Lecture 3 (2.11.08)
Color and Video
Shahram Ebadollahi
2/11/2008
DIP ELEN E4830
1
Lecture Outline
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1
1
1
Review of Lecture 2
1 Finishing Compandor and Dither
Color
1 Visual Perception
1 Color Representation
1 Color Models and Transformations
1 Color Sampling and Interpolation
Video
1 Fundamentals of Analog and Digital Video
1 Video Sampling
1 Video Processing
Multivariate Imaging (time permitting)
1 Introduction and Examples
1 Principal Component Analysis
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2
Compandor
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3
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4
Quantization:
Contouring Problem
1-bit
2-bit
5-bit
6-bit
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3-bit
7-bit
4-bit
8-bit
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Dithering
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Dithering: Ordered vs. Random
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Half-tone
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Half-tone: how many gray-levels
per block?
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Eye Physiology & Visual Perception
I ( x, y , λ ) = r ( x , y , λ ) L ( x , y , λ )
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Eye Physiology & Visual Perception
•75~150 Million
•Sensitive to low illumination
•Distributed over Retina
•6~7 Million
• Scotopic (dim light) vision
•Highly sensitive to color
•Concentrated in Fovea
•Photopic (day light) vision
Rods & Cones Distribution in Retina
Photoreceptor Cells
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Visual Perception: Luminence
Spectral Power
Distribution of the
Stimulus
I ( x, y , λ ) = r ( x , y , λ ) L ( x , y , λ )
∞
F ( x, y ) = ∫ I ( x, y, λ )V (λ )dλ
0
Luminance (intensity)
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Visual Perception: Color
1
Humans perceive only a few dozen
gray levels but thousands of colors
3 types of Cone Photoreceptors
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Color perceptual attributes:
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1
1
Brightness (perceived Luminence)
Hue (“redness”, “greenness”, …)
Saturation
∫ S (λ )C (λ )dλ
α1 (C )
∫S
(λ )C (λ )dλ
α 2 (C )
∫ S (λ )C (λ )dλ
α 3 (C )
1
C (λ )
2
3
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S 3 (λ )
S 2 (λ ) S1 (λ )
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Primary & Secondary Colors
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CIE Chromacity Diagram
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Color Monitor & Printer Color Gamut
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RGB Color Cube
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Color Interpolation
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2
3
4
5
6
7
8
1
G
B
G
B
G
B
G
B
2
R
G
R
G
R
G
R
G
3
G
B
G
B
G
B
G
B
4
R
G
R
G
R
G
R
G
5
G
B
G
B
G
B
G
B
6
R
G
R
G
R
G
R
G
7
G
B
G
B
G
B
G
B
8
R
G
R
G
R
G
R
G
Bayer Pattern
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(a color filter array CFA pattern)
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CMY and CMYK Color Model
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1
1
Used in printers
Primary pigment colors,
secondary light colors
Subtractive vs. Additive
 C  1  R 
 M  = 1 − G 
    
 Y  1  B 
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HSI Color Model
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1
1
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Intensity
Hue
Saturation
Cube at different
intensity crosssections
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HSI Color Model
1
Saturated colors on the outer
points
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Max. saturation at intermediate
intensity levels
1
Distance between colors:
D (C1 , C2 ) = w1∆H + w2 ∆S + w3∆I
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Manipulation HSI images
• HSI values of primary and secondary
colors
• Hue of Green & Blue set to Zero
• HSI allows for independent
manipulation of colors
• Intensity of white reduced by ½
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• Saturation of Cyan reduced by ½
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Color Image Processing:
Point vs. Kernel Processing
 f R ( x, y ) 
f ( x, y ) =  f G ( x, y )
 f B ( x, y ) 
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g ( x , y ) = T [ f ( x, y ) ]
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