Tristimulus values

Tristimulus values are three numbers obtained by applying specified color-matching functions to a color stimulus. Together, they represent that stimulus within a defined colorimetric system.

Color-matching functions: Weighting functions that describe how strongly each wavelength contributes to a color-matching response. They are applied to the stimulus spectrum to calculate each tristimulus value.
Standard observer: A standardized model of human color-matching responses used in colorimetry. The chosen observer determines the functions used to calculate tristimulus values.
Colorimetry: The science of measuring and specifying color using standardized methods and instruments. Tristimulus values are a central output of instrumental color measurement.
Spectral color: A color produced by light concentrated in a narrow range of wavelengths. A spectral description preserves wavelength information that three values compress.
Spectral power distribution: A description of radiant power across the wavelengths in a light spectrum. It supplies the spectral information integrated against color-matching functions.
Illuminant: A defined source of light, specified by its spectral distribution or by a standard designation. Reflected-color measurements depend on the illuminant illuminating the sample.
Colorimeter: An instrument that measures color using filtered detectors approximating color-matching functions. A tristimulus colorimeter estimates three values directly from detector responses.
RGB color model: An additive color model that represents colors through red, green, and blue component values. RGB values depend on chosen primaries and encoding, unlike standardized XYZ tristimulus values.
Color matching: The process of adjusting one or more lights until their combined appearance matches a target color. Tristimulus values formalize matches made in color-matching experiments.
Reflectance: The fraction of incident light reflected by a surface at each wavelength. For an object, reflectance combines with the illuminant spectrum to form the measured stimulus.

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