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.
