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Colorimetry: CIELAB Color Space

The 1976 CIELAB color space is a second attempt at providing a perceptually uniform color space. In this color space, the distance between two points also approximately tells how different the colors are in luminance, chroma, and hue. The 1976 CIELAB coordinates (L*, a*, b*) in this color space can be calculated from the tristimulus values XYZ with the following formulas. The subscript n denotes the values for the white point.

The color difference ΔE between two colors in the CIELAB space is

A value of ΔE of unity represents a just noticeable difference (JND). These coordinates can also be expressed in cylindrical coordinates with chroma being defined as

and hue being defined as