Colour Separation

Colour separation is the process by which the original full-colour digital files are divided into separate colour components for four-colour process printing. Each element in the file is printed in a combination of four colours: cyan, magenta, yellow and black, known in the world of commercial printing as CMYK.

By combining these four ink colours, a wide spectrum of colours can be produced on the printed page

In the four-colour printing process, each of the four colour partitions is applied to a separate printing plate and placed on a cylinder of a printing press. As the sheet of paper moves through the printing press, each plate transfers the image to the paper in one of four colours. Colours — which are applied as minuscule dots — combine to form a full-colour image.

CMYK colour model is for print projects

The actual work of creating colour separation is typically handled by a commercial printing company, which uses proprietary software to separate your digital files into four CMYK colours and transfer colour-separated information to plates or directly to the digital press.

Most print designers work in the CMYK model to more accurately approximate the appearance of colours in the final printed product.

RGB is best for onscreen viewing
  • They are best constructed using the RGB (red, green, blue) colour model. The RGB model has more colour possibilities than the CMYK model because the human eye can see more colour than ink on paper.
  • CMYK is not the best colour model for documents viewed onscreen.
  • However, in the process of converting colours from RGB to CMYK, what you see onscreen being colour reproducible on paper can cause a colour change.
  • If you use RGB in your design files and send the files to a commercial printer, they are still separated into four CMYK colours for print.
Setting Up Digital Files For Color Separation

Graphic designers should install their digital files destined for four-colour separation in CMYK mode to avoid unpleasant colour surprises. All high-end software — Adobe Photoshop, Illustrator and InDesign, Corel Draw, QuarkExpress, and many other programs — offer this capability. It is just a matter of changing the preference.

Exception: If your printed project has a spot colour, a colour that usually must exactly match a specific colour, that colour should not be marked as CMYK colour. It should be left as a spot colour so that when the colour is differentiated, it will automatically look different and be printed in its own coloured ink.


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