In
colorimetry, the CIE 1976 ''L''*, ''u''*, ''v''* color space, commonly known by its abbreviation CIELUV, is a
color space adopted by the
International Commission on Illumination (CIE) in 1976, as a simple-to-compute transformation of the 1931
CIE XYZ color space
The CIE 1931 color spaces are the first defined quantitative links between distributions of wavelengths in the electromagnetic visible spectrum, and physiologically perceived colors in human color vision. The mathematical relationships that defi ...
, but which attempted
perceptual uniformity. It is extensively used for applications such as computer graphics which deal with colored lights. Although additive mixtures of different colored lights will fall on a line in CIELUV's uniform
chromaticity diagram (called the ''CIE 1976 UCS''), such additive mixtures will not, contrary to popular belief, fall along a line in the CIELUV color space unless the mixtures are constant in
lightness.
Historical background
CIELUV is an
Adams chromatic valence color space and is an update of the
CIE 1964 (''U''*, ''V''*, ''W''*) color space (CIEUVW). The differences include a slightly modified
lightness scale and a modified uniform chromaticity scale, in which one of the coordinates, ''v''′, is 1.5 times as large as ''v'' in its
1960 predecessor. CIELUV and
CIELAB were adopted simultaneously by the CIE when no clear consensus could be formed behind only one or the other of these two color spaces.
CIELUV uses Judd-type (translational)
white point adaptation (in contrast with CIELAB, which uses a
"wrong" Kries transform). This can produce useful results when working with a single illuminant, but can predict
imaginary color
Impossible colors are colors that do not appear in ordinary visual functioning. Different color theories suggest different hypothetical colors that humans are incapable of perceiving for one reason or another, and fictional colors are rou ...
s (i.e., outside the
spectral locus
A spectral color is a color that is evoked by ''monochromatic light'', i.e. either a single wavelength of light in the visible spectrum, or by a relatively narrow band of wavelengths (e.g. lasers). Every wavelength of visible light is percei ...
) when attempting to use it as a
chromatic adaptation transform.
[Mark D. Fairchild, ''Color Appearance Models''. Reading, MA: Addison-Wesley, 1998.] The translational adaptation transform used in CIELUV has also been shown to perform poorly in predicting corresponding colors.
[D. H. Alman, R. S. Berns, G. D. Snyder, and W. A. Larson, "Performance testing of color difference metrics using a color-tolerance dataset". ''Color Research and Application'', 21:174–188 (1989).]
XYZ → CIELUV and CIELUV → XYZ conversions
For typical images, ''u''* and ''v''* range ±100 %. By definition, .
The forward transformation
CIELUV is based on CIEUVW and is another attempt to define an encoding with uniformity in the perceptibility of
color differences.
[ The non-linear relations for ''L''*, ''u''*, and ''v''* are given below:]
:
The quantities ''u''′''n'' and ''v''′''n'' are the chromaticity coordinates of a "specified white object" – which may be termed the white point – and ''Y''''n'' is its luminance. In reflection mode, this is often (but not always) taken as the of the perfect reflecting diffuser under that illuminant. (For example, for the 2° observer and standard illuminant C, , .) Equations for ''u''′ and ''v''′ are given below:[''Colorimetry,'' second edition: CIE publication 15.2. Vienna: Bureau Central CIE, 1986.][
:
]
The reverse transformation
The transformation from to is:[
:
The transformation from CIELUV to XYZ is performed as follows:][
:
]
Cylindrical representation (CIELCh)
CIELChuv, or HCL color space (hue–chroma–luminance) is increasingly seen in the information visualization community as a way to help with presenting data without the bias implicit in using varying saturation.
The cylindrical version of CIELUV is known as CIELChuv, or CIELChuv, CIELCh(uv) or CIEHLCuv, where ''C''*''uv'' is the chroma and ''h''''uv'' is the hue:[
:
:
where atan2 function, a "two-argument arctangent", computes the ]polar
Polar may refer to:
Geography
Polar may refer to:
* Geographical pole, either of two fixed points on the surface of a rotating body or planet, at 90 degrees from the equator, based on the axis around which a body rotates
*Polar climate, the cli ...
angle from a Cartesian coordinate pair.
Furthermore, the saturation correlate can be defined as
:
Similar correlates of chroma and hue, but not saturation, exist for CIELAB. See Colorfulness for more discussion on saturation.
Color and hue difference
The color difference can be calculated using the Euclidean distance of the coordinates. It follows that a chromaticity distance of corresponds to the same Δ''E''*''uv'' as a lightness difference of , in direct analogy to CIEUVW.
The Euclidean metric can also be used in CIELCh, with that component of Δ''E''*''uv'' attributable to difference in hue as[ , where .
]
See also
* YUV
* CIELAB color space
References
External links
Chromaticity diagrams, including the CIE 1931, CIE 1960, CIE 1976
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.).
{{Color space
Color space
1976 introductions