color space

A system for describing color numerically. Also known as a "color model," the most widely used color spaces are RGB for scanners, cameras and displays, CMYK for color printing and YUV for TV/video. Prior to the proliferation of electronic displays, which are all RGB, color spaces were developed that were closer to the way people think about color. For example, the CIE Lab model uses lightness (L) and values on red-green (a) and blue-yellow (b) axes, while HSB uses hue, saturation and brightness. See CIE Lab, HSB, HSL, RGB, sRGB, YUV, xvYCC and color space conversion.

HSB, CIE Lab, RGB and CMYK

All four color spaces in this Photoshop color picker relate to each other. Although numbers can be entered, users mostly move the vertical slider or point into the box to select a color. In this example, the R in RGB is selected, and moving the slider changes Red from 0 to 255 and all related values in the other color spaces at the same time.

A More Intuitive Model

In the 1970s, Alvy Ray Smith developed the HSB model for color selection. Changing red to pink by reducing saturation (S) is more intuitive than changing green and blue in RGB. For details, see HSB. For invaluable information about color spaces and computer graphics (CG) from one of the country's most distinguished experts, visit www.alvyray.com, and click Papers and CG.

Color Space Conversion

Since displays, printers and TV/video all use different color spaces, conversion between them is necessary and commonplace.