PHIGURE has a certain number of colour table creation functions. All these functions generate the types of colour tables most often used to obtain gradations. There are functions to generate monochrome gradation colour tables, 2-, 3- or 4-colour gradation colour tables, or general gradation colour tables, as well as a definition of colour tables of any colours.
To make colour gradation colour tables, PHIGURE uses the HLS colour system defined by the PHIGS standard: a colour is defined by the three following components:
H = hue hue of colour corresponding to an angle from 0° to 360° ( 0 <=H<= 1)
L = lightness intensity of light, (black = 0<=L<=1 = white)
S = saturation color saturation (not satured = 0<=S<=1 = satured)
The following diagram shows the distribution of colours according to this system:
Black corresponds to lightness L=0, with any hue and saturation.
White corresponds to lightness L=1, with any hue and saturation.
A saturation value of S=0 gives a grey which is lighter or darker depending on the lightness value L.