file is basically a `set palette defined (<gradient>)` where <gradient> 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 <filename> 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`. 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