# Color saturation

The CIE standard color table shows low color saturation in the center, increasing towards the outside

The color saturation (also brilliance, degree of color, chroma, degree of chroma, chromaticity, colourfulness, color intensity, color strength, color depth, intensity, purity, degree of purity, saturation) is a color characteristic . In addition to hue and lightness , saturation is one of the three characteristics or properties of a color that people perceive to be fundamental . It describes the quality of the color nuance, whether it tends towards bright or achromatic colors. The opposite of high color saturation describes the gray cast or dullness.

• Achromatic colors are white , black and their mixtures in different shades of gray . Their color saturation is zero, they leave no color impression and are without any color cast .
• Colorful colors are colors with a colorful effect, i.e. colors that clearly differ from black, white and neutral gray .
• Pure colors are colors with maximum color saturation. The purest colors are the spectral colors .

Contrary to the general use of languages in the chromatics white, gray and black as "colors". In order to differentiate these from the bright colors, they are called the achromatic colors. Black and white are called pure, achromatic colors or pure non-colors. All colors that do not belong to black, white or shades of gray are indicated as "colorful", which everyday language calls "colored".

## Basics

A color can be clearly described in a color model by specifying the three color characteristics hue, lightness and saturation . If they are quantified , the Cartesian product of all possible values spans a three-dimensional space, the color space .

In principle, the axes can be placed anywhere in the color space. The axis of the hue is determined by the main wavelength that occurs. The axis of brightness is set quite plausibly as a physical measurement of the luminous flux . The choice of the third axis, which describes the color saturation, is not so easy and there are different definitions depending on the color model. In addition, some effects of color perception come into play that go beyond the three-dimensional model. A five-dimensional color perception model would be required which includes the background lighting ( ambient contrast ) and the total incidence of light or (more correctly) the adaptation of the eye .

### Measured values ​​in color spaces

#### Hue, hue ( hue )

This component is primarily based on the color names , which describe the type of color perception in terms. On the basis of the color wheel , verbal designations can also be represented alphanumerically , as in Munsell's system .

#### Saturation ( saturation )

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The saturation describes “how strongly a colored stimulus differs from an achromatic stimulus regardless of its brightness”, that is, its distance from the achromatic axis (black-white axis). This means that all color tones (hues) have a saturation of up to 100%, and white, gray and black a saturation of 0.

Use:

#### Colorfulness ( chroma )

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The chroma describes the relative color effect in relation to reference white , i.e. in comparison to a certain brightest point in a color space . The chroma is suitable as a measured value for conical color spaces, for example, where measurements can be made from the tip. These systems are useful in printing, where paper white is the neutral color and just as much paint is necessary for rich black as for rich red. White has a chroma of 0, the hues (hues) and deep black up to 100%, medium gray 50%. Use:

#### Chromaticity ( chromaticity )

The CIE color model speaks explicitly of English chromaticity (as a chromaticity diagram for the CIE standard color table, the well-known xy “shoe soles” image), so that there is also German chromaticity for this . The expression is intended to be differentiated from the general English expression chroma for 'colorful, colored'. Since the xy diagram is a projection of the color space along the black and white axis, the distance to the achromatic point and that to the white point coincide because they are projected onto the same x / y coordinate - this point is usually shown in white in diagrams , it is therefore a view of the color space "from above", not a section along the xy plane of the CIE model. So here white and the color tones (hues) have a chroma of 100% and black a chroma of 0. The white point is therefore in the middle of the color wheel.

#### Gray component (gray tint, grayness )

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The gray component (gray tint) is the shift of a color location in the direction of the gray point ; it indicates how much a color is "desaturated" in gray . Here all colors (hues), white as well as black have a gray component of 0, and gray of 100%. In this respect, white and black are just as intense color perceptions as red or blue.

This measured value is therefore particularly suitable for spherical models and is the distance to the center of the sphere: Colors with the same gray component have the same "gray cast", regardless of whether they are white, black or a hue. However, since different color models apply different scales to the black and white axis, the gray point, the "middle" between black and white, is of a different color brightness in the various models. Such possible scalings are photometric or visual, linear or logarithmic (following the Weber-Fechner law ) or brightness values ​​approximated by powers. These models meet different requirements of applications for a neutral gray .

The gray value can be specified for a single color as a vector or globally as a vector field : This is used, for example, in image processing for color correction or gamut matching , the adaptation of the available colors to the colors that can be displayed.

### Values ​​of color perception

The following terms go beyond a purely three-dimensional color model and deal with color perception of a color in the context of an environment and the subtleties of the visual system .

#### Colourfulness or color intensity

The colourfulness or color intensity , also known as colorfulness or chromaticness in English , is the perceived chroma and represents an expanded concept of saturation.

With increasing luminance , the impression of saturation also increases - illuminated surfaces appear more colorful than when there is little light, although measured as being equally saturated (dark colors appear more colorful than light, equally saturated), conversely, when there is insufficient lighting, any ability to perceive chromaticity disappears ( dark vision , "At night all the cats are grey").

${\ displaystyle \ mathrm {S {\ ddot {a}} saturation} = {\ frac {\ text {Colorfulness}} {\ text {relative brightness}}} = {\ frac {\ text {Colorfulness}} {\ text {Brightness}}}}$
relative brightness is the colorimetric brightness , brightness is the photometric brightness

The saturation can be described with a definition that goes back to Manfred Richter . According to this, the saturation is the chromatic component of the overall color impression. Eva Lübbe converted this definition into the following formula, which has been proven experimentally to match the visual impression of saturation.

${\ displaystyle S = {\ frac {C} {\ sqrt {C ^ {2} + L ^ {2}}}} \, 100 \, \%}$

With

${\ displaystyle S}$: Saturation,
${\ displaystyle L}$: Brightness,
${\ displaystyle C}$: Chroma, colorfulness
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However, blue tones - with the same colorimetric saturation and the same lighting - appear significantly darker than other color tones . By nature, yellow looks particularly bright. In order to achieve visually uniform scales, colorant-oriented systems therefore use concepts of color effect that depend on the photometric saturation and the hue.

Use:

#### Color depth

Also known as color depth , brilliance ( brilliance ) and color purity ( hue purity referred).

The color depth describes the apparent saturation of real colorants in the application and is a measure of how strongly the color strength (coloring power) of the agent affects the application of color. The sheer thickness of the layer of paint itself affects the color as well as the shining through of the surface. Some oil paints from the tube appear dull or simply black and only show their color strength when they are finely painted ( wash colors ). The same goes for watercolors . This phenomenon can also be found in Chinese ink painting , where even with (saturated) black inks , the finest color casts of the colorant in the wash and the interaction with the paintwork create an enormous color effect.

The color effect is a consequence of the spectral distribution ; different spectra can definitely achieve the same color impression. As a result, body colors are no longer subject to a theoretical additive color mixture; two highly colorful, beautiful pigments can be mixed together to produce an astonishingly cloudy color. Brilliance is a measure of the spectral distribution - in relation to color, color purity is the portion of the spectrum that is attributable to the frequency of the same spectral color: the more brilliant the spectrum, the more saturated the color, and the more suitable these pigments or dyes are for saturated and color-pure mixing with each other.

In addition, there are numerous other effects that influence the color effect of colored surfaces. Shine depends on the directed light from point-like light sources, which are created on shiny surfaces or transparent materials by reflecting the light source or refraction of light. For this reason, for example, varnished oil paintings appear more colorful than those without a top coat and wet surfaces more colorful than dry ones. Effects such as the depth of light (reflections from the inside of the color body) also come into play, which is supported in the painting technique by careful ("old master") painting layers. This technique experienced a heyday of the intensely colored pictures, even though they were painted in broken - achromatic - colors in the Renaissance and Baroque periods, as in the Dutch around Rembrandt , or the sfumato of da Vinci, hence the expression. These effects disappear in reproductions of such objects; they can only be seen in the original.

## Applications

Levels of saturation, increasing from bottom left to top to bottom right: a black and white image at the bottom left, an exaggerated color image at the right

### Colorfulness in everyday life

In not particularly precise expression, “colorful” - in addition to “multicolored” - also means “with high color depth” in common parlance. Achromatic means "not colored" and is not used in everyday language. The color gray is imprecisely referred to as “ colorless ”, black is equated with “ dark ” and white is assumed to be the usual color of the background (which should be ignored).

In the context of the restrictions imposed on the use of colorants, pigments of abnormally high saturation, such as Prussian blue and carmine, are referred to as “highly colored”. These colors cannot be reproduced correctly either by printing or on screens .

In the context of the expression "brilliance", saturated or brightly colored surfaces, color-intensive luminous colors , deep- colored signal colors and shiny surfaces with gloss varnish or effect pigments ( pearlescent , metallic ), as well as generally illuminated and self-luminous surfaces in the general understanding are "luminous", "colorful", " colored "or" colorful ", also" neon colors ". All in all, all these color impressions set the surface apart from its surroundings and are advantageous in security and advertising . The technical development and the resulting possibilities led to something like an "inflation of colourfulness", which consequently requires new colorants or technical effects.

### Photography and cinematography

In analogue recording technology, the photographer can only intervene to a limited extent in the color saturation at the time of recording ; Optical filters such as skylight or polarizing filters are aids here . In digital recording technology, on the other hand, the color saturation can be varied at the time of recording. A color-neutral image is only obtained in the raw data format , while the camera electronics are otherwise without exception already processing images.

### Image editing, desktop publishing and printing

Because the three dimensions of hue, saturation and brightness simulate human color vision much better than, for example, the RGB color system or YUV color system , which is decisive in electronic-optical representation, and the CMYK color system of printing, image processing only works with HSV systems to post-process images.

Color spaces are ideal structures and are limited by the technical possibilities of color display on screens and monitors or in print . Therefore, in the high-end sector, it is essential to take into account the maximum color saturation of the display, gamut matching - but this also fluctuates depending on the color.

• In general, saturated color tones cannot be represented optically and technically, and green tones are much more difficult than red and blue tones. The wide-gamut RGB triangle given in the input image, which represents the saturation range of a modern monitor, and its color differences to the edge of the CIE diagram (i.e. the most saturated color tones) represent what is technically feasible against the performance of the human eye.
• The problem with color display with monitors is that the green and red illuminants far surpass the blue in terms of color effect . On CRT monitors , this was corrected by the higher energy density of the cathode ray. The development of flat screens ( LED screens ) only became possible in the 1990s with the development of highly brilliant blue LEDs; suitable red and green LEDs had been around since the 1960s.
• Usual screens work on the basis of an RGB space (red, green, blue). Yellow, turquoise (cyan) and magenta are "mixed" by activating two pixels; these are twice as bright , but less saturated - the visual perception system compensates for this somewhat with the consequent higher (visual) color (color intensity). In printing, the pigments for cyan, magenta and yellow (CMY) are the basic colors, for this purpose red, green and blue are only "mixed" and technically, in the case of high demands, six-color printing or spot colors are used to compensate for the necessary highly saturated colors.

### Printing and painting media

Solid colors are colors with the maximum representable color saturation or chroma, both in the absolute colorimetrically sense, and in printing, where they are used as decorative colors , or as tinting colors with high tinting power in paints .

### Aging

Almost all colorants age, for example dyes and pigments through chemical decomposition or screens through constant stimulation. As a result, the pure (emitted or remitted) light yield decreases and, in particular, the saturation becomes increasingly lower.

Because screens are based on additive color mixing, i.e. the color saturation is a direct consequence of the emitted light, only the absolute saturation decreases, but not the relative to maximum white (color). Aging screens therefore become “dull” overall. However, the three colorants of the pixel basic colors age at different rates; these deviations are hardly noticeable in the case of commercial goods during their service life - in the critical commercial sector, however, they are regularly recalibrated .

In painting and printing, aging is directly dependent on the colorants; each one loses its color differently. Colorants are not only more valuable the more brilliant they are fresh, but also how long they last. The green chlorophyll or the chemically related red hemoglobin , but also cinnabar, would be extremely rich colorants, but they “age” to brown within a short time due to oxidation processes. On the other hand, iron oxide pigments hardly age , but are only slightly saturated in color .

In the history of painting, one was always looking for brilliant and stable pigments, which is why precious stones were often pulverized into colorants. Like lapis lazuli , a color-rich pigment that has only rarely been surpassed to this day. Other little aging, high color-saturated colorants are gold leaf and other percussion metals , highly toxic to good part of pigments, such as arsenic Schweinfurt green (arsenic), orange-red lead-containing red lead , lead and chromium containing chromium yellow and -red and red to yellow cadmium colors .

In addition, many colorants are not resistant to other influences, such as UV radiation or acids and bases . In the case of historical pictures, an estimate of the original color effect is actually only possible in the fresco , where a reduced set (church painter's palette) of chemically stable pigments could be used. Michelangelo's blaze of color, which was evident during the pioneering restoration of the Sixtine, is surprising . After around 150 years of colorant development, colorants such as cobalt pigments (blue to green), Hansa yellow , spinel and rutile mixed-phase oxide pigments (green / blue, yellow), phthalocyanines (blue to green, related to chlorophyll and hemoglobin) or pyrrole pigments ( red) and quinacridones (yellow, orange, red to magenta) a whole range of highly brilliant and stable colorants are available.

Commons : colorful  - collection of images, videos and audio files

## Individual evidence

1. Definition: Zwisler, Farbe after Wyszecki and Stiles (1982, p. 487) (May 10, 2006)
2. Rainer Zwisler: Color Perception. Physical and physiological basics. Special phenomena . Retrieved May 10, 2006
3. Zwiesler, Color (May 10, 2006)
4. Eva Lübbe: Color in the head - color systems in reality . Muster-Schmidt Gleichen, Zurich 2008, ISBN 978-3-7881-4057-1 .
5. Coloroid system. In: virtual color museum. echo productions, archived from the original on November 28, 2007 ; accessed on March 15, 2010 (English).
6. NCS Color Center for the UK and Ireland: Explanations of terms relating to the Natural Color System: Chromaticness ( Memento of March 31, 2012 in the Internet Archive )
7. MacEvoy gives a detailed definition of the term. (May 10, 2006)
8. the secret of glowing color . Handprint
9. hue purity of watercolor paints . Handprint
10. a b Fig. CIELAB estimates of chroma and hue purity in color making attributes → optimal color stimuli . Handprint
(1) These scales are numerically homogeneous, the fluctuations between the color tones are due to the effects described in the article
(2) Neutral gray of a standard monitor gamma
(3) Numerical neutral gray