CYMK and Spot Colour in Offset Printing

CMYK, or four colour printing is the most commonly-used method of transferring ink to print media. Where offset printing is concerned, the CYMK process is vital. This is because, in order for an image to be printed in this manner, it must be separated into four colours. However, there are also instances where special colours such as those produced by the Pantone brand are more feasible.

How Colours are Separated

After it’s been sent to a printing company, an image’s four colours are separated into channels with computer software. When the image reaches the prepress department, each colour’s artwork is identified, and then rasterised individually. Then each rasterised image is transferred to a printing plate. Each plate will contain only those parts of the image which correspond to the colour being printed. So for example, the cyan plate will only contain the spots of the image which are cyan in colour, the magenta plate the magenta portions of the image, and so on. This ‘computer to plate’ technique involves the use of a recorder which transfers the image on the computer to the offset printing plates.

How Offset Printing Works

The process of offset printing relies on the hydrophilic and lipophilic properties of the printing plate to apply ink to printed materials. Each offset printing plate contains areas which absorb ink and water. The parts which absorb ink, or the lipophilic areas occupy space on the plate with areas that are hydrophilic, or which absorb water. The ink-absorbing areas will transfer to the next stage, which is a rubber blanket, where the water-absorbent areas will not. The blanket is then pressed onto the media being printed. The cyan, magenta, yellow and black colours are layered onto the printing substrate to create a complete image.

Process Colour, Explained

If you’ve ever heard the term ‘process colour’ and wondered what it was, wonder no more. Process colour is what the combination of CMYK colours creates during the offset printing process. Process colour is defined either by number or in some other format.

Should a colour need to be exact, a more specialised brand such as Pantone will need to be applied. Pantone is a popular choice for businesses who want to have their colours included on various materials without losing shade accuracy. Standardised brands like Pantone ensure that a colour will look the same whether it’s been printed on glossy business cards or matte security labels.

Sometimes, a company will supply its own colour guide consisting of their custom colours. This makes it much easier for printers to reproduce them. Colours can be created by combining just the cyan, magenta, yellow and black shades, but this usually insufficient for the production of requested colours.

Multi-Colour Printing

Where more than four colours are needed, and special colours required for the uniformity throughout a range of printed products for a business, the multicolour printing process is employed. This process involves the set-up for five channels of colour or more, depending on how many special colours are required.

Typically, there are several instances which call for the multicolour printing process. When colours are needed that fall outside the range of CYMK, special colours can come to the rescue. Companies needing booklets or catalogues printed will also benefit from the use of special colours, as these allow for colour consistency on each page. Even a slight variation in colour balance can give pages an inconsistent appearance.

Another case for special colours is when large areas require smooth coverage, such as a sign or billboard. This will allow for colour consistency regardless of the distance from which the sign is viewed.

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