In common with most computer based interfaces which use images as a method of displaying information, Radiance uses the RGB colour model. This is the technology of the TV screen and computer monitor, beams of electrons are fired at a screen composed of 3 different phosphors, Red, Green and Blue. [known as the additive primary colours, as against the subtractive primary colours, Yellow, Magenta and Cyan, which are used in printing] Varying levels of these three colours are mixed to give the impression of all possible colours from Black to White. It is possible to visualizing the 3 colours as the X, Y and Z axes in conventional 3D space. The volume bounded by the minimum and maximum values of each colour forms a cube. The origin (0,0,0) represents Black and the diagonally opposite corner (1,1,1) represents White. [the scale is sometimes defined as 0.0 to 1.0 in real numbers and sometimes as 0 to 255 in integer numbers] Thus any colour can be represented by the co-ordinate location within the cube i.e. the amount of each primary colour.
