Tristimulus colorimeter

A Tristimulus colorimeter, colloquially shortened to colorimeter, is used in digital imaging, to profile and calibrate output devices. It takes a limited number of wideband spectral energy readings along the visible spectrum by using filtered photodetectors; e.g. silicon photodiodes.

A tristimulus colorimeter is a tool used in digital image processing processes to profile and calibrate graphic output devices such as computer displays. Applied to the surface of the screen, the colorimeter is able to precisely record the colors reproduced by the screen itself, thanks to a grid of photodetectors equipped with filters. Calibration is performed by a software application that produces a range of colors on the screen and records the corresponding colorimeter readings, using them to generate an ICC profile for the screen itself. The product profile is then installed in the computer operating system or otherwise made available to applications equipped with color management. Details of the calibration process may vary.

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 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 (de) by Robert Luther (de) (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.

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