CIE Lab color space

A device-independent, perceptually uniform color space defined relative to a white point -- equal numeric distance tracks equal perceived difference.

CIE Lab is derived from device-independent CIE XYZ (built from measurements of human color perception) and defined relative to a white point $(X_n,Y_n,Z_n)$ : $L^*=116f(Y/Y_n)-16$ , $a^*=500(f(X/X_n)-f(Y/Y_n))$ , $b^*=200(f(Y/Y_n)-f(Z/Z_n))$ , with $f(t)=t^{1/3}$ above a small threshold. Any neutral gray has $a^*=b^*=0$ exactly, since a neutral color scales evenly toward the white point. Unlike RGB, HSV, HSL, or YCbCr, equal Lab distance corresponds approximately to equal PERCEIVED color difference.