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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)
Different saturation levels in an image

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 colorâ€”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. ...

### 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.

Results from FactBites:

 color theory (1156 words) Color theory is an immensely complicated subject, and is understood differently by scientists, printers, web designers and painters. Colors are classified by three properties: hue, purity and value — terms that are often misunderstood. Warm colors lie at the orange-red end of the spectrum, and are 'active', causing them to 'advance'.
 Basic color schemes: Color Theory Introduction (803 words) Colors that are opposite each other on the color wheel are considered to be complementary colors (example: red and green). Analogous color schemes are often found in nature and are harmonious and pleasing to the eye. The split-complementary color scheme is a variation of the complementary color scheme.
More results at FactBites »

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