Summary of Topic 2
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G52IIP, School of Computer Science, University of Nottingham 1 Summary of Topic 2 Human visual system Cones Photopic or bright-light vision Highly sensitive to color Rods Not involved in color vision Sensitive to low level of illumination (scotopic or dim-light vision)
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Summary of Topic 2. Human visual system Cones Photopic or bright-light vision Highly sensitive to color Rods Not involved in color vision Sensitive to low level of illumination (scotopic or dim-light vision). Summary of Topic 2. Human visual system Brightness adaptation - PowerPoint PPT Presentation
Transcript of Summary of Topic 2
G52IIP, School of Computer Science, University of Nottingham
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Summary of Topic 2
Human visual system
Cones Photopic or bright-light vision Highly sensitive to color
Rods Not involved in color vision Sensitive to low level of illumination (scotopic or dim-light
vision)
G52IIP, School of Computer Science, University of Nottingham
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Summary of Topic 2
Human visual system
Brightness adaptation Subjective brightness is a logarithmic function of the light
intensity incident on the eye The HVS cannot operate on the full perceptible brightness
range (~10 orders of magnitude) simultaneously The total brightness range the HVS can discriminate
simultaneously is rather small in comparison (about 4 orders of magnitude)
It accomplishes this through (brightness) adaptation
G52IIP, School of Computer Science, University of Nottingham
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Summary of Topic 2
Human visual system
Brightness discrimination Perceivable changes at a given adaptation level Weber ratio, I/I, where I is background, I intensity change Small Weber ratio - good discrimination Larger Weber ratio - poor discrimination
Perceived brightness is not a simple function of intensity Mach band pattern Simultaneous contrast
G52IIP, School of Computer Science, University of Nottingham
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Summary of Topic 2
A simple image model
Sampling Quantization
G52IIP, School of Computer Science, University of Nottingham
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Summary of Topic 2
Colour image
The RGB Color Model R, G, B at 3 axis ranging in [0 1] each Gray scale along the diagonal If each component is quantized into 256 levels [0:255], the total
number of different colors that can be produced is (28)3 = 224 =16,777,216 colors.
The YIQ Color Model Video (NTSC) standard Y encodes luminance; I and Q encode chrominance (“color”) Black and white TV shows only the Y channel Backward compatibility; efficiency
YCbCr
G52IIP, School of Computer Science, University of Nottingham
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Summary of Topic 2
Colour image representation
