CMYK color model
Encyclopedia
The CMYK color model is a subtractive
color model, used in color printing
, and is also used to describe the printing process itself. CMYK refers to the four inks used in some color printing: cyan
, magenta
, yellow
, and key (black
). Though it varies by print house, press
operator, press manufacturer and press run, ink is typically applied in the order of the abbreviation.
The "K" in CMYK stands for key since in four-color printing cyan, magenta, and yellow printing plates are carefully keyed or aligned with the key of the black key plate
. Some sources suggest that the "K" in CMYK comes from the last letter in "black" and was chosen because B already means blue. However, this explanation, though plausible and useful as a mnemonic
, is incorrect.
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" brightness
from white.
In additive color
models such as RGB
, white is the "additive" combination of all primary
colored lights, while 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, while black results from a full combination of colored inks. To save money 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.
With CMYK printing, halftoning
(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 human beings perceive
a solid color. Magenta printed with a 20% halftone, for example, produces a pink color, because the eye perceives the tiny magenta large dots and the white paper between the dots as lighter and less saturated than the color of pure magenta ink.
Without halftoning, the three primary process colors could be printed only as solid blocks of color, and therefore could produce only seven colors: the three primaries themselves, plus three complementary colors produced by layering two of the primaries: cyan and yellow produce green, cyan and magenta produce a purplish blue, yellow and magenta produce red (these subtractive complementary colors correspond roughly to the additive primary colors) plus layering all three of them resulting in black. With halftoning, a full continuous range of colors can be produced.
s, the screen for each color is set at a different angle. While the angles depend on how many colors are used and the preference of the press operator, typical CMYK process printing uses any of the following screen angles:
The "black" generated by mixing cyan, magenta and yellow primaries
is unsatisfactory, and so four-color printing uses black ink in addition to the subtractive primaries. Common reasons for using black ink include:
When a very dark area is desirable, 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
. A black made with just CMY inks is sometimes called a composite black or process black.
The amount of black to use to replace amounts of the other ink 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.
printing, in which specific colored inks are used to produce 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, may 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 process printers often have a relatively small color gamut
. Processes such as Pantone
's proprietary six-color (CMYKOG) Hexachrome
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 printers, including desktop models.
Similar to monitors, the inks used in printing produce a colour gamut that is "only a subset of the visible spectrum" although both colour 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 colour modes are being combined in both mediums. When designing items to be printed, designers view the colours which they are choosing on an RGB colour mode (their computer screen), and it is often difficult to visualise the way in which the colour will turn out post printing because of this.
systems, using color profiles that describe the spaces being converted. Nevertheless, the conversions cannot be exact, particularly where these spaces have different gamut
s.
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 ("dot gain
") 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.
Subtractive color
A subtractive color model explains the mixing of paints, dyes, inks, and natural colorants to create a full range of colors, each caused by subtracting some wavelengths of light and reflecting the others...
color model, used in color printing
Color printing
Color printing or Colour printing is the reproduction of an image or text in color...
, and is also used to describe the printing process itself. CMYK refers to the four inks used in some color printing: cyan
Cyan
Cyan from , transliterated: kýanos, meaning "dark blue substance") may be used as the name of any of a number of colors in the blue/green range of the spectrum. In reference to the visible spectrum cyan is used to refer to the color obtained by mixing equal amounts of green and blue light or the...
, magenta
Magenta
Magenta is a color evoked by light stronger in blue and red wavelengths than in yellowish-green wavelengths . In light experiments, magenta can be produced by removing the lime-green wavelengths from white light...
, yellow
Yellow
Yellow is the color evoked by light that stimulates both the L and M cone cells of the retina about equally, with no significant stimulation of the S cone cells. Light with a wavelength of 570–590 nm is yellow, as is light with a suitable mixture of red and green...
, and key (black
Black
Black is the color of objects that do not emit or reflect light in any part of the visible spectrum; they absorb all such frequencies of light...
). Though it varies by print house, press
Printing press
A printing press is a device for applying pressure to an inked surface resting upon a print medium , thereby transferring the ink...
operator, press manufacturer and press run, ink is typically applied in the order of the abbreviation.
The "K" in CMYK stands for key since in four-color printing cyan, magenta, and yellow printing plates are carefully keyed or aligned with the key of the black key plate
Key plate
In printing, a key plate is the plate which prints the detail in an image.When printing color images by combining multiple colors of inks, the colored inks usually do not contain much image detail...
. Some sources suggest that the "K" in CMYK comes from the last letter in "black" and was chosen because B already means blue. However, this explanation, though plausible and useful as a mnemonic
Mnemonic
A mnemonic , or mnemonic device, is any learning technique that aids memory. To improve long term memory, mnemonic systems are used to make memorization easier. Commonly encountered mnemonics are often verbal, such as a very short poem or a special word used to help a person remember something,...
, is incorrect.
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" brightness
Brightness
Brightness is an attribute of visual perception in which a source appears to be radiating or reflecting light. In other words, brightness is the perception elicited by the luminance of a visual target...
from white.
In additive color
Additive color
An additive color model involves light emitted directly from a source or illuminant of some sort. The additive reproduction process usually uses red, green and blue light to produce the other colors. Combining one of these additive primary colors with another in equal amounts produces the...
models such as RGB
RGB color model
The RGB color model is an additive color model in which red, green, and blue light is added together in various ways to reproduce a broad array of colors...
, white is the "additive" combination of all primary
Primary Colors
Primary Colors: A Novel of Politics is a roman à clef, a work of fiction that purports to describe real life characters and events — namely, Bill Clinton's first presidential campaign in 1992...
colored lights, while 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, while black results from a full combination of colored inks. To save money on ink, and to produce deeper black tones, unsaturated
Saturation (color theory)
In colorimetry and color theory, colorfulness, chroma, and saturation are related but distinct concepts referring to the perceived intensity of a specific color. Colorfulness is the degree of difference between a color and gray. Chroma is the colorfulness relative to the brightness of another color...
and dark colors are produced by using black ink instead of the combination of cyan, magenta and yellow.
Halftoning
With CMYK printing, halftoning
Halftone
Halftone is the reprographic technique that simulates continuous tone imagery through the use of dots, varying either in size, in shape or in spacing...
(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 human beings perceive
Color vision
Color vision is the capacity of an organism or machine to distinguish objects based on the wavelengths of the light they reflect, emit, or transmit...
a solid color. Magenta printed with a 20% halftone, for example, produces a pink color, because the eye perceives the tiny magenta large dots and the white paper between the dots as lighter and less saturated than the color of pure magenta ink.
Without halftoning, the three primary process colors could be printed only as solid blocks of color, and therefore could produce only seven colors: the three primaries themselves, plus three complementary colors produced by layering two of the primaries: cyan and yellow produce green, cyan and magenta produce a purplish blue, yellow and magenta produce red (these subtractive complementary colors correspond roughly to the additive primary colors) plus layering all three of them resulting in black. With halftoning, a full continuous range of colors can be produced.
Screen angle
To improve print quality and reduce moiré patternMoiré pattern
In physics, a moiré pattern is an interference pattern created, for example, when two grids are overlaid at an angle, or when they have slightly different mesh sizes.- Etymology :...
s, the screen for each color is set at a different angle. While the angles depend on how many colors are used and the preference of the press operator, typical CMYK process printing uses any of the following screen angles:
| C | 15° | 15° | 105° |
|---|---|---|---|
| M | 75° | 45° | 75° |
| Y | 0° | 0° | 90° |
| K | 45° | 75° | 15° |
Benefits of using black ink
Primary color
Primary colors are sets of colors that can be combined to make a useful range of colors. For human applications, three primary colors are usually used, since human color vision is trichromatic....
is unsatisfactory, and 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 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 serifSerifIn typography, serifs are semi-structural details on the ends of some of the strokes that make up letters and symbols. A typeface with serifs is called a serif typeface . A typeface without serifs is called sans serif or sans-serif, from the French sans, meaning “without”...
s), so to reproduce text or other finely detailed outlines using three inks without slight blurring would require impractically accurate registrationPrinting registrationIn color printing, registration is the method of correlating overlapping colors on one single image. There are many different styles and types of registration, many of which employ the alignment of specific marks.-Purpose:...
.
- A combination of 100% cyan, magenta, and yellow inks soaks the paper with ink, making it slower to dry, and sometimes impractically so. This also can cause the ink to bleed.
- A combination of 100% cyan, magenta, and yellow inks often results in a muddy dark brown color that does not quite appear black. Adding black ink absorbs more light, and yields much darker blacks.
- Using black ink is less expensive than using the corresponding amounts of colored inks.
When a very dark area is desirable, 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 black
Rich black, in printing, is an ink mixture of solid black over one or more of the other CMYK colors, resulting in a darker tone than black ink alone generates in a printing process....
. A black made with just CMY inks is sometimes called a composite black or process black.
The amount of black to use to replace amounts of the other ink is variable, and the choice depends on the technology, paper and ink in use. Processes called under color removal
Under color removal
Ideally, CMY without black should complete the printing process; however, sufficiently pure CMY ink has not been developed, and for this reason, black ink is used to add details and darkness in shadowed areas...
, under color addition
Under color addition
In four-color printing , under color addition is a technique for darkening areas of the printed image by adding colored inks...
, and gray component replacement 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 colorSpot color
In offset printing, a spot color is any color generated by an ink that is printed using a single run.The widely spread offset-printing process is composed of four spot colors: Cyan, Magenta, Yellow, and Key commonly referred to as CMYK...
printing, in which specific colored inks are used to produce 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, may 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 process printers often have a relatively small color gamut
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 circumstance, such as within a given color space or by a...
. Processes such as Pantone
Pantone
Pantone Inc. is a corporation headquartered in Carlstadt, New Jersey, USA. The company is best known for its Pantone Matching System , a proprietary color space...
's proprietary six-color (CMYKOG) Hexachrome
Hexachrome
Hexachrome was a six-color printing process designed by Pantone Inc. In addition to custom CMYK inks, Hexachrome added orange and green inks to expand the color gamut, for better color reproduction. It was therefore also known as a CMYKOG process....
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
CcMmYK color model
CcMmYK, sometimes referred to as CMYKLcLm, is a six color printing process used in some inkjet printers optimized for photo printing. It extends the customary four color CMYK process, which stands for Cyan, Magenta, Yellow and Key , by adding light cyan and light magenta...
, with the addition of light cyan and magenta inks to CMYK, can solve these problems, and such a process is used by many inkjet printers, including desktop models.
Comparison with RGB displays
Comparisons between RGB displays and CMYK prints can be difficult, since the color reproduction technologies and properties are so different. A computer monitor mixes shades of red, green, and blue to create color pictures. A CMYK printer instead uses light-absorbing cyan, magenta and yellow inks, whose colors are mixed using dithering, halftoning, or some other optical technique.Similar to monitors, the inks used in printing produce a colour gamut that is "only a subset of the visible spectrum" although both colour 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 colour modes are being combined in both mediums. When designing items to be printed, designers view the colours which they are choosing on an RGB colour mode (their computer screen), and it is often difficult to visualise the way in which the colour will turn out post printing because of this.
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 managementColor management
In digital imaging systems, color management is the controlled conversion between the color representations of various devices, such as image scanners, digital cameras, monitors, TV screens, film printers, computer printers, offset presses, and corresponding media.The primary goal of color...
systems, using color profiles that describe the spaces being converted. Nevertheless, the conversions cannot be exact, particularly where these spaces have different gamut
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 circumstance, such as within a given color space or by a...
s.
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 ("dot gain
Dot gain
Dot gain 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 and the final printed result...
") 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.
See also
- HexachromeHexachromeHexachrome was a six-color printing process designed by Pantone Inc. In addition to custom CMYK inks, Hexachrome added orange and green inks to expand the color gamut, for better color reproduction. It was therefore also known as a CMYKOG process....
- Spot colorSpot colorIn offset printing, a spot color is any color generated by an ink that is printed using a single run.The widely spread offset-printing process is composed of four spot colors: Cyan, Magenta, Yellow, and Key commonly referred to as CMYK...
- CcMmYK color modelCcMmYK color modelCcMmYK, sometimes referred to as CMYKLcLm, is a six color printing process used in some inkjet printers optimized for photo printing. It extends the customary four color CMYK process, which stands for Cyan, Magenta, Yellow and Key , by adding light cyan and light magenta...
- Grey component replacementGrey component replacementWithin the CMY color space, any hue angle can be achieved by combining two of the three primaries. The intention of the third color is to move that hue towards grey , and is known as the greying agent. However, as that greying agent has an inherent hue of its own, it also shifts the hue as it...
- Under color removalUnder color removalIdeally, CMY without black should complete the printing process; however, sufficiently pure CMY ink has not been developed, and for this reason, black ink is used to add details and darkness in shadowed areas...
- Under color additionUnder color additionIn four-color printing , under color addition is a technique for darkening areas of the printed image by adding colored inks...
- Rich blackRich blackRich black, in printing, is an ink mixture of solid black over one or more of the other CMYK colors, resulting in a darker tone than black ink alone generates in a printing process....
- Jacob Christoph Le BlonJacob Christoph Le BlonJacob Christoph Le Blon, or Jakob Christoffel Le Blon, was a German painter and engraver who invented the system of three- and four-colour printing, using an RYBK color model similar to the modern CMYK system.[2] He used the mezzotint method to engrave three or four metal plates to make prints...
- SWOP CMYK standard
- RGBY
External links
- XCmyk—CMYK to RGB Calculator with source code
- Color Space Fundamentals—animated illustration of RGB vs. CMYK
- Color Separation Process—animation and activity
- Four Colour Process (CMYK) explained—basic explanation for novice print-buyers, including animated demonstration