### 4.3. The hue-saturation-value (HSV) color model

Another way to characterize a color is in terms of the HSV model.

• The hue (H) of a color refers to which pure color it resembles. All tints, tones and shades of red have the same hue.

Hues are described by a number that specifies the position of the corresponding pure color on the color wheel, as a fraction between 0 and 1. Value 0 refers to red; 1/6 is yellow; 1/3 is green; and so forth around the color wheel.

• The saturation (S) of a color describes how white the color is. A pure red is fully saturated, with a saturation of 1; tints of red have saturations less than 1; and white has a saturation of 0.

• The value (V) of a color, also called its lightness, describes how dark the color is. A value of 0 is black, with increasing lightness moving away from black.

This diagram, called the single-hexcone model of color space, can help you visualize the meaning of the H, S, and V parameters.

• The outer edge of the top of the cone is the color wheel, with all the pure colors. The H parameter describes the angle around the wheel.

• The S (saturation) is zero for any color on the axis of the cone; the center of the top circle is white. An increase in the value of S corresponds to a movement away from the axis.

• The V (value or lightness) is zero for black. An increase in the value of V corresponds to a movement away from black and toward the top of the cone.

The Ostwald diagram corresponds to a slice of this cone. For example, the triangle between red, white, and black is the Ostwald diagram for the varieties of red.