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Encyclopedia > Saturation (color theory)
It has been suggested that this article or section be merged with Chromaticity. (Discuss)
Scale of saturation (0% at bottom)
Scale of saturation (0% at bottom)
Different saturation levels in an image
Different saturation levels in an image

In color theory, saturation or purity is the intensity of a specific hue. It is based on the color's purity; a highly saturated hue has a vivid, intense color, while a less saturated hue appears more muted and grey. With no saturation at all, the hue becomes a shade of grey. Saturation is one of three coordinates in the HSL color space and the HSV color space. Wikipedia does not have an article with this exact name. ... Chromaticity is the quality of a color as determined by its purity and dominant wavelength. ... Image File history File links Author: Coyne Tibbets (CoyneT), 03/18/2005 Description: This image shows a scale of saturation from 0% (at the bottom) to 100%. When there is 0% saturation, the color appears grey. ... Image File history File links Author: Coyne Tibbets (CoyneT), 03/18/2005 Description: This image shows a scale of saturation from 0% (at the bottom) to 100%. When there is 0% saturation, the color appears grey. ... Image File history File linksMetadata Download high resolution version (800x899, 141 KB) Summary Saturation of an image altered in photoshop. ... Image File history File linksMetadata Download high resolution version (800x899, 141 KB) Summary Saturation of an image altered in photoshop. ... In the arts of painting, web design, and photography, color theory is a set of basic rules for mixing color to achieve a desired result. ... e gradation of color; for the city in Vietnam, see Huế. A hue refers to the gradation of color within the optical spectrum, or visible spectrum, of light. ... ... The HSL color space, also called HLS or HSI, stands for Hue, Saturation, Lightness (also Luminance or Luminosity) / Intensity. ... The HSV (Hue, Saturation, Value) model, also called HSB (Hue, Saturation, Brightness), defines a color space in terms of three constituent components: HSV color space as a color wheel Hue, the color type (such as red, blue, or yellow): Ranges from 0-360 (but normalized to 0-100% in some...


The saturation of a color is determined by a combination of light intensity and how much it is distributed across the spectrum of different wavelengths. The purest colour is achieved by using just one wavelength at a high intensity such as in laser light. If the intensity drops the saturation also drops. To desaturate a color in a subtractive system (such as watercolor), the person can add white, black, gray, or the hue's complement. Subtractive color explains the theory of mixing paints, dyes, inks, and natural colorants to create colors which absorb some wavelengths of light and reflect others. ... Watercolor is a painting technique making use of water-soluble pigments that are either transparent or opaque and are formulated with gum to bond the pigment to the paper. ... White is a color, (more accurately it contains all the colors of the visible spectrum and is sometimes described as an achromatic color—black is the absence of color) that has high brightness but zero hue. ... Black is a color with several subtle differences in meaning. ... Gray or grey is a color seen commonly in nature. ... Complementary colors are pairs of colors that are in some way opposites of each other. ...

Contents


Purity in CIE 1931 XYZ color space

In the CIE XYZ color space, the purity or saturation is the Euclidean distance between the position of the color (x,y) and the illuminant's white point (xI,yI) on the CIE xy projective plane, divided by the same distance for a pure (monochromatic, or dichromatic on the purple line) color with the same hue (xP,yP) = ρmax(xxI,yyI) + (xI,yI) : In the study of the perception of color, one of the first mathematically defined color spaces was the CIE XYZ color space (also known as CIE 1931 color space), created by the International Commission on Illumination (CIE) in 1931. ... In mathematics, Euclidean geometry is the familiar kind of geometry on the plane or in three dimensions. ... A white point is one of a number of reference illuminants used in colorimetry which serve to define the color white. Depending on the application, different definitions of white are needed to give acceptable results. ... Something which is monochromatic has a single color. ...

p = sqrt{frac{(x - x_{I})^2 + (y - y_{I})^2}{(x - x_{P})^2 + (y - y_{P})^2}}

and ρmax maximal within the boundary of the chromaticity diagram.


Saturation in RGB color space

In an RGB color space, saturation can be thought of as the standard deviation & sigma; of the color coordinates R(red), G(green), and B(blue). Letting & mu; represent the brightness, then An RGB color space is any additive color space based on the RGB color model. ... In probability and statistics, the standard deviation is the most common measure of statistical dispersion. ... Brightness is an attribute of visual perception in which a source appears to emit a given amount of light. ...

sigma = sqrt{ (R - mu)^2 + (G - mu)^2 + (B - mu)^2 over 3}.

An example of saturation in layman's terms in the RGB color model is one in which a person has maximum saturation if he or she has 100% brightness in the red channel while having 0% brightness in the other channels; he or she would have no saturation if all the color channels were equal. Thus, saturation is the difference between the values of the channels.


In term of absolute colorimetry, this simple definition in the RGB color space exhibits several problems. The RGB color space is not an absolute colorimetric space; therefore, the value of saturation is arbitrary, depending on the choice of the color primaries and the white point illuminant. For example, the RGB colorspace does not necessarily have an unitary Jacobian in term of absolute colorimetry. Colorimetry is the science that describe colors in numbers, or provides a physical color match using a variety of measurement instruments. ... In vector calculus, the Jacobian is shorthand for either the Jacobian matrix or its determinant, the Jacobian determinant. ...


Chromaticity in CIE 1976 L*a*b* and L*u*v* color spaces

The naïve definition of saturation does not specify its response function. In the CIE XYZ and RGB color spaces, the saturation is defined in terms of additive color mixing and has the property of being proportional to any scaling centered at white or the white point illuminant. However, both color spaces are not linear in term of psychovisually perceived color differences. It is also possible and sometimes desirable to define a saturation-like quantity that is linearized in term of the psychovisual perception.


In the CIE 1976 L*a*b* and L*u*v* color spaces, the unnormalized chromaticity is the radial component of the cylindrical coordinate CIE L*C*h (luminance, chromaticity, hue) representation of the L*a*b* and L*u*v* color spaces, also denoted as CIE L*C*h(a*b*) or CIE L*C*h for short and CIE L*C*h(u*v*). The transformation of (a * ,b * ) to (C * ,h) is given by CIE L*a*b* (CIELAB) is the most complete color model used conventionally to describe all the colors visible to the human eye. ...

C^{*} = sqrt{a^{*2} + b^{*2}}
h = arctan frac{b^{*}}{a^{*}}

and analogously for CIE L*C*h(u*v*).


The chromaticity in the CIE L*C*h(a*b*) and CIE L*C*h(u*v*) coordinates has the advantage of being more psychovisually linear, yet they are non-linear in the in term of linear component color mixing. Therefore, chromaticity in CIE 1976 L*a*b* and L*u*v* color spaces is very different from the traditional sense of "saturation".


Chromaticity in color appearance models

Another, psychovisually even more accurate, more complex method to obtain or specify the saturation is to use the color appearance model, like CIECAM. The chromaticity component of the JCh (lightness, chromaticity, hue) coordinate and becomes a function of parameters like the chrominance and physical brightness of the illumination, or the characteristics of the emitting/reflecting surface, which is also psychovisually more sensible.


See also


  Results from FactBites:
 
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