RGB is what is known as a ‘device-dependent’ colour model. This means that different displays will reproduce a given RGB value differently - so what RGB colour I see on my computer monitor can differ to the colour you see on your computer monitor, and again on your smartphone. It is important to remember this when designing and also when sending and viewing design proofs.
The range of colours produced by a colour model is known as it’s ‘gamut’. The RGB colour gamut can reproduce around 70 percent of the colours visible to the human eye. The CMYK colour model can’t reproduce as much as RGB so when designing be aware of this limitation. It is a common mistake of designers (both hobbyists and professionals alike) to submit artwork for printing in RGB. The results upon completion can be slightly underwhelming! RGB is able to reproduce brighter, more saturated colours simply because it is based on light. Your monitor is not a piece of paper!
RGB is used for anything that will be displayed on-screen for example; websites, apps and web advertisements.
CMYK stands for Cyan, Magenta, Yellow and Black and it is a subtractive colour model used for colour printing. Inks in the CMYK model ‘subtract’ brightness from the white or brightness of the paper, reducing the amount of light being reflected. CMYK is the opposite of RGB where white is the natural colour of the paper and mixing the coloured inks together results in black. The ‘K’ in CMYK stands for ‘Key’ - when printing, the three colours Cyan, Magenta and Yellow align with the Black, making it the ‘key’. Another way of explaining it, although not correct, is that because ‘B’ is already being used by Blue in RGB, ‘K’ is used as it is the last letter in Black.
The important thing to remember is that the CMYK colour model is also ‘device-dependent’, so colours can vary from printer to printer. As is the case with RGB, CMYK only reproduces a subset of the spectrum visible to the human eye. As mentioned in RGB above, the gamut of CMYK is less than that of RGB, making it a difficult proposition to design a printed piece, as you are viewing it on an RGB screen.
In colour printing, the four colours of CMYK mix together to create millions of colours. This process is often referred to as ‘full colour printing’ and can also be known as ‘four colour printing’.
We will cover CMYK and printing in more depth when we discuss the different printing processes in the coming weeks.