I remember when I first started out as a designer.  I had no formal training (shh don’t tell!) and it was a mad scramble to learn the basics so that I could carry out my everyday job.  One of these basics was an understanding of the difference between CMYK and RGB colour and when each should be used, especially when sending files to print.

RGB colour is generally a format used in digital imaging devices such as scanners, digital cameras and computers, and also in designing for web.

Offset printing presses and digital printing machines however, print full colour images using a different set of colours to RGB.  The colour process that forms the basis of printing is CMYK.  This acronym stands for the four colours of pigment: Cyan, Magenta, Yellow and Black.  It can also be referred to as “process colour” or “four colour process”.  Combinations of these four colours creates the full range of colours that you see in printed material and results in a smooth, continuous tone.

It is recommended that if you are producing material for print by a professional service such as Astroprint, that you convert your images to CMYK before sending the print files.  Doing this will allow you to tweak any images that do not convert well and have a different appearance to their RGB originals.  Unfortunately, not all RGB colours will convert well to CMYK – these colours are said to be “out of the CMYK colour gamut”.  To accommodate for this, you should convert your RGB images in your favourite imaging program (e.g. Photoshop) and check them against the original RGB image. It is at this stage that you can tweak the colours if you find that their appearance is dull or not as you expected.  If you do not convert your images to CMYK before sending them to Astroprint, we will run a script in Adobe Acrobat that will convert them to CMYK, however we generally do not check the images after the conversion as this would be far too time consuming (especially to make any colour tweaks that might be necessary), so we recommend you convert your images before sending your files to us.

Below is an example of colours that do not convert well from RGB to CMYK.

An example of an RGB image that has not been converted to CMYK.

An example of an RGB image after conversion to CMYK.

Don’t let the above example startle you. It is generally these vibrant, flat colours that suffer the most during the conversion process.  Photographs and images with continuous tone generally convert much better.  Look at the examples below – you can hardly notice any difference.

An example of an RGB photograph that has not been converted to CMYK.

An example of an RGB photograph after conversion to CMYK.

For best results we recommend working in CMYK from the outset if you know your design is destined for print.  Programs such as Illustrator and Photoshop allow you to choose between CMYK and RGB fairly easily.  If you are designing for web then ensure you work in RGB.

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Written by Dario Paolini
Director – AstroPrint.com.au