GCSE ICT - Printers

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Extra notes on Colour printing

The thousands of colours that you see on a colour print out are usually created by mixing tiny dots of just three different colours - CYAN, MAGENTA and YELLOW on the paper.

How the 3 coloured dots (CMY) can combine when printing:

White
paper
a printer pixel

This diagram shows how ink dots of the 3 secondary colours CYAN, MAGENTA and YELLOW (CMY) can be combined together to form the three primary colours and black. Varying the amount of these secondary colours produces all the other possible colours.

C + M = blue
M + Y = red
Y + C = green
C + M + Y = black*

(*Most printers use black ink or toner to produce black, rather than adding all the secondary colours together)

Printer inks

Remember - WHITE light is made up of RED, GREEN and BLUE light (RGB).

Why a colour printer DOES NOT USE the three primary colours: red, green and blue:

Imagine we wanted to combine GREEN and RED ink to try and produce another colour.

If you shine white light on RED ink it reflects RED light (it absorbs GREEN and BLUE light).
If you shine white light on GREEN ink it reflects GREEN light (it absorbs RED and BLUE light).
If GREEN and RED inks are mixed then all three colours in the WHITE light would be absorbed. NO light would be reflected so the ink would just look black.
Any combination of the three primary colours will produce this result so trying to produce other colours by mixing primary colours is a waste of time!

Why a colour printer DOES USE the three secondary colours: cyan, magenta and yellow:

Imagine we wanted to combine YELLOW and CYAN inks to produce another colour.

CYAN ink reflects BLUE and GREEN light and absorbs RED light.
YELLOW ink reflects RED and GREEN light and absorbs BLUE light.
If CYAN and YELLOW inks are mixed then the BLUE light is absorbed by the mixture but GREEN is reflected (it is the only colour they have in common) so the mixture will look GREEN.
Any combination of the three secondary colours (CMY) will produce one of the primary colours (RGB) and varying the amount of each secondary coloured ink will produce all the colours possible.