There are two ways of producing a colour, the additive process and the subtractive one. In the subtractive process a colour is produced by subtracting colours from white light. So to produce yellow, for example, blue is subtracted from white.

The three filters associated with this process are

• blue-green (called cyan) which is white minus red,
• magenta, which is white minus green, and
• yellow, which is white minus blue.

This forms the basis of the current colour photographic systems.


By Dr. Robert Leggat