colorimetry

Colorimetry is the scientific discipline concerned with quantifying and describing colors as perceived by the human eye. It links spectral power distributions and sample reflectance to standardized color coordinates that aim to be observer- and device-independent.

Human vision relies on three types of cone photoreceptors. Colorimetry uses color matching experiments to derive color matching functions, which convert spectral data into tristimulus values (X, Y, Z) for a standard observer, most commonly the CIE 1931 2-degree observer. A light source and a sample are mixed until the observer perceives a neutral match; the amounts of primaries are recorded as coordinates. The XYZ values can be transformed into perceptual color spaces such as Lab or Luv.

Colorimeters and spectrophotometers are used to obtain colorimetric data. Colorimeters use fixed filters to approximate cone responses, while spectrophotometers measure reflectance or transmittance across the visible spectrum and compute XYZ or Lab values. Illuminants such as D65 or A define the reference lighting for measurements.

Colorimetry underpins color reproduction in displays, printers, textiles, paints, and lighting. It is essential for color quality control, calibration, and color management. Standards bodies such as the CIE and ISO publish color spaces, color-difference formulas (Delta E), and procedure guidelines. Metamerism, where colors match under one light but not another, is a notable consideration.

History in colorimetry began with color matching experiments by Wright and Guild, which led to the CIE 1931 standard observer and the XYZ color space. Subsequent developments include perceptually uniform spaces such as Lab and Luv and refined color-difference metrics like Delta E2000.