A Tristimulus colorimeter, colloquially shortened to a colorimeter, is used in digital imaging, to profile and calibrate output devices by measuring color differences. It takes a limited number of wideband spectral energy readings along the visible spectrum by using filtered photodetectors; e.g. silicon photodiodes.
A colorimeter with the known value of absolute error allows measuring (x,y)-chromaticity coordinates in red, green, blue, and white colors. Measured values are used for the calculation of LCD profile coefficients.
Originally, three glass filters whose transmittance spectra mimicked the CIE color-matching functions (shown below) were employed. A filter bank may be used to decompose the individual color matching functions if more accuracy is desired.
A camera or colorimeter is said to be colorimetric if it satisfies the Luther condition by Robert Luther (1868–1945) (also called the "Maxwell-Ives criterion"), reducing observer metamerism color errors if the product of the spectral responsivity of the photoreceptor and the spectral transmittance of the filters is a linear combination of the CMFs.
A colorimeter or a digital camera with a color filter array can, under certain conditions, be used as an alternative to a spectrophotometer.
The illuminant and observer conditions should be specified when citing a measurement (e.g. D65/10°).
The quality of a colorimeter may be assessed using the means in CIE publication 179:2007.
There are various calibration methods for tristimulus colorimeters.