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