When we look at a computer monitor, we see lots of colours that are all made up from Red, Green and Blue (RGB) pixels. These pixels are tiny lights that emit red, green and blue at different intensities to each other to produce a large range of colours. This range is known as a Gamut. The RGB gamut consists of lots of colours produced by different numeric values of Red, Green & Blue. These numbers range from 0 to 255. If you had the highest value for each of these numbers all mixed together, you would see white light.
Where monitors emit light, printed material reflects light. The colours we see in magazines are made from four colours: cyan, magenta, yellow and black (CMYK). These colours are also known as Process Colours. We see these colours when white light shines on them because they reflect coloured light back. To make the colours on the paper look the same as they do on the monitor is difficult because the RGB values must be converted to CMYK values. The numeric values for RGB range from 0 – 255 and the number values for CMYK range from 0 – 100%. The equation that converts each of the colours is known as a Colour Profile. It works by opposites. For example, on a monitor, to make a colour darker, you reduce the RGB values, but on paper, you increase the CMYK values. It’s easy to understand with Black and White:
R:255, G:255, B:255 (Bright White Light) becomes C:0, M:0, Y:0, K:0 (White Paper)
If you were to make all of the RGB values zero, you would have no light
R:0, G:0, B:0 (No Light or Black) becomes C:100, M: 100, Y: 100, K: 100 (Black on Paper)
In a similar way, the colours are opposite each other too. Cyan is the opposite of Red, Green is the opposite of Magenta and Yellow is the opposite of Blue. The diagram below illustrates this:
By altering the proportions of Cyan, Magenta, Yellow and Black, it is possible to produce a whole range of colours. e.g. Magenta100% + Yellow100% equals Red:255 (100%)
Sometimes customers may want a colour that cannot be produced by mixing CMYK because the colour they want may be out of gamut. When this happens, printers use what’s known as the Pantone Matching System (PMS) to reproduce that colour. These PMS colours are always the same when they are printed and have a code number to identify them. Corporate companies often have PMS codes for their company colours so that their stationery is printed with the same colours every time they order.