Three colours become 16 million
Red, green and blue are known as ‘additive’ colours and have been used to create colour images since the early days of photography. By mixing these colours in different amounts and strengths over 16 million different colours are possible (though you might not be able to distinguish between them all). Black is the absence of all three colours. White is a mix of all three colours at their full strengths.
By now you have probably realised that you are familiar with images composed of red, green and blue colours. This is where the acronym ‘RGB’ comes from.
Some Canon digital cameras offer the choice of saving the image file in one of two RGB types – sRGB or Adobe RGB. These are known as ‘colour spaces’. If you don’t know the difference between the two, set your camera to sRGB.
Colour representation for print
Ink-jet printers can’t use RGB. On a computer screen, red, green and blue would create white. If you mix red, green and blue inks you get a muddy brown.
Instead, printers use CMYK. Paper is usually white so this colour is produced by an absence of all others. Other colours are produced by varying the level of cyan (C), magenta (M) and yellow (Y) ink droplets. Most ink-jet printers also have a separate ink-cartridge for black (K).
But how do you convert from RGB to CMYK? The answer lies in the ‘driver’ – the piece of software that acts as an interface between your computer and your printer. One of the jobs of the printer driver is to convert the RGB colours to CMYK colours.