Chromaticity is an objective specification of the quality of a color regardless of its

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 withi ...

. Chromaticity consists of two independent parameters, often specified as hue (h) and

colorfulness Colorfulness, chroma and saturation are attributes of perceived color relating to chromatic intensity. As defined formally by the International Commission on Illumination (CIE) they respectively describe three different aspects of chromatic ...

(s), where the latter is alternatively called saturation, chroma, intensity, or excitation purity. This number of parameters follows from trichromacy of vision of most humans, which is assumed by most models in color science.

Quantitative description

In color science, the white point of an illuminant or of a display is a neutral reference characterized by a chromaticity; all other chromaticities may be defined in relation to this reference using polar coordinates. The ''hue'' is the angular component, and the ''purity'' is the radial component, normalized by the maximum radius for that hue. Purity is roughly equivalent to the term " saturation" in the HSV color model. The property " hue" is as used in general color theory and in specific color models such as

HSV and HSL HSL (for hue, saturation, lightness) and HSV (for hue, saturation, value; also known as HSB, for hue, saturation, brightness) are alternative representations of the RGB color model, designed in the 1970s by computer graphics researchers to more ...

color spaces, though it is 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 gre ...

in color models such as Munsell,

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 confusion ...

or CIECAM02. Some color spaces separate the three dimensions of color into one

dimension and a pair of chromaticity dimensions. For example, the white point of an

sRGB sRGB is a standard RGB (red, green, blue) color space that HP and Microsoft created cooperatively in 1996 to use on monitors, printers, and the World Wide Web. It was subsequently standardized by the International Electrotechnical Commission ( ...

display is an , chromaticity of (0.3127, 0.3290), where and coordinates are used in the xyY space. These pairs determine a chromaticity as affine coordinates on a triangle in a 2D-space, which contains all possible chromaticities. These and are used because of simplicity of expression in

CIE 1931 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 defin ...

(see below) and have no inherent advantage. Other

coordinate system In geometry, a coordinate system is a system that uses one or more numbers, or coordinates, to uniquely determine the position of the points or other geometric elements on a manifold such as Euclidean space. The order of the coordinates is sig ...

s on the same X-Y-Z triangle, or other color triangles, can be used. On the other hand, some color spaces such as RGB and XYZ do not separate out chromaticity, but chromaticity is defined by a mapping that normalizes out intensity, and its coordinates, such as and or and , can be calculated through the division operation, such as , and so on. The xyY space is a cross between the CIE XYZ and its normalized chromaticity coordinates xyz, such that the luminance Y is preserved and augmented with just the required two chromaticity dimensions.

References

External links

* Stanford University CS 17
interactive Flash demo
explaining chromaticity diagrams.
JOES application software for calculation and plotting of CIE 1931 and 1976 from spectra
ref name=joes> {{color topics Color Photometry

Quantitative description

See also

References

External links