HSV COLOR MODEL

                                         Instead of a group of color primaries, the HSV model uses color descriptions that have a more intuitive appeal to a user. to allow a color specification, a user selects a chromatic color and therefore the amounts of white and black that's to be added to get different shades, tints, and tones. Color parameters during this model are hue (H), saturation (9, and value (V).

The three-dimensional representation of the HSV model springs from the RGB cube. If we imagine viewing the cube along the diagonal from the white vertex to the origin (black), we see a top level view of the cube that has the hexagon shape shown in Fig. 15-15. The boundary of the hexagon represents the assorted hues, and it's used because the top of the HSV hexcone (Fig. 15-16). within the hexcone, saturation is measured along a horizontal ad, and value is along a vertical axis through the middle of the hexcone. Hue is represented as an angle about the vertical axis, starting from 0o at red through 360". Vertices of the hexagon are separated by 60" intervals. Yellow is at 60•, green at 120•, and cyan opposite red at H = 180'. Complementary colors are 180" apart.

 
Saturation S varies from 0 to 1. it's represented during this model because the ratio of the purity of a specific hue to its maximum purity at S = 1. a specific hue is claimed to be one-quarter pure at the worth S = 0.25. At S = 0, we've the grey scale.

Value V varies from 0 at the apex of the hexcone to I at the highest. The apex represents black. At the highest of the hexcone, colors have their maximum intensity. When V = 1 and S = 1, we've the "pure" hues. White is that the point at V = 1 and S =0.

This is a more intuitive model for many users. Starting with a range for a pure hue, which specifies the hue angle H and sets V = 5 = 1, we describe the colour we wish in terms of adding either white or black to the pure hue. Adding black decreases the setting for V while S is held constant. to induce a navy blue, V might be set to 0.4 with S = 1 and H = 240". Similarly, when white is to be added to the hue selected, parameter S is decreased while keeping V constant. a light-weight blue might be designated with S = 0.3 while V = 1 and H = 240". By adding some black and a few white, we decrease both V and S. An interface for this model typically presents the HSV parameter choices in an exceedingly color palette.

Color concepts related to the terms shades, tints, and tones are represented in an exceedingly cross-sectional plane of the HSV hexcone (Fig. 15-17). Adding black to a pure hue decreases V down the side of the hexcone. Thus, various shades are represented with values S - 1 and 0 <= S <= l. Adding white to a sound produces different tints across the highest plane of the hexcone, where parameter values are V = 1 and 0 <= S <= l. Various tones are specified by adding both black and white, producing color points within the triangular cross-sectional area of the hexcone.

The human eye can distinguish about 128 different hues and about 130 different tints (saturation levels). for every of those, variety of shades (value set- tings) is detected, betting on the hue selected. About 23 shades are discernible with yellow colors, and about 16 different shades is seen at the blue end of the spectrum. this suggests that we will distinguish about 128 x 130 x 23 = 82,720 different colors. for many graphics applications, 128 hues, 8 saturation levels, and 15 value settings are sufficient. With this range of parameters within the HSV color model, 16,384 colors would be available to a user, and therefore the system would wish 14 bits of color storage per pixel. Color lookup tables might be accustomed re- duce the storage requirements per pixel and to extend the quantity of obtainable colors.