Colour separation is the opposite of colour mixing. It refers to the process of extracting specific colours one by one from a mixed colour, thereby returning it to its basic constituent colours. Colour filters, much like coloured cellophane, are used to perform colour separation. Each filter allows only one colour to pass through it; it absorbs all other colours. Colour separation for colour copiers or colour printers is performed using blue, green, and red filters(corresponding to the three primary colours of light).

Blue filter

Only blue light passes through; all other colours are absorbed.

Green filter

Only green light passes through; all other colours are absorbed.

Red filter

Only red light passes through; all other colours are absorbed.