Editing Primary color (section)

=== Subtractive models ===
{{See also|CMYK color model}}
[[File:SubtractiveColor.svg|thumb|Subtractive primary color model]]
[[File:Halftoningcolor.svg|thumb|upright=1.4|A magnified representation of small partially overlapping spots of cyan, magenta, yellow, and key (black) [[halftone]]s in [[CMYK]] process printing. Each row represents the pattern of partially overlapping ink "rosettes" so that the patterns would be perceived as blue, green, and red when viewed on white paper from a typical viewing distance. The overlapping ink layers mix subtractively while additive mixing predicts the color appearance from the light reflected from the rosettes and white paper in between them.]]

The [[subtractive color]] mixing model predicts the resultant spectral power distribution of light filtered through overlaid partially absorbing materials, usually in the context of an underlying reflective surface such as white paper.<ref name="Williamson1983"/>{{rp|22–23}}<ref>{{cite book |last1=Berns |first1=Roy S. |title=Billmeyer and Saltzman's Principles of Color Technology |date=9 April 2019 |publisher=John Wiley & Sons |isbn=978-1-119-36722-2 |pages=195–209 |url=https://books.google.com/books?id=8GGLDwAAQBAJ |language=en}}</ref> Each layer partially absorbs some wavelengths of light from the illumination while letting others pass through, resulting in a colored appearance. The resultant spectral power distribution is predicted by the wavelength-by-wavelength product of the spectral reflectance of the illumination and the product of the spectral reflectances of all of the layers.<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> Overlapping layers of ink in printing mix subtractively over reflecting white paper, while the reflected light mixes in a partitive way to generate color images.<ref name="Williamson1983"/>{{rp|30–33}}<ref>{{cite journal |last1=Kuehni |first1=Rolf |title=Color mixture |journal=Scholarpedia |date=2011 |volume=6 |issue=1 |pages=10686 |doi=10.4249/scholarpedia.10686|bibcode=2011SchpJ...610686K |doi-access=free }}</ref> Importantly, unlike additive mixture, the color of the mixture is not well predicted by the colors of the individual dyes or inks. The typical number of inks in such a printing process is 3 (CMY) or 4 ([[CMYK]]), but can commonly range to 6 (e.g., [[hexachrome|Pantone hexachrome]]). In general, using fewer inks as primaries results in more economical printing but using more may result in better color reproduction.<ref>{{cite book |last1=Sharma |first1=Abhay |title=Understanding color management |date=2018 |location=Hoboken, NJ |isbn=9781119223634 |page=235 |edition=2nd}}</ref>

[[Cyan]] (C), [[magenta]] (M), and [[yellow]] (Y) are good chromatic subtractive primaries in that filters with those colors can be overlaid to yield a surprisingly large chromaticity gamut.<ref>{{cite book |last1=Westland |first1=Stephen |last2=Cheung |first2=Vien |editor1-last=Chen |editor1-first=Janglin |editor2-last=Cranton |editor2-first=Wayne |editor3-last=Fihn |editor3-first=Mark |title=Handbook of visual display technology |date=2012 |publisher=Springer |location=Cham, Switzerland |isbn=978-3-540-79567-4 |page=155 |edition=2nd|quote="The optimum primaries of the subtractive color system are cyan, magenta, and yellow. The use of cyan, magenta, and yellow subtractive primaries allows a surprisingly large – albeit limited – gamut of colors to be reproduced."}}</ref> A black (K) ink (from the older "[[key plate]]") is also used in CMYK systems to augment C, M and Y inks or dyes: this is more efficient in terms of time and expense and less likely to introduce visible defects.<ref>{{cite web |last1=Poynton |first1=Charles |title=Color FAQ - Frequently Asked Questions Color |url=https://poynton.ca/notes/colour_and_gamma/ColorFAQ.html#RTFToC25 |website=poynton.ca | quote=Printing black by overlaying cyan, yellow and magenta ink in offset printing has three major problems. First, coloured ink is expensive. Replacing coloured ink by black ink – which is primarily carbon – makes economic sense. Second, printing three ink layers causes the printed paper to become quite wet. If three inks can be replaced by one, the ink will dry more quickly, the press can be run faster, and the job will be less expensive. Third, if black is printed by combining three inks, and mechanical tolerances cause the three inks to be printed slightly out of register, then black edges will suffer coloured tinges. Vision is most demanding of spatial detail in black and white areas. Printing black with a single ink minimizes the visibility of registration errors. |access-date=27 April 2021}}</ref> Before the color names ''cyan'' and ''magenta'' were in common use, these primaries were often known as blue and red, respectively, and their exact color has changed over time with access to new pigments and technologies.<ref>{{cite book
| title     = General Physics and Its Application to Industry and Everyday Life
| author    = Ervin Sidney Ferry
| publisher = John Wiley & Sons
| year      = 1921
| url       = https://books.google.com/books?id=3rYXAAAAIAAJ&q=date:0-1923+additive+color+mixing+primary&pg=PA621
}}</ref> Organizations such as [[Fogra]],<ref>{{cite web |title=FOGRA characterization data |url=https://www.color.org/chardata/fogra.xalter |website=International Color Consortium |access-date=26 April 2021}}</ref> [[European Color Initiative]] and [[Specifications for Web Offset Publications|SWOP]] publish [[colorimetry|colorimetric]] CMYK standards for the printing industry.<ref>{{cite book |last1=Homann |first1=Jan-Peter |title=Digital color management : principles and strategies for the standardized print production |date=2009 |publisher=Springer |location=Berlin |isbn=9783540693772}}</ref>
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