Print Colours Explained

Print /  18 November 16 / by Dale Brett    
Print Colours Explained

CMYK vs RGB

If you have ever had to supply digital artwork to a printer you will more than likely have been asked to supply the images as CMYK as opposed to RGB, but what do all those letters stand for, and how do they relate to print?


Colour Spaces

CMYK and RGB are different colour models, also known as colour spaces, which are mathematical models describing a range of colours as a series of numbers. Each number indicates the intensity of a base colour, the combinations of values indicate how the base colours should be mixed to create different resulting colours.


RGB

The RGB colour model mixes different amounts of Red, Green, and Blue light. RGB is known as an additive colour model, by mixing different levels and combinations of the three colours we can create the full spectrum of visible colours.

When pure red, blue, and green are combined the resulting colour perceived is white; with no light present the resulting colour perceived is black.

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RGB is typically used on electronic displays such as mobile phones, computer monitors, and televisions; all of these displays work by projecting light, images created using RGB should ideally be displayed on such devices.

RGB colours are normally represented by a group of three values ranging from 0-255, with white being R:255, G:255, B:255, or #FFFFFF in hexadecimal; and black being R:0, G:0, B:0, or #000000 in hexadecimal.


CMYK

CMYK is the colour model used for printing; unlike RGB which uses light, CMYK is used when applying ink to paper.

CMYK is known as a subtractive model because white is created when there is a complete lack of pigment applied to white paper, the more ink added to a page the darker the resulting pigment.

CMYK indicates that four ink colours are to be used, Cyan, Magenta, Yellow and BlacK, which will produce a range of colours when combined in different amounts.

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Unlike RGB, the full spectrum of colours cannot be reproduced with CMYK because paper can only reflect light, this is why printed colour lacks the brightness and intensity of projected colour.

Artwork supplied to printers in an RGB format cannot be produced as displayed onscreen and will appear much duller than expected.

Printers make use of a method called Halftoning which allows for less than full saturation of the primary colours; instead, tiny dots of each colour can be printed in patterns small enough that the human eye perceives a solid block of colour. The lighter the halftoning, the lighter the colour perceived.


Colour Conversion

Colours produced by printers are subjective and depend on many factors such as the ink being used, the substrate (paper) being printed upon, the model of printer, and the light under which the produced item is being viewed. This means that a one to one conversion between RGB and CMYK does not exist, instead printers must rely on colour profiling and printer calibration to approximate the correct colours.

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Colour Matching

The Pantone Matching System is a proprietary colour space used in the printing industry; it is a standardised set of colours that can be used by different companies to "colour match" specific colours when a design is printed, regardless of the printer or equipment used to produce the colour.

If a print design uses a known Pantone colour but the resulting printed colour doesn't match the reference, the printer can be re-calibrated in an attempt to more accurately reproduce the desired colour.


Spot Colours

CMYK printing often makes use of "spot colours" which are special inks that are applied to produce a consistent colour, e.g. to meet a company's colour scheme or logo.

Spot colours could also be specialised inks such as metallic silver or gold, or Spot UV which is a coating technique for printed materials that bounces the light in such a way to produce a "shiny, shimmering" effect.

Although printed imagery cannot have the brightness and intensity of an image displayed on a screen, the clever application of specialist inks can often provide the impact that may be missing.


Summary

Colour isn't as simple as it first appears, different colour models can often play havok with printers and print clients; it is important to have an understanding of the differences between RGB and CMYK so you know how to design for print and what to expect once your design has been produced.

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