Abney’s law

What is Abney’s Law?

(Abney’s Law in French: loi d’Abney) The luminance L of a displayed RGB color shade is composed of the primary valences R, G, B with their respective luminance coefficients: In the standard CIEXYZ valence system, for reasons of mathematical simplicity, the standard chromatic values X and Z make no contribution to brightness, but only Y, so that Y itself can be interpreted there as brightness.