CMYK color model

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CMYK color swatches.svg
Color printing typically uses ink of four colors: cyan, magenta, yellow, and black.
CMYK subtractive color mixing.svg
When CMY “secondary” are combined at full strength, the resulting “primary” mixtures are red, green, and blue. Mixing all three gives an imperfect black or a perfect grey.
CMYK closeup.jpg
CMYK under a microscope.jpg
What appears as cerulean () in the top image is actually a blend of cyan, magenta, yellow and black, as magnification under a microscope demonstrates.

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. CMYK refers to the four ink plates used in some color printing: cyan, magenta, yellow, and key (black).

Contents

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 models, such as RGB, white is the "additive" combination of all primary 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

This diagram shows three examples of color halftoning with CMYK separations, as well as the combined halftone pattern and how the human eye would observe the combined halftone pattern from a sufficient distance. Halftoningcolor.svg
This diagram shows three examples of color halftoning with CMYK separations, as well as the combined halftone pattern and how the human eye would observe the combined halftone pattern from a sufficient distance.

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 humans perceive a solid color. [1] 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.[ citation needed ]

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 secondary colors produced by layering two of the primaries: cyan and yellow produce green, cyan and magenta produce blue, yellow and magenta produce red (these subtractive secondary 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

Typical halftone screen angles. CMYK screen angles.svg
Typical halftone screen angles.

To improve print quality and reduce moiré patterns, 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: [2] [3]

Angles used in CMYK printing
C15°15°105°165°
M75°45°75°45°
Y90°90°
K45°75°15°105°

Benefits of using black ink

A color photograph of the Teton Range. Barns grand tetons.jpg
A color photograph of the Teton Range.
CMY separation - no black.jpg
CMYK separation - maximum black.jpg
The image above, (left) separated for printing with process cyan, magenta, and yellow (CMY) inks; (right) separated for CMY and black (K).
inspection CMYK colors of offset printing on a paper CMYK offset on paper2.jpg
inspection CMYK colors of offset printing on a paper

The "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: [4]

A black made with just CMY inks is sometimes called a composite black. [6]

When a very dark area is wanted, a coloured 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 . [7]

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. [8]

Other printer color models

CMYK or process color printing is contrasted with spot color 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. [9]

CMYK are the process printers which often have a relatively small color gamut. Processes such as Pantone's proprietary six-color (CMYKOG) Hexachrome considerably expand the gamut. [10] 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. [11]

Comparison with RGB displays

Comparison of some RGB and CMYK color gamut on a CIE 1931 xy chromaticity diagram. CIE1931xy gamut comparison.svg
Comparison of some RGB and CMYK color gamut on a CIE 1931 xy chromaticity diagram.

Comparisons between RGB 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, halftoning, or some other optical technique. [12]

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. [13] 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). [14]


Spectrum of the visible wavelengths on printed paper (SCA Graphosilk). Shown is the transition from Red to Yellow. White, red, blue, and green are shown for reference. Readings from a white orchid flower, a rose (red and yellow petals), and a red cyclamen flower are shown for comparison. The units of spectral power are simply raw sensor values (with a linear response at specific wavelengths). CMYK Spectrum printed paper.pdf
Spectrum of the visible wavelengths on printed paper (SCA Graphosilk). Shown is the transition from Red to Yellow. White, red, blue, and green are shown for reference. Readings from a white orchid flower, a rose (red and yellow petals), and a red cyclamen flower are shown for comparison. The units of spectral power are simply raw sensor values (with a linear response at specific wavelengths).

Conversion

Early representation of the three-color process (1902). NIEdot367.jpg
Early representation of the three-color process (1902).

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 systems, using color profiles 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 gamuts do not generally match, the rendering intent 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, 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. [15] 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. [15]

Standardization of printing practices allow for some profiles to be predefined. One of them is the US Specifications for Web Offset Publications (SWOP), which has its ICC color profile built into many software including Microsoft Office (as Agfa RSWOP.icm).[ citation needed ]

See also

Related Research Articles

Cyan Color visible between blue and green; subtractive (CMY) secondary color

Cyan is the color between green and blue on the scale of visible light. It is evoked by light with a predominant wavelength of between 490 and 520 nm, between the wavelengths of green and blue.

Magenta Colour

Magenta is a shade of purple that is variously defined as purplish-red, reddish-purple or mauvish-crimson. On color wheels of the RGB (additive) and CMY (subtractive) color models, it is located exactly midway between red and blue. It is one of the four colors of ink used in color printing by an inkjet printer, along with yellow, black, and cyan, to make all other colors. The tone of magenta used in printing is called "printer's magenta".

Additive color Model for predicting color created by mixing visible light

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 colors. Modern formulations of Grassmann's laws describe the additivity in the color perception of light mixtures in terms of algebraic equations. Additive color predicts perception and not any sort of change in the photons of light themselves. These predictions are only applicable in the limited scope of color matching experiments where viewers match small patches of uniform color isolated against a grey or black background.

Complementary colors pairs of colors

Complementary colors are pairs of colors which, when combined or mixed, cancel each other out by producing a grayscale color like white or black. When placed next to each other, they create the strongest contrast for those two colors. Complementary colors may also be called "opposite colors".

Gamut Color reproduction

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 certain output device.

In the visual arts, color theory is a body of practical guidance to color mixing and the visual effects of a specific color combination. There are also definitions of colors based on the color wheel: primary color, secondary color, and tertiary color. Although color theory principles first appeared in the writings of Leone Battista Alberti and the notebooks of Leonardo da Vinci, a tradition of "colory theory" began in the 18th century, initially within a partisan controversy over Isaac Newton's theory of color and the nature of primary colors. From there it developed as an independent artistic tradition with only superficial reference to colorimetry and vision science.

Subtractive color Model applied in predicting the spectral composition of light reflected from photographic film and color printed paper

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 dyes and inks 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.

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 separation process. Under color removal is used in four-color printing. Black ink used to add details and darkness in shadowed areas is called a Skeletal Black.

RYB color model

RYB is a subtractive color model used in art and applied design in which red, yellow, and blue pigments are considered primary colors. Under traditional color theory, this set of primary colors was advocated by Moses Harris, Michel Eugène Chevreul, Johannes Itten and Josef Albers, and applied by countless artists and designers. The RYB color model underpinned the color curriculum of the Bauhaus, Ulm School of Design and numerous art and design schools that were influenced by the Bauhaus, including the IIT Institute of Design, Black Mountain College, Design Department Yale University, the Shillito Design School, Sydney, and Parsons School of Design, New York.

Color printing or colour printing is the reproduction of an image or text in color. Any natural scene or color photograph can be optically and physiologically dissected into three primary colors, red, green and blue, roughly equal amounts of which give rise to the perception of white, and different proportions of which give rise to the visual sensations of all other colors. The additive combination of any two primary colors in roughly equal proportion gives rise to the perception of a secondary color. For example, red and green yields yellow, red and blue yields magenta, and green and blue yield cyan. Only yellow is counter-intuitive. Yellow, cyan and magenta are merely the "basic" secondary colors: unequal mixtures of the primaries give rise to perception of many other colors all of which may be considered "tertiary."

Secondary color

A secondary color is a color made by mixing of two primary colors in a given color space.

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 components are to be interpreted, the resulting set of colors is called "color space." This section describes ways in which human color vision can be modeled.

Tertiary color

A tertiary color or intermediate color is a color made by mixing full saturation of one primary color with half saturation of another primary color and none of a third primary color, in a given color space such as RGB, CMYK or RYB (traditional).

The Neugebauer equations are a set of equations used to model color printing systems, developed by Hans E. J. Neugebauer. They were intended to predict the color produced by a combination of halftones printed in cyan, magenta, and yellow inks.

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 Key (black), by adding light cyan and light magenta. Individually, light cyan is often abbreviated to Lc or c, and light magenta is represented as Lm or m.

Color mixing

There are two types of color mixing: additive and subtractive. In both cases, mixing is typically described in terms of three color and three secondary colors. All subtractive colors combined in equal amounts make dark brown, while all additive colors combined in equal amounts make white.

Color space Standard that defines a specific range of colors

A color space is a specific organization of colors. In combination with color profiling supported by various physical devices, it supports reproducible representations of color -- whether such representation entails an analog or a digital representation. A color space may be arbitrary, i.e. with physically realized colors assigned to a set of physical color swatches with corresponding assigned color names, or structured with mathematical rigor. A "color space" is a useful conceptual tool for understanding the color capabilities of a particular device or digital file. When trying to reproduce color on another device, color spaces can show whether you will be able to retain shadow/highlight detail, color saturation, and by how much either will be compromised.

CMY color model Subtractive color model for dyes and pigments

The CMY color model is a subtractive color model in which cyan, magenta and yellow pigments or dyes 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 subtractive primary colors: cyan, magenta, and yellow.

References

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