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If you’ve ever produced a commercially printed document, you’ve probably come across the mysterious letters CMYK. These stand for cyan, magenta, yellow and black (K), which are the four inks that are normally combined to create the illusion of full colour printing. There are some alternative processes that use different numbers of inks, but CMYK is far and away the most common.

CMYK printers mimic a wide spectrum of colours by printing different amounts of each of the four inks at different locations on the page. Each colour is printed as a collection of dots. Depending on how large these dots are, and how close together they are, they can look darker or lighter. To create the illusion of a pale colour, smaller dots are printed with more white space around them. To create a darker colour, larger dots are printed surrounded by less white space. Printing four different patterns of dots (one each for cyan, magenta, yellow and black) on the same sheet of paper creates the illusion of a wide spectrum of colour.

The photo on the right (click to enlarge) illustrates how effectively CMYK can trick us into thinking we are seeing a wide spectrum of colour, when in fact the original printed image is only made up of four colours. In a future blog post we’ll look at different types of inks called spot colours that can be used to extend the range of CMYK.