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C O L O R IMAGE PROCESSING. C O L O R IMAGE PROCESSING. Pseudo-color processing - an assignment of color to an intensity (grey scale) image Full color processing - the enhancement or modification of image acquired with a full color sensor. Color Fundamentals - PowerPoint PPT Presentation
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COLOR IMAGE PROCESSING
COLOR IMAGE PROCESSING
Pseudo-color processing - an assignment of colorto an intensity (grey scale) image
Full color processing - the enhancement or modification of image acquired with a full color sensor
Color Fundamentals
Chromatic light - light which exhibits visible color, 400-700 nm
Color is perceived when light of a certain wavelength is reflected from the surface of an object and detected by the color sensitive cones in the human eye.
Color Fundamentals
Radiance - amount of energy emitted from a light source (watts)
Luminance - amount of energy perceived by an observer (lumens)
Brightness - subjective notion of achromatic intensity
Color Fundamentals
Subtractive color - reflected light
Additive color - emitted light
Subtractive color -
Additive color -
Additive Color Mixing
red
bluegreen
additive primary colors
white
white
cyan
yellow magenta
red
bluegreen
secondary
secondarysecondary
Additive Color Mixing
Color Perception
Color perception is enabled by cones in the retina.
Cones contain photosenstive chemicals, calledphotopigments.
There are three types of cones, which are sensitive to wavelengths of light corresponding to the colorsred, green and blue.
Color is perceived when light of a certain wavelengthis reflected from the surface of an object and detected by the color sensitive cones.
Color Display Systems
The interior of the screen is composed of an array of electron-sensitive phosphor dots arranged in linear or triangular groups (triads).
One dot emits red light when excited by an electron gun. Another emits green light and a third emits blue light excited in the same manner.
The nature and arrangement of these triads determines an upper level on the spatial resolution of a displayed image.
Color Models:
CIE (Chromaticity Diagram)
RGB Cube
CYM (CYMK)
YIQ
HSV
HSI
CIE (Chromaticity Diagram)
RGB Cube
CYM (CYMK)
YIQ
HSV
HSI
CIE (Chromaticity Diagram)
X (red)
Y(green)
Z(blue) = (1-(X+Y))
Color gamut:The color range produced by an RGB monitor
Color printing gamut is irregular and more limited
Color Models:
CIE (Chromaticity Diagram)
RGB Cube
CYM (CYMK)
YIQ
HSV
HSI
CIE (Chromaticity Diagram)
RGB Cube
CYM (CYMK)
YIQ
HSV
HSI
RGB color model
(0,0,0)
(1,1,1)
RGB color model
RED(1,0,0)
BLUE(0,0,1)
GREEN(0,1,0)
RGB color model
MAGENTA (1,0,1)
CYAN(0,1,1)
YELLOW (1,1,0)
RGB color model
shades of grey
FULL COLOR IMAGE
FULL COLOR IMAGE
RED GREEN BLUE
Color Models:
CIE (Chromaticity Diagram)
RGB Cube
CYM (CYMK)
YIQ
HSV
HSI
CIE (Chromaticity Diagram)
RGB Cube
CYM (CYMK)
YIQ
HSV
HSI
CMY Color Model
CMY
111
RGB
= -
Used primarily for color hardcopy generation.
Color Models:
CIE (Chromaticity Diagram)
RGB Cube
CYM (CYMK)
YIQ
HSV
HSI
CIE (Chromaticity Diagram)
RGB Cube
CYM (CYMK)
YIQ
HSV
HSI
YIQ Color Model
Y IQ
0.299 0.587 0.1140.596 -0.275 -0.3210.212 -0.523 0.311
RGB
=
Used in commercial color TV broadcasting
YIQ Color Model
Y IQ
0.299 0.587 0.1140.596 -0.275 -0.3210.212 -0.523 0.311
RGB
=
Y - luminance - conveys tonal values) I - inphaseQ - quadrature convey chrominance information
YIQ Color Model
Y IQ
0.299 0.587 0.1140.596 -0.275 -0.3210.212 -0.523 0.311
RGB
=
Inphase and quadrature modulate the chrominance subcarrier. Its amplitude indicates the color’s saturation; its phase indicates hue.
YIQ Color Model
Y IQ
0.299 0.587 0.1140.596 -0.275 -0.3210.212 -0.523 0.311
RGB
=
YIQ representation enables intensity transformations to be performed on only the intensity portion of a color image.
FULL COLOR IMAGE
FULL COLOR IMAGE
RED GREEN BLUE
FULL COLOR IMAGE
RED GREEN BLUE
(each channel, histogram equalized)
FULL COLOR IMAGEINCORRECT HIST EQUALIZATION
FULL COLOR IMAGE
INTENSITY IMAGE
FULL COLOR IMAGE
INTENSITY HIST EQUALIZATION
INTENSITY IMAGE
FULL COLOR IMAGE
INTENSITY HIST EQUALIZATION
INTENSITY IMAGE
CORRECT HIST EQUALIZATION
YIQ Color Model
Y IQ
0.299 0.587 0.1140.596 -0.275 -0.3210.212 -0.523 0.311
RGB
=
1.0 0.956 0.6201.0 -0.272 -0.6471.0 -1.108 1.705
RGB
=
Y IQ
YIQ Color Model
Y IQ
0.299 0.587 0.1140.596 -0.275 -0.3210.212 -0.523 0.311
25500
=
Given a RED pixel: R = 255, G = 0, B = 0
Y = .299(255) + .587(0) + .114(0) = 76.25 ~ 76 I = .596(255) - .275(0) - .321(0) = 151.98 ~ 152Q = .212(255) - .523(0) + .311(0) = 54.06 ~ 54
YIQ Color Model
Given a YIQ value: Y = 76, I = 152, Q = 54
R = .1.0(76) + .956(152) + .620(54) = 254.79 ~ 255G = 1.0(76) - .272(152) -.647(54) = -0.282 ~ 0B = 1.0(76) -1.108(152) + 1.705(54) = -0.346 ~ 0
1.0 0.956 0.6201.0 -0.272 -0.6471.0 -1.108 1.705
RGB
=
Y IQ
R = 255, G = 0, B = 0; a RED pixel !
Color Models:
CIE (Chromaticity Diagram)
RGB Cube
CYM (CYMK)
YIQ
HSV
HSI
CIE (Chromaticity Diagram)
RGB Cube
CYM (CYMK)
YIQ
HSV
HSI
HSV Color Model
(tint, shade and tone for artists)
Hue - color attribute that describes pure color
Saturation - degree to which pure color is diluted by white light
Value - intensity, lightness, brightness
HSV Color Model
Hue, Saturation and Value (tint, shade and tone for artists)
HSV Color Model
Hue - an angle around the vertical axis
HSV Color Model
Saturation - (color purity) 0 at the center, to 1 on the sides
HSV Color Model
Value - ranges from 0 to 1; indicates lightness/darkness
// RGB to HSV conversion// r,g,b values are from 0 to 1// h = [0,360], s = [0,1], v = [0,1]// if s == 0, then h = -1 (undefined)void RGBtoHSV( float r, float g, float b, float *h, float *s, float *v ){
float min, max, delta;min = MIN( r, g, b );max = MAX( r, g, b );*v = max; // vdelta = max - min;if( max != 0 )
*s = delta / max; // selse {
// r = g = b = 0 // s = 0, v is undefined*s = 0;*h = -1;return;
}if( r == max )
*h = ( g - b ) / delta; // between yellow & magentaelse if( g == max )
*h = 2 + ( b - r ) / delta; // between cyan & yellowelse
*h = 4 + ( r - g ) / delta; // between magenta & cyan*h *= 60; // degreesif( *h < 0 )
*h += 360;} *from http://www.cs.rit.edu/~ncs/color/t_convert.html#RGB to HSV & HSV to RGB
Color Models:
CIE (Chromaticity Diagram)
RGB Cube
CYM (CYMK)
YIQ
HSV
HSI
CIE (Chromaticity Diagram)
RGB Cube
CYM (CYMK)
YIQ
HSV
HSI
HSI Color Model
( HUE, SATURATION, INTENSITY )
Hue - angle around vertical axis
Saturation - distance from vertical axis
Intensity - perpendicular distance from the point corresponding to black
COLOR IMAGE PROCESSING
Full color processing - the enhancement or modification of image acquired with a full color sensor
Pseudo-color processing - an assignment of colorto an intensity (grey scale) image
Color Palette (LUT)
1
2
0
3
255
4
5
..
.
1
2
0
3
255
4
5
..
.
1
2
0
3
255
4
5
..
.
1
2
0
3
255
4
5
..
.
R G BIndex: Color:
5
Image Display
Pixel value (0-255) Color Palette (LUT)
8 bit gray scale
1
2
0
3
255
4
5
...
255 0 0
ORIGINAL INTENSITY IMAGE
IMAGE WITH PSEUDOCOLOR LUT