Chromaticity is an objective specification of the quality of a

color Color (or colour in English in the Commonwealth of Nations, Commonwealth English; American and British English spelling differences#-our, -or, see spelling differences) is the visual perception based on the electromagnetic spectrum. Though co ...

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 wit ...

. Chromaticity consists of two independent parameters, often specified as ''

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

'' (''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 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 ...

''. This number of parameters follows from

trichromacy Trichromacy or trichromatism is the possession 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 expl ...

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

color science Color science is the science, scientific study of color including lighting and optics; Photometry (optics), measurement of light and colorimetry, color; the physiology, psychophysics, and color model, modeling of color vision; and color reproductio ...

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 o ...

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 specifies a given point (mathematics), point in a plane (mathematics), plane by using a distance and an angle as its two coordinate system, coordinates. These are *the point's distance from a reference ...

. 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 ''

'' is as used in general color theory and in specific

color model In color science, 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 ...

s such as

HSL and HSV HSL and HSV are the two most common cylindrical coordinate system, cylindrical-coordinate representations of points in an RGB color model. The two representations rearrange the geometry of RGB in an attempt to be more intuitive and color vision, ...

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 great ...

in color models such as

Munsell Munsell may refer to: * Albert Henry Munsell (1858–1918), American painter, teacher of art, and the inventor of the Munsell color system * Harvey M. Munsell, American soldier in the Civil War. * Munsell Color Company *Munsell color system The ...

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. It expresses color as three values: ''L*'' for perceptual lightness and ''a*'' and ''b* ...

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 Color appe ...

. 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 represe ...

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 (standard RGB) is a colorspace, for use on monitors, printers, and the World Wide Web. It was initially proposed by HP and Microsoft in 1996 and became an official standard of the International Electrotechnical Commission (IEC) as IEC 6 ...

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 related ...

on a

triangle A triangle is a polygon with three corners and three sides, one of the basic shapes in geometry. The corners, also called ''vertices'', are zero-dimensional points while the sides connecting them, also called ''edges'', are one-dimension ...

in a 2D-space, which contains all possible chromaticities. These and are used because of simplicity of expression in CIE 1931 (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 and standardize the position of the points or other geometric elements on a manifold such as Euclidean space. The coordinates are ...

s 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 or subtractive combination of three primary colors at its corners. An additive color space defined by three primary colors has a chromaticity gamut that is ...

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 ...

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