Lecture 3 (2.9.09)
Sampling (extensions to general lattice), Video, and Color
Shahram Ebadollahi
02/09/09
DIP ELEN E4830
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Lecture Outline
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Review of Lecture 2
Sampling on general lattice
Video
 Fundamentals of Analog and Digital Video
Color
 Visual Perception
 Color Representation
 Color Models and Transformations
 Color Sampling and Interpolation
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Progressive:
Interlaced:
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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 
Well lit scene
∞
F  x,y =∫ I  x,y,λ V  λ  dλ
0
Luminance (intensity)
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Visual Perception: Color
3 types of Cone Photoreceptors
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Humans perceive only a few dozen gray levels but thousands of colors
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Color perceptual attributes:
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S 3 λ 
S 2  λ  S 1 λ
Brightness (perceived Luminence)
Hue (“redness”, “greenness”, …)
Saturation
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Cones: 65% (R), 33% (G), 2% (B)
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Color Representation
Cλ 
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∫ S 1 λ C λ dλ
α1  C 
∫ S 2  λC λ dλ
α 2 C 
∫ S 3 λ C  λdλ
α 3C 
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Painting, printing
Monitors, projectors, digital camera, scanner
Primary & Secondary Colors
Images above from: http://www.rgbworld.com/color.html
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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
1
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 02/09/09
(a color filter array CFA pattern)
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CMY and CMYK Color Model
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Used in printers
Primary pigment colors, secondary light colors
Subtractive vs. Additive
[ ][][ ]
1
C
R
M =1 −G
Y
1
B
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HSI Color Model
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Intensity
Hue
Saturation
Cube at different intensity cross­
sections
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HSI Color Model
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Saturated colors on the outer points
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Max. saturation at intermediate intensity levels
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Distance between colors:
D C1 ,C 2 =w1 ΔH+w2 ΔS+w3 ΔI
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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 
g x,y =T [ f  x,y  ]
f B  x,y 
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