Tristimulus Values

Three parameters corresponding to the stimulus levels of the three Cones. In principle, the Tristimulus Values can represent any human color sensation. The three parameters, denoted “S”, “M”, and “L”, are indicated using a 3-dimensional Color Space called LMS.

The absorption spectrum of each of the cones determines the transformation from the spectrum hitting the retina to the LMS values. Even though a set of Tristimulus Values always corresponds to one color, those values can come from a number of different spectra. The different spectra that map to the same Tristimulus Values are called Metamers.

The Tristimulus values usually refer to the three parameters of the LMS Color Space, but can also refer to the CIEXYZ Color Space, or sometimes any other three dimensional color space represented by three parameters that is used to represent Trichromatic perception, including the Opponent Channels and HSV.