The CIE 1964 (U*, V*, W*) color space, also known as CIEUVW, is based on the CIE 1960 UCS:[1]
- Failed to parse (Missing texvc executable; please see math/README to configure.): U^*=13W^*(u-u_0), \quad V^*=13W^*(v-v_0), \quad W^*=25Y^{1/3}-17
where (u0, v0) is the white point and Y is the luminous tristimulus value of the object. The asterisks in the exponent indicates that the variable represent a more perceptually uniform color space than its predecessor (compare with CIELAB).
Wyszecki invented the UVW color space in order to be able to calculate color differences without having to hold the luminance constant. He defined a lightness index W* by simplifying expressions suggested earlier by Ladd and Pinney,[2] and Glasser et al..[3] The chromaticity components U* and V* are defined such that the white point maps to the origin, as in Adams chromatic valence color spaces. This arrangement has the benefit of being able to express the loci of chromaticities with constant saturation simply as (U*)2 + (V*)2 = C for a constant C. Furthermore, the chromaticity axes are scaled by the lightness "so as to account for the apparent increase or decrease in saturation when the lightness index is increased or decreased, respectively, and the chromaticity (u, v) is kept constant".[4]
Chromaticity and color difference [link]
The chromaticity co-efficients were chosen "on the basis of the spacing of the Munsell system. A lightness difference ΔW = 1 is assumed to correspond to a chromatic-ness difference Failed to parse (Missing texvc executable; please see math/README to configure.): \sqrt{\Delta U^2 +\Delta V^2} = 13
(approximately)."[4]
With the co-efficients thus selected, the color difference in CIEUVW is simply the Euclidean distance:
Failed to parse (Missing texvc executable; please see math/README to configure.): \Delta E_{CIEUVW}=\sqrt{ (\Delta U^*)^2 + (\Delta V^*)^2 + (\Delta W^*)^2}
References [link]
- ^ Janos Schanda (2007). Colorimetry: Understanding the CIE System. Wiley Interscience. p. 81.
- ^ Ladd, J.H.; Pinney, J.E. (September 1955). "Empirical relationships with the Munsell Value scale". Proceedings of the Institute of Radio Engineers 43 (9): 1137. DOI:10.1109/JRPROC.1955.277892.
- ^ Glasser, L.G.; A.H. McKinney, C.D. Reilly, and P.D. Schnelle (October 1958). "Cube-root color coordinate system". JOSA 48 (10): 736–740. DOI:10.1364/JOSA.48.000736. https://www.opticsinfobase.org/abstract.cfm?URI=josa-48-10-736.
- ^ a b Wyszecki, Günther (November 1963). "Proposal for a New Color-Difference Formula". Journal of the Optical Society of America (JOSA) 53 (11): 1318–1319. DOI:10.1364/JOSA.53.001318. https://www.opticsinfobase.org/josa/abstract.cfm?URI=josa-53-11-1318. Note: The asterisks are not used in the paper.
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Color space
A color space is a specific organization of colors. In combination with physical device profiling, it allows for reproducible representations of color, in both analog and digital representations. A color space may be arbitrary, with particular colors assigned to a set of physical color swatches and corresponding assigned names or numbers such as with the Pantone system, or structured mathematically, as with Adobe RGB or sRGB. A color model is an abstract mathematical model describing the way colors can be represented as tuples of numbers (e.g. triples in RGB or quadruples in CMYK); however, a color model with no associated mapping function to an absolute color space is a more or less arbitrary color system with no connection to any globally understood system of color interpretation. Adding a specific mapping function between a color model and a reference color space establishes within the reference color space a definite "footprint", known as a gamut, and for a given color model this defines a color space. For example, Adobe RGB and sRGB are two different absolute color spaces, both based on the RGB color model. When defining a color space, the usual reference standard is the CIELAB or CIEXYZ color spaces, which were specifically designed to encompass all colors the average human can see.
International Commission on Illumination
The International Commission on Illumination (usually abbreviated CIE for its French name, Commission internationale de l'éclairage) is the international authority on light, illumination, colour, and colour spaces. It was established in 1913 as a successor to the Commission Internationale de Photométrie and is today based in Vienna, Austria. The President from 2015 is Yoshihiro Ohno from the US.
Organization
The CIE has eight divisions, each of which establishes technical committees to carry out its program under the supervision of the division's director:
