Gray-to-rgb mapping can be manually set by use of defined: A color gradient is defined and used to give the rgb values. Such a gradient is a piecewise linear mapping from gray values in [0,1] to the RGB space [0,1]x[0,1]x[0,1]. You have to specify the gray values and the corresponding RGB values in between a linear interpolation shall take place:
Syntax:
set palette defined { ( <gray1> <color1> {, <grayN> <colorN>}... ) }
<grayX> are gray values which are mapped to [0,1] and <colorX> are the corresponding rgb colors. The color can be specified in three different ways:
<color> := { <r> <g> <b> | '<color-name>' | '#rrggbb' }
Either by three numbers (each in [0,1]) for red, green and blue, separated by whitespace, or the name of the color in quotes or X style color specifiers also in quotes. You may freely mix the three types in a gradient definition, but the named color "red" will be something strange if RGB is not selected as color space. Use colornames for a list of known color names.
Please note, that even if written as <r>, this might actually be the <H> component in HSV color space or <X> in CIE-XYZ space, or ... depending on the selected color model.
The <gray> values have to form an ascending sequence of real numbers; the sequence will be automatically rescaled to [0,1].
defined (without a gradient definition in braces) switches to RGB color space and uses a preset full-spectrum color gradient. Use `show palette gradient` to display the gradient.
Examples:
To produce a gray palette (useless but instructive) use:
set palette model RGB
set palette defined ( 0 "black", 1 "white" )
To produce a blue yellow red palette use (all equivalent):
set palette defined ( 0 "blue", 1 "yellow", 2 "red" )
set palette defined ( 0 0 0 1, 1 1 1 0, 2 1 0 0 )
set palette defined ( 0 "#0000ff", 1 "#ffff00", 2 "#ff0000" )
To produce some rainbow-like palette use:
set palette defined ( 0 "blue", 3 "green", 6 "yellow", 10 "red" )
Full color spectrum within HSV color space:
set palette model HSV
set palette defined ( 0 0 1 1, 1 1 1 1 )
set palette defined ( 0 0 1 0, 1 0 1 1, 6 0.8333 1 1, 7 0.8333 0 1)
To produce a palette with few colors only use:
set palette model RGB maxcolors 4
set palette defined ( 0 "blue", 1 "green", 2 "yellow", 3 "red" )
'Traffic light' palette (non-smooth color jumps at gray = 1/3 and 2/3).
set palette model RGB
set palette defined (0 "dark-green", 1 "green", 1 "yellow", \
2 "dark-yellow", 2 "red", 3 "dark-red" )