Full colour printing is, as the term suggests, the creation of a graphical image, photograph or text in colour. The alternative is black-and-white, or monochrome printing. Of the two, colour printing is far more effective at making a statement, whether it’s a photograph in a brochure, a company logo on a business card or a textural statement on an event flyer.

In order to understand how full colour printing is achieved, it helps to understand the optical physics underlying it. In school art lessons, we are told that the 3 primary colours are red, blue and yellow. However, for printing purposes the primary colours are red, green and blue. Any colour image or photograph can be optically broken down into these three colours, which mixed in different percentages will create the perception of the full colour spectrum.

The secondary colours – printing inks

Combined equally, the three primary colours create the colour white. Removing one of the colours and combining the other two in equal proportions produces what is known as a secondary colour. Thus red and green produce yellow; red and blue yield magenta (a kind of purple), and green and blue create cyan, which is a turquoise colour. These are the three basic colours used in full colour printing, familiar to anyone with a colour computer printer. Black, added to create darker hues, is called the key colour.

Yellow, cyan and magenta are known as the three basic secondary colours. Unequal mixtures of these – plus black – produce lifelike reproductions of all the colours seen in nature – of which there are literally hundreds. Of course, in printing this is all very carefully controlled. Printers use a system called the percentage colour, or CMYK chart, CMYK being short for Cyan, Magenta, Yellow and black.

Every hue on the chart is expressed as a percentage of each colour i.e. c%, m%, y% and k%. The colours are visually displayed next to these values as colour swatches. Officially, there are only 16 named colours in the system, the rest being expressed as hexadecimal codes. However, many people use descriptive naming terms as well. Pure black, for example, is expressed as: c0%, m0%, y0%, and k100%. The colour popularly called amethyst is quoted as c0%, m32%, y16%, and k38%.

The colour separation process

A common method for full colour printing, colour separation begins by separating the original coloured image into its red, green and blue components. Today, this is done by digital scanning, but previously it was done by photographing the image through a series of filters. In either case, the result is three greyscale reproductions, each representing one of the three primary colours i.e. red, green, and blue.

The next stage involves inverting these images to produce cyan, magenta and yellow separation negatives. Black separation is also used to clarify tones and create shadow and contrast. Another cutting-edge process, called computer-to-plate technology, combines lasers with dot-matrix screen-printing.
 

The author has worked in the print industry for over 30 years. Lyndon spent much of that time working in Australia, before returning to the UK several years ago where he worked as a print manager for a UK design agency. Lyndon writes for Minuteman Press UK; a full colour printing franchise organisation that can help with all printing requirements.