Importance of Color
• Painters first used
charcoal
• Early artists used ochre
to add red
• Colors are not always
the same from culture
to culture
Blackbody Radiators
• A theoretical model of
how objects emit
radiation based on
temperature
• Examples
– Incandescent light 2854K
– Direct sunlight 4874K
Emotional Response to Color
• Temperature is
associated with colors
– Blue is cold
– Red is warm
• Depends on overall
scene illumination
Thomas Young
• English Physician
• 1773-1829
• Every color can be
matched by adding
three primaries
Hermann Helmholtz
• German Scientist
– 1821-1894
• Verified Young's theory
by identifying three
types of receptors in
the eye in 1852-3
• Invented
opthalmoscope
Retinal Structure
Color Vision
• Each cone type is
sensitive to a different
range
• Research indicates we can
see about 10 million
colors
• How can one color be
distinguished from
another?
• How are colors specified?
Color Vision
• Depends on relative
stimulation of
photoreceptors
• Depends on wavelength
• Monomers
– Same colors
– Different spectra
• Color depends on
surrounding colors
Color Deficiency
• About 10% have some
deficiency
– 9% men
– 1% women
– Most missing red or green
cones
• Red and green percieved as
brown
• Monochromats have only
rods
• Dichromats have 2 of the
three cones
• Low light vision is not
affected
• Care needs to be taken
when creating visual
materials for others
– Web pages
– Brochures
– Design in black and white,
then add color
Color Blindness
• Protanopia
– No red cones
– Red, orange, and yellow
are shifted toward green
– Violet is shifted towards
blue
– severe cases
• traffic lights are black
• Purple flowers are blue
• Problems in extreme
lighting conditions
Color Blindness
• Deutanopia
– No green cones
– Green, yellow, and
orange are shifted
toward red
– Poor discrimination of
blues
Color Blindness
• Tritanopia
– No blue cones
Ishihara Tests
Quantifying Color
• CIE
– Commision
Internationale
d'Eclairage
– began work in 1931
– First chart in 1947
CIE Chart
• Revised in 1976
• Spectral colors (pure
tones) are around
perimeter curve
• Purple line is not
• Neutral color point
• Complementary colors
• Primary hue
CIE Chart
Color Gamut
• Only a small subset of
possible perceivable
colors can be
reproduced
– Fall into convex hull of
primaries
• Two primaries results in a
line
• Three primaries results in
a triangle
RGB Color Model
• Additive colors
• Three primaries
– Red
– Green
– Blue
• Roughly match the
sensitivities of cones
• Used in digital images
• Used in emissive color
displays
CYMK Color Model
• Subtractive color model
– Starts with white
– Reduces reflected light
• Three primaries
– Cyan
– Yellow
– Magenta
• Black (key) is used to
reduce brightness
without changing the hue
CYMK Color Model
Complementary colors
• Opposites
• Enhance one another
because of optimal
color contrast