Re: [Plplot-devel] cmap0.pal and cmap1.pal support

[Andrew R. <and...@us...>]

On Sun, Jul 05, 2009 at 09:15:24PM -0400, Hazen Babcock wrote:
> 
> Hello,
> 
> As of v10119 you can now specify the color table to use for color table 
> 0 or color table 1 as a command line argument to PLplot. For example:
> 
> ./x01c -cmap0 /path/to/cmap0a.pal -dev xcairo
> 
> Will load the cmap0a.pal file and use the information in that file to 
> initialize PLplot's color table 0 prior to plotting. Similarly:
> 
> ./x01c -cmap1 /path/to/cmap1a.pal -dev xcairo
> 
> Will load the cmap1a.pal file and use the information in that file to 
> initialize PLplot's color table 1 prior to plotting.
> 
> As part of this effort the PLplot API has two new additions:
> plspal0(filename) - Set the color table 0 palette based on the cmap0.pal 
> format file specified by filename.
> plspal1(filename) - Set the color table 1 palette based on the cmap1.pal 
> format file specified by filename.
> 
> Example .pal format files can be found in plplot-source/bindings/tk. 
> Hopefully this addition will make it easier for people to use their 
> preferred color scheme.

Hazen,

Sorry for joining this thread rather late in the day, but I've just
got chance to try this out. Firstly, I think it is a great idea, so
thank you Hazen for implementing it. Some comments.

1) The .pal files in bindings/tk are pretty hideous! Can we get some
better examples. I have some palettes I regularly use which I would
be willing to donate...

2) When I tried to create a .pal file I realised that the current file
format assumes that the position value is an integer in the range 0-100,
whereas plplot actually uses a PLFLT in the range 0-1. This might not
be significant for most purposes, but for example I sometimes use
continuous colour scales with a narrow band of values picked out in a 
different colour, either for emphasis or for ensuring that values around
zero are white. The resolution offered by the .pal files might not be
sufficient and I would rather not saddle us with something now that might
cause problems later on. I think the original reason was that tk provided 
poor float support. Let's not saddle the rest of plplot with that.

Andrew