to suggest precision when promoting high-tech
products.
Blue is a masculine color; according to studies, it is highly accepted among males. Dark blue is
associated with depth, expertise, and stability; it is a preferred color for corporate America.
Avoid using blue when promoting food and cooking, because blue suppresses appetite. When
used together with warm colors like yellow or red, blue can create high-impact, vibrant designs; for
example, blue-yellow-red is a perfect color scheme for a superhero.
Light blue is associated with health, healing, tranquility, understanding, and softness.
Dark blue represents knowledge, power, integrity, and seriousness.
vi) Purple combines the stability of blue and the energy of red. Purple is associated with royalty. It
symbolizes power, nobility, luxury, and ambition. It conveys wealth and extravagance. Purple is
associated with wisdom, dignity, independence, creativity, mystery, and magic.
According to surveys, almost 75 percent of pre-adolescent children prefer purple to all other
colors. Purple is a very rare color in nature; some people consider it to be artificial.
Light purple is a good choice for a feminine design. You can use bright purple when promoting
children's products.
Light purple evokes romantic and nostalgic feelings.
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Dark purple evokes gloom and sad feelings. It can cause frustration.
vii) White is associated with light, goodness, innocence, purity, and virginity. It is considered to be
the color of perfection.
White means safety, purity, and cleanliness. As opposed to black, white usually has a positive
connotation. White can represent a successful beginning. In heraldry, white depicts faith and purity.
In advertising, white is associated with coolness and cleanliness because it's the color of snow.
You can use white to suggest simplicity in high-tech products. White is an appropriate color for
charitable organizations; angels are usually imagined wearing white clothes. White is associated with
hospitals, doctors, and sterility, so you can use white to suggest safety when promoting medical
products. White is often associated with low weight, low-fat food, and dairy products.
viii) Black is associated with power, elegance, formality, death, evil, and mystery.
Black is a mysterious color associated with fear and the unknown (black holes). It usually has a
negative connotation (blacklist, black humor, 'black death'). Black denotes strength and authority; it is
considered to be a very formal, elegant, and prestigious color (black tie, black Mercedes). In heraldry,
black is the symbol of grief.
Black gives the feeling of perspective and depth, but a black background diminishes readability.
A black suit or dress can make you look thinner. When designing for a gallery of art or photography,
you can use a black or gray background to make the other colors stand out. Black contrasts well with
bright colors. Combined with red or orange – other very powerful colors – black gives a very
aggressive color scheme.
The following is a list of colours that go together
•
•
Red and White
Pink and White
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•
•
•
•
•
•
•
•
•
•
•
•
Silver and Blue
Black and Yellow
Red and Blue
Green and Yellow
Purple and Blue
Brown and Orange
Green and Black
Blue and Orange
Gold and Silver
Black and Blue
Gold and Black
Black and White
Black and Red
4.3 COOL COLOURS
Cool colors are typified by blue, green and light purple. They have the ability to calm and soothe.
Where warm colors remind us of heat and sunshine, cool colors remind us of water and sky, even ice
and snow. Unlike warm colors, cool colors look as though they recede, making them great for small
rooms you want to appear larger.
If you have a tiny bedroom or powder room that you want to visually enlarge, try painting a color
such as light blue to make it seem more spacious.
Cool colors make you feel calm, relaxed and refreshed. Their receding effect can even make you
meditative, as though you are loosing yourself in an endless blue sky. That's why cool hues are a
natural for bedrooms and baths, places where we go to unwind and relax.
4.4 WARM COLOURS THE COLOURS OF EXCITEMENT
Warm colors are made with orange, red,
yellow and combinations of these and similar
colors. As the name indicates, they tend to make
you think of warm things, such sunlight and heat.
Visually, warm colors look as though they come
closer, or advance (as do dark colors), which is
why they're often used to make large rooms
seem cozier. If you have a huge bedroom that
you want to look more intimate, try painting it a
warm color such as terra cotta or brown to make
it feel cozier
Warm colors are associated with heightened
emotions and passion as well as joy and
playfulness. Think of the vibrancy of a bright
orange or the intensity of a deep, rich red. Warm
colors can be stimulating, making them a good
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choice for rooms that see a lot of activity
4.5 MIXED WARM AND COOL COLOUR SCHEME
Colours which have qualities of both cool and warm colours can generate excitement and
calmness. These colours are produced by mixing together cool and a warm colour (example: blue and
yellow or blue and red).
To create deep purples end pale lavenders, a combination of cool blue and a warm red are used.
Shades of green - especially teal end turquoise—also have both the cooling effects induced out of
warm yellow and cool blue and warming colour, but to a lesser magnitude. Warm and cool feelings of
purple and green are also stimulated by some light neutrals such as cream, pale beige and teupe. The
opposite colour of green is purple and that of purple is green.
The profiles of each of these mixed colours includes the definition of their nature, cultural colour
meanings, how one can use each colour in design work and also which colours go together.
4.6 NEUTRAL COLOURS
(www.marleyandalfie.com/black-and-white-2/)
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Neutral (NOO-trul) colors don't usually show up on the color wheel. Neutral colors include black,
white, gray, and sometimes brown and beige. They are sometimes called “earth tones.”
In Circus, Georges Seurat uses many different neutral colors. You can see a few glimpses of red,
blue, and yellow in this painting. But the overall effect is of natural brown and gray colors, like those
you might see in rocks or in sand, dirt, and clay.
4.7 MORE ABOUT COLOURS
(Source : Wikipedia, color)
Spectral colors
The familiar colors of the rainbow in the spectrum – named using the Latin word for appearance
or apparition by Isaac Newton in 1671 – include all those colors that can be produced by visible light
of a single wavelength only, the pure spectral or monochromatic colors. The table at right shows
approximate frequencies (in terahertz) and wavelengths (in nanometers) for various pure spectral
colors. The wavelengths listed are as measured in air or vacuum (see refractive index).
The color table should not be interpreted as a definitive list – the pure spectral colors form a
continuous spectrum, and how it is divided into distinct colors linguistically is a matter of culture and
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historical contingency (although people everywhere have been shown to perceive colors in the same
way. A common list identifies six main bands: red, oorange,
range, yellow, green, blue, and violet. Newton's
conception included a seventh color, indigo,, between blue and violet. It is possible that what Newton
referred to as blue is nearer to what today is known aas cyan,, and that indigo was simply the dark blue
of the indigo dye that was being imported at the time.
The intensity of a spectral color, relative to the
the context in which it is viewed, may alter its
perception considerably; for example, a low
low-intensity orange-yellow is brown,, and a low-intensity
low
yellow-green is olive-green.
Color of objects
The color of an object depends on both the physics of the object in its environment and the
characteristics of the perceiving eye and brain. Physically, objects can be said to have the color of the
light leaving their surfaces, which normally depends on the spectrum of the incident illumination and
the reflectance properties of the surface, as well as potentially on the angles of illumination and
viewing. Some objects not only reflect light, but also transmit light or emit light themselves, which
also contribute to the color. A viewer's perception of the object's color depends not only on the
spectrum of the light leaving its surface, but also on a host of contextual cues, so that color differences
between objects can be discerned mostly independent of the lighting spect
spectrum,
rum, viewing angle, etc.
This effect is known as color constancy
constancy.
Fig 4.01:The
The upper disk and the lower disk have exactly the same objective color, and are in
identical gray surroundings; based on context differences, humans perceive the squares as having
different reflectance,, and may interpret the colors as different color categories; see checker shadow
illusion.
Some generalizations
ations of the physics can be drawn, neglecting perceptual effects for now:
•
•
Light arriving at an opaque surface is either reflected "specularly"" (that is, in the
manner of a mirror), scattered (that is, reflected with diffuse scattering), or absorbed – or
some combination of these.
Opaque objects that do not reflect specularly (which tend to have rough surfaces)
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•
•
•
have their color determined by which wavelengths of light they scatter str
strongly
ongly (with the light
that is not scattered being absorbed). If objects scatter all wavelengths with roughly equal
strength, they appear white. If they absorb all wavelengths, they appear black.
Opaque objects that specularly reflect light of different wa
wavelengths
velengths with different
efficiencies look like mirrors tinted with colors determined by those differences. An object
that reflects some fraction of impinging light and absorbs the rest may look black but also be
faintly reflective; examples are black objects
objects coated with layers of enamel or lacquer.
Objects that transmit light are either translucent (scattering the transmitted light) or
transparent (not scattering the transmitted lig
light).
ht). If they also absorb (or reflect) light of
various wavelengths differentially, they appear tinted with a color determined by the nature of
that absorption (or that reflectance).
Objects may emit light that they generate from having excited electrons, rather than
merely reflecting or transmitting light. The electrons may be excited due to elevated
temperature (incandescence
incandescence), as a result of chemical reactions (chemoluminescence
chemoluminescence), after
absorbing light of other frequencies ("fluorescence"
("
or "phosphorescence")
") or from elec
electrical
contacts as in light emitting diodes
diodes, or other light sources.
To summarize, the color of an object is a complex result
result of its surface properties, its transmission
properties, and its emission properties, all of which contribute to the mix of wavelengths in the light
leaving the surface of the object. The perceived color is then further conditioned by the nature of the
ambient
bient illumination, and by the color properties of other objects nearby, and via other characteristics
of the perceiving eye and brain.
Color in the eye
Fig 4.02: Normalized typical human cone cell responses
esponses (S, M, and L types) to monochromatic
spectral stimuli
The ability of the human eye to distinguish colors is based upon the varying sensitivity of
different cells in the retina to light of different wavelengths. Humans are trichromatic—
—the retina
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contains three types of color receptor cells,
c
or cones.. One type, relatively distinct from the other two,
is most responsive to light that is perceived as blue or blue
blue-violet,
violet, with wavelengths around 450 nm;
cones of this type are sometimes called short
short-wavelength
wavelength cones, S cones, or blue cones. The other two
types are closely related genetically and chemically: middle
middle-wavelength
wavelength cones, M cones, or green
cones are most sensitive to light perceived
per
as green, with wavelengths around 540 nm, while the longlong
wavelength cones, L cones, or red cones, are most sensitive to light is perceived as greenish yellow,
with wavelengths around 570 nm.
Light, no matter how complex its composition of wavelengths,
wavelengths, is reduced to three color
components by the eye. Each cone type adheres to the Principle of Univariance,, which is that each
cone's output is determined by the amount of light that fal
falls
ls on it over all wavelengths. For each
location in the visual field, the three types of cones yield three signals based on the extent to which
each is stimulated. These amounts of stimulation are sometimes called tristimulus values.
The response curve as a function of wavelength varies for each type of cone. Because the curves
overlap, some tristimulus values do not occur for any incoming light combination. For example, it is
not possible to stimulate only the mid
mid-wavelength (so-called "green") cones; the other cones will
inevitably be stimulated to some degree at the same time. The set of all possible tristimulus values
determines the human color space. It has been estimated that humans can distinguish roughly 10
million different colors.
The other type of light-sensitive
sensitive cell in the eye, the rod,, has a different response curve. In normal
situations, when light is bright enough to strongly stimulate the cones, rods play virtually no role in
vision at all. On the other hand, in dim light, the cones are understimulated leaving only the signal
from the rods, resulting in a colorless response. (Furthermore, the rods are barely sensitive to light in
thee "red" range.) In certain conditions of intermediate illumination, the rod response and a weak cone
response can together result in color discriminations not accounted for by cone responses alone. These
effects, combined, are summarized also in the Kruithof curve,, that describes the change of color
perception and pleasingness of light as function of temperature and intensity.
Color in the brain
•
The visual dorsal stream (green) and ventral stream (purple) are shown. The ventral stream is
responsible for color perception.
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•
•
While the mechanisms of color vision at the level of the retina are well-described in terms of
tristimulus values, color processing after that point is organized differently. A dominant
theory of color vision proposes that color information is transmitted out of the eye by three
opponent processes, or opponent channels, each constructed from the raw output of the cones:
a red–green channel, a blue–yellow channel, and a black–white "luminance" channel. This
theory has been supported by neurobiology, and accounts for the structure of our subjective
color experience. Specifically, it explains why humans cannot perceive a "reddish green" or
"yellowish blue", and it predicts the color wheel: it is the collection of colors for which at
least one of the two color channels measures a value at one of its extremes.
The exact nature of color perception beyond the processing already described, and indeed the
status of color as a feature of the perceived world or rather as a feature of our perception of
the world – a type of qualia – is a matter of complex and continuing philosophical dispute.
Color naming
Colors vary in several different ways, including hue (shades of red, orange, yellow, green, blue,
and violet), saturation, brightness, and gloss. Some color words are derived from the name of an
object of that color, such as "orange" or "salmon", while others are abstract, like "red".
In the 1969 study Basic Color Terms: Their Universality and Evolution, Brent Berlin and Paul
Kay describe a pattern in naming "basic" colors (like "red" but not "red-orange" or "dark red" or
"blood red", which are "shades" of red). All languages that have two "basic" color names distinguish
dark/cool colors from bright/warm colors. The next colors to be distinguished are usually red and then
yellow or green. All languages with six "basic" colors include black, white, red, green, blue, and
yellow. The pattern holds up to a set of twelve: black, gray, white, pink, red, orange, yellow, green,
blue, purple, brown, and azure (distinct from blue in Russian and Italian, but not English).
Associations
Individual colors have a variety of cultural associations such as national colors (in general
described in individual color articles and color symbolism). The field of color psychology attempts to
identify the effects of color on human emotion and activity. Chromotherapy is a form of alternative
medicine attributed to various Eastern traditions. Colors have different associations in different
countries and cultures.Different colors have been demonstrated to have effects on cognition. For
example, researchers at the University of Linz in Austria demonstrated that the color red significantly
decreases cognitive functioning in men.
4.8 SUMMARY
•
•
•
•
Colour has been used to mold and define our lives, our everyday habits, our central values
end our feelings throughout the ages.
A colour may have different meanings depending on your origins, i.e., which part of the
world you come from and also your culture.
Cool colours produce a calming effect. They are cold, impersonal, antiseptic colours at one
end of the spectrum and are comforting and nurturing at the other end.
In nature, warm colours are associated with change as in the changing of the seasons. Red,
yellow and orangeade warm colours
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•
•
•
Mixed colours are produced by mixing together a cool and a warm colour.
Neutral colours are produced by mixing pure colours with either white or black or it can also
be created by mixing two complementary colours.
The colour of an object is a very complex result of its transmission properties, emission
properties and surface properties, all of which contribute to the mix of wavelengths in the
light leaving the surface of the object.
4.9 KEY TERMS
•
•
•
•
•
•
•
Brightness: A characteristic of yisual perception according to which an area seems to emit
more or less amount of light.
Red: Associated with energy, danger, power, war, strength, determination as well as desire,
passion and love.
Orange: Associated with energy, action, power end strength
Gold: Symbolises stability efficiency, planing, dependability. and maintenance of culture and
organisation
Blue: Associated wall calmness, loyalty and a sense of belonging.
Cone: One of the two main classes of photoreceptors found in the eyes of vertebrate.
Hue: A feature of visual sensation by which colour names such as: red, blue, green yellow
and purple are derived.
4.10 END QUESTIONS
I. What does the colour red signify?
2. What are cool colours?
3. Give en example of mixed warm and cool colours.
4. How do eyes perceive colour?
5. Analyse the meanings of different colours in various cultures
6. What are warm and cool colours? Add a note on neutral colours.
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UNIT 5 COLOUR MODEL
5.0 INTRODUCTION
A colour model is an abstract mathematical model which explains the way colours can be
represented as n-tuples (usually a triple) of numbers, normally as three or four values or colour
components (Example: RGB and CMYK are colour models). However, a colour model with no
companion mopping function to an absolute colour space is a more or less capricious colour system
with no connection to any globally-understood system of colour interpretation. In this unit, you will
learn about RGB and CMY colour models.
The unit also explains the HSV colour model and intuitive colour concepts. Understanding of
color models is extremely important for you as a student and as a professional in media, graphics and
animation. Which color to choose for a graphic, animation or photograph is of crucial importance.
You will decide on the basis of the demand of the project, which color schemes to chose. The topics
covered under this course will help you understand various concepts covered in all other courses like
photoshop, illustrator, 3Ds max or Maya animation courses which you will study as part of your study
in BSc(MGA).
5.1 UNIT OBJECTIVES
Alter going though this unit, you will be able to:
•
•
•
•
•
Explain the basics of light
Elaborate on the CIE chromaticity diagram
Describe as clear ideas the different colour models
Analyse the characteristics of various Colour Models
Differentiate between CMY and RGB colour models
5.2 OVERVIEW OF COLOUR MODEL
A color model is an abstract mathematical model describing the way colors can be represented as
tuples of numbers, typically as three or four values or colour components. When this model is
associated with a precise description of how the components are to be interpreted (viewing conditions,
etc.), the resulting set of colours is called colour space. This section describes ways in which human
color vision can be modelled.
5.2.1 Tristimulus color space
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Fig 5.01: 3D representation of the human color space.
One can picture this space as a region in three-dimensional Euclidean space if one identifies the x,
y, and z axes with the stimuli for the long-wavelength (L), medium-wavelength (M), and shortwavelength (S) light receptors. The origin, (S,M,L) = (0,0,0), corresponds to black. White has no
definite position in this diagram; rather it is defined according to the color temperature or white
balance as desired or as available from ambient lighting. The human color space is a horse-shoeshaped cone such as shown here (see also CIE chromaticity diagram below), extending from the
origin to, in principle, infinity. In practice, the human color receptors will be saturated or even be
damaged at extremely high light intensities, but such behavior is not part of the CIE color space and
neither is the changing color perception at low light levels (see: Kruithof curve).
The most saturated colors are located at the outer rim of the region, with brighter colors farther
removed from the origin. As far as the responses of the receptors in the eye are concerned, there is no
such thing as "brown" or "gray" light. The latter color names refer to orange and white light
respectively, with an intensity that is lower than the light from surrounding areas. One can observe
this by watching the screen of an overhead projector during a meeting: one sees black lettering on a
white background, even though the "black" has in fact not become darker than the white screen on
which it is projected before the projector was turned on. The "black" areas have not actually become
darker but appear "black" relative to the higher intensity "white" projected onto the screen around it.
See also color constancy.
The human tristimulus space has the property that additive mixing of colors corresponds to the
adding of vectors in this space. This makes it easy to, for example, describe the possible colors
(gamut) that can be constructed from the red, green, and blue primaries in a computer display.
5.2.2 CIE XYZ color space
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Fig 5.02: CIE 1931 Standard C
Colorimetric
olorimetric Observer functions between 380 nm and 780 nm (at 5
nm intervals).
One of the first mathematically defined color spaces is the CIE XYZ color space (also known as
CIE 1931 color space), created by the International Commission on Illumination in 11931.
931. These data
were measured for human observers and a 2-degree
2 degree field of view. In 1964, supplemental data for a
10-degree
degree field of view were published.
Note that the tabulated sensitivity curves have a certain amount of arbitrariness in them. The
shapes off the individual X, Y and Z sensitivity curves can be measured with a reasonable accuracy.
However, the overall luminosity function (which in fact is a weighted sum of these three curves) is
subjective, since it involves asking a test person whether two light
light sources have the same brightness,
even if they are in completely different colors. Along the same lines, the relative magnitudes of the X,
Y, and Z curves are arbitrarily chosen to produce equal areas under the curves. One could as well
define a valid color space with an X sensitivity curve that has twice the amplitude. This new color
space would have a different shape. The sensitivity curves in the CIE 1931 and 1964 xyz color space
are scaled to have equal areas under the curves.
Sometimes XYZ colors are
re represented by the luminance, Y, and chromaticity coordinates x and
y, defined by:
Mathematically, x and y are projective coordinates and the colors of the chromaticity diagram
occupy a region of the real projective plane. Because the CIE sensitivity curves have equal areas
under the curves, light with a flat energy spectrum corresponds to the point (x,y) = (0.333,0.333).
The values for X, Y, and Z are obtained by integrating the product of the spectrum of a light beam
and the published color-matching functions.
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5.2.3 RGB color model
Fig 5.03: The RGB color space mapped to a unit cube, with corner cut
cut-away
away shown.
Media that transmit light (such as television) use additive color mixing with primary colors of
red, green, and blue, each of which stimulat
stimulates
es one of the three types of the eye's color receptors with
as little stimulation as possible of the other two. This is called "RGB" color space. Mixtures of light of
these primary colors cover a large part of the human color space and thus produce a large part of
human color experiences. This is why color television sets or color computer monitors need only
produce mixtures of red, green and blue light. See Additive color.
Other primary colors could in principle be used, but with red, green and blue the la
largest
rgest portion of
the human color space can be captured. Unfortunately there is no exact consensus as to what loci in
the chromaticity diagram the red, green, and blue colors should have, so the same RGB values can
give rise to slightly different colors on different screens.
5.2.4 HSV and HSL representations
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Fig 5.04: HSL and HSV are two cylindrical representations of the RGB gamut, created in the
mid-1970s and used mostly in image editing and computer graphics. Shown are cut-away 3d models
of HSL and HSV on top, along with three 2D plots (for each model) where one parameter is held
constant and the other two are varied.
Recognizing that the geometry of the RGB model is poorly aligned with the color-making
attributes recognized by human vision, computer graphics researchers developed two alternate
representations of RGB, HSV and HSL (hue, saturation, value and hue, saturation, lightness), in the
late 1970s. HSV and HSL improve on the color cube representation of RGB by arranging colors of
each hue in a radial slice, around a central axis of neutral colors which ranges from black at the
bottom to white at the top. The fully saturated colors of each hue then lie in a circle, a color wheel.
HSV models itself on paint mixture, with its saturation and value dimensions resembling mixtures
of a brightly colored paint with, respectively, white and black. HSL tries to resemble more perceptual
color models such as NCS or Munsell. It places the fully saturated colors in a circle of lightness ½, so
that lightness 1 always implies white, and lightness 0 always implies black.
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HSV and HSL are both widely used in computer graphics, particularly as color pickers in image
editing software. The mathematical transformation from RGB to HSV or HSL could be computed in
real time, even on computers of the 1970s, and there is an easy-to-understand mapping between colors
in either of these spaces and their manifestation on a physical RGB device.
5.2.5 CMYK color model
It is possible to achieve a large range of colors seen by humans by combining cyan, magenta, and
yellow transparent dyes/inks on a white substrate. These are the subtractive primary colors. Often a
fourth ink, black, is added to improve reproduction of some dark colors. This is called "CMY" or
"CMYK" color space.
The cyan ink absorbs red light but transmits green and blue, the magenta ink absorbs green light
but transmits red and blue, and the yellow ink absorbs blue light but transmits red and green. The
white substrate reflects the transmitted light back to the viewer. Because in practice the CMY inks
suitable for printing also reflect a little bit of color, making a deep and neutral black impossible, the K
(black ink) component, usually printed last, is needed to compensate for their deficiencies. Use of a
separate black ink is also economically driven when a lot of black content is expected, e.g. in text
media, to reduce simultaneous use of the three colored inks. The dyes used in traditional color
photographic prints and slides are much more perfectly transparent, so a K component is normally not
needed or used in those media.
Comparison between RGB and CMYK Models
Fig 5.05: A comparison of CMYK and RGB color models. This image demonstrates the difference
between how colors will look on a computer monitor (RGB) compared to how they will reproduce in a
CMYK print process.
Colors can be created in printing with color spaces based on the CMYK color model, using the
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subtractive primary colors of pigment (cyan (C), magenta (M), yellow (Y), and black (K)). To create a
three-dimensional representation of a given color space, we can assign the amount of magenta color to
the representation's X axis, the amount of cyan to its Y axis, and the amount of yellow to its Z axis.
The resulting 3-D space provides a unique position for every possible color that can be created by
combining those three pigments.
Colors can be created on computer monitors with color spaces based on the RGB color model,
using the additive primary colors (red, green, and blue). A three-dimensional representation would
assign each of the three colors to the X, Y, and Z axes. Note that colors generated on given monitor
will be limited by the reproduction medium, such as the phosphor (in a CRT monitor) or filters and
backlight (LCD monitor).
Another way of creating colors on a monitor is with an HSL or HSV color space, based on hue,
saturation, brightness (value/brightness). With such a space, the variables are assigned to cylindrical
coordinates.
Many color spaces can be represented as three-dimensional values in this manner, but some have
more, or fewer dimensions, and some, such as Pantone, cannot be represented in this way at all.
Conversion
Color space conversion is the translation of the representation of a color from one basis to
another. This typically occurs in the context of converting an image that is represented in one color
space to another color space, the goal being to make the translated image look as similar as possible to
the original.
RGB density
The RGB color model is implemented in different ways, depending on the capabilities of the
system used. By far the most common general-used incarnation as of 2006 is the 24-bit
implementation, with 8 bits, or 256 discrete levels of color per channel. Any color space based on
such a 24-bit RGB model is thus limited to a range of 256×256×256 ≈ 16.7 million colors. Some
implementations use 16 bits per component for 48 bits total, resulting in the same gamut with a larger
number of distinct colors. This is especially important when working with wide-gamut color spaces
(where most of the more common colors are located relatively close together), or when a large
number of digital filtering algorithms are used consecutively. The same principle applies for any color
space based on the same color model, but implemented in different bit depths.
5.2.6 Color systems
There are various types of color systems that classify color and analyse their effects. The
American Munsell color system devised by Albert H. Munsell is a famous classification that
organises various colors into a color solid based on hue, saturation and value. Other important color
systems include the Swedish Natural Color System (NCS), the Optical Society of America's Uniform
Color Space (OSA-UCS), and the Hungarian Coloroid system developed by Antal Nemcsics from the
Budapest University of Technology and Economics. Of those, the NCS is based on the opponentprocess color model, while the Munsell, the OSA-UCS and the Coloroid attempt to model color
uniformity. The American Pantone and the German RAL commercial color-matching systems differ
from the previous ones in that their color spaces are not based on an underlying color model.
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5.2.7 Other uses of "color model"
We also use "color model" to indicate a model or mechanism of color vision for explaining how
color signals are processed from visual cones to ganglion cells. For simplicity, we call these models
color mechanism models. The classical color mechanism models are Young–Helmholtz's trichromatic
model and Hering's opponent-process model. Though these two theories were initially thought to be at
odds, it later came to be understood that the mechanisms responsible for color opponency receive
signals from the three types of cones and process them at a more complex level.
5.2.7 Vertebrate evolution of color vision
Vertebrate animals were primitively tetrachromatic. They possessed four types of cones—long,
mid, short wavelength cones, and ultraviolet sensitive cones. Today, fish, reptiles and birds are all
tetrachromatic. Placental mammals lost both the mid and short wavelength cones. Thus, most
mammals do not have complex color vision—they are dichromatic but they are sensitive to ultraviolet
light, though they cannot see its colors. Human trichromatic color vision is a recent evolutionary
novelty that first evolved in the common ancestor of the Old World Primates. Our trichromatic color
vision evolved by duplication of the long wavelength sensitive opsin, found on the X chromosome.
One of these copies evolved to be sensitive to green light and constitutes our mid wavelength opsin.
At the same time, our short wavelength opsin evolved from the ultraviolet opsin of our vertebrate and
mammalian ancestors.
Human red-green color blindness occurs because the two copies of the red and green opsin genes
remain in close proximity on the X chromosome. Because of frequent recombination during meiosis,
these gene pairs can get easily rearranged, creating versions of the genes that do not have distinct
spectral sensitivities.
CHECK YOUR PROGRESS
Explain the aspects of a color model.
Elaborate the importance of tristimulus color space.
Explain the concept of CIE XYZ or CIE 1932 color space.
Describe the concept of HSL and HSV representations.
Discuss the CMYK color model.
Explain the Color systems.
Explain the Vertebrate evolution of color vision.
5.3 LIGHT
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Light is electromagnetic radiation within a certain portion of the electromagnetic spectrum. The
word usually refers to visible light, which is visible to the human eye and is responsible for the sense
of sight. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres
(nm), or 4.00 × 10−7 to 7.00 × 10−7 m, between the infrared (with longer wavelengths) and the
ultraviolet (with shorter wavelengths). This wavelength means a frequency range of roughly 430–750
terahertz (THz).
The main source of light on Earth is the Sun. Sunlight provides the energy that green plants use to
create sugars mostly in the form of starches, which release energy into the living things that digest
them. This process of photosynthesis provides virtually all the energy used by living things.
Historically, another important source of light for humans has been fire, from ancient campfires to
modern kerosene lamps. With the development of electric lights and power systems, electric lighting
has effectively replaced firelight. Some species of animals generate their own light, a process called
bioluminescence. For example, fireflies use light to locate mates, and vampire squids use it to hide
themselves from prey.
The primary properties of visible light are intensity, propagation direction, frequency or
wavelength spectrum, and polarization, while its speed in a vacuum, 299,792,458 metres per second,
is one of the fundamental constants of nature. Visible light, as with all types of electromagnetic
radiation (EMR), is experimentally found to always move at this speed in a vacuum.
In physics, the term light sometimes refers to electromagnetic radiation of any wavelength,
whether visible or not. In this sense, gamma rays, X-rays, microwaves and radio waves are also light.
Like all types of light, visible light is emitted and absorbed in tiny "packets" called photons and
exhibits properties of both waves and particles. This property is referred to as the wave–particle
duality. The study of light, known as optics, is an important research area in modern physics.
5.3.1 Electromagnetic spectrum and visible light
Fig 5.06: Electromagnetic spectrum with light highlighted
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Generally, EM radiation, or EMR (the designation "radiation"
"radiation" excludes static electric and
magnetic and near fields), is classified by wavelength into radio, microwave, infrared, the visible
region that we perceive as light, ultraviolet, X-rays
X
and gamma rays.
The behavior of EMR depends on its wavelength. Higher
Higher frequencies have shorter wavelengths,
and lower frequencies have longer wavelengths. When EMR interacts with single atoms and
molecules, its behavior depends on the amount of energy per quantum it carries.
EMR in the visible light region consists of quan
quanta
ta (called photons) that are at the lower end of the
energies that are capable of causing electronic excitation within molecules, which leads to changes in
the bonding or chemistry of the molecule. At the lower end of the visible light spectrum, EMR
becomess invisible to humans (infrared) because its photons no longer have enough individual energy
to cause a lasting molecular change (a change in conformation) in the visual molecule retinal in the
human retina, which change triggers the sensation of vision.
There
here exist animals that are sensitive to various types of infrared, but not by means of quantumquantum
absorption. Infrared sensing in snakes depends on a kind of natural thermal imaging, in which tiny
packets of cellular water are raised in temperature by the in
infrared
frared radiation. EMR in this range causes
molecular vibration and heating effects, which is how these animals detect it.
Above the range of visible light, ultraviolet light becomes invisible to humans, mostly because it
is absorbed by the cornea below 360 nanometers and the internal lens below 400. Furthermore, the
rods and cones located in the retina of the human eye cannot detect the very short (below 360 nm)
ultraviolet wavelengths and are in fact damaged by ultraviolet. Many animals with eyes that do not
n
require lenses (such as insects and shrimp) are able to detect ultraviolet, by quantum photon
photonabsorption mechanisms, in much the same chemical way that humans detect visible light.
Various sources define visible light as narrowly as 420 to 680 to as broadly
broadly as 380 to 800 nm.
Under ideal laboratory conditions, people can see infrared up to at least 1050 nm; children and young
adults may perceive ultraviolet wavelengths down to about 310 to 313 nm.
Plant growth is also affected by the color spectrum of lig
light, a process known as
photomorphogenesis.
Fig 5.07: A linear representation of the visible light spectrum.
5.3.2 Speed of light
The speed of light in a vacuum is defined to be exactly 299,792,458 m/s (approx. 186,282 miles
per second). The fixed value of the speed of light in SI units results from the fact that the metre is now
defined in terms of the speed of light. All forms of electromagnetic radiation move at exactly this
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same speed in vacuum.
Different physicists have attempted to measure the speed of light throughout history. Galileo
attempted to measure the speed of light in the seventeenth century. An early experiment to measure
the speed of light was conducted by Ole Rømer, a Danish physicist, in 1676. Using a telescope,
Rømer observed the motions of Jupiter and one of its moons, Io. Noting discrepancies in the apparent
period of Io's orbit, he calculated that light takes about 22 minutes to traverse the diameter of Earth's
orbit. However, its size was not known at that time. If Rømer had known the diameter of the Earth's
orbit, he would have calculated a speed of 227,000,000 m/s.
Another, more accurate, measurement of the speed of light was performed in Europe by
Hippolyte Fizeau in 1849. Fizeau directed a beam of light at a mirror several kilometers away. A
rotating cog wheel was placed in the path of the light beam as it traveled from the source, to the
mirror and then returned to its origin. Fizeau found that at a certain rate of rotation, the beam would
pass through one gap in the wheel on the way out and the next gap on the way back. Knowing the
distance to the mirror, the number of teeth on the wheel, and the rate of rotation, Fizeau was able to
calculate the speed of light as 313,000,000 m/s.
Léon Foucault carried out an experiment which used rotating mirrors to obtain a value of
298,000,000 m/s in 1862. Albert A. Michelson conducted experiments on the speed of light from
1877 until his death in 1931. He refined Foucault's methods in 1926 using improved rotating mirrors
to measure the time it took light to make a round trip from Mount Wilson to Mount San Antonio in
California. The precise measurements yielded a speed of 299,796,000 m/s.
The effective velocity of light in various transparent substances containing ordinary matter, is less
than in vacuum. For example, the speed of light in water is about 3/4 of that in vacuum.
Two independent teams of physicists were said to bring light to a "complete standstill" by passing
it through a Bose–Einstein condensate of the element rubidium, one team at Harvard University and
the Rowland Institute for Science in Cambridge, Massachusetts, and the other at the Harvard–
Smithsonian Center for Astrophysics, also in Cambridge. However, the popular description of light
being "stopped" in these experiments refers only to light being stored in the excited states of atoms,
then re-emitted at an arbitrary later time, as stimulated by a second laser pulse. During the time it had
"stopped" it had ceased to be light.
5.3.3 Light sources
There are many sources of light. A body at a given temperature emits a characteristic spectrum of
black-body radiation. A simple thermal source is sunlight, the radiation emitted by the chromosphere
of the Sun at around 6,000 kelvins (5,730 degrees Celsius; 10,340 degrees Fahrenheit) peaks in the
visible region of the electromagnetic spectrum when plotted in wavelength units and roughly 44% of
sunlight energy that reaches the ground is visible. Another example is incandescent light bulbs, which
emit only around 10% of their energy as visible light and the remainder as infrared. A common
thermal light source in history is the glowing solid particles in flames, but these also emit most of
their radiation in the infrared, and only a fraction in the visible spectrum.
The peak of the blackbody spectrum is in the deep infrared, at about 10 micrometre wavelength,
for relatively cool objects like human beings. As the temperature increases, the peak shifts to shorter
wavelengths, producing first a red glow, then a white one, and finally a blue-white colour as the peak
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moves out of the visible part of the spectrum and into the ultraviolet. These colours can be seen when
metal is heated to "red hot" or "white hot". Blue-white thermal emission is not often seen, except in
stars (the commonly seen pure-blue colour in a gas flame or a welder's torch is in fact due to
molecular emission, notably by CH radicals (emitting a wavelength band around 425 nm, and is not
seen in stars or pure thermal radiation).
Atoms emit and absorb light at characteristic energies. This produces "emission lines" in the
spectrum of each atom. Emission can be spontaneous, as in light-emitting diodes, gas discharge lamps
(such as neon lamps and neon signs, mercury-vapor lamps, etc.), and flames (light from the hot gas
itself—so, for example, sodium in a gas flame emits characteristic yellow light). Emission can also be
stimulated, as in a laser or a microwave maser.
Deceleration of a free charged particle, such as an electron, can produce visible radiation:
cyclotron radiation, synchrotron radiation, and bremsstrahlung radiation are all examples of this.
Particles moving through a medium faster than the speed of light in that medium can produce visible
Cherenkov radiation. Certain chemicals produce visible radiation by chemoluminescence. In living
things, this process is called bioluminescence. For example, fireflies produce light by this means, and
boats moving through water can disturb plankton which produce a glowing wake.
Certain substances produce light when they are illuminated by more energetic radiation, a process
known as fluorescence. Some substances emit light slowly after excitation by more energetic
radiation. This is known as phosphorescence. Phosphorescent materials can also be excited by
bombarding them with subatomic particles. Cathodoluminescence is one example. This mechanism is
used in cathode ray tube television sets and computer monitors.
5.3.4 Units and measures
Light is measured with two main alternative sets of units: radiometry consists of measurements of
light power at all wavelengths, while photometry measures light with wavelength weighted with
respect to a standardised model of human brightness perception. Photometry is useful, for example, to
quantify Illumination (lighting) intended for human use. The SI units for both systems are
summarised in the following tables.
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5.3.5 Historical theories about light, in chronological order
Classical Greece and Hellenism
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In the fifth century BC, Empedocles postulated that everything was composed of four elements;
fire, air, earth and water. He believed that Aphrodite made the human eye out of the four elements and
that she lit the fire in the eye which shone out from the eye making sight possible. If this were true,
then one could see during the night just as well as during the day, so Empedocles postulated an
interaction between rays from the eyes and rays from a source such as the sun.
In about 300 BC, Euclid wrote Optica, in which he studied the properties of light. Euclid
postulated that light travelled in straight lines and he described the laws of reflection and studied them
mathematically. He questioned that sight is the result of a beam from the eye, for he asks how one
sees the stars immediately, if one closes one's eyes, then opens them at night. Of course if the beam
from the eye travels infinitely fast this is not a problem.
In 55 BC, Lucretius, a Roman who carried on the ideas of earlier Greek atomists, wrote that "The
light & heat of the sun; these are composed of minute atoms which, when they are shoved off, lose no
time in shooting right across the interspace of air in the direction imparted by the shove." (from On
the nature of the Universe). Despite being similar to later particle theories, Lucretius's views were not
generally accepted. Ptolemy (c. 2nd century) wrote about the refraction of light in his book Optics.
Classical India
In ancient India, the Hindu schools of Samkhya and Vaisheshika, from around the early centuries
AD developed theories on light. According to the Samkhya school, light is one of the five
fundamental "subtle" elements (tanmatra) out of which emerge the gross elements. The atomicity of
these elements is not specifically mentioned and it appears that they were actually taken to be
continuous. On the other hand, the Vaisheshika school gives an atomic theory of the physical world
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on the non-atomic ground of ether, space and time. (See Indian atomism.) The basic atoms are those
of earth (prthivi), water (pani), fire (agni), and air (vayu) Light rays are taken to be a stream of high
velocity of tejas (fire) atoms. The particles of light can exhibit different characteristics depending on
the speed and the arrangements of the tejas atoms. The Vishnu Purana refers to sunlight as "the seven
rays of the sun".
The Indian Buddhists, such as Dignāga in the 5th century and Dharmakirti in the 7th century,
developed a type of atomism that is a philosophy about reality being composed of atomic entities that
are momentary flashes of light or energy. They viewed light as being an atomic entity equivalent to
energy.
Descartes
Fig 5.08: Portrait of René Descartes (1596-1650) After Frans Hals (1582/1583–1666)
René Descartes (1596–1650) held that light was a mechanical property of the luminous body,
rejecting the "forms" of Ibn al-Haytham and Witelo as well as the "species" of Bacon, Grosseteste,
and Kepler. In 1637 he published a theory of the refraction of light that assumed, incorrectly, that
light travelled faster in a denser medium than in a less dense medium. Descartes arrived at this
conclusion by analogy with the behaviour of sound waves. Although Descartes was incorrect about
the relative speeds, he was correct in assuming that light behaved like a wave and in concluding that
refraction could be explained by the speed of light in different media.
Descartes is not the first to use the mechanical analogies but because he clearly asserts that light
is only a mechanical property of the luminous body and the transmitting medium, Descartes' theory of
light is regarded as the start of modern physical optics.
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Particle theory
Pierre Gassendi.
Pierre Gassendi (1592–1655), an atomist, proposed a particle theory of light which was published
posthumously in the 1660s. Isaac Newton studied Gassendi's work at an early age, and preferred his
view to Descartes' theory of the plenum. He stated in his Hypothesis of Light of 1675 that light was
composed of corpuscles (particles of matter) which were emitted in all directions from a source. One
of Newton's arguments against the wave nature of light was that waves were known to bend around
obstacles, while light travelled only in straight lines. He did, however, explain the phenomenon of the
diffraction of light (which had been observed by Francesco Grimaldi) by allowing that a light particle
could create a localised wave in the aether.
Fig 5.09: Sir Issac Newton at 46, painting by Godfrey Kneller (1646–1723)
The corpuscular theory was largely developed by Sir Isaac Newton. Newton's theory was
predominant for more than 100 years and took precedence over Huygens' wave front theory, partly
because of Newton’s great prestige. When the corpuscular theory failed to adequately explain the
diffraction, interference and polarization of light it was abandoned in favour of Huygens' wave theory.
To some extent, Newton's corpuscular (particle) theory of light re-emerged in the 20th century, as
light phenomenon is currently explained as particle and wave.
Newton's corpuscular theory was an elaboration of his view of reality as interactions of material
points through forces. Note Albert Einstein's description of Newton's conception of physical reality:
[Newton's] physical reality is characterised by concepts of space, time, the material point and
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force (interaction between material points). Physical events are to be thought of as movements
according to law of material points in space. The material point is the only representative of reality in
so far as it is subject to change. The concept of the material point is obviously due to observable
bodies; one conceived of the material point on the analogy of movable bodies by omitting
characteristics of extension, form, spatial locality, and all their 'inner' qualities, retaining only inertia,
translation, and the additional concept of force.
•
•
Every source of light emits large numbers of tiny particles known as corpuscles in a
medium surrounding the source.
These corpuscles are perfectly elastic, rigid, and weightless.
Newton's theory could be used to predict the reflection of light, but could only explain refraction
by incorrectly assuming that light accelerated upon entering a denser medium because the
gravitational pull was greater. Newton published the final version of his theory in his Opticks of 1704.
His reputation helped the particle theory of light to hold sway during the 18th century. The particle
theory of light led Laplace to argue that a body could be so massive that light could not escape from
it. In other words, it would become what is now called a black hole. Laplace withdrew his suggestion
later, after a wave theory of light became firmly established as the model for light (as has been
explained, neither a particle or wave theory is fully correct). A translation of Newton's essay on light
appears in The large scale structure of space-time, by Stephen Hawking and George F. R. Ellis.
The fact that light could be polarized was for the first time qualitatively explained by Newton
using the particle theory. Étienne-Louis Malus in 1810 created a mathematical particle theory of
polarization. Jean-Baptiste Biot in 1812 showed that this theory explained all known phenomena of
light polarization. At that time the polarization was considered as the proof of the particle theory.
Wave theory
To explain the origin of colors, Robert Hooke (1635-1703) developed a "pulse theory" and
compared the spreading of light to that of waves in water in his 1665 work Micrographia
("Observation IX"). In 1672 Hooke suggested that light's vibrations could be perpendicular to the
direction of propagation. Christiaan Huygens (1629-1695) worked out a mathematical wave theory of
light in 1678, and published it in his Treatise on light in 1690. He proposed that light was emitted in
all directions as a series of waves in a medium called the Luminiferous ether. As waves are not
affected by gravity, it was assumed that they slowed down upon entering a denser medium.
Christian Huygens.
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Fig 5.10: Thomas Young's sketch of a double-slit experiment showing diffraction. Young's
experiments supported the theory that light consists of waves.
The wave theory predicted that light waves could interfere with each other like sound waves (as
noted around 1800 by Thomas Young). Young showed by means of a diffraction experiment that light
behaved as waves. He also proposed that different colours were caused by different wavelengths of
light, and explained colour vision in terms of three-coloured receptors in the eye. Another supporter
of the wave theory was Leonhard Euler. He argued in Nova theoria lucis et colorum (1746) that
diffraction could more easily be explained by a wave theory. In 1816 André-Marie Ampère gave
Augustin-Jean Fresnel an idea that the polarization of light can be explained by the wave theory if
light were a transverse wave.
Later, Fresnel independently worked out his own wave theory of light, and presented it to the
Académie des Sciences in 1817. Siméon Denis Poisson added to Fresnel's mathematical work to
produce a convincing argument in favour of the wave theory, helping to overturn Newton's
corpuscular theory. By the year 1821, Fresnel was able to show via mathematical methods that
polarisation could be explained by the wave theory of light and only if light was entirely transverse,
with no longitudinal vibration whatsoever.
The weakness of the wave theory was that light waves, like sound waves, would need a medium
for transmission. The existence of the hypothetical substance luminiferous aether proposed by
Huygens in 1678 was cast into strong doubt in the late nineteenth century by the Michelson–Morley
experiment.
Newton's corpuscular theory implied that light would travel faster in a denser medium, while the
wave theory of Huygens and others implied the opposite. At that time, the speed of light could not be
measured accurately enough to decide which theory was correct. The first to make a sufficiently
accurate measurement was Léon Foucault, in 1850. His result supported the wave theory, and the
classical particle theory was finally abandoned, only to partly re-emerge in the 20th century.
Electromagnetic theory
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Fig 5.11: A 3–dimensional
dimensional rendering of linearly polarised light wave frozen in time and showing
the two oscillating components
nents of light; an electric field and a magnetic field perpendicular to each
other and to the direction of motion (a transverse wave).
In 1845, Michael Faraday discovered that the plane of polarisation of linearly polarised light is
rotated when the light rays travel along the magnetic field direction in the presence of a transparent
dielectric, an effect now known as Faraday rotation. This was the first evidence that light was related
to electromagnetism. In 1846 he speculated that light might be some form of disturbance propagating
along magnetic field lines. Faraday proposed in 1847 that light was a high
high-frequency
frequency electromagnetic
vibration, which could propagate even in the absence of a medium such as the ether.
Faraday's work inspired James Clerk Maxwell
Maxwell to study electromagnetic radiation and light.
Maxwell discovered that self-propagating
propagating electromagnetic waves would travel through space at a
constant speed, which happened to be equal to the previously measured speed of light. From this,
Maxwell concluded
d that light was a form of electromagnetic radiation: he first stated this result in
1862 in On Physical Lines of Force. In 1873, he published A Treatise on Electricity and Magnetism,
which contained a full mathematical description of the behaviour of elec
electric
tric and magnetic fields, still
known as Maxwell's equations. Soon after, Heinrich Hertz confirmed Maxwell's theory
experimentally by generating and detecting radio waves in the laboratory, and demonstrating that
these waves behaved exactly like visible li
light,
ght, exhibiting properties such as reflection, refraction,
diffraction, and interference. Maxwell's theory and Hertz's experiments led directly to the
development of modern radio, radar, television, electromagnetic imaging, and wireless
communications.
In the quantum theory, photons are seen as wave packets of the waves described in the classical
theory of Maxwell. The quantum theory was needed to explain effects even with visual light that
Maxwell's classical theory could not (such as spectral lines).
Quantum theory
In 1900 Max Planck, attempting to explain black body radiation suggested that although light was
a wave, these waves could gain or lose energy only in finite amounts related to their frequency.
Planck called these "lumps" of light energy "quanta"
"quanta" (from a Latin word for "how much"). In 1905,
Albert Einstein used the idea of light quanta to explain the photoelectric effect, and suggested that
these light quanta had a "real" existence. In 1923 Arthur Holly Compton showed that the wavelength
shift seen when low intensity X-rays
rays scattered from electrons (so called Compton scattering) could be
explained by a particle-theory of X--rays,
rays, but not a wave theory. In 1926 Gilbert N. Lewis named these
light quanta particles photons.
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Eventually the modern theory of quantum mechanics came to picture light as (in some sense) both
a particle and a wave, and (in another sense), as a phenomenon which is neither a particle nor a wave
(which actually are macroscopic phenomena, such as baseballs or ocean waves). Instead, modern
physics sees light as something that can be described sometimes with mathematics appropriate to one
type of macroscopic metaphor (particles), and sometimes another macroscopic metaphor (water
waves), but is actually something that cannot be fully imagined. As in the case for radio waves and
the X-rays involved in Compton scattering, physicists have noted that electromagnetic radiation tends
to behave more like a classical wave at lower frequencies, but more like a classical particle at higher
frequencies, but never completely loses all qualities of one or the other. Visible light, which occupies
a middle ground in frequency, can easily be shown in experiments to be describable using either a
wave or particle model, or sometimes both.
CHECK YOUR PROGRESS
Explain the concept of light.
Elaborate the importance of Electromagnetic spectrum and visible light.
Explain the concept of Speed of light.
Describe the concept of Light sources.
Discuss the radiometric and photometric measurements of light mentioning the SI units and
description for at least five parameters.
Explain the historic theories of light briefly mentioning their contributions.
Elaborate the contribution of Isaac Newton to the theoretical understanding of light.
Discuss the contribution of proponents of wave theory to the theoretical understanding of light.
Describe the contribution of proponents of particle theory to the theoretical understanding of
light.
Elaborate the contribution of quantum mechanics to the theoretical understanding of light.
Descibe the current state of the theoretical understanding of light.
5.4 CIE CHROMATICITY DIAGRAM(CIE 1931 COLOR
SPACE)
The CIE 1931 color spaces were the first defined quantitative links between physical pure colors
(i.e. wavelengths) in the electromagnetic visible spectrum, and physiological perceived colors in
human color vision. The mathematical relationships that define these color spaces are essential tools
for color management, important when dealing with color inks, illuminated displays, and recording
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devices such as digital cameras.
The CIE 1931 RGB color space and CIE 1931 XYZ color space were created by the International
Commission on Illumination (CIE) in 1931. They resulted from a series of experiments done in the
late 1920s by William David Wright and John Guild. The experimental results were combined into
the specification of the CIE RGB color space, from which the CIE XYZ color space was derived.
The CIE 1931 color spaces are still widely used, as is the 1976 CIELUV color space.
5.4.1 Tristimulus values
Fig 5.12: The normalized spectral sensitivity of human cone cells of short-, middle- and longwavelength (in nm)types.
The human eye with normal vision has three kinds of cone cells that sense light, having peaks of
spectral sensitivity in short ("S", 420 nm – 440 nm), middle ("M", 530 nm – 540 nm), and long ("L",
560 nm – 580 nm) wavelengths. These cone cells underlie human color perception in conditions of
medium and high brightness; in very dim light color vision diminishes, and the low-brightness,
monochromatic "night vision" receptors, denominated "rod cells", become effective. Thus, three
parameters corresponding to levels of stimulus of the three kinds of cone cells, in principle describe
any human color sensation. Weighting a total light power spectrum by the individual spectral
sensitivities of the three kinds of cone cells renders three effective values of stimulus; these three
values compose a tristimulus specification of the objective color of the light spectrum. The three
parameters, denoted "S", "M", and "L", are indicated using a 3-dimensional space denominated the
"LMS color space", which is one of many color spaces devised to quantify human color vision.
A color space maps a range of physically produced colors from mixed light, pigments, etc. to an
objective description of color sensations registered in the human eye, typically in terms of tristimulus
values, but not usually in the LMS color space defined by the spectral sensitivities of the cone cells.
The tristimulus values associated with a color space can be conceptualized as amounts of three
primary colors in a tri-chromatic, additive color model. In some color spaces, including the LMS and
XYZ spaces, the primary colors used are not real colors in the sense that they cannot be generated in
any light spectrum.
The CIE XYZ color space encompasses all color sensations that are visible to a person with
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average eyesight. That is why CIE XYZ (Tristimulus values) is a device-invariant representation of
color. It serves as a standard reference against which many other color spaces are defined. A set of
color-matching functions, like the spectral sensitivity curves of the LMS color space, but not
restricted to non-negative sensitivities, associates physically produced light spectra with specific
tristimulus values.
Consider two light sources composed of different mixtures of various wavelengths. Such light
sources may appear to be the same color; this effect is denominated "metamerism". Such light sources
have the same apparent color to an observer when they produce the same tristimulus values,
regardless of the spectral power distributions of the sources.
Most wavelengths stimulate two or all three kinds of cone cell because the spectral sensitivity
curves of the three kinds overlap. Certain tristimulus values are thus physically impossible, for
example LMS tristimulus values that are non-zero for the M component and zero for both the L and S
components. Furthermore, LMS tristimulus values for pure spectral colors would, in any normal
trichromatic additive color space, e. g. the RGB color spaces, imply negative values for at least one of
the three primaries because the chromaticity would be outside the color triangle defined by the
primary colors. To avoid these negative RGB values, and to have one component that describes the
perceived brightness, "imaginary" primary colors and corresponding color-matching functions were
formulated. The CIE 1931 color space defines the resulting tristimulus values, in which they are
denoted by "X", "Y", and "Z". In XYZ space, all combinations of non-negative coordinates are
meaningful, but many, such as the primary locations [1, 0, 0], [0, 1, 0], and [0, 0, 1], correspond to
imaginary colors outside the space of possible LMS coordinates; imaginary colors do not correspond
to any spectral distribution of wavelengths and therefore have no physical reality.
5.4.2 Meaning of X, Y and Z
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A comparison between a typical normalised M cone's spectral sensitivity and the CIE 1931
luminosity function for a standard observer in photopic vision.
When judging the relative luminance (brightness) of different colors in well-lit situations, humans
tend to perceive light within the green parts of the spectrum as brighter than red or blue light of equal
power. The luminosity function that describes the perceived brightnesses of different wavelengths is
thus roughly analogous to the spectral sensitivity of M cones.
The CIE model capitalises on this fact by defining Y as luminance. Z is quasi-equal to blue
stimulation, or the S cone response, and X is a mix (a linear combination) of cone response curves
chosen to be nonnegative. The XYZ tristimulus values are thus analogous to, but different from, the
LMS cone responses of the human eye. Defining Y as luminance has the useful result that for any
given Y value, the XZ plane will contain all possible chromaticities at that luminance.
The unit of the tristimulus values X, Y, and Z is often arbitrarily chosen so that Y = 1 or Y = 100
is the brightest white that a color display supports. The corresponding whitepoint values for X and Z
can then be inferred using the standard illuminants.
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5.4.3 CIE standard observer
Due to the distribution of cones in the eye, the tristimulus values depend on the observer's field of
view. To eliminate this variable, the CIE defined a color-mapping
mapping function called the standard
(colorimetric) observer, to represent an average human's chromatic response within a 2° arc inside the
fovea. This angle was chosen owing to the belief that the color
color-sensitive
sensitive cones resided within a 2° arc
of the fovea. Thus the CIE 1931 Standard Observer function is also known as the CIE 1931 2°
Standard Observer. A more modern but less
less-used
used alternative is the CIE 1964 10° Standard Observer,
which is derived from the work of Stiles and Burch, and Speranskaya.
Speran
For the 10° experiments, the observers were instructed to ignore the central 2° spot. The 1964
Supplementary Standard Observer function is recommended when dealing with more than about a 4°
field of view. Both standard observer functions are discret
discretized
ized at 5 nm wavelength intervals from 380
nm to 780 nm and distributed by the CIE. All corresponding values have been calculated from
experimentally obtained data using interpolation. The standard observer is characterized by three
color matching functions.
The derivation of the CIE standard observer from color matching experiments is given below,
after the description of the CIE RGB space.
Color matching functions
Fig 5.13: The CIE standard observer color matching functions.
The CIE's color matching functions
ctions
are the numerical description of the
chromatic response of the observer (described above). They can be thought of as the spectral
sensitivity curves of three linear light detectors yielding the CIE tristimulus values X, Y and Z.
Collectively, these
se three functions are known as the CIE standard observer.
Other observers, such as for the CIE RGB space or other RGB color spaces, are defined by other
sets of three color-matching
matching functions, and lead to tristimulus values in those other spaces.
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5.4.4 Computing XYZ From Spectral Data
Emissive Case
The tristimulus values for a color with a spectral radiance Le,Ω,λ are given in terms of the standard
observer by:
Where λ is the wavelength of the equivalent monochromatic light (measured in nanometers), and
the standard limits of the integral are λ ∈ [ 380 , 780 ]. The values of X, Y, and Z are bounded if the
radiance spectrum Le,Ω,λ are bounded.
Reflective and Transmissive Cases
The reflective and transmissive cases are very similar to the emissive case, with a few differences.
The spectral radiance Le,Ω,λ is replaced by the spectral reflectance (or transmittance) S(λ) of the
object being measured, multiplied by the spectral power distribution of the illuminant I(λ).
K is a scaling factor (usually 1 or 100), and λ is the wavelength of the equivalent monochromatic
light (measured in nanometers), and the standard limits of the integral are λ ∈ [ 380 , 780 ].
5.4.5 CIE xy chromaticity diagram and the CIE xyY color space
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Fog 5.00: The CIE 1931 color space chromaticity
chromaticity diagram. The outer curved boundary is the
spectral (or monochromatic) locus, with wavelengths shown in nanometers. Note that the colors your
screen displays in this image are specified using sRGB, so the colors outside the sRGB gamut are not
displayed
ayed properly. Depending on the color space and calibration of your display device, the sRGB
colors may not be displayed properly either. This diagram displays the maximally saturated bright
colors that can be produced by a computer monitor or television sset.
The CIE 1931 color space chromaticity diagram rendered in terms of the colors of lower
saturation and value than those displayed in the diagram above that can be produced by pigments,
such as those used in printing. The color names are from the Munsell color system.
Since the human eye has three types of color sensors that respond to different ranges of
wavelengths, a full plot of all visible colors is a three-dimensional
three dimensional figure. However, the concept of
color can be divided into two parts: brightness an
and
d chromaticity. For example, the color white is a
bright color, while the color grey is considered to be a less bright version of that same white. In other
words, the chromaticity of white and grey are the same while their brightness differs.
The CIE XYZ color
olor space was deliberately designed so that the Y parameter is a measure of the
luminance of a color. The chromaticity of a color is then specified by the two derived parameters x
and y, two of the three normalized values being functions of all three tris
tristimulus
timulus values X, Y, and Z:
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The derived color space specified by x, y, and Y is known as the CIE xyY color space and is
widely used to specify colors in practice.
The X and Z tristimulus values can be calculated back from the chromaticity values x and y and
the Y tristimulus value:
The figure above (caption The CIE 1931 color space chromaticity diagram) shows the related
chromaticity diagram. The outer curved boundary is the spectral locus, with wavelengths shown in
nanometers. Note that the chromaticity diagram is a tool to specify how the human eye will
experience light with a given spectrum. It cannot specify colors of objects (or printing inks), since the
chromaticity observed while looking at an object depends on the light source as well.
Mathematically the colors of the chromaticity diagram occupy a region of the real projective
plane.
The chromaticity diagram illustrates a number of interesting properties of the CIE XYZ color
space:
•
•
•
The diagram represents all of the chromaticities visible to the average person. These are
shown in color and this region is called the gamut of human vision. The gamut of all visible
chromaticities on the CIE plot is the tongue-shaped or horseshoe-shaped figure shown in
color. The curved edge of the gamut is called the spectral locus and corresponds to
monochromatic light (each point representing a pure hue of a single wavelength), with
wavelengths listed in nanometers. The straight edge on the lower part of the gamut is called
the line of purples. These colors, although they are on the border of the gamut, have no
counterpart in monochromatic light. Less saturated colors appear in the interior of the figure
with white at the center.
It is seen that all visible chromaticities correspond to non-negative values of x, y, and z
(and therefore to non-negative values of X, Y, and Z).
If one chooses any two points of color on the chromaticity diagram, then all the colors that
lie in a straight line between the two points can be formed by mixing these two colors. It
follows that the gamut of colors must be convex in shape. All colors that can be formed by
mixing three sources are found inside the triangle formed by the source points on the
chromaticity diagram (and so on for multiple sources).
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•
•
•
An equal mixture of two
o equally bright colors will not generally lie on the midpoint of that
line segment. In more general terms, a distance on the CIE xy chromaticity diagram does not
correspond to the degree of difference between two colors. In the early 1940s, David
MacAdam studied the nature of visual sensitivity to color differences, and summarized his
results in the concept of a MacAdam ellipse. Based on the work of MacAdam, the CIE 1960,
CIE 1964, and CIE 1976 color spaces were developed, with the goal of achieving percep
perceptual
uniformity (have an equal distance in the color space correspond to equal differences in
color). Although they were a distinct improvement over the CIE 1931 system, they were not
completely free of distortion.
It can be seen that, given three real sources, these sources cannot cover the gamut of human
vision. Geometrically stated, there are no three points within the gamut that form a triangle
that includes the entire gamut; or more simply, the gamut of human vision is not a triangle.
Light with
h a flat power spectrum in terms of wavelength (equal power in every 1 nm
interval) corresponds to the point (x, y) = (1/3, 1/3).
5.4.6 Definition of the CIE XYZ color space
CIE RGB color space
The CIE RGB color space is one of many RGB color spaces, distinguished
distinguished by a particular set of
monochromatic (single-wavelength)
wavelength) primary colors.
In the 1920s, W. David Wright and John Guild independently conducted a series of experiments
on human sight which laid the foundation for the specification of the CIE XYZ co
color
lor space. Wright
carried out trichromatic color matching experiments with ten observers. Guild actually conducted his
experiments with seven observers.
Fig 5.14: Gamut of the CIE RGB primaries and location of primaries on the CIE 1931 xy
chromaticity diagram.
The experiments were conducted by using a circular split screen (a bipartite field) 2 degrees in
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diameter, which is the angular size of the human fovea. On one side of the field a test color was
projected and on the other side, an observer-adjustable
observer
e color was projected. The adjustable color was
a mixture of three primary colors, each with fixed chromaticity, but with adjustable brightness.
The observer would alter the brightness of each of the three primary beams until a match to the
test color was observed. Not all test colors could be matched using this technique. When this was the
case, a variable amount of one of the primaries could be added to the test color, and a match with the
remaining two primaries was carried out with the variable color sp
spot.
ot. For these cases, the amount of
the primary added to the test color was considered to be a negative value. In this way, the entire range
of human color perception could be covered. When the test colors were monochromatic, a plot could
be made of the amount
unt of each primary used as a function of the wavelength of the test color. These
three functions are called the color matching functions for that particular experiment.
Fig 5.15: The CIE 1931 RGB color matching functions. The color matching functions ar
are the
amounts of primaries needed to match the monochromatic test color at the wavelength shown on the
horizontal scale.
Although Wright and Guild's experiments were carried out using various primaries at various
intensities, and although they used a number
number of different observers, all of their results were
summarized by the standardized CIE RGB color matching functions
obtained
using three monochromatic primaries at standardized wavelengths of 700 nm (red), 546.1 nm (green)
and 435.8 nm (blue). The color matching functions are the amounts of primaries needed to match the
monochromatic test primary. These functions are shown in the plot in figure above (with caption The
CIE 1931 RGB color matching functions).
functions) Note that r ¯ ( λ ) and g ¯ ( λ ) are zero at 435.8 nm, r ¯ ( λ
) and b ¯ ( λ ) are zero at 546.1 nm and g ¯ ( λ ) and b ¯ ( λ ) are zero at 700 nm, since in these cases
the test color is one of the primaries. The primaries with wavelengths 546.1 nm and 435.8 nm were
chosen because they are easily reproducible monochromatic lines of a mercury vapor discharge. The
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700 nm wavelength, which in 1931 was difficult to reproduce as a monochromatic beam, was chosen
because the eye's perception of color is rather unchanging at this wavelength, and therefore small
errors in wavelength of this primary would have little effect on the results.
The color matching functions and primaries were settled upon by a CIE special commission after
considerable deliberation. The cut-offs at the short- and long-wavelength side of the diagram are
chosen somewhat arbitrarily; the human eye can actually see light with wavelengths up to about 810
nm, but with a sensitivity that is many thousand times lower than for green light. These color
matching functions define what is known as the "1931 CIE standard observer". Note that rather than
specify the brightness of each primary, the curves are normalized to have constant area beneath them.
This area is fixed to a particular value by specifying that
The resulting normalized color matching functions are then scaled in the r:g:b ratio of
1:4.5907:0.0601 for source luminance and 72.0962:1.3791:1 for source radiance to reproduce the true
color matching functions. By proposing that the primaries be standardized, the CIE established an
international system of objective color notation.
Given these scaled color matching functions, the RGB tristimulus values for a color with a
spectral power distribution S ( λ ) would then be given by:
These are all inner products and can be thought of as a projection of an infinite-dimensional
spectrum to a three-dimensional color.
Grassmann's law
One might ask: "Why is it possible that Wright and Guild's results can be summarized using
different primaries and different intensities from those actually used?" One might also ask: "What
about the case when the test colors being matched are not monochromatic?" The answer to both of
these questions lies in the (near) linearity of human color perception. This linearity is expressed in
Grassmann's law.
An early statement of law, attributed to Grassmann, is: “ If two simple but non-complementary
spectral colors be mixed with each other, they give rise to the color sensation which may be
represented by a color in the spectrum lying between both and mixed with a certain quantity of
white.”
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Fig 5.16: Grassmann expressed his law with respect to a circular arrangement of spectral colors
in this 1853 illustration
If a test color is the combination of two other colors, then in a matching experiment based on
mixing primary light colors, an observer's matching value of each primary will be the sum of the
matching values for each of the other test colors when viewed separately.
In other words, if beam 1 and 2 are the initial colors, and the observer chooses (R1, G1, B1) as the
strengths of the primaries that match beam 1 and (R2, G2, B2) as the strengths of the primaries that
match beam 2, then if the two beams were combined, the matching values will be the sums of the
components. Precisely, they will be (R , G , B ), where:
The CIE RGB space can be used to define chromaticity in the usual way: The chromaticity
coordinates are r and g where:
Construction of the CIE XYZ color space from the Wright–Guild data
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Fig 5.17: Diagram in CIE rg chromaticity space showing the construction of the triangle
specifying the CIE XYZ color space. The triangle Cb-Cg-Cr is just the xy = (0, 0), (0, 1), (1, 0)
triangle in CIE xy chromaticity space. The line connecting Cb and Cr is the alychne. Notice that the
spectral locus passes through rg = (0, 0) at 435.8 nm, through rg = (0, 1) at 546.1 nm and through rg
= (1, 0) at 700 nm. Also, the equal energy point (E) is at rg = xy = (1/3, 1/3).
Having developed an RGB model of human vision using the CIE RGB matching functions, the
members of the special commission wished to develop another color space that would relate to the
CIE RGB color space. It was assumed that Grassmann's law held, and the new space would be related
to the CIE RGB space by a linear transformation. The new space would be defined in terms of three
new color matching functions
as described above. The new color space
would be chosen to have the following desirable properties:
•
The new color matching functions were to be everywhere greater than or equal to zero. In
1931, computations were done by hand or slide rule, and the specification of positive values
was a useful computational simplification.
•
The color matching function would be exactly equal to the photopic luminous efficiency
function V(λ) for the "CIE standard photopic observer". The luminance function describes the
variation of perceived brightness with wavelength. The fact that the luminance function could
be constructed by a linear combination of the RGB color matching functions was not
guaranteed by any means but might be expected to be nearly true due to the near-linear nature
of human sight. Again, the main reason for this requirement was computational
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•
•
•
simplification.
For the constant energy white point, it was required that x = y = z = 1/3.
By virtue of the definition of chromaticity and the requirement of positive values of x and y, it
can be seen that the gamut of all colors will lie inside the triangle [1, 0], [0, 0], [0, 1]. It was
required that the gamut fill this space practically completely.
It was found that the z ¯ ( λ ) color matching function could be set to zero above 650 nm
while remaining within the bounds of experimental error. For computational simplicity, it was
specified that this would be so.
In geometrical terms, choosing the new color space amounts to choosing a new triangle in rg
chromaticity space. In the figure above-right, the rg chromaticity coordinates are shown on the two
axes in black, along with the gamut of the 1931 standard observer. Shown in red are the CIE xy
chromaticity axes which were determined by the above requirements. The requirement that the XYZ
coordinates be non-negative means that the triangle formed by Cr, Cg, Cb must encompass the entire
gamut of the standard observer. The line connecting Cr and Cb is fixed by the requirement that the y ¯
( λ ) function be equal to the luminance function. This line is the line of zero luminance, and is called
the alychne. The requirement that the z ¯ ( λ ) function be zero above 650 nm means that the line
connecting Cg and Cr must be tangent to the gamut in the region of Kr. This defines the location of
point Cr. The requirement that the equal energy point be defined by x = y = 1/3 puts a restriction on
the line joining Cb and Cg, and finally, the requirement that the gamut fill the space puts a second
restriction on this line to be very close to the gamut in the green region, which specifies the location
of Cg and Cb. The above described transformation is a linear transformation from the CIE RGB space
to XYZ space. The standardized transformation settled upon by the CIE special commission was as
follows:
The numbers in the conversion matrix below are exact, with the number of digits specified in CIE
standards.
While the above matrix is exactly specified in standards, going the other direction uses an
inverse matrix that is not exactly specified, but is approximately:
The integrals of the XYZ color matching functions must all be equal by requirement 3 above,
and this is set by the integral of the photopic luminous efficiency function by requirement 2 above.
The tabulated sensitivity curves have a certain amount of arbitrariness in them. The shapes of the
individual X, Y and Z sensitivity curves can be measured with a reasonable accuracy. However, the
overall luminosity curve (which in fact is a weighted sum of these three curves) is subjective, since it
involves asking a test person whether two light sources have the same brightness, even if they are in
completely different colors. Along the same lines, the relative magnitudes of the X, Y, and Z curves
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are arbitrary. Furthermore, one could define a valid color space with an X sensitivity curve that has
twice the amplitude. This new color space would have a different shape. The sensitivity curves in the
CIE 1931 and 1964 XYZ color spaces are scaled to have equal areas under the curves.
CHECK YOUR PROGRESS
Explain the importance of CIE 1932 color space.
Elaborate the how Tristimulus values are used in CIE color space.
Explain the meaning of X,Y,Z in CIE color space.
Describe the concept of CIE standard observer.
Discuss how X,Y, Z can be calculated from spectral data.
Explain the concept of CIE xy chromaticity diagram and the CIE xyY color space
Discuss various interesting properties of the CIE XYZ color space.
Explain the Definition of the CIE XYZ color space.
Describe the CIE 1931 RGB color matching functions.
Explain the contribution of Grassmann's law in the theoretical understanding of CIE color space.
5.5 RGB COLOR MODEL
The RGB color model is an additive color model in which red, green and blue light are added
together in various ways to reproduce a broad array of colors. The name of the model comes from the
initials of the three additive primary colors, red, green, and blue.
Fig 5.18: Additive color mixing: adding red to green yields yellow; adding red to blue yields
magenta; adding green to blue yields cyan; adding all three primary colors together yields white.
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The main purpose of the RGB color model is for the sensing, representation and display of
images in electronic systems, such as televisions and computers, though it has also been used in
conventional photography. Before the electronic age, the RGB color model already had a solid theory
behind it, based in human perception of colors.
RGB is a device-dependent color model: different devices detect or reproduce a given RGB value
differently, since the color elements (such as phosphors or dyes) and their response to the individual
R, G, and B levels vary from manufacturer to manufacturer, or even in the same device over time.
Thus a RGB value does not define the same color across devices without some kind of color
management.
Typical RGB input devices are color TV and video cameras, image scanners, and digital cameras.
Typical RGB output devices are TV sets of various technologies (CRT, LCD, plasma, OLED,
quantum dots, etc.), computer and mobile phone displays, video projectors, multicolor LED displays
and large screens such as JumboTron. Color printers, on the other hand are not RGB devices, but
subtractive color devices (typically CMYK color model).
To form a color with RGB, three light beams (one red, one green, and one blue) must be
superimposed (for example by emission from a black screen or by reflection from a white screen).
Each of the three beams is called a component of that color, and each of them can have an arbitrary
intensity, from fully off to fully on, in the mixture.
Additive colors
The RGB color model is additive in the sense that the three light beams are added together, and
their light spectra add, wavelength for wavelength, to make the final color's spectrum. This is
essentially opposite to the subtractive color model that applies to paints, inks, dyes, and other
substances whose color depends on reflecting the light under which we see them.
Zero intensity for each component gives the darkest color (no light, considered the black), and
full intensity of each gives a white; the quality of this white depends on the nature of the primary light
sources, but if they are properly balanced, the result is a neutral white matching the system's white
point. When the intensities for all the components are the same, the result is a shade of gray, darker or
lighter depending on the intensity. When the intensities are different, the result is a colorized hue,
more or less saturated depending on the difference of the strongest and weakest of the intensities of
the primary colors employed.
When one of the components has the strongest intensity, the color is a hue near this primary color
(reddish, greenish or bluish), and when two components have the same strongest intensity, then the
color is a hue of a secondary color (a shade of cyan, magenta or yellow). A secondary color is formed
by the sum of two primary colors of equal intensity: cyan is green+blue, magenta is red+blue, and
yellow is red+green. Every secondary color is the complement of one primary color; when a primary
and its complementary secondary color are added together, the result is white: cyan complements red,
magenta complements green, and yellow complements blue.
The RGB color model itself does not define what is meant by red, green and blue
colorimetrically, and so the results of mixing them are not specified as absolute, but relative to the
primary colors. When the exact chromaticities of the red, green, and blue primaries are defined, the
color model then becomes an absolute color space, such as sRGB or Adobe RGB; see RGB color
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spaces for more details.
History of RGB color model theory and usage
The RGB color model is based on the Young–Helmholtz theory of trichromatic color vision,
developed by Thomas Young and Hermann Helmholtz in the early to mid nineteenth century, and on
James Clerk Maxwell's color triangle that elaborated that theory (circa 1860).
Fig 5.19: The first permanent color photograph, taken by J.C. Maxwell in 1861 using three
filters, specifically red, green, and violet-blue.
Photography
The first experiments with RGB in early color photography were made in 1861 by Maxwell
himself, and involved the process of combining three color-filtered separate takes. To reproduce the
color photograph, three matching projections over a screen in a dark room were necessary.
The additive RGB model and variants such as orange–green–violet were also used in the
Autochrome Lumière color plates and other screen-plate technologies such as the Joly color screen
and the Paget process in the early twentieth century. Color photography by taking three separate
plates was used by other pioneers, such as the Russian Sergey Prokudin-Gorsky in the period 1909
through 1915. Such methods lasted until about 1960 using the expensive and extremely complex tricolor carbro Autotype process.
When employed, the reproduction of prints from three-plate photos was done by dyes or pigments
using the complementary CMY model, by simply using the negative plates of the filtered takes:
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reverse red gives the cyan plate, and so on.
Television
Fig 5.20: Cutaway rendering of a color CRT: 1. Electron guns 2. Electron beams 3. Focusing
coils 4. Deflection coils 5. Anode connection 6. Mask for separating beams for red, green, and blue
part of displayed image 7. Phosphor layer with red, green, and blue zones 8. Close-up of the
phosphor-coated inner side of the screen
Before the development of practical electronic TV, there were patents on mechanically scanned
color systems as early as 1889 in Russia. The color TV pioneer John Logie Baird demonstrated the
world's first RGB color transmission in 1928, and also the world's first color broadcast in 1938, in
London. In his experiments, scanning and display were done mechanically by spinning colorized
wheels.
The Columbia Broadcasting System (CBS) began an experimental RGB field-sequential color
system in 1940. Images were scanned electrically, but the system still used a moving part: the
transparent RGB color wheel rotating at above 1,200 rpm in synchronism with the vertical scan. The
camera and the cathode-ray tube (CRT) were both monochromatic. Color was provided by color
wheels in the camera and the receiver. More recently, color wheels have been used in field-sequential
projection TV receivers based on the Texas Instruments monochrome DLP imager.
The modern RGB shadow mask technology for color CRT displays was patented by Werner
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Flechsig in Germany in 1938.
Personal computers
Early personal computers of the late 1970s and early 1980s, such as those from Apple, Atari and
Commodore, did not use RGB as their main method to manage colors, but rather composite video.
IBM introduced a 16-color scheme (four bits—one bit each for red, green, blue, and intensity) with
the Color Graphics Adapter (CGA) for its first IBM PC (1981), later improved with the Enhanced
Graphics Adapter (EGA) in 1984. The first manufacturer of a truecolor graphic card for PCs (the
TARGA) was Truevision in 1987, but it was not until the arrival of the Video Graphics Array (VGA)
in 1987 that RGB became popular, mainly due to the analog signals in the connection between the
adapter and the monitor which allowed a very wide range of RGB colors. Actually, it had to wait a
few more years because the original VGA cards were palette-driven just like EGA, although with
more freedom than VGA, but because the VGA connectors were analogue, later variants of VGA
(made by various manufacturers under the informal name Super VGA) eventually added truecolor. In
1992, magazines heavily advertised truecolor Super VGA hardware.
RGB devices
Fig 5.21: Color wheel with RGB pixels of the colors
One common application of the RGB color model is the display of colors on a cathode ray tube
(CRT), liquid crystal display (LCD), plasma display, or organic light emitting diode (OLED) display
such as a television, a computer’s monitor, or a large scale screen. Each pixel on the screen is built by
driving three small and very close but still separated RGB light sources. At common viewing
distance, the separate sources are indistinguishable, which tricks the eye to see a given solid color. All
the pixels together arranged in the rectangular screen surface conforms the color image.
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Fig 5.22: RGB phosphor dots in a CRT monitor
During digital image processing each pixel can be represented in the computer memory or
interface hardware (for example, a graphics card) as binary values for the red, green, and blue color
components. When properly managed, these values are converted into intensities or voltages via
gamma correction to correct the inherent nonlinearity of some devices, such that the intended
intensities are reproduced on the display.
The Quattron released by Sharp uses RGB color and adds yellow as a sub-pixel, supposedly
allowing an increase in the number of available colors.
Video electronics
RGB is also the term referring to a type of component video signal used in the video electronics
industry. It consists of three signals—red, green, and blue—carried on three separate cables/pins.
RGB signal formats are often based on modified versions of the RS-170 and RS-343 standards for
monochrome video. This type of video signal is widely used in Europe since it is the best quality
signal that can be carried on the standard SCART connector. This signal is known as RGBS (4
BNC/RCA terminated cables exist as well), but it is directly compatible with RGBHV used for
computer monitors (usually carried on 15-pin cables terminated with 15-pin D-sub or 5 BNC
connectors), which carries separate horizontal and vertical sync signals.
Outside Europe, RGB is not very popular as a video signal format; S-Video takes that spot in
most non-European regions. However, almost all computer monitors around the world use RGB.
Video framebuffer
A framebuffer is a digital device for computers which stores data in the so-called video memory
(comprising an array of Video RAM or similar chips). This data goes either to three digital-to-analog
converters (DACs) (for analog monitors), one per primary color, or directly to digital monitors.
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Driven by software, the CPU (or other specialized chips) write the appropriate bytes into the video
memory to define the image. Modern systems encode pixel color values by devoting eight bits to each
of the R, G, and B components. RGB information can be either carried directly by the pixel bits
themselves or provided by a separate color look-up table (CLUT) if indexed color graphic modes are
used.
A CLUT is a specialized RAM that stores R, G, and B values that define specific colors. Each
color has its own address (index)—consider it as a descriptive reference number that provides that
specific color when the image needs it. The content of the CLUT is much like a palette of colors.
Image data that uses indexed color specifies addresses within the CLUT to provide the required R, G,
and B values for each specific pixel, one pixel at a time. Of course, before displaying, the CLUT has
to be loaded with R, G, and B values that define the palette of colors required for each image to be
rendered. Some video applications store such palettes in PAL files (Microsoft AOE game, for
example uses over half-a-dozen) and can combine CLUTs on screen.
RGB24 and RGB32
This indirect scheme restricts the number of available colors in an image CLUT —typically 256cubed (8 bits in three color channels with values of 0–255)— although each color in the RGB24
CLUT table has only 8 bits representing 256 codes for each of the R, G, and B primaries
combinatorial math theory says this means that any given color can be one of 16,777,216 possible
colors. However, the advantage is that an indexed-color image file can be significantly smaller than it
would be with only 8 bits per pixel for each primary.
Modern storage, however, is far less costly, greatly reducing the need to minimize image file size.
By using an appropriate combination of red, green, and blue intensities, many colors can be displayed.
Current typical display adapters use up to 24-bits of information for each pixel: 8-bit per component
multiplied by three components (see the Digital representations section below (24bits = 2563, each
primary value of 8 bits with values of 0–255). With this system, 16,777,216 (2563 or 224) discrete
combinations of R, G, and B values are allowed, providing millions of different (though not
necessarily distinguishable) hue, saturation and lightness shades. Increased shading has been
implemented in various ways, some formats such as .png and .tga files among others using a fourth
greyscale color channel as a masking layer, often called RGB32.
For images with a modest range of brightnesses from the darkest to the lightest, eight bits per
primary color provides good-quality images, but extreme images require more bits per primary color
as well as advanced display technology. For more information see High Dynamic Range (HDR)
imaging.
Nonlinearity
In classic cathode ray tube (CRT) devices, the brightness of a given point over the fluorescent
screen due to the impact of accelerated electrons is not proportional to the voltages applied to the
electron gun control grids, but to an expansive function of that voltage. The amount of this deviation
is known as its gamma value ( γ), the argument for a power law function, which closely describes this
behavior. A linear response is given by a gamma value of 1.0, but actual CRT nonlinearities have a
gamma value around 2.0 to 2.5.
Similarly, the intensity of the output on TV and computer display devices is not directly
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proportional to the R, G, and B applied electric signals (or file data values which drive them through
Digital-to-Analog Converters). On a typical standard 2.2-gamma CRT display, an input intensity
RGB value of (0.5, 0.5, 0.5) only outputs about 22% of full brightness (1.0, 1.0, 1.0), instead of 50%.
To obtain the correct response, a gamma correction is used in encoding the image data, and possibly
further corrections as part of the color calibration process of the device. Gamma affects black-andwhite TV as well as color. In standard color TV, broadcast signals are gamma corrected.
RGB and cameras
Fig 5.23: The Bayer filter arrangement of color filters on the pixel array of a digital image sensor
In color television and video cameras manufactured before the 1990s, the incoming light was
separated by prisms and filters into the three RGB primary colors feeding each color into a separate
video camera tube (or pickup tube). These tubes are a type of cathode ray tube, not to be confused
with that of CRT displays.
With the arrival of commercially viable charge-coupled device (CCD) technology in the 1980s,
first the pickup tubes were replaced with this kind of sensor. Later, higher scale integration electronics
was applied (mainly by Sony), simplifying and even removing the intermediate optics, thereby
reducing the size of home video cameras and eventually leading to the development of full
camcorders. Current webcams and mobile phones with cameras are the most miniaturized commercial
forms of such technology.
Photographic digital cameras that use a CMOS or CCD image sensor often operate with some
variation of the RGB model. In a Bayer filter arrangement, green is given twice as many detectors as
red and blue (ratio 1:2:1) in order to achieve higher luminance resolution than chrominance
resolution. The sensor has a grid of red, green, and blue detectors arranged so that the first row is
RGRGRGRG, the next is GBGBGBGB, and that sequence is repeated in subsequent rows. For every
channel, missing pixels are obtained by interpolation in the demosaicing process to build up the
complete image. Also, other processes used to be applied in order to map the camera RGB
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measurements into a standard RGB color space as sRGB.
RGB and scanners
In computing, an image scanner is a device that optically scans images (printed text, handwriting,
or an object) and converts it to a digital image which is transferred to a computer. Among other
formats, flat, drum and film scanners exist, and most of them support RGB color. They can be
considered the successors of early telephotography input devices, which were able to send
consecutive scan lines as analog amplitude modulation signals through standard telephonic lines to
appropriate receivers; such systems were in use in press since the 1920s to the mid-1990s. Color
telephotographs were sent as three separated RGB filtered images consecutively.
Currently available scanners typically use charge-coupled device (CCD) or contact image sensor
(CIS) as the image sensor, whereas older drum scanners use a photomultiplier tube as the image
sensor. Early color film scanners used a halogen lamp and a three-color filter wheel, so three
exposures were needed to scan a single color image. Due to heating problems, the worst of them
being the potential destruction of the scanned film, this technology was later replaced by non-heating
light sources such as color LEDs.
CHECK YOUR PROGRESS
Explain the importance of RGB color model.
Elaborate the how RGB color model is additive.
Explain the application of RGB color model in photography.
Explain the application of RGB color model in television.
Explain the application of RGB color model in personal computers.
Describe the concept of Color Look Up Table in video framebuffers.
Discuss RGB 24 and RGB32.
Explain the concept of gamma correction for CRT tube.
Discuss the Bayer filter arrangement of color filters on the pixel array of a digital image sensor.
5.6 CMYK MODEL
The CMYK color model (process color, four color) is a subtractive color model, used in color
printing, and is also used to describe the printing process itself. CMYK refers to the four inks used in
some color printing: cyan, magenta, yellow, and key (black). Although it varies by print house, press
operator, press manufacturer, and press run, ink is typically applied in the order of the abbreviation.
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The "K" in CMYK stands for key because in four-color printing, cyan, magenta, and yellow
printing plates are carefully keyed, or aligned, with the key of the black key plate. Some sources
suggest that the "K" in CMYK comes from the last letter in "black" and was chosen because B
already means blue. However, some people disagree with this because C for Cyan is classed as the
blue when printing in CMYK format. Some sources claim this explanation, although useful as a
mnemonic, is incorrect, that K comes only from "Key" because black is often used as outline and
printed first.
The CMYK model works by partially or entirely masking colors on a lighter, usually white,
background. The ink reduces the light that would otherwise be reflected. Such a model is called
subtractive because inks "subtract" brightness from white.
Fig 5.24: When CMY “primaries” are combined at full strength, the resulting “secondary”
mixtures are red, green, and blue. Mixing all three gives an imperfect black
In additive color models, such as RGB, white is the "additive" combination of all primary colored
lights, while black is the absence of light. In the CMYK model, it is the opposite: white is the natural
color of the paper or other background, while black results from a full combination of colored inks.
To save cost on ink, and to produce deeper black tones, unsaturated and dark colors are produced by
using black ink instead of the combination of cyan, magenta, and yellow.
Fig 5.25: Color printing typically uses ink of four colors: cyan, magenta, yellow, and key (black).
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5.6.1 Halftoning
This diagram shows three examples of color halftoning with CMYK separations, as well as the
combined halftone pattern and how the human eye would observe the combined halftone pattern from
a sufficient distance.
With CMYK printing, halftoning (also called screening) allows for less than full saturation of the
primary colors; tiny dots of each primary color are printed in a pattern small enough that human
beings perceive a solid color. Magenta printed with a 20% halftone, for example, produces a pink
color, because the eye perceives the tiny magenta dots on the large white paper as lighter and less
saturated than the color of pure magenta ink.
Without halftoning, the three primary process colors could be printed only as solid blocks of
color, and therefore could produce only seven colors: the three primaries themselves, plus three
secondary colors produced by layering two of the primaries: cyan and yellow produce green, cyan and
magenta produce blue, yellow and magenta produce red (these subtractive secondary colors
correspond roughly to the additive primary colors), plus layering all three of them resulting in black.
With halftoning, a full continuous range of colors can be produced.
Screen angle
Fig 5.26: Typical halftone screen angles.
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To improve print quality and reduce moiré patterns, the screen for each color is set at a different
angle. While the angles depend on how many colors are used and the preference of the press operator,
typical CMYK process printing uses any of the following screen angles:
5.6.2 Benefits of using black ink
Fig 5.27: A color photograph of the Teton Range.
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Fig 5.28: The image above, separated for printing with process cyan, magenta, and yellow inks.
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Fig 5.29: The same image, this time separated with maximum black, to minimize colored-inks
use.
The "black" generated by mixing commercially practical cyan, magenta, and yellow inks is
unsatisfactory, so four-color printing uses black ink in addition to the subtractive primaries. Common
reasons for using black ink include:
•
•
•
In traditional preparation of color separations, a red keyline on the black line art marked the
outline of solid or tint color areas. In some cases a black keyline was used when it served as
both a color indicator and an outline to be printed in black. Because usually the black plate
contained the keyline, the K in CMYK represents the keyline or black plate, also sometimes
called the key plate.
Text is typically printed in black and includes fine detail (such as serifs), so to reproduce text
or other finely detailed outlines, without slight blurring, using three inks would require
impractically accurate registration.
A combination of 100% cyan, magenta, and yellow inks soaks the paper with ink, making
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•
•
it slower to dry, causing bleeding, or (especially on cheap paper such as newsprint)
weakening the paper so much that it tears.
Although a combination of 100% cyan, magenta, and yellow inks should, in theory,
completely absorb the entire visible spectrum of light and produce a perfect black, practical
inks fall short of their ideal characteristics and the result is actually a dark muddy color that
does not quite appear black. Adding black ink absorbs more light and yields much better
blacks.
Using black ink is less expensive than using the corresponding amounts of colored inks.
When a very dark area is desirable, a colored or gray CMY "bedding" is applied first, then a full
black layer is applied on top, making a rich, deep black; this is called rich black. A black made with
just CMY inks is sometimes called a composite black.
The amount of black to use to replace amounts of the other ink is variable, and the choice depends
on the technology, paper and ink in use. Processes called under color removal, under color addition,
and gray component replacement are used to decide on the final mix; different CMYK recipes will be
used depending on the printing task.
5.6.3 Other printer color models
CMYK or process color printing is contrasted with spot color printing, in which specific colored
inks are used to generate the colors appearing on paper. Some printing presses are capable of printing
with both four-color process inks and additional spot color inks at the same time. High-quality printed
materials, such as marketing brochures and books, often include photographs requiring process-color
printing, other graphic effects requiring spot colors (such as metallic inks), and finishes such as
varnish, which enhances the glossy appearance of the printed piece.
CMYK are the process printers which often have a relatively small color gamut. Processes such
as Pantone's proprietary six-color (CMYKOG) Hexachrome considerably expand the gamut. Light,
saturated colors often cannot be created with CMYK, and light colors in general may make visible the
halftone pattern. Using a CcMmYK process, with the addition of light cyan and magenta inks to
CMYK, can solve these problems, and such a process is used by many inkjet printers, including
desktop models.
5.6.4 Comparison with RGB displays Comparisons between RGB displays and CMYK prints can
be difficult, since the color reproduction technologies and properties are very different. A computer
monitor mixes shades of red, green, and blue light to create color pictures. A CMYK printer instead
uses light-absorbing cyan, magenta, and yellow inks, whose colors are mixed using dithering,
halftoning, or some other optical technique.
Similar to monitors, the inks used in printing produce a color gamut that is "only a subset of the
visible spectrum" although both color modes have their own specific ranges. As a result of this items
which are displayed on a computer monitor may not completely match the look of items which are
printed if opposite color modes are being combined in both mediums. When designing items to be
printed, designers view the colors which they are choosing on an RGB color mode (their computer
screen), and it is often difficult to visualize the way in which the color will turn out post printing
because of this.
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Fig 5.30: Comparison of some RGB and CMYK color gamut on a CIE 1931 xy chromaticity
diagram.
Spectrum of Printed Paper
To reproduce color, the CMYK color model codes for absorbing light rather than emitting it (as is
assumed by RGB). The 'K' component absorbs all wavelengths and is therefore achromatic. The
Cyan, Magenta, and Yellow components are used for color reproduction and they may be viewed
viewe as
the inverse of RGB. Cyan absorbs Red, Magenta absorbs Green, and Yellow absorbs Blue ((-R,-G,-B).
Spectrum of the visible wavelengths on printed paper (SCA Graphosilk). Shown is the transition
from Red to Yellow. White, red, blue, and green are shown for reference. Readings from a white
orchid flower, a rose (red and yellow petals), and a red cyclamen flower are shown for comparison.
The units of spectral power are simply raw sensor values (with a linear response at specific
wavelengths).
5.6.5 Conversion
Since RGB and CMYK spaces are both device-dependent
device dependent spaces, there is no simple or general
conversion formula that converts between them. Conversions are generally done through color
management systems, using color profiles that describe the spaces bein
being
g converted. Nevertheless, the
conversions cannot be exact, particularly where these spaces have different gamuts.
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Fig 5.31: Early representation of the three color process (1902).
The problem of computing a colorimetric estimate of the color that results from printing various
combinations of ink has been addressed by many scientists. A general method that has emerged for
the case of halftone printing is to treat each tiny overlap of color dots as one of 8 (combinations of
CMY) or of 16 (combinations of CMYK) colors, which in this context are known as Neugebauer
primaries. The resultant color would be an area-weighted colorimetric combination of these primary
colors, except that the Yule–Nielsen effect ("dot gain") of scattered light between and within the areas
complicates the physics and the analysis; empirical formulas for such analysis have been developed,
in terms of detailed dye combination absorption spectra and empirical parameters.
CHECK YOUR PROGRESS
Explain the importance of CMYK color model.
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Elaborate the how CMYK color model is subtractive
subtractive.
Explain the reasons for using black as additional pigment in printing.
Explain the concept of halftones.
Explain the concept of screen angles in CMYK printing.
Describe the color models other than CMYK use
used in color printing.
Discuss how RGB and CMYK color models can be compared.
Explain how RGB and CMYK color spaces can be converted from one space to another.
5.7 HUE
Hue is one of the main properties (called color appearance parameters) of a color, defined
defin
technically (in the CIECAM02 model), as "the degree to which a stimulus can be described as similar
to or different from stimuli that are described as red, green, blue, and yellow", (which in certain
theories of colour vision are called unique hues). Hue
Hue can typically be represented quantitatively by
single number, often corresponding to an angular position around a central or neutral point or axis on
a colorspace coordinate diagram (such as a chromaticity diagram) or color wheel, or by its dominant
wavelength
length or that of its complementary color. The other color appearance parameters are
colorfulness, chroma (not video chroma), saturation, lightness, and brightness.
Usually, colors with the same hue are distinguished with adjectives referring to their lightness
ligh
or
colorfulness, such as with "light blue", "pastel blue", "vivid blue". Exceptions include brown, which is
a dark orange.
In painting color theory, a hue refers to a pure pigment—one
pigment one without tint or shade (added white
or black pigment, respectively).. Hues are first processed in the brain in areas in the extended V4
called globs..
Fig5.00:
5.00: Hue in the HSB/HSL encodings of RGB
5.7.1 Computing hue
In opponent color spaces in which two of the axes are perceptually orthogonal to lightness, such
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as the CIE 1976 (L*, a*, b*) (CIELAB) and 1976 (L*, u*, v*) (CIELUV) color spaces, hue may be
computed together with chroma by converting these coordinates from rectangular form to polar form.
Hue is the angular component of the polar representation, while chroma is the radial component.
Specifically in CIELAB,
Tan(hab) = b*/a*
Or,
(Here atan2(b,a) is the angle in radians between positive X-axis and a point (a,b) in the
rectangular cartestian coordinate system. It is called two-argument tan inverse or arc tan function.)
In CIELUV system:
Defining hue in terms of RGB
Preucil describes a color hexagon, similar to a trilinear plot described by Evans, Hanson, and
Brewer, which may be used to compute hue from RGB. To place red at 0°, green at 120°, and blue at
240°,
Equivalently, one may solve
Preucil used a polar plot, which he termed a color circle. Using R, G, and B, one may compute
hue angle using the following scheme: determine which of the six possible orderings of R, G, and B
prevail, then apply the formula given in the table below
. Note that in each case the formula contains the fraction (M – L)/ (H – L), where H is the highest
of R, G, and B; L is the lowest, and M is the mid one between the other two. This is referred to as the
"Preucil hue error" and was used in the computation of mask strength in photomechanical color
reproduction.
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Hue angles computed for the Preucil circle agree with the hue angle computed for the Preucil
hexagon at integer multiples of 30° (red, yellow, green, cyan, blue, magenta, and the colors midway
between contiguous pairs) and differ by approximately 1.2° at odd integer multiples of 15° (based on
the circle formula), the maximal divergence between the two.
The process of converting an RGB color into an HSL color space or HSV color space is usually
based on a 6-piece piecewise mapping, treating the HSV cone as a hexacone, or the HSL double cone
as a double hexacone. The formulae used are those in the table above.
Fig 5.32: HSV color space as a conical object
5.7.2 Hue vs. dominant wavelength
Dominant wavelength (or sometimes equivalent wavelength) is a physical analog to the
perceptual attribute hue. On a chromaticity diagram, a line is drawn from a white point through the
coordinates of the color in question, until it intersects the spectral locus. The wavelength at which the
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line intersects the spectrum locus is identified as the color's dominant wavelength if the point is on the
same side of the white point as the spectral locus, and as the color's complementary wavelength if the
point is on the opposite side.
5.7.3 Hue difference:
There are two main ways in which hue difference is quantified.
The first is the simple difference between the two hue angles. The symbol for this expression of
hue difference is
in CIELAB and
in CIELUV.
The other is computed as the residual total color difference after Lightness and Chroma
differences have been accounted for; its symbol is ∆ H* ab in CIELAB and ∆ H* u v in CIELUV.
5.7.4 Names and other notations for hues
There exists some correspondence, more or less precise, between hue values and color terms
(names). One approach in color science is to use traditional color terms but try to give them more
precise definitions. See spectral color#Table of spectral or near-spectral colors for names of highly
saturated colors with the hue from ≈ 0° (red) up to ≈ 275° (violet), and line of purples#Table of
highly-saturated purple colors for color terms of the remaining part of the color wheel.
Alternative approach is to use a systematic notation. It can be a standard angle notation for certain
color model such as HSL/HSV mentioned above, CIELUV, or CIECAM02. Alphanumeric notations
such as of Munsell color system, NCS, and Pantone Matching System are also used.
CHECK YOUR PROGRESS
Explain the importance of ‘hue’ in a color model.
Elaborate the hue can be computed in terms of R,G,B values.
Compare ‘hue’ with the ‘dominant wavelength’.
Explain the difference between ∆ H* ab and ∆ h ab .
5.8 SATURATION
Saturation is also referred to as “intensity” and “chroma.” It refers to the dominance of hue in the
color. On the outer edge of the hue wheel are the ‘pure’ hues. As you move into the center of the
wheel, the hue we are using to describe the color dominates less and less. When you reach the center
of the wheel, no hue dominates. These colors directly on the central axis are considered desaturated.
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Fig 5.33: Desaturation: hue becomes less dominant, moves to circle’s center
Naturally, the opposite of the image above is to saturate color. The first example below describes
the general direction color must move on the color circle to become more saturated (towards the
outside). The second example depicts how a single color looks completely saturated, having no other
hues present in the color.
Fig 5.34: General Saturation Direction
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Fig 5.35: “Pure” Hue With Complete Saturation: no other hues present
5.9 VALUE COLOR MODEL
Now let’s add “value” to the HSV scale. Value is the dimension of lightness/darkness. In terms
of a spectral definition of color, value describes the overall intensity or strength of the light. If hue can
be thought of as a dimension going around a wheel, then value is a linear axis running through the
middle of the wheel, as seen below:
Fig 5.36: HSV Model with Hue, Saturation, and Value Explained
To better visualize even more, look at the example below showing a full color range for a single
hue:
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Fig 5.37: HSV Model With Full Range of Single Hue
Now, if you imagine that each hue was also represented as a slice like the one above, we would
have a solid, upside-down cone of colors. The example above can be considered a slice of the cone.
Notice how the right-most edge of this cone slice shows the greatest amount of the dominant red hue
(least amount of other competing hues), and how as you go down vertically, it gets darker in “value.”
Also notice that as we travel from right to left in the cone, the hue becomes less dominant and
eventually becomes completely desaturated along the vertical center of the cone. This vertical center
axis of complete desaturation is referred to as grayscale. See how this slice below translates into
some isolated color swatches:
Fig 5.38: Cone Slice Swatches
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Color Pickers
With this explanation, it might be much easier to then understand how modern color pickers
work. There are many types of color pickers, but this example will focus on the common Adobe
software interface picker, continuing to use the red hue as the exa
example
mple below. By the way, relate the
similarity of our cone-shaped
shaped red slice above to the “Select Color” window below to better visualize
how this works.
In Figure-1
1 below, first notice the center vertical slider. This is where we select the hue. It is
currently
ntly set to the lowest selection and corresponds to the “H:0” radio button value on the right. The
“H” indicates “Hue,” and the zero value describes which numerical hue assignment we have selected.
Below it, you will see that “Red” is set to “255,” or the fullest level of light represented on a computer
(0 = lowest). Notice that Blue and Green are set to zero, indicating that Red is at its fullest level of
saturation.
Next, notice where the picker circle is in the “Select Color” window. It is located at the top-right,
indicating where on the scale you want the saturation to fall. As we said, the sample is equivalent to
the purest red hue with full saturation, and it corresponds to the outermost edge of the color wheel.
The “S:100%” on the right describes the level of saturation in the color we have selected, and the
“B:100%” corresponds to the brightness, or value.
As a side note, notice that under the CMYK levels that Yellow and Magenta are basically equally
represented at their fullest capacities. This supp
supports
orts how in the Subtractive Color Model, red is a
secondary color of yellow and magenta.
Fig 5.
5.39: RGB Color Mode – Pure Red Hue
Now, as a means of comparison, look at the next model. Do you see the difference?
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Fig 5.40
40: RGB Color
Mode – Pure Red Hue
In case you don’t see the difference, it is in the Hue number setting and where the slider is
located. This is essentially the same hue as in the previous Figure-1,
Figure 1, except that the setting has gone
from 0 to 360. This is because we are basing it on the HSV cone
cone model as illustrated earlier, and the
hues at the top of the upside-down
down cone are in a full 360-degree
360 degree circle. Thus, we have completed the
circle by starting at the zero-level
level red and moving through the full visible spectrum to the same 360
360level red.
To get a more complete picture of how this works, lets look at the RGB equivalent of “cyan”,
which is directly across from it on the color wheel, and is thus red’s complementary hue.
Fig 5.41:: RGB Models rendering of the secondary Cyan
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Notice that in Figure-3 that the hue setting is “180,” or located at 180-degrees on the color circle,
half of 360. This is what numerically indicates the cyan is red’s complement. Also, you’ll notice that
it is the secondary RGB color produced by mixing equal parts Blue and Green, where Blue=255, and
Green=255. As a quick reminder of the basic color wheel to help you visualize, here is how cyan
relates to red:
Fig 5.42: Figure showing complementary colors along with primry additive and substractive
colors
HSL and HSV are the two most common cylindrical-coordinate representations of points in
an RGB color model. The two representations rearrange the geometry of RGB in an attempt to be
more intuitive and perceptually relevant than the cartesian (cube) representation. Developed in the
1970s for computer graphics applications, HSL and HSV are used today in color pickers, in image
editing software, and less commonly in image analysis and computer vision.
HSL stands for hue, saturation, and lightness (or luminosity), and is also often
called HLS. HSV stands for hue, saturation, and value, and is also often
called HSB (B for brightness). A third model, common in computer vision applications,
is HSI (I for intensity). However, while typically consistent, these definitions are not standardized,
and any of these abbreviations might be used for any of these three or several other related cylindrical
models. (For technical definitions of these terms, see below.)
In each cylinder, the angle around the central vertical axis corresponds to "hue", the distance from
the axis corresponds to "saturation", and the distance along the axis corresponds to "lightness",
"value" or "brightness". Note that while "hue" in HSL and HSV refers to the same attribute, their
definitions of "saturation" differ dramatically.
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Because HSL and HSV are simple transformations of device
device-dependent
dependent RGB models, the
physical colors they define depend on the colors of the red, gre
green, and blue primaries of the device or
of the particular RGB space, and on the gamma correction used to represent the amounts of those
primaries. As a result, each unique RGB device has unique HSL and HSV absolute color spaces to
accompany it (just as it has unique RGB absolute color space to accompany it), and the same
numerical HSL or HSV values (just
just as numerical RGB values) may be displayed differently by
different devices.
Both of these representations are used widely in computer graphics, and one or the other of them
is often more convenient than RGB, but both are also criticized for not adequa
adequately
tely separating colorcolor
making attributes, or for their lack of perceptual uniformity. Other more computationally intensive
models, such as CIELAB or CIECAM02
CIECAM02, are said to better achieve these goals.
Hue and chroma
Fig 5.43: Both hue and chroma are defined based on the projection of the RGB cube onto a
hexagon in the "chromaticity plane". Chroma is the relative size of the hexag
hexagon
on passing through a
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point, and hue is how far around that hexagon’s edge the point lies.
In each of our models, we calculate both hue and what this article will call chroma, after Joblove
and Greenberg, in the same way—that is, the hue of a color has the same numerical values in all of
these models, as does its chroma. If we take our tilted RGB cube, and project it onto the
"chromaticity plane" perpendicular to the neutral axis, our projection takes the shape of a hexagon,
with red, yellow, green, cyan, blue, and magenta at its corners (fig. 9). Hue is roughly the angle of
the vector to a point in the projection, with red at 0°, while chroma is roughly the distance of the point
from the origin..
More precisely, both hue and chroma in this model are defined with respect to the hexagonal
shape of the projection. The chroma is the proportion of the distance from the origin to the edge of the
hexagon. In the lower part of the adjacent diagram, this is the ratio of lengths OP/OP′, or alternately
the ratio of the radii of the two hexagons. This ratio is the difference between the largest and smallest
values among R, G, or B in a color. To make our definitions easier to write, we’ll define these
maximum, minimum, and chroma component values as M, m, and C, respectively.
To understand why chroma can be written as M − m, notice that any neutral color,
with R = G = B, projects onto the origin and so has 0 chroma. Thus if we add or subtract the same
amount from all three of R, G, and B, we move vertically within our tilted cube, and do not change the
projection. Therefore, any two colors (R, G, B) and (R − m, G − m, B − m) project on the same point,
and have the same chroma. The chroma of a color with one of its components equal to zero (m = 0) is
simply the maximum of the other two components. This chroma is M in the particular case of a color
with a zero component, and M − m in general.
The hue is the proportion of the distance around the edge of the hexagon which passes through
the projected point, originally measured on the range [0, 1) but now typically measured in degrees [0°,
360°). For points which project onto the origin in the chromaticity plane (i.e., grays), hue is
undefined. Mathematically, this definition of hue is written piecewise.
Sometimes, neutral colors (i.e. with C = 0) are assigned a hue of 0° for convenience of
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representation.
The definitions of hue and chroma in HSL and HSV have the effect of warping hexagons into
circles.
These definitions amount to a geometric warping of hexagons into circles: each side of the
hexagon is mapped linearly onto a 60° arc of the circle (fig. 10). After such a transformation, hue is
precisely the angle around the origin and chroma the distance from the origin: the angle and
magnitude of the vector pointing to a color.
Constructing rectangular chromaticity coordinates α and β,, and then transforming those into
hue H2 and chroma C2 yields slightly different
diffe
values than computing hexagonal hue H and chroma C:
compare the numbers in this diagram to those earlier in this section.
Sometimes for image analysis applications, this hexagon-to-circle
hexagon circle transformation is skipped,
and hue and chroma (we’ll denote these
the H2 and C2) are defined by the usual cartesian-to
to-polar
coordinate transformations (fig. 11). The easiest way to derive those is via a pair of cartesian
chromaticity coordinates which we’ll call α and β:
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(The atan2 function, a "two-argument
argument arctangent", has been described in section 5.7.1.)
5.7.1
Notice that these two definitions of hue (H
( and H2) nearly coincide, with a maximum difference
differenc
between them for any color of about 1.12°
1.12°—which
which occurs at twelve particular hues, for instance H =
13.38°, H2 = 12.26°—and with H = H2 for every multiple of 30°. The two definitions of chroma
(C and C2) differ more substantially: they are equal at the co
corners
rners of our hexagon, but at points
halfway between two corners, such as H = H2 = 30°, we have C = 1, but C2 = √¾ ≈ 0.866, a difference
of about 13.4%.
Lightness
Fig 5.44: Four different possible "lightness" dimensions, plotted against chroma, for a pair of
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complementary hues. Each plot is a vertical cross-section of its three-dimensional color solid.
While the definition of hue is relatively uncontroversial—it roughly satisfies the criterion that
colors of the same perceived hue should have the same numerical hue—the definition of
a lightness or value dimension is less obvious: there are several possibilities depending on the purpose
and goals of the representation. Here are four of the most common (fig. 12; three of these are also
shown in fig):
The simplest definition is just the average of the three components, in the HSI model
called intensity (fig. 12a). This is simply the projection of a point onto the neutral axis—the vertical
height of a point in our tilted cube. The advantage is that, together with Euclidean-distance
calculations of hue and chroma, this representation preserves distances and angles from the geometry
of the RGB cube.
In the HSV "hexcone" model, value is defined as the largest component of a color, our M above
(fig. 12b). This places all three primaries, and also all of the "secondary colors"—cyan, yellow, and
magenta—into a plane with white, forming a hexagonal pyramid out of the RGB cube.
V=M
In the HSL "bi-hexcone" model, lightness is defined as the average of the largest and smallest
color components (fig. 12c). This definition also puts the primary and secondary colors into a plane,
but a plane passing halfway between white and black. The resulting color solid is a double-cone
similar to Ostwald’s, shown above.
A more perceptually relevant alternative is to use luma, Y′, as a lightness dimension (fig. 12d).
Luma is the weighted average of gamma-corrected R, G, and B, based on their contribution to
perceived luminance, long used as the monochromatic dimension in color television broadcast. For
the Rec. 709 primaries used in sRGB, Y′709 = 0.21R + 0.72G + 0.07B; for the Rec.
601 NTSC primaries, Y′601 ≈ 0.30R + 0.59G + 0.11B; for other primaries different coefficients should
be used.
5.10 INTUITIVE COLOR CONCEPT
The HSV (Hue, Saturation, and Value) color model is more intuitive than the RGB color model.
The user specifies a color (hue) and then adds white or black. There are 3 color parameters: Hue,
Saturation, and Value. Changing the saturation parameter corresponds to adding or subtracting white
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and changing the value parameter corresponds to adding or subtracting black.
The 3D representation of the HSV model is derived from the RGB mode cube. If we look at the
RGB cube along the gray diagonal we can see a hexagon that is the HSV hexcone. The hue is given
by the angle about the vertical axis with red at 0, yellow at 60, green at 120, cyan at 180, blue at 240,
and magenta at 300. Note that the complementary colors are 180 apart.
The saturation varies between 0.0 <= s <=1.0 and is the ratio of purity of a related hue to its
maximum purity at s="1." at s equals 0 is the gray scale, that is the diagonal of the RGB cube
corresponds to v of the HSV hexcone. notice the complementary colors( red + cyan, blue + yellow,
green + magenta ) are diagonally opposite.
So to choose a color we do the following:
1. select pure hue (specifies H and sets S = V = 1)
To add black decrease V and/or to add white decrease S.
For Example: pure blue H = 240, S = V = 1
dark blue H = 240, S = 1, V = 0.40
light blue H = 240, S = .3, V = 1.0
Intuitive color concepts
Artists start with a "pure color or hue", and then add black pigment to produce different shades.
The more black pigment the darker the shade. They add white pigment and get different tints. Adding
both black and white pigments gives different tones. If we look at the cross-section of the hexcone we
can see the analogy with the artist’s model.
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The human eye can distinguish about 128 different hues, 130 different tints (saturation levels),
and from 16 (blue part of spectrum) to 23 (yellow part of spectrum) different shades. So we can
distinguish about 128 X 130 X 23 = 380,000 colors.
Color Temperature Meter
The color temperature of a light source is the temperature of an ideal black-body radiator that
radiates light of a color comparable to that of the light source. Color temperature is a characteristic
of visible light that has important applications
in lighting, photography, videography, publishing, manufacturing, astrophysics, horticulture, and
other fields. In practice, color temperature is meaningful only for light sources that do in fact
correspond somewhat closely to the radiation of some black body, i.e., those on a line from
reddish/orange via yellow and more or less white to blueish white; it does not make sense to speak of
the color temperature of, e.g., a green or a purple light. Color temperature is conventionally expressed
in kelvins, using the symbol K, a unit of measure for absolute temperature.
Color temperatures over 5000 K are called "cool colors" (bluish white), while lower color
temperatures (2700–3000 K) are called "warm colors" (yellowish white through red). "Warm" in this
context is an analogy to radiated heat flux of traditional incandescent lighting rather than temperature.
The spectral peak of warm-coloured light is closer to infrared, and most natural warm-coloured light
sources emit significant infrared radiation. The fact that "warm" lighting in this sense actually has a
"cooler" color temperature often leads to confusion.
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Fig 5.45
45: Color Temperatures of various colors
CHECK YOUR PROGRESS
Explain the importance of ‘saturation’ in a color model
model.
Elaborate the HSV color
or model.
model
Compare ‘chroma’ with the ‘hue’.
5.11 SUMMARY
A color model is an abstract mathematical model that specifies the way colors
can be represented as tuples of numbers, typically as three or four values or
color components.
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When this model is used with a precise definition of how the components are to
be interpreted (viewing conditions, etc.), the set of colors’ which is obtained is
known as color space.
Color space conversion is the interpretation of the representation of a color
from one basis to another.
RGB is a form o f additive color mixing.
CMKY is a form of subtractive color mixing which describes the type of ink
which should be applied so that the light reflected from the substrate and through
the inks gives a desired color.
Luminance defines the amount of light that passes through or is emitted from a
given area, and falls within a given solid angle.
Light exists in tiny packets known as photons, which show properties of both
fragments and waves.
The RGB color model is an additive color model in which red, green and blue
light are combined in various ways to reproduce a wide range of colors’.
Chroma is the colorfulness relative to the brightness of another color which
appears white under similar viewing conditions '
Value is a property of color, or a dimension of color space.
5.12 KEY TERMS
Achromatic color: Color lacking hue and is neutral such as black, white or
gray.
Anomaloscope: The instrument used for testing color blindness and measure
the degree of anomalies in color perception.
Assimilation: A perceptual phenomenon in which the color of an area seems
to be closer to the color of the surround than it would if viewed in isolation.
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Brightness: A characteristic of a visual perception according to which an area
seems to emit more or less amount of light.
Chroma: A feature of a visual sensation that allows a judgment to be formed
of the amounts of pure chromatic color present, irrespective of the amount of
Achromatic color.
Chromaticity diagram: A diagram representation of the unit plane (where the
plane is defined by the equation X+Y+Z=l) in a tristimulus space.
5.13 END QUESTIONS
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
Explain the aspects of a color model.
Elaborate the importance of tristimulus color space.
Explain the concept of CIE XYZ or CIE 1932 color space.
Describe the concept of HSL and HSV representations.
Discuss the CMYK color model.
Explain the Color systems.
Explain the Vertebrate evolution of color vision.
Explain the concept of light.
Elaborate the importance of Electromagnetic spectrum and visible light.
Explain the concept of Speed of light.
Describe the concept of Light sources.
Discuss the radiometric and photometric measurements of light mentioning the SI units and
description for at least five parameters.
Explain the historic theories of light briefly mentioning their contributions.
Elaborate the contribution of Isaac Newton to the theoretical understanding of light.
Discuss the contribution of proponents of wave theory to the theoretical understanding of
light.
Describe the contribution of proponents of particle theory to the theoretical understanding of
light.
Elaborate the contribution of quantum mechanics to the theoretical understanding of light.
Descibe the current state of the theoretical understanding of light
Explain the importance of CIE 1932 color space.
Elaborate the how Tristimulus values are used in CIE color space.
Explain the meaning of X,Y,Z in CIE color space.
Describe the concept of CIE standard observer.
Discuss how X,Y, Z can be calculated from spectral data.
Explain the concept of CIE xy chromaticity diagram and the CIE xyY color space
Discuss various interesting properties of the CIE XYZ color space.
Explain the Definition of the CIE XYZ color space.
Describe the CIE 1931 RGB color matching functions.
Explain the contribution of Grassmann's law in the theoretical understanding of CIE color
space.
Explain the importance of RGB color model.
Elaborate the how RGB color model is additive.
Explain the application of RGB color model in photography.
Explain the application of RGB color model in television.
Explain the application of RGB color model in personal computers.
Describe the concept of Color Look Up Table in video framebuffers.
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35. Discuss RGB 24 and RGB32.
36. Explain the concept of gamma correction for CRT tube.
37. Discuss the Bayer filter arrangement of color filters on the pixel array of a digital image
sensor.
38. Explain the importance of CMYK color model.
39. Elaborate the how CMYK color model is subtractive.
40. Explain the reasons for using black as additional pigment in printing.
41. Explain the concept of halftones.
42. Explain the concept of screen angles in CMYK printing.
43. Describe the color models other than CMYK used in color printing.
44. Discuss how RGB and CMYK color models can be compared.
45. Explain how RGB and CMYK color spaces can be converted from one space to another.
46. Explain the importance of ‘hue’ in a color model.
47. Elaborate the hue can be computed in terms of R,G,B values.
48. Compare ‘hue’ with the ‘dominant wavelength’.
49. Explain the difference between ∆ H* ab and ∆ h ab .
50. Explain the importance of ‘saturation’ in a color model.
51. Elaborate the HSV color model.
52. Compare ‘chroma’ with the ‘hue’.
5.14 REFERENCES
Wikipedia, (Color Space, light, CIE 1931 Color Space, RGB Color Space, Grassmann’s
law(Optics), CMY Color Space, Hue, Value, Saturation, Color Temperature)
https://www.siggraph.org/education/materials/HyperGraph/color/colorhs.htm
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UNIT 6 PSYCHOLOGY OF COLOUR
6.0 INTRODUCTION
Colour psychology refers to the investigation of the effect of colour on human behaviour and
feeling. Colour psychology is very different from phototherapy, which use ultraviolet lighted treat
conditions some infantile jaundice or psoriasis. As colour type dependent upon a large body of
evidence, it becomes a debatable area of study, based upon a brief account of some incident. Data
from well-designed scientific studies does not support colour symbolism.
Understanding of color psychology is extremely important for you as a student and as a
professional in media, graphics and animation. Which color to choose for a graphic, animation or
photograph is of crucial importance. You will decide on the basis of the demand of the project, which
color schemes to chose. The topics covered under this course will help you understand various
concepts covered in all other courses like photoshop, illustrator, 3Ds max or Maya animation courses
which you will study as part of your study in BSc(MGA).
6.1 UNIT OBJECTIVES
After going through this unit, you will be able to:
•
•
•
Describe the psychology of colour
Explain one‘s coour combinations
Elaborate how colours can be used to influence our physiological processes
6.2 COLOUR PSYCHOLOGY: AN OVERVIEW
Color psychology is the study of hues as a determinant of human behavior. Color influences
perceptions that are not obvious, such as the taste of food. Colours can also enhance the effectiveness
of placebos. For example, red or orange pills are generally used as stimulants. Colour can indeed
influence a person; however, it is important to remember that these effects differ between people.
Factors such as gender, age, and culture can influence how an individual perceives color. For
instance, heterosexual men tend to report that red outfits enhance female attractiveness, while
heterosexual females deny any outfit color impacting that of men.
Color psychology is also widely used in marketing and branding. Many marketers see color as an
important part of marketing because color can be used to influence consumers' emotions and
perceptions of goods and services. Companies also use color when deciding on brand logos. These
logos seem to attract more customers when the color of the brand logo matches the personality of the
goods or services, such as the color pink being heavily used on Victoria's Secret branding. However,
colors are not only important for logos and products, but also for window displays in stores. Research
shows that warm colors tended to attract spontaneous purchasers, despite cooler colors being more
favorable.
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6.2.1 Influence of color on perception
Perceptions not obviously related to color, such as the palatability of food, may in fact be partially
determined by color. Not only the color of the food itself but also that of everything in the eater's field
of vision can affect this. (Alcaide, J. et al., 2012). Josef Albers' role in the understanding of color
perception was through his research of how colors interact with each other at the edges. He also
studied the optical illusions of color and how different hues looked the same. This was during his
tenure at Yale University.
Placebo effect
The color of placebo pills is reported to be a factor in their effectiveness, with "hot-colored" pills
working better as stimulants and "cool-colored" pills working better as depressants. This relationship
is believed to be a consequence of the patient's expectations and not a direct effect of the color itself.
Consequently, these effects appear to be culture-dependent.
Blue public lighting
In 2000, Glasgow installed blue street lighting in certain neighborhoods and subsequently
reported the anecdotal finding of reduced crime in these areas. This report was picked up by several
news outlets. A railroad company in Japan installed blue lighting on its stations in October 2009 in an
effort to reduce the number of suicide attempts, although the effect of this technique has been
questioned.
6.2.2 Color preference and associations between color and mood
Color has long been used to create feelings of coziness or spaciousness. However, how people are
affected by different color stimuli varies from person to person.
Blue is the top choice for 35% of Americans, followed by green (16%), purple (10%) and red
(9%).
A preference for blue and green may be due to a preference for certain habitats that were
beneficial in the ancestral environment as explained in the evolutionary aesthetics article.
There is evidence that color preference may depend on ambient temperature. People who are cold
prefer warm colors like red and yellow while people who are hot prefer cool colors like blue and
green.
Some research has concluded that women and men respectively prefer "warm" and "cool" colors.
A few studies have shown that cultural background has a strong influence on color preference.
These studies have shown that people from the same region regardless of race will have the same
color preferences. Also, one region may have different preferences than another region (i.e., a
different country or a different area of the same country), regardless of race.
Children's preferences for colors they find to be pleasant and comforting can be changed and can
vary, while adult color preference is usually non-malleable.
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Some studies find that color can affect mood. However, these studies do not agree on precisely
which moods are brought out by which colors.
A study by psychologist Andrew J. Elliot tested to see if the color of a person's clothing could
make them appear more sexually appealing. He found that, to heterosexual men, women dressed in
the color red were significantly more likely to attract romantic attention than women in any other
color. The colour did not affect heterosexual women's assessment of other women's attractiveness.
Other studies have shown a preference for men dressed in red among heterosexual women.
Common associations connecting a color to a particular mood may differ cross-culturally. For
instance, one study examined color associations and moods using participants from Germany,
Mexico, Poland, Russia, and the United States. The researchers did find some consistencies, including
the fact that all nations associated red and black with anger. However, only Poles associated purple
with both anger and jealousy and only Germans associated jealousy with yellow. These differences
highlight how culture influences peoples' perceptions of color and color's relationship to mood.
Despite cross-cultural differences regarding the 'meanings' of different colors, one study revealed
that there were cross-cultural similarities regarding which emotional states people associated with
particular colors: for example, the color red was perceived as strong and active.
Light, color, and surroundings
Light and color can influence how people perceive the area around them. Different light sources
affect how the colors of walls and other objects are seen. Specific hues of colors seen under natural
sunlight may vary when seen under the light from an incandescent (tungsten) light-bulb: lighter colors
may appear to be more orange or "brownish" and darker colors may appear even darker. Light and the
color of an object can affect how one perceives its positioning. If light or shadow, or the color of the
object, masks an object's true contour (outline of a figure) it can appear to be shaped differently from
reality. Objects under a uniform light-source will promote better impression of three-dimensional
shape. The color of an object may affect whether or not it seems to be in motion. In particular, the
trajectories of objects under a light source whose intensity varies with space are more difficult to
determine than identical objects under a uniform light source. This could possibly be interpreted as
interference between motion and color perception, both of which are more difficult under variable
lighting.
Carl Jung is most prominently associated with the pioneering stages of color psychology. Jung
was most interested in colors' properties and meanings, as well as in art's potential as a tool for
psychotherapy. His studies in and writings on color symbolism cover a broad range of topics, from
mandalas to the works of Picasso to the near-universal sovereignty of the color gold, the lattermost of
which, according to Charles A. Riley II, "expresses ... the apex of spirituality, and intuition". In
pursuing his studies of color usage and effects across cultures and time periods, as well as in
examining his patients' self-created mandalas, Jung attempted to unlock and develop a language, or
code, the ciphers of which would be colors. He looked to alchemy to further his understanding of the
secret language of color, finding the key to his research in alchemical transmutation. His work has
historically informed the modern field of color psychology.
6.2.3 General model
The general model of color psychology relies on six basic principles:
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•
•
•
•
•
•
Color can carry a specific meaning.
Color meaning is either based in learned meaning or biologically innate meaning.
The perception of a color causes evaluation automatically by the person perceiving.
The evaluation process forces color
color-motivated behavior.
Color usually
ally exerts its influence automatically.
Color meaning and effect has to do with context as well.
Uses in marketing
Since color is an important factor in the visual appearance of products as well as in brand
recognition, color psychology has become imp
important
ortant to marketing. Recent work in marketing has
shown that color can be used to communicate brand personality.
Marketers must be aware of the application of color in different media (e.g. print vs. web), as well
as the varying meanings and emotions that a particular audience can assign to color. Even though
there are attempts to classify consumer response to different colors, everyone perceives color
differently. The physiological and emotional effect of color in each person is influenced by several
factors
rs such as past experiences, culture, religion, natural environment, gender, race, and nationality.
When making color decisions, it is important to determine the target audience in order to convey the
right message. Color decisions can influence both direct
direct messages and secondary brand values and
attributes in any communication. Color should be carefully selected to align with the key message and
emotions being conveyed in a piece.
Research on the effects of color on product preference and marketing shows that
that product color
could affect consumer preference and hence purchasing culture. Most results show that it is not a
specific color that attracts all audiences, but that certain colors are deemed appropriate for certain
products.
Brand meaning
Fig 6.01: The Color Wheel
Color is a very influential source of information when people are making a purchasing decision.
Customers generally make an initial judgment on a product within 90 seconds of interaction with that
product and about 62%-90%
90% of that judgment is based on color. People often see the logo of a brand
or company as a representation of that company. Without prior experience to a logo, we begin to
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associate a brand with certain characteristics based on the primary logo color.
Color mapping provides a means of identifying potential logo colors for new brands and ensuring
brand differentiation within a visually cluttered marketplace.
A study on logo color asked participants to rate how appropriate the logo color was for fictional
companies based on the products each company produced. Participants were presented with fictional
products in eight different colors and had to rate the appropriateness of the color for each product.
This study showed a pattern of logo color appropriateness based on product function. If the product
was considered functional, fulfills a need or solves a problem, then a functional color was seen as
most appropriate. If the product was seen as sensory-social, conveys attitudes, status, or social
approval, then a sensory-social colors were seen as more appropriate. Companies should decide what
types of products to produce and then choose a logo color that is connotative with their products'
functions.
Company logos can portray meaning just through the use of color. Color affects people's
perceptions of a new or unknown company. Some companies such as Victoria's Secret and H&R
Block used color to change their corporate image and create a new brand personality for a specific
target audience. Research done on the relationship between logo color and five personality traits had
participants rate a computer made logo in different colors on scales relating to the dimensions of
brand personality. Relationships were found between color and sincerity, excitement, competence,
sophistication, and ruggedness. A follow up study tested the effects of perceived brand personality
and purchasing intentions. Participants were presented with a product and a summary of the preferred
brand personality and had to rate the likelihood of purchasing a product based on packaging color.
Purchasing intent was greater if the perceived personality matched the marketed product or service. In
turn color affects perceived brand personality and brand personality affects purchasing intent.
Although color can be useful in marketing, its value and extent of use depends on how it is used
and the audience it is used on. The use of color will have different effects on different people,
therefore experimental findings cannot be taken as universally true.
6.2.4 Specific color meaning
Different colors are perceived to mean different things. For example, tones of red lead to feelings
of arousal while blue tones are often associated with feelings of relaxation. Both of these emotions are
pleasant, so therefore, the colors themselves procure positive feelings in advertisements. The chart
below gives perceived meanings of different colors in the United States.
Functional (F): fulfills a need or solves a problem
Sensory-Social (S): conveys attitudes, status, or social approval
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Combining colors
Fig 6.02: Target Logo
Although some companies use a single color to represent their brand, many other companies use a
combination of colors in their logo, and can be perceived in different ways than those colors
independently. When asked to rate color
color pair preference of preselected pairs, people generally prefer
color pairs with similar hues when the two colors are both in the foreground, however, greater
contrast between the figure and the background is preferred.
In contrast to a strong preference
preference for similar color combinations, some people like to accent with
a highly contrasting color. A study on preference for color in Nike, Inc. sneakers, people generally
combined colors near each other on the color wheel, such as blue and dark blue. However, fewer
others preferred to have the Nike swoosh accentuated in a different, contrasting color. Most of the
people also used a relatively small number of colors when designing their ideal athletic shoe. This
finding has relevance for companies that produce m
multicolored
ulticolored merchandise. To appeal to consumer
preferences, companies should consider minimizing the number of colors visible and use similar hues
in a single product.
Color name
Although different colors can be perceived in different ways, the name of tho
those
se colors matters as
well. Many products and companies focus on producing a wide range of product colors to attract the
largest population of consumers. For example, cosmetics brands produce a rainbow for eye shadow
and nail polish colors for every type of person. Even companies such as Apple Inc. and Dell make
iPods and laptops with color personalization to attract buyers. But, color name, not only the actual
color, can actually attract or repel buyers as well. When asked to rate either color swatches or
products
roducts with generic color names, such as brown, or fancy color names, such as mocha, participants
rated items with fancy names as significantly more likable than items with generic names. In fact the
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same paint color swatch with two different names produced different rating levels. The same effect
was found when participants rated the pleasantness of towels with fancy and generic names. This
shows a greater favorability for fancy names compared to generic names for exactly the same colors.
Fancy names are not only liked more, but cause the product to be liked more, hence increasing
purchasing intent. Jelly beans with atypical color names, such as razzmatazz, were more likely to be
chosen than jelly beans with typical names such as lemon yellow. This could be due to greater interest
in the atypical names and willingness to figure out why that name was given. Purchasing intent of
custom sweatshirts from an online provider also showed preferences for atypical names. Participants
were asked to imagine buying sweatshirts and were provided with a variety of color options, some
typical, some atypical. Colors that were atypical were selected more than colors that were typical,
showing a preference to purchase items with atypical color names. Those who chose atypical colors
were also more content with their choice than those who chose typical color sweatshirts.
Attracting attention
Color is used as a means to attract consumer attention to a product that then influences buying
behavior. Consumers use color to identify for known brands or search for new alternatives. Variety
seekers look for non-typical colors when selecting new brands. And attractive color packaging
receives more consumer attention than unattractive color packaging, which can then influence buying
behavior. A study that looked at visual color cues focused on predicted purchasing behavior for
known and unknown brands. Participants were shown the same product in four different colors and
brands. The results showed that people picked packages based on colors that attracted their voluntary
and involuntary attention. Associations made with that color such as 'green fits menthol', also affected
their decision. Based on these findings implications can be made on the best color choices for
packages. New companies or new products could consider using dissimilar colors to attract attention
to the brand, however, off brand companies could consider using similar colors to the leading brand to
emphasize product similarity. If a company is changing the look of a product, but keeping the product
the same, they consider keeping the same color scheme since people use color to identify and search
for brands. This can be seen in Crayola crayons, where the logo has changed many times since 1934,
but the basic package colors, gold and green, have been kept throughout.
Attention is captured subconsciously before people can consciously attend to something.
Research looking at electroencephalography (EEGs) while people made decisions on color preference
found brain activation when a favorite color is present before the participants consciously focused on
it. When looking a various colors on a screen people focus on their favorite color, or the color stands
out more, before they purposefully turn their attention to it. This implies that products can capture
someone's attention based on color, before the person willingly looks at the product.
Store and display color
Color is not only used in products to attract attention, but also in window displays and stores.
When people are exposed to different colored walls and images of window displays and store interiors
they tend to be drawn to some colors and not to others. Findings showed that people were physically
drawn to warm colored displays; however, they rated cool colored displays as more favorable. This
implies that warm colored store displays are more appropriate for spontaneous and unplanned
purchases, whereas cool colored displays and store entrances may be a better fit for purchases where a
lot of planning and customer deliberation occurs. This is especially relevant in shopping malls were
patrons could easily walk into a store that attracts their attention without previous planning.
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Fig 6.03: Warm colored window display
Other research has confirmed that store color, and not just the product, influences buying
behavior. When people are exposed to different store color scenarios and then surveyed on intended
buying behavior store color, among various other factors, seems important for purchasing intentions.
Particularly blue, a cool color, was rated as more favorable and produced higher purchasing intentions
than orange, a warm color. However, all negative effects to orange were neutralized when orange
store color was paired with soft lighting. This shows that store color and lighting actually interact.
Lighting color could have a strong effect on perceived experience in stores and other situation.
For example, time seems to pass more slowly under red lights and time seems to pass quickly under
blue light. Casinos take full advantage of this phenomenon by using color to get people to spend more
time and hence more money in their casino.
6.2.5 Individual differences
Gender
Children's toys are often categorized as either boys or girls toys solely based on color. In a study
on color effects on perception, adult participants were shown blurred images of children's toys where
the only decipherable feature visible was the toy's color. In general participants categorized the toys
into girl and boy toys based on the visible color of the image. This can be seen in companies
interested in marketing masculine toys, such as building sets, to boys. For example, Lego uses pink to
specifically advertise some sets to girls rather than boys. The classification of 'girl' and 'boy' toys on
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the Disney Store website also uses color associations for each gender. An analysis of the colors used
showed that bold colored toys, such as red and black, were generally classified as 'boy only' toys and
pastel colored toys, such as pink and purple, were classified as 'girl only' toys. Toys that were
classified as both boy and girl toys took on 'boy only' toy colors. This again emphasizes the
distinction in color use for children's toys.
Fig 6.04: Pink girls section of toy store
Gender differences in color associations can also be seen amongst adults. Differences were noted
for male and female participants, where the two genders did not agree on which color pairs they
enjoyed the most when presented with a variety of colors. Men and women also did not agree on
which colors should be classified as masculine and feminine. This could imply that men and women
generally prefer different colors when purchasing items. Men and women also misperceive what
colors the opposite gender views as fitting for them.
Age
Children's toys for younger age groups are often marketed based on color, however, as the age
group increases color becomes less gender-stereotyped. In general many toys become gender neutral
and hence adopt gender-neutral colors. In the United States it is common to associate baby girls with
pink and baby boys with blue. This difference in young children is a learned difference rather than an
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inborn one. Research has looked at young children's, ages 7 months to 5 years, preference for small
objects in different colors. The results showed that by the age of 2–2.5 years socially constructed
gendered colors affects children's color preference, where girls prefer pink and boys avoid pink, but
show no preference for other colors.
Slightly older children who have developed a sense of favorite color often tend to pick items that
are in that color. However, when their favorite color is not available for a desired item children
choose colors that they think matches the product best. Children's preferences for chocolate bar
wrappers showed that although one third of the children picked a wrapper of their favorite color, the
remaining two thirds picked a wrapper they perceived as fitting the product best. For example, most
children thought that a white wrapper was most fitting for white chocolate and a black wrapper for
most fitting for a dark chocolate bar and therefore chose those options for those two bars. This
application can be seen in The Hershey Company chocolate bars where the company strategically has
light wrappers for white chocolate and brown wrappers for milk chocolate, making the product easily
identifiable and understandable.
Culture
Many cultural differences exist on perceived color personality, meaning, and preference. When
deciding on brand and product logos, companies should take into account their target consumer, since
cultural differences exist. A study looked at color preference in British and Chinese participants. Each
participant was presented with a total of 20 color swatches one at a time and had to rate the color on
10 different emotions. Results showed that British participants and Chinese participants differed on
the like-dislike scale the most. Chinese participants tended to like colors that they self rated as clean,
fresh, and modern, whereas British participants showed no such pattern. When evaluating purchasing
intent, color preference affects buying behavior, where liked colors are more likely to be bought than
disliked colors. This implies that companies should consider choosing their target consumer first and
then make product colors based on the target's color preferences.
Wollard, (2000) seems to think that color can affect one’s mood, but the effect also can depend on
one’s culture and what one’s personal reflection may be. For example, someone from Japan may not
associate red with anger, as people from the U.S. tend to do. Also, a person who likes the color brown
may associate brown with happiness. However, Wollard does think that colors can make everyone
feel the same, or close to the same, mood.
6.2.6 Color and sports performance
In particular, the color red has been found to influence sports performance. During the 2004
Summer Olympics the competitors in boxing, taekwondo, freestyle wrestling, and Greco-Roman
wrestling were randomly given blue or red uniforms. A later study found that those wearing red won
55% of all the bouts which was a statistically significant increase over the expected 50%. The colors
affected bouts where the competitors were closely matched in ability, where those wearing red won
60% of the bouts, but not bouts between more unevenly matched competitors. In England, since
WWII, teams wearing red uniforms have averaged higher league positions and have had more league
winners than teams using other colors. In cities with more than one team, the teams wearing red
outperformed the teams wearing other colors. A study of the UEFA Euro 2004 found similar results.
Another study found that those taking penalty kicks performed worst when the goalkeeper had a red
uniform. More anecdotal is the historical dominance of the domestic honors by red-wearing teams
such AFC Ajax, FC Bayern Munich, Liverpool F.C., and Manchester United F.C. Videos of
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taekwondo bouts were manipulated in one study so that the red and blue colors of the protective gears
were reversed. Both the original and the manipulated videos were shown to referees. The competitors
wearing red were given higher scores despite the videos otherwise being identical. A study on
experienced players of first-person shooters found that those assigned to wear red instead of blue won
55% of the matches.
There are several different explanations for this effect. Red is used in stop signs and traffic lights
which may associate the color with halting. Red is also perceived as a strong and active color which
may influence both the person wearing it and others. An evolutionary psychology explanation is that
red may signal health as opposed to anemic paleness, or indicate anger due to flushing instead of
paleness due to fear. It has been argued that detecting flushing may have influenced the development
of primate trichromate vision. Primate studies have found that some species evaluate rivals and
possible mates depending on red color characteristics. Facial redness is associated with testosterone
levels in humans, and male skin tends to be redder than female skin.
6.2.7 Color and time perception
Recent results showed that the perceived duration of a red screen was longer than was that of a
blue screen. The results reflected sex differences; men, but not women, overestimated the duration of
the red screen. Additionally, the reaction times to a red screen were faster than those to a blue screen.
Participants who reacted quickly to a red screen overestimated its duration. In a demo with 150 people
chosen at random, it was found that inside a pod bathed in blue color the average perceived duration
of a minute was 11 second shorter than in a pod bathed in red color.
CHECK YOUR PROGRESS
Explain the importance of psychology of color.
Elaborate the Influence of color on perception.
Explain the concept of placebo effect in colored pills .
Explain the Color preference and associations between color and mood.
Describe how light and color can influence people perceive the area around them.
Discuss six basic principles on which general model of color psychology relies on.
Elaborate how color is a very influential source of information when people are making a
purchasing decision.
Discuss the role of color in branding.
Explain why some companies use a single color to represent their brand, some other companies
use a combination of colors in their logo.
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Discuss how color name, not only the actual color, can actually attract or repel buyers as well.
Explain how color is used as a means to attract consumer attention to a product that then
influences buying behavior.
Describe the role of color in respect to its perception among children, men and women.
Elaborate how various cultural differences exist on perceived color personality, meaning, and
preference.
Explain the contribution of color in sports performance.
Discuss why the perceived duration of a red screen was longer than was that of a blue screen, as
per a recent study.
6.3 UTILIZING PSYCHOLOGICAL EFFECTS IN
PAINTING
The psychology of art is an interdisciplinary field that studies the perception, cognition and
characteristics of art and its production. For the use of art materials as a form of psychotherapy, see
art therapy. The psychology of art is related to architectural psychology and environmental
psychology.
The work of Theodor Lipps, a Munich-based research psychologist, played an important role in
the early development of the concept of art psychology in the early decade of the twentieth century.
His most important contribution in this respect was his attempt to theorize the question of
Einfuehlung or "empathy", a term that was to become a key element in many subsequent theories of
art psychology
Fig 6.05: Vincent van Gogh, July 1890, Wheatfield with Crows The sense of the artist's life
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coming to an end.
Painting is the practice of applying paint, colour, pigment, or other medium to a surface known as
support base. in art, the term painting specifies both the act and the result, which is known as a
painting. Paintings may be decorated with gold leaf, and some prevailing paintings use other materials
including clay, scraps of paper and sometimes sand. Paintings may have for their support such
surfaces as paper, canvas, walls wood, lacquer, glass, clay or even concrete.
Painting is a method of expression, and the forms vary accordingly. Abstraction, drawing or
constituent and other aesthetics may serve to manifest the expressiveness of the practitioners of art
and conceptual intention. Paintings can be representational and naturalistic (as in a landscape painting
or in a still life), abstract, photographic, be loaded with narrative content, emotion symbolism or be
political in nature.
The following is a great artist’s observation about the essence of painting:
The boundary of things in the second plane will not be discerned like those in the first. Therefore,
painter, do not produce boundaries between the first and the second, because the boundary of one
object and another is of the nature of a mathematical line but not an actual line, in that the boundary
of one colour is the start of another colour and is not to be accorded the status of an actual line,
because nothing intervenes between the boundary of one colour which placed against another.
Therefore, painter, do not make the boundaries pronounced at a distance.
Fig. 6.00 Viewpoint and Expression of intensity of a Painting
What painting makes possible is the viewpoint and expression of intensity. Every point in space
has intensity which is different, which can be represented in painting by white and black and all the
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grey shades in between. In practice, painters can join shapes by putting surfaces side by side of
different intensities; by using just colour (of the same intensity) one can only represent symbolic
shapes. In more technical drawings, thickness of line is also ideal, separating ideal outlines of an
object within a perceptual frame different from the one employed by painters. Thus, the basic means
of painting are very particular from ideological means, such as geometrical figures, various points of
view and symbols and organization (perspective). For example, a painter identifies that a particular
white wall has intensity which is different at each point and due to shades and reflections from nearby
objects, but in reality, a white wall is still a white wall in pitch darkness.
There arc artists who know exactly what colours to use (example, the artist who paints cityscapes
right after the rain}. One can see the clouds disappearing. There are some small pools of rainwater,
but the sun is out, and everything looks cheerful and fresh. One has to have the absolute knowledge of
louts and their effects as this kind of painting demands.
Another method an artist employs to create a psychological effect is an optical illusion (also
called a visual illusion). It is characterized by visually perceived images that is different from
objective reality. The information collected by the eye is processed in the brain to give a percept that
does not mark with a physical measurement of the stimulus source. There are three main types of
illusion:
Literal optical illusion. This type of illusion generates images that are different from the
objects that make them.
Physiological illusion. This type of illusion is the effects on the eyes and brain of excessive
stimulation of a specific type (tilt, colour, brightness movement).
Cognitive illusion. In this type of illusion, the eye and brain make unconscious inferences.
Fig. 6.00 Visual
illusion
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Fig 6.06: Psychological illusion
Cognitive illusions
Instead of demonstrating a physiological base they interact with different levels of perceptual
rocessing, in-built assumptions or ‘knowledge’ are misdirected. Cognitive illusions are commonly
divided into ambiguous illusions, distorting illusions, paradox illusions, or fiction illusions. They
often exploit the predictive hypotheses of early visual processing. Stereogram's are based on a
cognitive visual illusion.
Ambiguous illusions are pictures or objects that offer significant changes in appearance.
Perception will ‘switch’ between the alternates as they are considered in turn as available data does
not confirm a single view. The Necker cube is a well known example, the motion parallax due to
movement is being misinterpreted, even in the face of other sensory data. Another popular is the
Rubin vase.
Paradox illusions offer objects that are paradoxical or impossible, such as the Penrose triangle or
impossible staircases seen, for example, in the work of M. C. Escher. The impossible triangle is an
illusion dependent on a cognitive misunderstanding that adjacent edges must join. They occur as a by
product of perceptual learning.
Distorting illusions are the most common, these illusions offer distortions of size, length, or
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curvature. They were simple to discover and are easily repeatable. Many are physiological illusions,
such as the Café wall illusion which exploits the early visual system encoding for edges.
Other distortions, such as converging line illusions, are more difficult to place as physiological or
cognitive as the depth-cue challenges they offer are not easily placed. All pictures that have
perspective cues are in effect illusions. Visual judgments as to size are controlled by perspective or
other depth-cues and can easily be wrongly set.
Fiction illusions are the perception of objects that are genuinely not there to all but a single
observer, such as those induced by schizophrenia or hallucinogenic drugs.
Cognitive Illusions – Examples
Fig 6.07 Rabbit or a Duck illusion
Fig. 6.00: Reversible figure and vase
Completion figures are figures which the mind rather unambiguously interprets in a particular
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way despite the fact that the input is incomplete relative to what is typically “seen”. Illusory contours
may be partly accounted for by low level contrast effects, partly by more cognitive processes inferring
the existence of occluding objects.
Fig. 6.00: Triangle Completion – Seeing what is not there!
Fig 6.08: These two Kalisz figures shown above illustrate the mind’s willingness to see an
equilateral triangle despite the fact that no border information about the center triangle is in the
picture.
Depth and motion perception
Depth perception is the visual ability to perceive the world in three dimensions (3D) and the
distance of an object. Depth sensation is the corresponding term for animals, since although it is
known that animals can sense the distance of an object (because of their ability to move accurately, or
to respond consistently, according to that distance), it is not known whether they "perceive" it in the
same subjective way that humans do.
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Depth perception arises from a variety of depth cues. These are typically classified
into binocular cues that are based on the receipt of sensory informatio
informationn in three dimensions from both
eyes and monocular cues that can be represented in just two dimensions and observed with just one
eye. Binocular cues include stereopsis
stereopsis, eye convergence, disparity,, and yielding depth from binocular
vision through exploitation of parallax.
parallax. Monocular cues include size: distant objects subtend
smaller visual angles than near objects, grain, size, and motion parallax.
Motion perception is the process of inferring the speed and direction of elements in a scene
based on visual,, vestibular and proprioceptive inputs. Although this process appears straightforward
to most observers, it has proven to be a difficult problem from a computational perspective, and
extraordinarily difficult to explain in terms of neural processing.
Fig 6.09: Ponzo illusion
Colour and Brightness constancy
Colour constancy is an example of subjective constancy and a feature of the human colour
perception system which ensures that the perceived colour of objects remains relatively constant
under varying illumination
ation conditions. A green apple for instance looks green to us at midday, when
the main illumination is white sunlight, and also at sunset, when the main illumination is red. This
helps us identify objects.
Fig 6.10: Constancy makes square A appear darker than square B, when in fact
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they are both exactly the same shade of grey
A sheet of white paper seen in the bright sunlight reflects a very different amount of light than the
same sheet of paper seen later that night in a softly lighted room. Yet we perceive the paper as having
the same whiteness in each case. This is an example of brightness constancy, our ability to see objects
as continuing to have the same brightness even though light may change their immediate sensory
properties. Psychologists have determined that an object will exhibit brightness constancy as long as
both the object and its surroundings are in light of the same intensity. If the background brightness
differs from the object, brightness constancy is not maintained. For example, if the background is
lighter than the object, the object appears darker.
Fig. 6.00: brightness constancy
CHECK YOUR PROGRESS
Explain the importance of psychology of art.
Elaborate how painting makes possible the viewpoint and expression of intensity.
Explain the concept of optical illusions used as a psychological effect by paiters .
Explain the three types of optical illusions used in painting or graphics .
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Describe the concepts of cognitive illusions used by painters or graphic designers..
Discuss use of depth and motion perception used by graphic designers.
Elaborate optical illusions based on Color and Brightness constancy.
6.4 HOW TO JUDGE YOUR COLOUR SELECTION
Basically, two major criteria are followed by which you might judge your selection of colours in
any field, be it in dress, home, or painting. One should know that neither of these criteria is easy, and
neither of them is foolproof, but it is worthwhile to try both of them. It is worth trying because there
seems to be no alternative that can be in use.
Follow a simple experiment. Do not look at your dress, work or home for a few days, do it until
your eyes are flesh enough to be able to see clearly. This is one way you can judge colours. You can
put a dress or suit in your closet and can turn a painting face against the wall You can shut your eyes
when you are home, or try to look at a small comer only. Going away for a while is the best idea.
After a Few days, do the reverse. Turn your painting face outwards, take your dress out of
the closet. "Turn all the lights on in your house, and look just look. You can judge a lot now and
criticize accordingly. In paintings, you can also turn the work upside down. You will find this simple
trick very helpful. You will be able to notice mistakes more quickly in an upside-down picture than in
a right side up painting. The other way of judging your colour select ion is by watching the reaction of
other people to your colours. it does not matter whether those people are friends or strangers, but
according to your preference, they are people whose judgement you consider satisfactory. Remember,
do not tell them anything and just watch them.
Even though people‘s tastes vary, most people in your own circle are most likely to agree on
what is attractive and what is not. This is the Fact because if such common agreements did not exist,
the world would be absolutely unbearable.
The other way of judging your colour select ion is by watching the reaction of other people to
your colours. It does not matter whether those people are friends or stagers, but according to your
preference, they are people whose judgement you consider satisfactory. Remember, do not tell them
anything and just watch them.
Even though people‘s tastes vary, most people in your own circle are most likely to agree on
what is attractive and what is not. This is the fact because if common agreements did not exist, the
world would be absolutely unbearable.
Watch those people’s reactions according to your taste and do allow them to make
suggestions. Always listen to them carefully and consider their criticism and advice.
6.5 CHARACTERISTIC COLOUR COMBINATIONS
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By a natural alliance of ideas, we think of spring as fi.1ll of intense colour. In our memory,
summer lives as a season of heat, without any fineness of colour, where everything is ripe and fully
grown. In a wide world, autumn is a symphony of colours and it ranges from still green leaves,
through yellow, orange, violet, through purple tones, to the dying brown foliage under a beautiful
clear blue sky. Winter is either of low spirits with its barren earth, dead trees and shrubs; or gives
vigour and energy with its bright blue
For centuries, artists have been mesmerized by seasons and weather. The seasons have often been
portrayed in combination with the ages of man, like childhood and spring; youth and summer;
maturity and autumn; old age and winter. Artists face a great challenge in painting the seasons. One
must go outdoors and paint attentively by watching the greater part of the year. During the cold
season, few artists go out in the open, but you can observe snowy scenery from a house or a shack.
One serious warning you should be careful about, do not paint outdoor scenes without a
complete attentive knowledge of reality. The name of colour is very completely different from its
actual appearance. So here again, you cannot paint a meadow glowing with red poppies just by
painting the lower half of your canvas green, and scattering it with many bright-red spots and the
result will look like a red-polka-dotted green textile. There are the frequent differences of shades,
values and even colours, because a meadow is not the same vegetation all over.
How blue is the sky‘? We speak of it almost every day. Which blue is to mix with how much
white in order to give us the blue we so love‘? One should observe that the blue sky is not the same
from top to bottom. What is the colour of a dirt road? What is the colour of an interesting rock
formation? The answer is that there is no dirt road colour; there is no rock formation colour. The key
is hue. Everything has many hues and many shades of each hue. Painting from memory alone is
nearly impossible. One should not practice without a vast knowledge.
6.6 COLOURS IN PHOTOGRAPHY VERSUS COLOURS IN
PAINTING
Colour photography is a colossal invention. The pictures in a colour magazine are clear and
extraordinarily beautiful. But the colours in such photographs are either dark blue, or too red, too
brown, or too green. Shadows in photographs are usually much too strong and without the variety of
shades that is observable in nature. Such pictures may remind you of hills, trees, flowers, or certain
basic colours of houses. Do not ever copy the colours as depicted in the photograph.
Some artists prefer black-and white photographs because but they are clearer and details are
not hidden by wild colours. Practice pencil sketching and always take notes refining to colours. If you
have adequate time, prepare a colour sketch in water colour or casein. Colour photographs will
remind you of such hues, even though in a highly represented manner.
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Fig 6.11: The reproductions of masterpiece
The reproductions of masterpieces by the finest colours give only an indianite idea of the original
colouring. You will realize that reproductions are very different from the originals if they are placed
next to each other. Colour slides made from paintings are the most painful and damaging difference.
Nowadays, online publication of painting is a big buzz. As wonderful as the medium of Internet
with great potential, it is not at all a good enough medium from which one can judge a painting.
6.7 COLOURS IN PAINTING VERSUS COLOURS IN A
ROOM
One should always keep in mind that a painting must be a complete entity. A painting should
compose ill colour and design, so that it should stand by itself If you execute a colourful painting in
all imaginable colours, it is not an ideal picture. An ideal picture is one which looks real to life,
cheerful, without disturbing our eyes. It is not necessarily important to have a painting match your
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drapery and furnishings in its colors. It does not matter whether you are a collector purchasing one or
an artist creating a masterpiece; you should know only one question in your mind, is the painting you
are buying or the painting you are producing appropriate in subject matter for the particular place
where it is to hang?
Remember, the frame separates and excludes the surroundings from the painting. The colour
scheme of the room and the colour scheme of the painting can thus live side-by-side, in peace and
harmony. It would be too unrealistic to insist that an artist should change certain colours in his
painting in order to match the colours of the room.
6.8 SUMMARY
It is important to know that colours have a strong psychological effect on us. Regardless of any
symbolism, colours affects us psychologically, and the psychological effects can be very different
from the symbolical significance of a colour.
Research shows that red hues increase bodily tension and excites the autonomic nervous system;
on the other hand, ‘cool’ hues release tension.
It is a very common knowledge that darker colours can convert a room which looks smaller,
while lighter colours such as white and yellow, tend to change the look of a room brighter and larger.
Green, blue and purple are some examples of cool colours, which tend to be relaxing and
soothing. Light blue is commonly thought of as the most calming colour, which is why you may see
schools, daycares, detention centres using it in their paint schemes. There are also warm colours like
red, orange and yellow which are inviting.
The three main types of illusion are literal illusion, physiological illusion and cognitive illusion
Cognitive deceptions arc usually divided into ambiguous illusions, distorting illusions, paradox
illusions and fiction illusions.
6.9 KEY TERMS
Colour psychology: Refers to the investigation of the effect of colour on human behaviour and
feelings.
Painting: The practice of applying paint, colour, pigment, or other medium to a surface known as
support base.
Literal optical illusions: The type of illusion generates images that are different from the objects
that make them.
Ambiguous illusions: Time types of illusions are objects orpiotures that elicit a perceptual
‘switch’ between alternative interpretations.
Ponzo illusion: Converging parallel lines inform the brain that the image higher in the visual field
is further away; as a result the brain identifies the image to be larger, admitting that the two images
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hitting the retina are of the size.
6.10 END QUESTIONS
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
Explain the importance of psychology of color.
Elaborate the Influence of color on perception.
Explain the concept of placebo effect in colored pills .
Explain the Color preference and associations between color and mood.
Describe how light and color can influence people perceive the area around them.
Discuss six basic principles on which general model of color psychology relies on.
Elaborate how color is a very influential source of information when people are making a
purchasing decision.
Discuss the role of color in branding.
Explain why some companies use a single color to represent their brand, some other
companies use a combination of colors in their logo.
Discuss how color name, not only the actual color, can actually attract or repel buyers as
well.
Explain how color is used as a means to attract consumer attention to a product that then
influences buying behavior.
Describe the role of color in respect to its perception among children, men and women.
Elaborate how various cultural differences exist on perceived color personality, meaning,
and preference.
Explain the contribution of color in sports performance.
Discuss why the perceived duration of a red screen was longer than was that of a blue
screen, as per a recent study.
Explain the importance of psychology of art.
Elaborate how painting makes possible the viewpoint and expression of intensity.
Explain the concept of optical illusions used as a psychological effect by paiters .
Explain the three types of optical illusions used in painting or graphics .
Describe the concepts of cognitive illusions used by painters or graphic designers..
Discuss use of depth and motion perception used by graphic designers.
Elaborate optical illusions based on Color and Brightness constancy.
What are the two major criteria by which you might judge your selection of colours in a
field?
What arc the various challenges faced by artists painting the seasons’?
Analyse how colour in photography is different from that in painting?
6.11 REFERENCES
Wikipedia (Psychology of Art, Psychology of color)
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