63 4:4:4 Co-Sited 4:2:2 Co-Sited 4:1:1 Co-Sited 4:2:0 4:2:0 Co-Sited Colour spaces CHAPTER 7.2 G' = 4.5 G select colors visually or specify Pantone colors. These B' = 4.51 B color spaces are discussed for historical interest. HLS for R, G, B < -0.018 (hue, lightness, saturation) is similar to HSI; the term -1.099 lightness is used rather than intensity. -0.099 The difference between HSI and HSV is the com- G' = -1.099 .45-0.099 putation of the brightness component (I or V), which -1.099 -0.099 determines the distribution and dynamic range of both From R'G'B' with a 0-255 range, a luma and two the brightness (I or V) and saturation (S). The HSI color chrominance signals (C1 and C2) are generated: space is best for traditional image processing functions such as convolution, equalization, histograms, and SO on, Y = 0.213R + 0.419G' + 0.081B which operate by manipulation of the brightness values C1 = - 0.131R' - 0.256G' + 0.387B' + 156 since I is equally dependent on R, G, and B. The HSV C2 = 0.373R - 0.312G' - 0.061B + 137 color space is preferred for manipulation of hue and saturation (to shift colors or adjust the amount of color) As an example, a 20% gray value (R, G, and B = 0.2) since it yields a greater dynamic range of saturation. would be recorded on the PhotoCD disc using the Figure 7.2-12 illustrates the single hexcone HSV color following values: model. The top of the hexcone corresponds to V = 1, or Y = 79 the maximum intensity colors. The point at the base of C1 = 156 the hexcone is black and here V = 0. Complementary C2 = 137 colors are 180° opposite one another as measured by H, the angle around the vertical axis (V), with red at 0°. The value of S is a ratio, ranging from 0 on the center line PhotoYCC to RGB vertical axis (V) to 1 on the sides of the hexcone. Any value of S between 0 and 1 may be associated with the Since PhotoYCC attempts to preserve the dynamic range point V = 0. The point S = 0, V = 1 is white. In- of film, decoding PhotoYCC images requires the selection termediate values of V for 