Colorimetry is "the science and technology used to quantify and describe physically the human
color perception".
It is similar to
spectrophotometry, but is distinguished by its interest in reducing spectra to the physical correlates of color perception, most often the
CIE 1931 XYZ color space tristimulus values and related quantities.
History
The
Duboscq colorimeter was invented by
Jules Duboscq in 1870.
Instruments
Colorimetric equipment is similar to that used in spectrophotometry. Some related equipment is also mentioned for completeness.
* A
tristimulus colorimeter measures the tristimulus values of a color.
* A
spectroradiometer measures the absolute spectral
radiance (intensity) or
irradiance of a light source.
* A
spectrophotometer measures the spectral
reflectance,
transmittance, or relative irradiance of a color sample.
[
* A ''color temperature meter'' measures the color temperature of an incident illuminant.
]
Tristimulus colorimeter
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 ...
, colorimeters are tristimulus devices used for color calibration. Accurate color profiles ensure consistency throughout the imaging workflow, from acquisition to output.
Spectroradiometer, spectrophotometer, spectrocolorimeter
The absolute spectral power distribution of a light source can be measured with a ''spectroradiometer'', which works by optically collecting the light, then passing it through a monochromator
A monochromator is an optics, optical device that transmits a mechanically selectable narrow band of wavelengths of light or other radiation chosen from a wider range of wavelengths available at the input. The name is .
Uses
A device that can ...
before reading it in narrow bands of wavelength.
Reflected color can be measured using a ''spectrophotometer'' (also called ''spectroreflectometer'' or ''reflectometer''), which takes measurements in the visible region (and a little beyond) of a given color sample. If the custom of taking readings at 10 nanometer increments is followed, the visible light range of 400–700 nm will yield 31 readings. These readings are typically used to draw the sample's spectral reflectance curve (how much it reflects, as a function of wavelength)—the most accurate data that can be provided regarding its characteristics.
The readings by themselves are typically not as useful as their tristimulus values, which can be converted into chromaticity co-ordinates and manipulated through color space transformations. For this purpose, a ''spectrocolorimeter'' may be used. A spectrocolorimeter is simply a spectrophotometer that can estimate tristimulus values by numerical integration
In analysis, numerical integration comprises a broad family of algorithms for calculating the numerical value of a definite integral.
The term numerical quadrature (often abbreviated to quadrature) is more or less a synonym for "numerical integr ...
(of the color matching functions' inner product
In mathematics, an inner product space (or, rarely, a Hausdorff pre-Hilbert space) is a real vector space or a complex vector space with an operation called an inner product. The inner product of two vectors in the space is a scalar, ofte ...
with the illuminant's spectral power distribution).[ One benefit of spectrocolorimeters over tristimulus colorimeters is that they do not have optical filters, which are subject to manufacturing variance, and have a fixed spectral transmittance curve—until they age. On the other hand, tristimulus colorimeters are purpose-built, cheaper, and easier to use.][ Sparser measurements fail to accurately characterize spiky emission spectra, such as that of the red phosphor of a CRT display, depicted aside.
]
Color temperature meter
Photographers and cinematographer
The cinematographer or director of photography (sometimes shortened to DP or DOP) is the person responsible for the recording of a film, television production, music video or other live-action piece. The cinematographer is the chief of the camera ...
s use information provided by these meters to decide what color balancing should be done to make different light sources appear to have the same color temperature. If the user enters the reference color temperature, the meter can calculate the mired difference between the measurement and the reference, enabling the user to choose a corrective color gel or photographic filter with the closest mired factor.[ The correlated color temperature can be calculated from the tristimulus values by first calculating the chromaticity co-ordinates in the CIE 1960 color space, then finding the closest point on the Planckian locus.
]
See also
* Color science
* Photometry
* Radiometry
Radiometry is a set of techniques for measurement, measuring electromagnetic radiation, including visible light. Radiometric techniques in optics characterize the distribution of the radiation's power (physics), power in space, as opposed to phot ...
References
Further reading
*
*
*
*
* Optronik �
Photometers
An informative brochure with background information and specifications of their equipment.
* Konica Minolta Sensing �
* HunterLab �
FAQ , How to Measure Color of a Sample & Use An Index
A guide to measuring color and appearance of objects. The section provides information on numerical scales and indices that are used throughout the world to remove subjective measurements and assumptions.
* NIST Publication
related to colorimetry
External links
MATLAB toolbox for color science computation and accurate color reproduction (by Jesus Malo and Maria Jose Luque, Universitat de Valencia). It includes CIE standard tristimulus colorimetry and transformations to a number of non-linear color appearance models (CIE Lab, CIE CAM, etc.).
{{Authority control
Color
Physical quantities
Measurement
Radiometry