gnuplot documentation

70 SET-SHOW gnuplot 4.3 125
70.50.3 Functions
Use set palette functions , , to define three formulae for the R(gray),
G(gray) and B(gray) mapping. The three formulae may depend on the variable gray which will take
values in [0,1] and should also produce values in [0,1]. Please note that might be a formula
for the H-value if HSV color space has been chosen (same for all other formulae and color spaces).
Examples:
To produce a full color palette use:
set palette model HSV functions gray, 1, 1
A nice black to gold palette:
set palette model XYZ functions gray**0.35, gray**0.5, gray**0.8
A gamma-corrected black and white palette
gamma = 2.2
color(gray) = gray**(1./gamma)
set palette model RGB functions color(gray), color(gray), color(gray)
70.50.4 File
set palette file is basically a set palette defined () where is read from a
datafile. Either 4 columns (gray,R,G,B) or just three columns (R,G,B) have to be selected via the using
data file modifier. In the three column case, the line number will be used as gray. The gray range is
automatically rescaled to [0,1]. The file is read as a normal data file, so all datafile modifiers can be
used. Please note, that R might actually be e.g. H if HSV color space is selected.
As usual may be ’-’ which means that the data follow the command inline and are terminated
by a single e on a line of its own.
Use show palette gradient to display the gradient.
Examples:
Read in a palette of RGB triples each in range [0,255]:
set palette file ’some-palette’ using ($1/255):($2/255):($3/255)
Equidistant rainbow (blue-green-yellow-red) palette:
set palette model RGB file "-"
0 0 1
0 1 0
1 1 0
1 0 0
e
Binary palette files are supported as well, see binary general (p. 66). Example: put 64 triplets of
R,G,B doubles into file palette.bin and load it by
set palette file "palette.bin" binary record=64 using 1:2:3
70.50.5 Gamma correction
For gray mappings gamma correction can be turned on by set palette gamma .
defaults to 1.5 which is quite suitable for most terminals.
For color mappings no automatic gamma correction is done by gnuplot. However, you may easily
implement gamma correction. Here is an example for a gray scale image by use of explicit functions for
the red, green and blue component with slightly different values of gamma
Example: