CIE colorimetric system
Colorimetry

For colorimetry to be accurate, it is necessary to agree on a fictitious subject, the reference observer, whose color vision is perfectly defined. This observer approximates the average of real, normal, young subjects who took part in the color equalization experiments of Wright and Guild (1929 to 1931).

Based on the RGB system with monochromatic real primaries defined by the CIE in 1931, an international classical colorimetry system was recommended, the XYZ system with unreal (or virtual) primaries, with the new trichromatic XYZ components linked to the RGB components by linear equations.

The colorimetric functions $$