Color Models(CIE-Lab)

CIELAB

CIELAB is the second of two systems adopted by CIE in 1976 as models that better showed uniform color spacing in their values. CIELAB is an opponent color system based on the earlier (1942) system of Richard Hunter called L, a, b. Color opposition correlates with discoveries in the mid-1960s that somewhere between the optical nerve and the brain, retinal color stimuli are translated into distinctions between light and dark, red and green, and blue and yellow. CIELAB indicates these values with three axes: L*, a*, and b*. (The full nomenclature is 1976 CIE L*a*b* Space.)

The central vertical axis represents lightness (signified as L*) whose values run from 0 (black) to 100 (white). This scale is closely related to Munsell's value axis except that the value of each step is much greater. This is the same lightness valuation used in CIELUV.

The color axes are based on the fact that a color can't be both red and green, or both blue and yellow, because these colors oppose each other. On each axis the values run from positive to negative. On the a-a' axis, positive values indicate amounts of red while negative values indicate amounts of green. On the b-b' axis, yellow is positive and blue is negative. For both axes, zero is neutral gray:

Therefore, values are only needed for two color axes and for the lightness or grayscale axis (L*), which is separate (unlike in RGB, CMY or XYZ where lightness depends on relative amounts of the three color channels).

CIELAB has become very important for desktop color. Like all CIE models, it is device independent (unlike RGB and CMYK), is the basic color model in Adobe PostScript (level 2 and level 3), and is used for color management as the device independent model of the ICC (International Color Consortium) device profiles.