C O L O R IMAGE PROCESSING

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 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

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