NationMaster - Encyclopedia: Color printing

Color printing is the reproduction of an image or text in color (as opposed to simpler black and white or monochrome printing). It may also commonly be called four-color process printing when only the colors cyan, magenta, yellow, and black (also known as CMYK) are used. Another emerging method of color printing is six-color process printing (for example, Pantone's Hexachrome system) which adds orange and green to the traditional CMYK for a larger and more vibrant gamut, or color range. Something which is monochromatic has a single color. ... Cyan, magenta, yellow, and key (black) CMYK (or sometimes YMCK) is a subtractive color model used in color printing. ... Pantone Inc. ... Hexachrome is Pantones six-color printing process. ... In computer graphics, the gamut, or color gamut, is a certain complete subset of colors. ...

Color printing involves a series of steps, or transformations, in order to generate a quality color reproduction. Here are the main steps when reproducing a color image in CMYK print, along with some historical perspective.

Color separation process

The process of color separation occurs when the original artwork is digitally scanned and separated into red, green, and blue components. Before digital imaging was developed, the traditional method of doing this was to photograph the image three times, using a filter for each color. However this is achieved, the desired result is three grayscale images, which represent the red, green, and blue (RGB) components of the original image: Digital imaging or digital image acquisition is the creation of digital images, typically from a physical object. ... Photography is the process of making pictures by means of the action of light. ... The RGB color model utilizes the additive model in which red, green, and blue light are combined in various ways to create other colors. ...

The next step is to invert each of these separations. When a negative image of the red component is produced, the resulting image represents the cyan component of the image. Likewise, negatives are produced of the green and blue components to produce magenta and yellow separations, respectively. This is done because cyan, magenta, and yellow are subtractive primaries which each represent two of the three additive primaries (RGB) after one additive primary has been subtracted from white light. separatedRGB File links The following pages link to this file: Color printing Categories: GFDL 1. ... Subtractive color explains the theory of mixing paints, dyes, inks, and natural colorants to create colors which absorb some wavelengths of light and reflect others. ... An additive color system involves light emitted directly from a source or illuminant of some sort. ...

Cyan, magenta, and yellow are the three main pigments used for color reproduction. When these three colors are combined in printing, the result should be a reasonable reproduction of the original, but it is not. Due to limitations in the ink pigments, the darker colors are dirty and muddied. To resolve this, a black separation is also created, which improves the shadow and contrast of the image. Numerous techniques exist to derive this black separation from the original image; these include grey component replacement, under color removal, and under color addition. This printing technique is referred to as CMYK (the "K" being short for "key." In this case, the key color is black). CMYseparations File links The following pages link to this file: Color printing Categories: GFDL 1. ... An ink is a liquid containing various pigments and / or dyes used for colouring a surface to render an image or text. ... In biology, pigment is any material resulting in color in plant or animal cells which is the result of selective absorption. ... In grey component replacement (GCR), contrary to under color removal the CMY values that add to grey all along the tone scale can be replaced with up to the highlights with black ink. ... In four-color printing (or more) under color removal (UCR) is the process of eliminating amounts of yellow, magenta, and cyan that would have added to a dark neutral (black) and replacing them with black ink during the color separation process. ... In under color addition (UCA) the same results as under color removal can be obtained, but from a different starting position. ... This article or section does not cite its references or sources. ...

Today's digital printing methods do not have the restriction of a single color space that traditional CMYK processes do. Many presses can print from files that were ripped with images using either RGB or CMYK modes. The color reproduction abilities of a particular color space can vary; the process of obtaining accurate colors within a color model is called color matching. This image has been released into the public domain by the copyright holder, its copyright has expired, or it is ineligible for copyright. ... A comparison of RGB and CMYK color spaces. ... The RGB color model is an additive model in which red, green and blue (often used in additive light models) are combined in various ways to reproduce other colors. ...

Screening

Inks used in color printing presses are semi-transparent and can be printed on top of each other to produce different hues. For example, green results from printing yellow and cyan inks on top of each other. However, a printing press cannot vary the amount of ink applied except through "screening," a process that represents lighter shades as tiny dots, rather than solid areas, of ink. This is analogous to mixing white paint into a color to lighten it, except the white is the paper itself. In process color printing, the screened image, or halftone for each ink color is printed in succession. The screen grids are set at different angles, and the dots therefore create tiny rosettes, which, through a kind of optical illusion, appear to form a continuous-tone image. You can view the halftone screens that create printed images under magnification. Halftoning is a method of printing shades using a single color ink. ... An optical illusion characterized by visually perceived images that, at least in common sense terms, are deceptive or misleading. ...

Traditionally, halftone screens were generated by inked lines on two sheets of glass that were cemented together at right angles. Each of the color separation films were then exposed through these screens. The resulting high-contrast image, once processed, had dots of varying diameter depending on the amount of exposure that area received, which was modulated by the grayscale separation film image. This image has been released into the public domain by the copyright holder, its copyright has expired, or it is ineligible for copyright. ... This image has been released into the public domain by the copyright holder, its copyright has expired, or it is ineligible for copyright. ... This article is about angles in geometry. ...

The glass screens were made obsolete by high-contrast films where the halftone dots were exposed with the separation film. This in turn was replaced by a process where the halftones are electronically generated directly on the film with a laser. Most recently, computer to plate (CTP) technology has allowed printers to bypass the film portion of the process entirely. CTP images the dots directly on the printing plate with a laser, saving money, increasing quality (by reducing the repeated generations), reducing lead-times, and saving the environment from toxic film-processing chemicals. Computer to plate (CTP) is an imaging technology in modern lithographic printing. ...

Screens with a "frequency" of 60 to 120 lines per inch (lpi) are used to reproduce color photographs in newspapers. The coarser the screen (lower frequency), the lower the quality of the printed image. Highly absorbent newsprint requires a lower screen frequency than less-absorbent coated paper stock used in magazines and books, where screen frequencies of 133 to 200 lpi and higher are used.

The measure of how much an ink dot spreads and becomes larger on paper is called dot gain. This phenomenon must be accounted for in photographic or digital preparation of screened images. Dot gain is higher on more absorbent, uncoated paper stock such as newsprint. A phenomenon in printing and graphic arts whereby printed dots are perceived and actually printed bigger as intended. ...

Stochastic screening

Digital imaging technology has also given rise to new approaches to the screening process. The best-known is stochastic screening. Because the dots are the same size and randomly placed, the moiré effects that are generated by traditional half-tones are eliminated. A side benefit of stochastic screening is the ability to obtain a wider gamut of colors using additional inks such as orange or green (hexachrome). Due to the high resolution of the screen, using computer to plate imaging gives optimal results. This image has been released into the public domain by the copyright holder, its copyright has expired, or it is ineligible for copyright. ... A moirÃ© pattern is an interference pattern created, for example, when two grids are overlaid at an angle, or when they have slightly different mesh sizes. ... Stochastic, from the Greek stochos or goal, means of, relating to, or characterized by conjecture; conjectural; random. ... In computer graphics, the gamut, or color gamut, is a certain complete subset of colors. ... Computer to plate (CTP) is an imaging technology in modern lithographic printing. ...

Almost all inkjet devices use stochastic screening. Take a magnifier (or loupe) if you own an inkjet printer at home and take a peek at any image you've printed. Inkjet printers are a type of computer printer that operates by propelling tiny droplets of liquid ink onto paper. ...

Stochastic screening or some hybrid of traditional linescreen and stochastic has become the standard screening method for many packaging applications.

References

Contents

Color separation process

Screening

Stochastic screening

References

See also