What is CMYK?

This blog explains the difference between what RGB and CMYK, why CMYK should be used for artwork sent to us and finally explain how to setup to design in CMYK colour.

RGB and CMYK – What’s the difference?

RGB stands for Red, Green and Blue. RGB is an additive gamut which takes the starting point of a black canvas and colours are added by using the percentage of Red, Green and Blue. RGB is used for graphics which appears on computer screens.
CMYK stands from Cyan, Magenta, Yellow and Black. CMYK colours are subtractive meaning the starting canvas is white and colours are added to block out parts of the spectrum.

The RGB colour spectrum is much larger than the CMYK spectrum. There are colours (such as a fluorescent orange or green) that can be created in RGB that cannot be created in CMYK. This can cause colour issues if you have designed your artwork in RGB when converted to CMYK.

Why not just print in RGB?

Commercial presses print onto white substrates using CMYK colours to get the best results. As such files should be prepared with CMYK in mind. If using RGB elements i.e. images in the design stage it is worth converting the elements into CMYK and re-balancing the colours during the design process. Below are examples of files submitted in RGB colour that have converted into CMYK before printing. The top file is the RGB original whilst below is the CMYK file. Things to note are that the luminous yellow bibs are much more muted in the CMYK version, as is the red shirt on the left hand of the screen. The blue shorts have also become much darker, becoming closer to black than the original blue. The contrast between the grass colours is much more defined on the CMYK version of the artwork and the writing on the ball is much clearer.
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Creating Files in CMYK.

When designing any file for print it is important to set up the artwork in CMYK colour. This will prevent issues trying to adjust colours afterwards which can be very difficult if not impossible. Not all software is able to create files in CMYK colour mode. Microsoft Word and Powerpoint are only able to create documents in RGB which must be converted before printing. Please consult guides relevant to your software for tips on how to convert to CMYK.

Finally, a couple of quick pointers to help you understanding the issue and assist in checking.
• Do use printed CMYK colour swatches to check colours if unsure.
• Do check proofs on screen using a colour calibrated monitor (if possible).
• Do print samples using a commercial proof printer.
• Don’t rely on uncalibrated screens colours as these will vary from monitor to monitor.
• Don’t check colours against desktop printer samples.