. HVS CONSISTENT COLOR SPACES
For effective color image processing, proper selection and use of color space is necessary so that IQA results are HVS consistent .
A. HSI Color space
RGB and CMY color models are designed for hardware implementations. They are not used for describing colors by human. Further human being cannot think of three primary colors those are combined to result into a specific color. HSI color space decouples color and intensity information and rearranges the geometry of RGB so that it becomes more intuitive in color description . In fact, human beings describe color by its hue, saturation and brightness or value. Hue is the dominant wavelength of light that enters into human eye. Hence the color perceived by human is represented by hue. Saturation defines the purity of color perceived. It is given by the amount of white light mixed with hue. Hue and Saturation together give the chrominance information while as intensity is also called as luminance or brightness.
B. YIQ and YUV Color spaces
YUV and YIQ both decouple the color image information into a luminance and a pair of chrominance planes . The luminance signal describes color intensity levels and each chrominance signal is formed by the difference between a color and a reference white light at the same luminance. The two chrominance values describe approximate amounts of blue and red content in the color. The YIQ and YUV color spaces are designed for color television broadcasting applications and they take advantage of low sensitivity of human eye to color signal YUV color space is used by the PAL (Phase Alternation by Line) composite video standard. YIQ color space is derived from YUV color space. Hence they are similar except that the YIQ color space is rotated 330 with respect to YUV color space. ‘I’ and ‘Q’ terms describe the quadrature modulation method used in television broadcasting. They are derived from words in phase and quadrature respectively. YIQ is used in NTSC composite color television broadcasting standard.
C. Gradient Domain and Natural Scene...