Digital Image Processing, 3rd ed.
Gonzalez & Woods
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Ch t 6
Chapter
Color Image Processing

10
20
18
10
16
10
14
10
12
10
10
10
8
10
6
10
4
10
10
© 1992–2008 R. C. Gonzalez & R. E. Woods
2
Ult i l t
Ultraviolet
Visible
Infrared
Microwave
FM Radio + TV
AM R
Radio
di
Digital Image Processing, 3rd ed.
Gonzalez & Woods
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Ch t 6
Chapter
Color Image Processing
Colorimetric
Color Perception involve Hue, Saturation, and Lightness
Hue :distinguish
g
amongg colors such as red,, ggreen,, and ppurple.
p
Saturation :refer to how color far from gray.
Lightness: the perceived intensity of a reflecting object.
Brightness :refer to the perceived intensity of self-luminous.
self luminous
Artists Terms
Tint: results of adding
g white ppigments
g
pure pigments
Shade: comes from adding black pigments
to pure pigments
Tone:results of adding both black and white
pigments to pure pigments
© 1992–2008 R. C. Gonzalez & R. E. Woods
“Pure”
color
White
Grays
Tones
Shades
Black
Digital Image Processing, 3rd ed.
Gonzalez & Woods
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Ch t 6
Chapter
Color Image Processing
Color Models:
Green
Yellow
Cyan
The Newton Color Circle
Red
Blue
Magenta
• The Newton color circle pprovides a convenient way
y to pperceive
the additive mixing properties of colors.
• The R,G,B and their complementary colors C,M,Y are placed on
the circle in the order of the wavelengths of the corresponding
spectral colors.
© 1992–2008 R. C. Gonzalez & R. E. Woods
Digital Image Processing, 3rd ed.
Gonzalez & Woods
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Ch t 6
Chapter
Color Image Processing
• The separation of colors by a prism expose a continuous range
of spectral colors
© 1992–2008 R. C. Gonzalez & R. E. Woods
Digital Image Processing, 3rd ed.
Gonzalez & Woods
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Ch t 6
Chapter
Color Image Processing
• A spectral
p
color is composed
p
of a single
g wavelength
g
• The helium-neon laser monochromatic light is red (632 nm).
• Most colored objects give off a range of wavelengths and the
characterization of color is much more than the statement of
wavelength.
© 1992–2008 R. C. Gonzalez & R. E. Woods
Digital Image Processing, 3rd ed.
Gonzalez & Woods
www.ImageProcessingPlace.com
Ch t 6
Chapter
Color Image Processing
© 1992–2008 R. C. Gonzalez & R. E. Woods
Digital Image Processing, 3rd ed.
Gonzalez & Woods
www.ImageProcessingPlace.com
Ch t 6
Chapter
Color Image Processing
Primary and Secondary colors
© 1992–2008 R. C. Gonzalez & R. E. Woods
Digital Image Processing, 3rd ed.
Gonzalez & Woods
www.ImageProcessingPlace.com
Ch t 6
Chapter
Color Image Processing
St d d C
Standard
Color
l M
Model
d l
Commission Intenationale de l’Eclairage (CIE), 1931 defined three standard
primaries,
i
i called
ll d X,Y,Z
X Y Z to
t replace
l
Red,
R d Green,
G
Blue.
Bl
The primaries are used to match color
by us
using
g tthree
ee co
corresponding
espo d g
color-matching functions
© 1992–2008 R. C. Gonzalez & R. E. Woods
Digital Image Processing, 3rd ed.
Gonzalez & Woods
www.ImageProcessingPlace.com
Ch t 6
Chapter
Color Image Processing
CIE Chromatic Diagram
g
Chromatic values depend on dominant
wavelength and saturation and independent
of luminous energy.
Consider a color C, the we can Write
C = XX + YY + ZZ
Normalize Against
g
X+Y+Z
x = X/(X+Y+Z)
y = Y/(X+Y+Z)
z = Z/(X+Y+Z)
We know that x+y+z = 1, and the luminance
information usually in Y (Y cef.), thus we
can recover X,Y,Z
X = Y ((x/y)
/ ) ; Y = Y ; Z = Y(1
Y(1-x-y)/y
)/
Plotting these parameters
© 1992–2008 R. C. Gonzalez & R. E. Woods
The XYZ space
Digital Image Processing, 3rd ed.
Gonzalez & Woods
XYZ Color Space
p
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Ch t 6
Chapter
Color Image Processing
© 1992–2008 R. C. Gonzalez & R. E. Woods
Digital Image Processing, 3rd ed.
Gonzalez & Woods
www.ImageProcessingPlace.com
Ch t 6
Chapter
Color Image Processing
© 1992–2008 R. C. Gonzalez & R. E. Woods
Digital Image Processing, 3rd ed.
Gonzalez & Woods
www.ImageProcessingPlace.com
Ch t 6
Chapter
Color Image Processing
W e two
When
wo color
co o A and
a d B are
a e added
together new color C lies on the line
connects both colors.
In the side Figure, B defines the dominant
wavelength, and the ratio AC to BC expressed
as a percent of the excitation purity of A.
The closer A to C the more light A includes.
Complementary colors are those that can be
mixed to produce white light. D and E on the
side Figure are complementary colors
colors.
Nonspectral color are those that can not be
defined by dominant wavelength such as F.
Color gamuts or color ranges is the effect of
adding colors together
© 1992–2008 R. C. Gonzalez & R. E. Woods
Digital Image Processing, 3rd ed.
Gonzalez & Woods
www.ImageProcessingPlace.com
Ch t 6
Chapter
Color Image Processing
© 1992–2008 R. C. Gonzalez & R. E. Woods
Digital Image Processing, 3rd ed.
Gonzalez & Woods
www.ImageProcessingPlace.com
Ch t 6
Chapter
Color Image Processing
© 1992–2008 R. C. Gonzalez & R. E. Woods
Digital Image Processing, 3rd ed.
Gonzalez & Woods
www.ImageProcessingPlace.com
Ch t 6
Chapter
Color Image Processing
RGB Color Model
The color range (gamut) RGB model is
defined by the CRT’s phosphor.
C = RR + GG + BB
Let us look at these colors in XYZ space
RGB NTSC
CIE
Monitor
R
(0.67, 0.33) (0.73, 0.26) (0.62, 0.34)
G
(0.21, 0.71) (0.27, 0.71) (0.26,
(0 26 0.59)
0 59)
B
(0.14, 0.08) (0.16, 0.01) (0.15, 0.07)
© 1992–2008 R. C. Gonzalez & R. E. Woods
Digital Image Processing, 3rd ed.
Gonzalez & Woods
www.ImageProcessingPlace.com
Ch t 6
Chapter
Color Image Processing
© 1992–2008 R. C. Gonzalez & R. E. Woods
Digital Image Processing, 3rd ed.
Gonzalez & Woods
www.ImageProcessingPlace.com
Ch t 6
Chapter
Color Image Processing
© 1992–2008 R. C. Gonzalez & R. E. Woods
Digital Image Processing, 3rd ed.
Gonzalez & Woods
CMY Color Model
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Ch t 6
Chapter
Color Image Processing
Cyan, magenta,
Cyan
magenta and blue are the complements of red,
red green,
green blue.
blue
CMY is important when dealing with hardcopy that deposit color
pigments onto paper.
1  R 1
 C  C
 M   1  G 1
  M = 
 Y  Y
1  B 1
 R  1R  C 1
G   1   M 
  G = 1
 B  1B  Y 1
© 1992–2008 R. C. Gonzalez & R. E. Woods
-
R
G
B
-
C
M
Y
Digital Image Processing, 3rd ed.
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Ch t 6
Chapter
YIQ is used
by the US commercial TV.
Color Image Processing
YIQ
Q Color Model
•
•
•
•
•
YIQ model exploits two properties of the visual system
– More sensitive to changes luminance than to change hue or saturation
– Object
Obj t that
th t cover an extremely
t
l small
ll partt off our field
fi ld off view,
i
produce
d
a
limit color sensation.
Y is the luminance (the same Y in XYZ space).
The
h chromaticity
h
i i is
i encoded
d d encoded
d d in
i I andd Q
Only Y component will show black/White TV
More bits are used for Y, and either I or Q has less bits than the other.
0.587
0.114   R 
Y   0.299
 I    0.596  0.275  0.321 G 
  
 
Q   0.212  0.528 0.311   B 
© 1992–2008 R. C. Gonzalez & R. E. Woods
Digital Image Processing, 3rd ed.
Gonzalez & Woods
www.ImageProcessingPlace.com
Ch t 6
Chapter
Color Image Processing
HSI Model
The relationship between
RGB and HSI
RGB to HSI
 
H 
360  
BG
BG


( R  G )  ( R  B)
2
1/ 2 
2
[(
R

G
)

(
R

B
)(
G

B
)
]

  cos 1 
3
[min( R, G, B)]
( R  G  B)
I  ( R  G  B) / 3
S  1
© 1992–2008 R. C. Gonzalez & R. E. Woods
Digital Image Processing, 3rd ed.
Gonzalez & Woods
www.ImageProcessingPlace.com
Ch t 6
Chapter
Color Image Processing
Hue and saturation in the HSI
color model.
• The angle from the red axis
gives the hue
• The length of the vector
i the
is
h saturation.
i
© 1992–2008 R. C. Gonzalez & R. E. Woods
Digital Image Processing, 3rd ed.
Gonzalez & Woods
www.ImageProcessingPlace.com
Ch t 6
Chapter
Color Image Processing
HSI to RGB
for (0  H  120 )
B  I (1  S )

S cos( H ) 
R  I 1 


 cos(60  H ) 
G  3I  ( R  B )
120  H  240  H  H  120
240  H  360  H  H  240
B  I (1  S )

S cos( H ) 
R  I 1 


 cos(60  H ) 
G  3I  ( R  B )
© 1992–2008 R. C. Gonzalez & R. E. Woods
Digital Image Processing, 3rd ed.
Gonzalez & Woods
www.ImageProcessingPlace.com
Ch t 6
Chapter
Color Image Processing
© 1992–2008 R. C. Gonzalez & R. E. Woods
Digital Image Processing, 3rd ed.
Gonzalez & Woods
www.ImageProcessingPlace.com
Ch t 6
Chapter
Color Image Processing
In various color processing
applications it is possible to
use the corresponding
p
g Red,,
Green, and Blue channels
© 1992–2008 R. C. Gonzalez & R. E. Woods
Digital Image Processing, 3rd ed.
Gonzalez & Woods
www.ImageProcessingPlace.com
Ch t 6
Chapter
Color Image Processing
© 1992–2008 R. C. Gonzalez & R. E. Woods
Digital Image Processing, 3rd ed.
Gonzalez & Woods
www.ImageProcessingPlace.com
Ch t 6
Chapter
Color Image Processing
© 1992–2008 R. C. Gonzalez & R. E. Woods
Digital Image Processing, 3rd ed.
Gonzalez & Woods
www.ImageProcessingPlace.com
Ch t 6
Chapter
Color Image Processing
Color
l Coding
di for
f
visualization
© 1992–2008 R. C. Gonzalez & R. E. Woods
Digital Image Processing, 3rd ed.
Gonzalez & Woods
www.ImageProcessingPlace.com
Ch t 6
Chapter
Color Image Processing
© 1992–2008 R. C. Gonzalez & R. E. Woods
Digital Image Processing, 3rd ed.
Gonzalez & Woods
www.ImageProcessingPlace.com
Ch t 6
Chapter
Color Image Processing
Color Image Processing
© 1992–2008 R. C. Gonzalez & R. E. Woods
Digital Image Processing, 3rd ed.
Gonzalez & Woods
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Ch t 6
Chapter
Color Image Processing
Color Transformation
© 1992–2008 R. C. Gonzalez & R. E. Woods
Digital Image Processing, 3rd ed.
Gonzalez & Woods
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Ch t 6
Chapter
Color Image Processing
© 1992–2008 R. C. Gonzalez & R. E. Woods
Digital Image Processing, 3rd ed.
Gonzalez & Woods
www.ImageProcessingPlace.com
Ch t 6
Chapter
Color Image Processing
© 1992–2008 R. C. Gonzalez & R. E. Woods
Digital Image Processing, 3rd ed.
Gonzalez & Woods
www.ImageProcessingPlace.com
Ch t 6
Chapter
Color Image Processing
© 1992–2008 R. C. Gonzalez & R. E. Woods
Digital Image Processing, 3rd ed.
Gonzalez & Woods
www.ImageProcessingPlace.com
Ch t 6
Chapter
Color Image Processing
© 1992–2008 R. C. Gonzalez & R. E. Woods
Digital Image Processing, 3rd ed.
Gonzalez & Woods
www.ImageProcessingPlace.com
Ch t 6
Chapter
Color Image Processing
© 1992–2008 R. C. Gonzalez & R. E. Woods
Digital Image Processing, 3rd ed.
Gonzalez & Woods
www.ImageProcessingPlace.com
Ch t 6
Chapter
Color Image Processing
© 1992–2008 R. C. Gonzalez & R. E. Woods
Digital Image Processing, 3rd ed.
Gonzalez & Woods
www.ImageProcessingPlace.com
Ch t 6
Chapter
Color Image Processing
© 1992–2008 R. C. Gonzalez & R. E. Woods
Digital Image Processing, 3rd ed.
Gonzalez & Woods
www.ImageProcessingPlace.com
Ch t 6
Chapter
Color Image Processing
© 1992–2008 R. C. Gonzalez & R. E. Woods
Digital Image Processing, 3rd ed.
Gonzalez & Woods
www.ImageProcessingPlace.com
Ch t 6
Chapter
Color Image Processing
© 1992–2008 R. C. Gonzalez & R. E. Woods
Digital Image Processing, 3rd ed.
Gonzalez & Woods
www.ImageProcessingPlace.com
Ch t 6
Chapter
Color Image Processing
© 1992–2008 R. C. Gonzalez & R. E. Woods
Digital Image Processing, 3rd ed.
Gonzalez & Woods
www.ImageProcessingPlace.com
Ch t 6
Chapter
Color Image Processing
© 1992–2008 R. C. Gonzalez & R. E. Woods
Digital Image Processing, 3rd ed.
Gonzalez & Woods
www.ImageProcessingPlace.com
Ch t 6
Chapter
Color Image Processing
© 1992–2008 R. C. Gonzalez & R. E. Woods
Digital Image Processing, 3rd ed.
Gonzalez & Woods
www.ImageProcessingPlace.com
Ch t 6
Chapter
Color Image Processing
© 1992–2008 R. C. Gonzalez & R. E. Woods
Digital Image Processing, 3rd ed.
Gonzalez & Woods
www.ImageProcessingPlace.com
Ch t 6
Chapter
Color Image Processing
© 1992–2008 R. C. Gonzalez & R. E. Woods
Digital Image Processing, 3rd ed.
Gonzalez & Woods
www.ImageProcessingPlace.com
Ch t 6
Chapter
Color Image Processing
© 1992–2008 R. C. Gonzalez & R. E. Woods
Digital Image Processing, 3rd ed.
Gonzalez & Woods
www.ImageProcessingPlace.com
Ch t 6
Chapter
Color Image Processing
© 1992–2008 R. C. Gonzalez & R. E. Woods
Digital Image Processing, 3rd ed.
Gonzalez & Woods
www.ImageProcessingPlace.com
Ch t 6
Chapter
Color Image Processing
© 1992–2008 R. C. Gonzalez & R. E. Woods
Digital Image Processing, 3rd ed.
Gonzalez & Woods
www.ImageProcessingPlace.com
Ch t 6
Chapter
Color Image Processing
© 1992–2008 R. C. Gonzalez & R. E. Woods
Digital Image Processing, 3rd ed.
Gonzalez & Woods
www.ImageProcessingPlace.com
Ch t 6
Chapter
Color Image Processing
© 1992–2008 R. C. Gonzalez & R. E. Woods
Digital Image Processing, 3rd ed.
Gonzalez & Woods
www.ImageProcessingPlace.com
Ch t 6
Chapter
Color Image Processing
© 1992–2008 R. C. Gonzalez & R. E. Woods
Digital Image Processing, 3rd ed.
Gonzalez & Woods
www.ImageProcessingPlace.com
Ch t 6
Chapter
Color Image Processing
© 1992–2008 R. C. Gonzalez & R. E. Woods