A tristimulus colorimeter, colloquially shortened to ''colorimeter'' or ''colourimeter'', is used in

digital imaging Digital imaging or digital image acquisition is the creation of a digital representation of the visual characteristics of an object, such as a physical scene or the interior structure of an object. The term is often assumed to imply or include ...

to profile and calibrate output devices. It takes a limited number of wideband spectral energy readings along the

visible spectrum The visible spectrum is the spectral band, band of the electromagnetic spectrum that is visual perception, visible to the human eye. Electromagnetic radiation in this range of wavelengths is called ''visible light'' (or simply light). The optica ...

by using filtered

photodetector Photodetectors, also called photosensors, are devices that detect light or other forms of electromagnetic radiation and convert it into an electrical signal. They are essential in a wide range of applications, from digital imaging and optical ...

s; 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 calculation of LCD profile coefficients. Originally, three glass filters whose

transmittance Electromagnetic radiation can be affected in several ways by the medium in which it propagates. It can be Scattering, scattered, Absorption (electromagnetic radiation), absorbed, and Fresnel equations, reflected and refracted at discontinui ...

spectra mimicked the CIE

color matching function In 1931, the International Commission on Illumination (CIE) published the CIE 1931 color spaces which define the relationship between the visible spectrum and human color vision. The CIE color spaces are mathematical models that comprise a "sta ...

s (shown below) were employed. A

filter bank In signal processing, a filter bank (or filterbank) is an array of bandpass filters that separates the input signal into multiple components, each one carrying a sub-band of the original signal. One application of a filter bank is a graphic equal ...

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 by (1868–1945) (also called the "

Maxwell Maxwell may refer to: People * Maxwell (surname), including a list of people and fictional characters with the name ** James Clerk Maxwell, mathematician and physicist * Justice Maxwell (disambiguation) * Maxwell baronets, in the Baronetage of N ...

–

Ives Ives is both a surname and a given name. Notable people with the name include: Surname * Alice Emma Ives (1876–1930), American dramatist, journalist * Burl Ives (1909–1995), American singer, author and actor * Charles Ives (1874–1954), Ame ...

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 In mathematics, a linear combination or superposition is an Expression (mathematics), expression constructed from a Set (mathematics), set of terms by multiplying each term by a constant and adding the results (e.g. a linear combination of ''x'' a ...

of the CMFs. A colorimeter or a digital camera with a

color filter array In digital imaging, a color filter array (CFA), or color filter mosaic (CFM), is a mosaic of tiny color filters placed over the pixel sensors of an image sensor to capture color information. The term is also used in reference to Electronic paper ...

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. File:Spyder4Elite color sensor.JPG, Color sensor of a colorimeter File:CIE 1931 XYZ Color Matching Functions.svg, The CIE 1931 XYZ color matching functions

References

{{reflist Color Spectrometers Laboratory equipment