Editing CMYK color model (section)

== Comparison to CMY <span class="anchor" id="Why black ink is used"></span><span class="anchor" id="CMY"></span>==
[[File:Barns grand tetons.jpg|thumb]]
{{multiple image|width=197|image1=CMY separation – no black.jpg|image2=CMYK separation – maximum black.jpg|197|footer=The image above, (left) separated for printing with process cyan, magenta, and yellow (CMY) inks, and (right) separated for CMY and black (K)}}
[[File:CMYK offset on paper2.jpg|thumb|Inspection [[CMYK]] colors of offset printing on a paper]]

The CMYK color model is based on the CMY color model, which omits the black ink. Four-color printing uses black ink in addition to subtractive primaries for several reasons:<ref>{{cite book |author=Roger Pring |url=https://archive.org/details/wwwcolor00prin |title=WWW.Color |publisher=Watson–Guptill |year=2000 |isbn=0-8230-5857-3 |page=178 |url-access=registration}}</ref>

* In traditional preparation of color separations, a red [[keyline]] on the black line art marked the outline of solid or tint color areas. In some cases a black keyline was used when it served as both a color indicator and an outline to be printed in black because usually the black plate contained the keyline. The ''K'' in ''CMYK'' represents the keyline, or black, plate, also sometimes called the ''key plate''.<ref>{{cite web|url=https://gizmodo.com/the-difference-between-rgb-and-cmyk-explained-1777830600|title=The Difference Between RGB and CMYK, Explained|last=Menegus|first=Bryan|website=[[Gizmodo]]|date=May 20, 2016|access-date=October 4, 2020}}</ref>
* Text is typically printed in black and includes fine detail (such as [[serif]]s). To avoid even slight blurring when reproducing text (or other finely detailed outlines) using three inks would require impractically accurate [[printing registration|registration]].
* A combination of 100% cyan, magenta, and yellow inks soaks the paper with ink, making it slower to dry, causing bleeding, or (especially on low-quality paper such as [[newsprint]]) weakening the paper so much that it tears.{{citation needed|date=October 2020}}
* Although a combination of 100% cyan, magenta, and yellow inks would, in theory, completely absorb the entire [[visible spectrum]] of light and produce a perfect black, practical inks fall short of their ideal characteristics, and the result is a dark, muddy color that is not quite black. Black ink absorbs more light and yields much better blacks. 
* Black ink is less expensive than the combination of colored inks that makes black.

A black made with just CMY inks is sometimes called a ''composite black''.<ref>{{cite book|url=https://books.google.com/books?id=3iuwCgAAQBAJ&pg=PA331|page=331|title=Forensic Chemistry: Fundamentals and Applications|last=Sigel|first=Jay A.|publisher=John Wiley & Sons|year=2015|isbn=978-1-118-89772-0}}</ref>

When a very dark area is wanted, a colored or gray CMY "bedding" is applied first, then a full black layer is applied on top, making a rich, deep black; this is called ''[[rich black]]''.<ref>{{cite book |title=The Guild Handbook of Scientific Illustration |author=R. S. Hodges|url=https://books.google.com/books?id=YWaOBSjevD0C&pg=PA242|page=242|year=2003|publisher=John Wiley and Sons |isbn=0-471-36011-2 }}</ref>

The amount of black to use to replace amounts of the other inks is variable, and the choice depends on the technology, paper and ink in use. Processes called ''[[under color removal]]'', ''[[under color addition]]'', and ''[[gray component replacement]]'' are used to decide on the final mix; different CMYK recipes will be used depending on the printing task.<ref>{{cite book|url=https://books.google.com/books?id=VrdqBRgSKasC&pg=PA87|page=87|title=Handbook of Print Media: Technologies and Production Methods|editor-last=Kipphan|editor-first=Helmut|publisher=Springer|year=2001|isbn=3-540-67326-1}}</ref>