Chromaticity is an objective specification of the quality of a

color Color (American English) or colour (British English) is the visual perceptual property deriving from the spectrum of light interacting with the photoreceptor cells of the eyes. Color categories and physical specifications of color are assoc ...

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 In color theory, hue is one of the main properties (called color appearance parameters) of a color, defined technically in the CIECAM02 model as "the degree to which a stimulus can be described as similar to or different from stimuli that ...

(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 Excitation, excite, exciting, or excitement may refer to: * Excitation (magnetic), provided with an electrical generator or alternator * Excite Ballpark, located in San Jose, California * Excite (web portal), web portal owned by IAC * Electron ex ...

. This number of parameters follows from

trichromacy Trichromacy or trichromatism is the possessing of three independent channels for conveying color information, derived from the three different types of cone cells in the eye. Organisms with trichromacy are called trichromats. The normal expla ...

of vision of most humans, which is assumed by most models in

color science Color science is the scientific study of color including lighting and optics; measurement of light and color; the physiology, psychophysics, and modeling of color vision; and color reproduction. History Organizations * International Commi ...

Quantitative description

In color science, 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 ...

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 In mathematics, the polar coordinate system is a two-dimensional coordinate system in which each point on a plane is determined by a distance from a reference point and an angle from a reference direction. The reference point (analogous to t ...

. 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 Saturation, saturated, unsaturation or unsaturated may refer to: Chemistry * Saturation, a property of organic compounds referring to carbon-carbon bonds **Saturated and unsaturated compounds **Degree of unsaturation **Saturated fat or fatty acid ...

" in the HSV color model. The property "

" is as used in general color theory and in specific

color model A color model is an abstract mathematical model describing the way colors can be represented as tuples of numbers, typically as three or four values or color components. When this model is associated with a precise description of how the compo ...

s 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, RGB color model, designed in the 1970s by computer graphics res ...

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 confusi ...

CIECAM02 In colorimetry, CIECAM02 is the color appearance model published in 2002 by the International Commission on Illumination (CIE) Technical Committee 8-01 (''Color Appearance Modelling for Color Management Systems'') and the successor of CIECAM97s. ...

. Some

color space A color space is a specific organization of colors. In combination with color profiling supported by various physical devices, it supports reproducible representations of colorwhether such representation entails an analog or a digital representa ...

s 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 In mathematics, an affine space is a geometric structure that generalizes some of the properties of Euclidean spaces in such a way that these are independent of the concepts of distance and measure of angles, keeping only the properties relate ...

on a

triangle A triangle is a polygon with three edges and three vertices. It is one of the basic shapes in geometry. A triangle with vertices ''A'', ''B'', and ''C'' is denoted \triangle ABC. In Euclidean geometry, any three points, when non- colli ...

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 systems on the same X-Y-Z triangle, or other

color triangle A color triangle is an arrangement of colors within a triangle, based on the additive combination of three primary colors at its corners. An additive color space defined by three primary colors has a chromaticity gamut that is a colo ...

s, can be used. On the other hand, some color spaces such as

RGB The RGB color model is an additive color model in which the red, green and blue primary colors of light are added together in various ways to reproduce a broad array of colors. The name of the model comes from the initials of the three additiv ...

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 Division or divider may refer to: Mathematics *Division (mathematics), the inverse of multiplication *Division algorithm, a method for computing the result of mathematical division Military * Division (military), a formation typically consisting ...

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