color space (redirected from Colour space)

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

Four Color Spaces

This Photoshop dialog box shows the current color in HSB, RGB, CIE Lab and CMYK color spaces. The vertical slider is used to adjust the component of the color space selected (in this case, the R in RGB). Moving the slider changes the R from 0 (bottom) to 255 (top). Clicking into the large color field on the left, changes the other two components.

More Intuitive Models

Color spaces that use hue, saturation and brightness (HSI, HLS, HSV, etc.) are more intuitive to people than RGB, CMYK and YUV. In the examples above, changing red to pink is done by reducing color saturation (S) from 100% to 50%, which is much more intuitive than changing green and blue to 127 in RGB. Changing from purple to green only requires the hue (H) to be changed.