Re: [ gnuplot-Bugs-1575425 ] "with image" ignores gamma for postscript output (fwd)

[Daniel J S. <dan...@ie...>]

Daniel J Sebald wrote:

> OK.  I'll have to consult the book to see images can use PostScript's
> gamma feature.  In the mean time, I've put a patch on SourceForge
> with the pow(gray,1.0/gamma) which seems to work.

Petr,

The Adobe book indicates that gamma correction can be implemented with what is called a transfer function (the second level of color mapping).  So, as an alternative, I simply added a line before the image definition (and a little extra cleanup):

if (sm_palette.colorMode == SMPAL_COLOR_MODE_GRAY)
    fprintf(gppsfile, "%s{1.0 %g div exp} settransfer\n", space, sm_palette.gamma);

What this does is create the line below:

  gsave
  {1.0 0.2 div exp} settransfer
  875 4740 translate
  4959 -4240 scale
  100 10 8
  [ 100 0 0 10 0 0 ]
  currentfile /ASCII85Decode filter
  image

I'll send you the patch separately so that you may place it on SourceForge.  [Would it be possible to change SF to allow attaching to someone else's bug report?]  Let me know if that works.

I'm guessing that transfer functions could be widened in scope.  So if you'd like to use a transfer function somehow rather than /pm3dGamma, let me know.

Dan