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The CMYK color model (also known as process color, or four color) is a subtractive
color model A color model is an abstract mathematical model describing the way colors can be represented as tuples of numbers, typically as three or four values or color components. When this model is associated with a precise description of how the compon ...
, based on the
CMY color model The CMYK color model (also known as process color, or four color) is a subtractive color model, based on the CMY color model, used in color printing, and is also used to describe the printing process itself. The abbreviation ''CMYK'' refers ...
, used in
color printing Color printing or colour printing is the reproduction of an image or text in color (as opposed to simpler black and white or monochrome printing). Any natural scene or color photograph can be optically and physiologically dissected into thre ...
, and is also used to describe the printing process itself. The abbreviation ''CMYK'' refers to the four ink plates used: cyan, magenta, yellow, and key (black). The CMYK model works by partially or entirely masking colors on a lighter, usually white, background. The ink reduces the light that would otherwise be reflected. Such a model is called ''subtractive'' because inks "subtract" the colors red, green and blue from white light. White light minus red leaves cyan, white light minus green leaves magenta, and white light minus blue leaves yellow. In
additive color Additive color or additive mixing is a property of a color model that predicts the appearance of colors made by coincident component lights, i.e. the perceived color can be predicted by summing the numeric representations of the component colo ...
models, such as
RGB The RGB color model is an additive color model in which the red, green and blue primary colors of light are added together in various ways to reproduce a broad array of colors. The name of the model comes from the initials of the three addi ...
, white is the "additive" combination of all
primary Primary or primaries may refer to: Arts, entertainment, and media Music Groups and labels * Primary (band), from Australia * Primary (musician), hip hop musician and record producer from South Korea * Primary Music, Israeli record label Works ...
colored lights, black is the absence of light. In the CMYK model, it is the opposite: white is the natural color of the paper or other background, black results from a full combination of colored inks. To save cost on ink, and to produce deeper black tones, unsaturated and dark colors are produced by using black ink instead of the combination of cyan, magenta, and yellow.


Halftoning

With CMYK printing, ''
halftoning Halftone is the reprographic technique that simulates continuous-tone imagery through the use of dots, varying either in size or in spacing, thus generating a gradient-like effect.Campbell, Alastair. The Designer's Lexicon. ©2000 Chronicle, ...
'' (also called ''screening'') allows for less than full saturation of the primary colors; tiny dots of each primary color are printed in a pattern small enough that humans perceive a solid color. Magenta printed with a 20% halftone, for example, produces a pink color, because the eye perceives the tiny magenta dots on the large white paper as lighter and less saturated than the color of pure magenta ink. Halftoning allows for a continuous variability of each color, which enables continuous color mixing of the primaries. Without halftoning, each primary would be binary, i.e. on/off, which only allows for the
reproduction Reproduction (or procreation or breeding) is the biological process by which new individual organisms – "offspring" – are produced from their "parent" or parents. Reproduction is a fundamental feature of all known life; each individual or ...
of seven colors: the three primaries, three secondaries and gray/black.


Comparison to CMY

The CMYK color model, is based on the CMY color model, which omits the black ink. However, the imperfect black generated by mixing commercially practical cyan, magenta, and yellow inks is unsatisfactory, so four-color printing uses black ink in addition to the subtractive primaries. Common reasons for using black ink include: * In traditional preparation of color separations, a red
keyline A keyline, in graphic design, is a boundary line that separates color and monochromatic areas or differently colored areas of printing on a given page or other printed piece. The line itself, usually consisting of a black (or other dark colored) ...
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. * Text is typically printed in black and includes fine detail (such as
serif In typography, a serif () is a small line or stroke regularly attached to the end of a larger stroke in a letter or symbol within a particular font or family of fonts. A typeface or "font family" making use of serifs is called a serif typeface ...
s). To avoid even slight blurring when reproducing text (or other finely detailed outlines) using three inks would require impractically accurate 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 Newsprint is a low-cost, non-archival paper consisting mainly of wood pulp and most commonly used to print newspapers and other publications and advertising material. Invented in 1844 by Charles Fenerty of Nova Scotia, Canada, it usually has a ...
) weakening the paper so much that it tears. * Although a combination of 100% cyan, magenta, and yellow inks should, in theory, completely absorb the entire
visible spectrum The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is called '' visible light'' or simply light. A typical human eye will respond to ...
of light and produce a perfect black, practical inks fall short of their ideal characteristics, and the result is actually a dark muddy color that does not quite appear 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''. 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 Rich may refer to: Common uses * Rich, an entity possessing wealth * Rich, an intense flavor, color, sound, texture, or feeling ** Rich (wine), a descriptor in wine tasting Places United States * Rich, Mississippi, an unincorporated comm ...
''. 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 In printing, under color removal (UCR) is a process of eliminating overlapping yellow, magenta, and cyan that would have added to a dark neutral (black) and replacing them with black ink only, called a ''Full Black'', during the color separatio ...
,
under color addition In four-color printing (or more), under color addition (UCA) is a technique for darkening areas of the printed image by adding colored inks. It is meant to achieve the same results as under color removal, but from a different starting position. U ...
, and
gray component replacement Within the CMY color space used in color printing, a range of colors can be achieved by combining the three primary colors. This combination can be thought of as a hue component (which will require a maximum of two primary colors) and a grey comp ...
are used to decide on the final mix; different CMYK recipes will be used depending on the printing task.


Other printer color models

CMYK or process color printing is contrasted with
spot color In offset printing, a spot color or solid color is any color generated by an ink (pure or mixed) that is printed using a ''single run'', whereas a process color is produced by printing a series of dots of different colors. The widespread offset ...
printing, in which specific colored inks are used to generate the colors appearing on paper. Some printing presses are capable of printing with both four-color process inks and additional spot color inks at the same time. High-quality printed materials, such as marketing brochures and books, often include photographs requiring process-color printing, other graphic effects requiring spot colors (such as metallic inks), and finishes such as varnish, which enhances the glossy appearance of the printed piece. CMYK are the process printers which often have a relatively small color
gamut In color reproduction, including computer graphics and photography, the gamut, or color gamut , is a certain ''complete subset'' of colors. The most common usage refers to the subset of colors which can be accurately represented in a given circ ...
. Processes such as
Pantone Pantone LLC (stylized as PANTONE) is a limited liability company headquartered in Carlstadt, New Jersey. The company is best known for its Pantone Matching System (PMS), a proprietary color space used in a variety of industries, notably graphi ...
's proprietary six-color (CMYKOG)
Hexachrome Hexachrome is a discontinued six-color printing process designed by Pantone Inc. In addition to custom CMYK inks, Hexachrome uses orange and green inks to expand the color gamut for better color reproduction. It is therefore also known as a CMYKOG p ...
considerably expand the gamut. Light, saturated colors often cannot be created with CMYK, and light colors in general may make visible the halftone pattern. Using a CcMmYK process, with the addition of light cyan and magenta inks to CMYK, can solve these problems, and such a process is used by many
inkjet Inkjet printing is a type of computer printing that recreates a digital image by propelling droplets of ink onto paper and plastic substrates. Inkjet printers were the most commonly used type of printer in 2008, and range from small inexpens ...
printers, including desktop models.


Comparison with RGB displays

Comparisons between
RGB The RGB color model is an additive color model in which the red, green and blue primary colors of light are added together in various ways to reproduce a broad array of colors. The name of the model comes from the initials of the three addi ...
displays and CMYK prints can be difficult, since the color reproduction technologies and properties are very different. A computer monitor mixes shades of red, green, and blue light to create color pictures. A CMYK printer instead uses light-absorbing cyan, magenta, and yellow inks, whose colors are mixed using
dithering Dither is an intentionally applied form of noise used to randomize quantization error, preventing large-scale patterns such as color banding in images. Dither is routinely used in processing of both digital audio and video data, and is often ...
,
halftoning Halftone is the reprographic technique that simulates continuous-tone imagery through the use of dots, varying either in size or in spacing, thus generating a gradient-like effect.Campbell, Alastair. The Designer's Lexicon. ©2000 Chronicle, ...
, or some other optical technique. Similar to monitors, the inks used in printing produce a color gamut that is "only a subset of the visible spectrum" although both color modes have their own specific ranges. As a result of this, items which are displayed on a computer monitor may not completely match the look of items which are printed if opposite color modes are being combined in both mediums. When designing items to be printed, designers view the colors which they are choosing on an RGB color mode (their computer screen), and it is often difficult to visualize the way in which the color will turn out post-printing because of this.


Spectrum of printed paper

To reproduce color, the CMYK color model codes for absorbing light rather than emitting it (as is assumed by RGB). The "K" component absorbs all wavelengths and is therefore achromatic. The cyan, magenta, and yellow components are used for color reproduction and they may be viewed as the inverse of RGB. Cyan absorbs red, magenta absorbs green, and yellow absorbs blue (-R,-G,-B).


Conversion

Since RGB and CMYK spaces are both device-dependent spaces, there is no simple or general conversion formula that converts between them. Conversions are generally done through
color management In digital imaging systems, color management (or colour management) is the controlled conversion between the color representations of various devices, such as image scanners, digital cameras, monitors, TV screens, film printers, computer printer ...
systems, using
color profile In color management, an ICC profile is a set of data that characterizes a color input or output device, or a color space, according to standards promulgated by the International Color Consortium (ICC). Profiles describe the color attributes of a ...
s that describe the spaces being converted. An ICC profile defines the bidirectional conversion between a neutral "profile connection" color space (CIE XYZ or Lab) and a colorspace we are interested in, in this case both RGB and CMYK. The precision of the conversion depends on the profile itself, the exact methodology, and because the
gamut In color reproduction, including computer graphics and photography, the gamut, or color gamut , is a certain ''complete subset'' of colors. The most common usage refers to the subset of colors which can be accurately represented in a given circ ...
s do not generally match, the
rendering intent In digital imaging systems, color management (or colour management) is the controlled conversion between the color representations of various devices, such as image scanners, digital cameras, monitors, TV screens, film printers, computer printe ...
and constraints such as ink limit. ICC profiles, internally built out of lookup tables and other transformation functions, are capable of handling many effects of ink blending. One example is the
dot gain Dot gain, or tonal value increase, is a phenomenon in offset lithography and some other forms of printing which causes printed material to look darker than intended. It is caused by halftone dots growing in area between the original printing film ...
, which show up as non-linear components in the color-to-density mapping. More complex interactions such as ''Neugebauer'' blending can be modelled in higher-dimension lookup tables. The problem of computing a colorimetric estimate of the color that results from printing various combinations of ink has been addressed by many scientists. A general method that has emerged for the case of halftone printing is to treat each tiny overlap of color dots as one of 8 (combinations of CMY) or of 16 (combinations of CMYK) colors, which in this context are known as '' Neugebauer primaries''. The resultant color would be an area-weighted colorimetric combination of these primary colors, except that the ''Yule–Nielsen'' effect of scattered light between and within the areas complicates the physics and the analysis; empirical formulas for such analysis have been developed, in terms of detailed dye combination absorption spectra and empirical parameters. Standardization of printing practices allow for some profiles to be predefined. One of them is the US
Specifications for Web Offset Publications Specifications for Web Offset Publications, invariably abbreviated to SWOP, is an organization and the name of a set of specifications that it produces, with the aim of improving the consistency and quality of professionally printed material in t ...
(SWOP), which has its ICC color profile built into many software including
Microsoft Office Microsoft Office, or simply Office, is the former name of a family of client software, server software, and services developed by Microsoft. It was first announced by Bill Gates on August 1, 1988, at COMDEX in Las Vegas. Initially a marketin ...
(as Agfa RSWOP.icm).


See also

*
CMY color model The CMYK color model (also known as process color, or four color) is a subtractive color model, based on the CMY color model, used in color printing, and is also used to describe the printing process itself. The abbreviation ''CMYK'' refers ...
*
CcMmYK color model CcMmYK, sometimes referred to as CMYKLcLm or CMYKcm, is a six-color printing process used in some inkjet printers optimized for photo printing. It complements the more common four color CMYK process, which stands for Cyan, Magenta, Yellow and K ...
*
Cycolor Cycolor is a tradename for a color printing process that uses a special film coated with millions of capsules filled with cyan, magenta, or yellow dyeprecursors, acrylic monomer, and photo-initiators. When exposed to red, green, and/or blue lig ...
*
RGB color model The RGB color model is an additive color model in which the red, green and blue primary colors of light are added together in various ways to reproduce a broad array of colors. The name of the model comes from the initials of the three ad ...
* Grey component replacement *
Jacob Christoph Le Blon Jacob Christoph Le Blon, or Jakob Christoffel Le Blon, (2 May 1667 – 16 May 1741) was a painter and engraver from Frankfurt who invented the system of three- and four-colour printing, using an RYB color model which segued into the modern CMY ...
* SWOP CMYK standard *
Color management In digital imaging systems, color management (or colour management) is the controlled conversion between the color representations of various devices, such as image scanners, digital cameras, monitors, TV screens, film printers, computer printer ...


References


External links


XCmyk
�� CMYK to RGB Calculator with source code

�� animated illustration of RGB vs. CMYK {{Photography Color space Printing Printing terminology