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Summary of Topic 2

Explore the human visual system, including cones and rods, photopic and scotopic vision, brightness adaptation, brightness discrimination, and color image representation. Understand how our eyes perceive color and adapt to different levels of brightness.

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Summary of Topic 2

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  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)

  2. 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

  3. Summary of Topic 2 • Human visual system • Brightness discrimination • Perceivable changes at a given adaptation level • Weber ratio, DI/I, where I is background, DI 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

  4. Summary of Topic 2 • A simple image model • Sampling • Quantization

  5. 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

  6. Summary of Topic 2 • Colour image representation

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