This entry is part 8 of 10 in the series Design Techniques & Terminology

Print colour systems

CMYK

Short for Cyan Magenta Yellow Key (the cyan, magenta, and yellow printing plates are carefully keyed or aligned with the key of the black key plate. Some suggest that the “K” comes from the last letter in “black“,  however, this explanation, though plausible and useful as a mnemonic, is incorrect). CMYK is a colour model in which all colours are described as a mixture of these four process colours. CMYK is the standard colour model used in printing for full-colour documents. Because such printing uses inks of these four basic colours, it is often called four-colour printing.

Whereas monitors emit light, inked paper absorbs or reflects specific wavelengths. Cyan, magenta and yellow pigments serve as filters, subtracting varying degrees of red, green and blue from white light to produce a selective gamut of spectral colours. Like monitors, printing inks also produce a colour gamut that is only a subset of the visible spectrum, although the range is not the same for both. Consequently, the same art displayed on a computer monitor may not match to that printed in a publication. Also, because printing processes such as offset lithography use CMYK (cyan, magenta, yellow, black) inks, digital art must be converted to CMYK colour for print.

Here you can see the drops of ink on paper, making up the colour. These tiny dots are printed in a pattern, each colour is offset from one another,  small enough that human beings perceive a solid colour by allowing the eye to mix the primary colour together (yellow and cyen makes green, for example).

 

Because process colour ink pigments are imperfect, pure black cannot be achieved by overprinting CMY inks. Consequently, black ink is introduced in addition to, or in substitution for, CMY inks. The combined value of all CMYK inks for a particular area or object cannot exceed a specified amount, or ink may not transfer effectively and printed sheets may not dry properly.

Colour Matching System

A Colour Matching System, or CMS, is a method used to ensure that colours remain as consistent as possible. These are pre-mixed inks so that no matter which printer you use the colour will match from one job to another. Keeping colour from varying across mediums is very difficult because not only is colour subjective to some extent, but also because devices use a wide range of technologies to display colour.

There are many different colour matching systems available, but by far the most popular is the Pantone Matching System, or PMS. PMS is a “solid-colour” matching system, used primarily for specifying extra colours to sit alongside CMYK.

A lot of companies will want to have a accurate reproduction of their brands main colour, e.g. for use in their logo, and so will print in 5 colours. This will help ensure a close match.

A common problem occurs when one tries to achieve the look of a PMS colour while printing 4-colour process. The only truly accurate way to use a PMS colour in a 4CP project is to add the PMS as a fifth colour to the job, which can become expensive. By definition, 4-colour process uses only four inks: Cyan, Magenta, Yellow, and Black, (also known as CMYK), and therefore cannot match a PMS colour which, by its nature, is composed of PMS base inks.

One compromise lies in Pantone’s Process Colour System, which attempts to simulate the PMS colours with CMYK inks. At lot of the PMS colours will have a CMYK breakdown too.

Screen colour systems

RGB

Display devices generally use a different colour model called RGB, which stands for Red-Green-Blue. Monitors emit colour as RGB light, these can be combined in various proportions to obtain any color in the visible spectrum. Levels of R, G, and B can each range from 0 to 100 percent of full intensity.

Here you can see the difference between RGB and CMYK.

Hex triplet

Web colours are colours used in designing web pages, and the methods for describing and specifying those colors.

A hex triplet is a six-digit, three-byte hexadecimal number, the bytes represent the red, green and blue components of the color. One byte represents a number in the range 00 to FF (in hexadecimal notation), or 0 to 255 in decimal notation. This represents the least (0/00) to the most (255/FF) intensity of each of the color components. The hex triplet is formed by concatenating three bytes in hexadecimal notation, in the following order:

Byte 1: red value (color type red)
Byte 2: green value (color type green)
Byte 3: blue value (color type blue)

For example, consider the color where the red/green/blue values are decimal numbers: red=36, green=104, blue=160 (a greyish-blue color). The decimal numbers 36, 104 and 160 are equivalent to the hexadecimal numbers 24, 68 and A0 respectively. The hex triplet is obtained by concatenating the 6 hexadecimal digits together, 2468A0 in this example, which in css would be written preceeded with a #, i.e. #2468A0.

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