Groups > comp.graphics.apps.gnuplot > #2164

Re: Bug on palette

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From	Ethan A Merritt <merritt@u.washington.edu>
Newsgroups	comp.graphics.apps.gnuplot
Subject	Re: Bug on palette
Date	Fri, 18 Oct 2013 17:18:40 -0700
Organization	University of Washington
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Vasilis wrote:

> Dear all,
> 
> this was a bug I've reported some time ago on version 4.3 but it 
> reappeared on version 4.6.x
> 
> set pm3d map explicit corners2color c1
> set palette defined ( 0 0 0 0, 0.25 0 0 1, 0.50 0 1 0, 0.75 1 0 0, 1 1 1 1
> ) set palette maxcolors 30
> set logscale cb
> splot x*y
> 
> At the "join" locations of the palette some strange brown color appears
> See the result on the plot
> http://pceet075.cern.ch/bnv/gnuplot_palette_bug.png

There is an inherent contradiction between requesting a gradient-based
palette and requesting a fixed number of colors.
I suppose it is possible to add more special-case tests for when
the gradient boundaries don't line up with the quantized palette 
boundaries. There will always be combinations where the result is
not pleasing.

I am curious why would you ever want to set maxcolors to 30?
What use case requires setting maxcolors at all?
In the days of 6-color pen plotters it made some sense, but what
real-world 21st century device is limited to exactly 30 colors?

And for those cases where you really do want a small fixed number
of colors N, I think palette coloring is no longer the best way to
create a plot.  I would recommend instead to define N separate linetype
colors and plot with "linecolor variable".  Then you have perfect 
control over the color that is used.

	Ethan

> 
> Thanks in advance
> Vasilis

Thread

Bug on palette Vasilis <vvlachoudis@gmail.com> - 2013-10-18 03:32 -0700
  Re: Bug on palette Ethan A Merritt <merritt@u.washington.edu> - 2013-10-18 17:18 -0700
    Re: Bug on palette Vasilis <vvlachoudis@gmail.com> - 2013-10-19 01:28 -0700
      Re: Bug on palette Olaf Schultz <o.schultz@enhydralutris.de> - 2013-10-19 13:28 +0200
      Re: Bug on palette Olaf Schultz <o.schultz@enhydralutris.de> - 2013-10-19 13:37 +0200
      Re: Bug on palette Ethan A Merritt <EAMerritt@gmail.com> - 2013-10-19 10:34 -0700
        Re: Bug on palette Ethan A Merritt <EAMerritt@gmail.com> - 2013-10-19 11:28 -0700
          Re: Bug on palette Vasilis <vvlachoudis@gmail.com> - 2013-10-20 05:27 -0700
          Re: Bug on palette Vasilis <vvlachoudis@gmail.com> - 2013-10-20 08:59 -0700
          Re: Bug on palette Vasilis <vvlachoudis@gmail.com> - 2013-10-20 09:37 -0700
            Re: Bug on palette sfeam <sfeam@users.sourceforge.net> - 2013-10-20 12:05 -0700
              Re: Bug on palette Vasilis <vvlachoudis@gmail.com> - 2013-10-21 00:28 -0700
                Re: Bug on palette sfeam <sfeam@users.sourceforge.net> - 2013-10-22 14:20 -0700
                Re: Bug on palette Vasilis <vvlachoudis@gmail.com> - 2013-10-23 00:42 -0700

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