A color is defined by the threefold combination “source-object-observer.”
Source: reference illuminant with a relative spectral energetic distribution .
Object: in general opaque, with a diffuse reflectance .
Observer: normalized by the CIE in 1931 (vision field of 2°) and later in 1964 (vision field of 10°) with the colorimetric functions , and .
This leads to the following trichromatic components , and :
By convention the scaling factor is defined by:
Notwithstanding the “color atlas” that one may use in order to visually compare colors, all colorimetry systems based on photoelectric measurements are based on the calculation of the trichromatic components , and derived from (19).
The main manufacturers of colorimetric measurement systems are Hunterlab and Gretag Macbeth. Other companies are now commercializing such systems, like Minolta, Zeiss or X-rit. Datacolor International is specialized in color control tools for textiles.