Editing Subtractive color

{{Short description|Light passing through successive filters}}
{{More footnotes|date=January 2012}}
[[File:SubtractiveColor.svg|thumb|Subtractive color mixing]]
[[File:Duhauron1877.jpg|thumb|200px|An 1877 color photo by [[Louis Ducos du Hauron]], a French pioneer of [[color photography]]. The overlapping subtractive yellow, cyan and red (magenta) image elements can be seen clearly along the edges of the image.]]

'''Subtractive color''' or '''subtractive color mixing''' predicts the [[spectral power distribution]] of light after it passes through successive layers of partially absorbing media. This idealized model is the essential principle of how [[dye]]s and [[pigment]]s are used in color printing and photography, where the perception of [[color]] is elicited after white light passes through microscopic "stacks" of partially absorbing media, allowing some wavelengths of [[light]] to reach the eye and not others. It is also a concept seen in painting, wherein the colors are mixed or applied in successive layers.

== Process ==
The subtractive color mixing model predicts the resultant [[spectral power distribution]] of light filtered through overlaid partially absorbing materials on a reflecting or transparent surface. Each layer partially absorbs some wavelengths of light from the illumination spectrum while letting others pass through, resulting in a colored appearance. The resultant spectral power distribution is predicted by sequentially taking the product of the spectral power distributions of the incoming light and transmissivity at each filter.<ref>{{cite web |last1=Levoy |first1=Marc |title=Additive versus subtractive color mixing |url=https://graphics.stanford.edu/courses/cs178-10/applets/colormixing.html |website=graphics.stanford.edu |access-date=4 November 2020 |quote="On the other hand, if you reflect light from a colored surface, or if you place a colored filter in front of a light, then some of the wavelengths present in the light may be partially or fully absorbed by the colored surface or filter. If we characterize the light as an SPD, and we characterize absorption by the surface or filter using a spectrum of reflectivity or transmissivity, respectively, i.e. the percentage of light reflected or transmitted at each wavelength, then the SPD of the outgoing light can be computed by multiplying the two spectra. This multiplication is (misleadingly) called subtractive mixing."}}</ref>

== Painting ==
The subtractive model also predicts the color resulting from a mixture of paints, or similar medium such as fabric dye, whether applied in layers or mixed together prior to application. In the case of paint mixed before application, incident light interacts with many different pigment particles at various depths inside the paint layer before emerging.<ref>{{cite book |last1=Williamson |first1=Samuel J |last2=Cummins |first2=Herman Z |title=Light and Color in Nature and Art |date=1983 |publisher=John Wiley & Sons, Inc. |location=New York |isbn=0-471-08374-7 |pages=28–30 |quote="Thus subtractive color mixing laws that successfully describe how light is altered by nonspectral filters also describes how light is altered by pigments."}}</ref> Art supply manufacturers offer colors that successfully fill the roles of the subtractive primary colors magenta and cyan. For example, [[copper phthalocyanine|the phthalocyanine blues]], which became available during the 1930s, and [[quinacridone]] magenta, first offered during the 1950s, together with yellow produce more highly-saturated violets and greens than do the traditional red and blue.

== RYB ==
{{Main|RYB color model}}
[[File:BYR color wheel.svg|thumb|left|An RYB color wheel]]

RYB (red, yellow, blue) is the traditional set of primary colors used for mixing pigments. It is used in art and art education, particularly in [[painting]]. It predated modern scientific [[color theory]].

Red, yellow, and blue are the primary colors of the RYB [[color wheel|color "wheel"]]. The secondary colors, violet (or purple), orange, and green (VOG) make up another triad, conceptually formed by mixing equal amounts of red and blue, red and yellow, and blue and yellow, respectively.

[[File:Pigment Colours - Classification.jpg|thumb|Classification of pigment colors]]

The RYB primary colors became the foundation of 18th-century theories of color vision as the fundamental sensory qualities blended in the perception of all physical colors and equally in the physical mixture of pigments or dyes. These theories were enhanced by 18th-century investigations of a variety of purely psychological color effects, in particular, the contrast between "complementary" or opposing hues produced by color afterimages and in the contrasting shadows in colored light. These ideas and many personal color observations were summarized in two founding documents in color theory: the ''[[Theory of Colours]]'' (1810) by the German poet and government minister [[Johann Wolfgang von Goethe]], and ''The Law of Simultaneous Color Contrast'' (1839) by the French industrial chemist [[Michel Eugène Chevreul]].

In late 19th and early to mid-20th-century commercial printing, use of the traditional RYB terminology persisted even though the more versatile CMY (cyan, magenta, yellow) triad had been adopted, with the cyan sometimes referred to as "process blue" and the magenta as "process red".

== CMY and CMYK color models and printing processes ==
{{Main|CMY color model|CMYK color model}}
[[File:CMY.jpg|Cyan, magenta and yellow color filters|thumb]]

In [[color printing]], the usual primary colors are [[cyan]], [[magenta]] and [[yellow]] (CMY). Cyan is the complement of red, meaning that the cyan serves as a filter that absorbs red. The amount of cyan ink applied to a white sheet of paper controls how much of the red light in white light will be reflected back from the paper. Ideally, the cyan ink is completely transparent to green and blue light and has no effect on those parts of the [[visible spectrum|spectrum]]. Magenta is the complement of [[green]], and yellow the complement of [[blue]]. Combinations of different amounts of the three inks can produce a wide range of colors with good [[saturation (color theory)|saturation]].

In [[inkjet printing|inkjet color printing]] and typical [[mass production]] [[lithography|photomechanical printing processes]], a black ink K (Key) component is included, resulting in the [[CMYK color model]]. The black ink serves to cover unwanted tints in dark areas of the printed image, which result from the imperfect transparency of commercially practical CMY inks; to improve image sharpness, which tends to be degraded by imperfect registration of the three color elements; and to reduce or eliminate consumption of the more expensive color inks where only black or gray is required.

Purely [[color photography|photographic color processes]] almost never include a K component, because in all common processes the CMY dyes used are much more perfectly transparent, there are no registration errors to camouflage, and substituting a black dye for a saturated CMY combination, a trivial prospective cost-benefit at best, is technologically impractical in non-electronic [[analog photography]].

==See also==
* [[Additive color]]
* [[Color mixing]]
* [[Color motion picture film]]
* [[Color space]]
* [[Color theory]]
* [[Primary color]]

== References ==
{{Reflist}}

== Further reading ==
* {{Cite book |last=Berns |first=Roy S. |year=2000 |title=Billmeyer and Saltzman's Principles of Color Technology |edition=3rd |location=New York |publisher=Wiley |isbn=0-471-19459-X}}
* {{Cite book |last1=Stroebel |first1=Leslie |last2=John |first2=Compton |last3=Ira |first3=Current |last4=Richard |first4=Zakia |year=2000 |title=Basic Photographic Materials and Processes |edition=2nd |location=Boston |publisher=Focal Press |isbn=0-240-80405-8}}
* {{Cite book |author1=Wyszecki, Günther |author2=W. S. Stiles |name-list-style=amp |year=1982 |title=Color Science: Concept and Methods, Quantitative Data and Formulae |location=New York |publisher=Wiley |isbn=0-471-02106-7}}

==External links==
{{Commons category|Subtractive colors}}
* Stanford University CS 178 [http://graphics.stanford.edu/courses/cs178/applets/colormixing.html interactive Flash demo] comparing additive and subtractive color mixing.

{{Color topics}}

[[Category:Color]]
[[Category:Color space]]