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Colorimetry: CIELAB Color Space
Excerpt from Field Guide to Visual and Ophthalmic Optics
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.
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