Viewing colours: RGB and CMYK

Different ways of looking at things

RGB? CMYK? What do these mean?

In printerspeak, there are two main ways of looking at colour.  RGB stands for Red Green Blue, and it’s the way you look at images on a TV set or a computer screen. These are known as the additive primary colours. They are basically colours that use transmitted light – the kind monitors and TV screens produce. We’ve all seen the picture of red, green and blue lights overlapping on a screen. When combined, they produce white.

CMYK stands for Cyan, Magenta, Yellow, and Black (K stands for black because it means “Key”, but I imagine it’s also because “B” could mean blue (cyan) or black – and that would be confusing; we wouldn’t want that. If you print Cyan, Magenta, and Yellow on top of each other, you get (more or less) black. These are called (wait for it…) the subtractive primary colours. These 3 colours along with black produce most of the colours you will see on the printed page.

Digital Cameras

Digital cameras take pictures in RGB mode, and they need to be changed to CMYK before they can be used on the printed page. Fortunately, designers routinely do this conversion, so it’s nothing to worry about. The file size goes up a little when the picture is converted, seeing as we are going from 3 channels (one each for Red Green and Blue) to 4 channels (one each for Cyan, Magenta, Yellow, and Black).

Colour Gamut

Although it sounds like some sort of Mongolian sheep feeder, gamut is actually a term that indicates range or breadth of something. Sometimes you will see a colour that can’t be printed by the conventional CMYK process; such colours are said to be out of gamut; that is, it’s just not possible to get that particular colour using combinations of cyan, magenta, yellow, and black. Usually these are fluorescent colours, and they require an extra pass through the printing press with special fluorescent ink. This is an important thing to remember when you’re costing out a job, because it will add to your expense.

For more information, give us a call at 604-773-0035. We love to talk about printing!