gnuplot documentation

122 gnuplot 4.3 70 SET-SHOW
70.50 Palette
Palette is a color storage for use by pm3d, filled color contours or polygons, color histograms, color
gradient background, and whatever it is or it will be implemented... Here it stands for a palette of
smooth "continuous" colors or grays, but let’s call it just a palette.
Color palettes require terminal entries for filled color polygons and palettes of smooth colors, are currently
available for terminals listed in help for set pm3d. The range of color values are adjustable independently
by set cbrange and set log cb. The whole color palette is visualized in the colorbox.
Syntax:
set palette
set palette {
{ gray | color }
{ gamma }
{ rgbformulae ,,
| defined { ( {, }... ) }
| file ’’ {datafile-modifiers}
| functions ,,
}
{ model { RGB | HSV | CMY | YIQ | XYZ } }
{ positive | negative }
{ nops_allcF | ps_allcF }
{ maxcolors }
}
show palette
show palette palette {{float | int}}
show palette gradient
show palette fit2rgbformulae
show palette rgbformulae
show palette colornames
set palette (i.e. without options) sets up the default values. Otherwise, the options can be given in
any order. show palette shows the current palette properties.
show palette gradient displays the gradient defining the palette (if appropriate). show palette rgbformulae
prints the available fixed gray –> color transformation formulae. show palette colornames
prints the implemented color names.
show palette palette prints to screen or to the file given by set output table of RGB triplets
calculated for the current palette settings and a palette having discrete colors. The default wide
table can be limited to 3 columns of r,g,b float values [0..1] or integer values [0..255] by options float or int,
respectively. This way, the current gnuplot color palette can be loaded into other imaging applications,
for example Octave. Additionally to this textual list of RGB table, you can enjoy command test palette
to draw graphically the R,G,B profiles for the current palette.
The following options determine the coloring properties.
Figure using this palette can be gray or color. For instance, in pm3d color surfaces the gray of each
small spot is obtained by mapping the averaged z-coordinate of the 4 corners of surface quadrangles
into the range [min z,max z] providing range of grays [0:1]. This value can be used directly as the gray
for gray maps. The color map requires a transformation gray –> (R,G,B), i.e. a mapping [0:1] –>
([0:1],[0:1],[0:1]).
Basically two different types of mappings can be used: Analytic formulae to convert gray to color,
or discrete mapping tables which are interpolated. palette rgbformulae and palette functions
use analytic formulae whereas palette defined and palette file use interpolated tables. palette
rgbformulae reduces the size of postscript output to a minimum.
The command show palette fit2rgbformulae finds the best matching set palette rgbformulae for
the current set palette. Naturally, it makes sense to use it for non-rgbformulae palettes. This command
can be found useful mainly for external programs using the same rgbformulae definition of palettes as
gnuplot, like zimg (