The CIE 1964 (''U''*, ''V''*, ''W''*) color space, also known as CIEUVW, is based on the CIE 1960 UCS: :

U^*=13W^*(u-u_0), \quad V^*=13W^*(v-v_0), \quad W^*=25Y^\frac13-17

where is the

white point A white point (often referred to as reference white or target white in technical documents) is a set of tristimulus values or chromaticity coordinates that serve to define the color "white" in image capture, encoding, or reproduction. Depending ...

and ''Y'' is the luminous tristimulus value of the object. The asterisks in the exponent indicates that the variable represent a more

perceptually uniform In color science, color difference or color distance is the separation between two colors. This metric allows quantified examination of a notion that formerly could only be described with adjectives. Quantification of these properties is of great ...

color space than its predecessor (compare with

CIELAB The CIELAB color space, also referred to as ''L*a*b*'' , is a color space defined by the International Commission on Illumination (abbreviated CIE) in 1976. (Referring to CIELAB as "Lab" without asterisks should be avoided to prevent confusio ...

). Wyszecki invented the UVW color space in order to be able to calculate

color difference In color science, color difference or color distance is the separation between two colors. This metric allows quantified examination of a notion that formerly could only be described with adjectives. Quantification of these properties is of great ...

s without having to hold the

luminance Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through, is emitted from, or is reflected from a particular area, and falls with ...

constant. He defined a

lightness Lightness is a visual perception of the luminance (L) of an object. It is often judged relative to a similarly lit object. In colorimetry and color appearance models, lightness is a prediction of how an illuminated color will appear to a stan ...

index ''W''* by simplifying expressions suggested earlier by Ladd and Pinney, and Glasser ''et al.''. The chromaticity components ''U''* and ''V''* are defined such that the white point maps to the origin, as in

Adams chromatic valence color space Adams chromatic valence color spaces are a class of color spaces suggested by Elliot Quincy Adams. Two important Adams chromatic valence spaces are CIELUV and Hunter Lab. Chromatic value/valence spaces are notable for incorporating the opponent pro ...

s. This arrangement has the benefit of being able to express the loci of chromaticities with constant saturation simply as 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 is kept constant".

Chromaticity and color difference

The chromaticity coefficients were chosen "on the basis of the spacing of the Munsell system. A lightness difference is assumed to correspond to a chromaticness difference (approximately)." ''Note:'' The asterisks are not used in the paper. With the coefficients thus selected, the

in CIEUVW is simply the

Euclidean distance In mathematics, the Euclidean distance between two points in Euclidean space is the length of a line segment between the two points. It can be calculated from the Cartesian coordinates of the points using the Pythagorean theorem, therefore ...

: :

\Delta E_\text=\sqrt

References

{{color-stub Color space