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Extending plot types - adding a CIE 1931 type diagram

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  Extending plot types - adding a CIE 1931 type diagram hvezdny.cestovatel@gmail.com - 2013-08-07 13:24 -0700
    Re: Extending plot types - adding a CIE 1931 type diagram sfeam <sfeam@users.sourceforge.net> - 2013-08-07 18:51 -0700
    Re: Extending plot types - adding a CIE 1931 type diagram Ingo Thies <ingo.thies@gmx.de> - 2013-08-08 10:30 +0200
      Re: Extending plot types - adding a CIE 1931 type diagram hvezdny.cestovatel@gmail.com - 2013-08-16 02:47 -0700

#1952 — Extending plot types - adding a CIE 1931 type diagram

Hello guys,

I would like to extends Gnuplot with the ability to generate a CIE1931 digram of color spectrum, basically looking like this one:

http://commons.wikimedia.org/wiki/File:CIExy1931.svg

This kind of generator is already present in netpbm package as ppmcie.

I would like Gnuplot to be able to provide this background for the plot, so one could easily plot curves over this background directly with 'plot' command, withou the need of fitting the background to the actual plot.

So the task would be:
1. generate the background color image with the right coordinates, so that
2. plot points and curves into that plot as usual, taking advance of the coordinate system of the CIE x-y diagram

Thanks in advance for ideas,
Martin

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#1953

hvezdny.cestovatel@gmail.com wrote:

> Hello guys,
> 
> I would like to extends Gnuplot with the ability to generate a CIE1931
> digram of color spectrum, basically looking like this one:
> 
> http://commons.wikimedia.org/wiki/File:CIExy1931.svg
> 
> This kind of generator is already present in netpbm package as ppmcie.
> 
> I would like Gnuplot to be able to provide this background for the
> plot, so one could easily plot curves over this background directly
> with 'plot' command, withou the need of fitting the background to the
> actual plot.
> 
> So the task would be:
> 1. generate the background color image with the right coordinates, so
> that 2. plot points and curves into that plot as usual, taking advance
> of the coordinate system of the CIE x-y diagram

If you already have such an image, it can be mapped onto a specific 
coordinate range of the plot area using the plot style "with rgbimage".
See for example

  http://gnuplot.sourceforge.net/demo_cvs/barchart_art.html


> 
> Thanks in advance for ideas,
> Martin

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#1954

Hi,

On 07.08.2013 22:24, hvezdny.cestovatel@gmail.com wrote:

> So the task would be:
> 1. generate the background color image with the right coordinates, so that
> 2. plot points and curves into that plot as usual, taking advance of the coordinate system of the CIE x-y diagram

If it is merely plotting over a background image it is already possible,
as Ethan said. Or do you also intend some RGB to x-y(-Y) or even
spectrum to x-y(-Y) conversion? This would require to include the RGB to
XYZ matrices and/or the CIE colour matching functions.

Another question would be whether it should be CIE 1931 2-deg standard
observer only or also include the CIE 1964 10-deg standard observer. CIE
1931 seems to be outdated although it is still used for the definition
of sRGB (the differences in the image would be small anyway).


Best wishes,

Ingo

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#1977

Hello, thanks for the ideas. 

> If it is merely plotting over a background image it is already possible,
> as Ethan said.

Plotting over an image will help a lot, I haven't noticed this feature.

> Or do you also intend some RGB to x-y(-Y) or even
> spectrum to x-y(-Y) conversion? This would require to include the RGB to
> XYZ matrices and/or the CIE colour matching functions.
> Another question would be whether it should be CIE 1931 2-deg standard
> observer only or also include the CIE 1964 10-deg standard observer. CIE
> 1931 seems to be outdated although it is still used for the definition
> of sRGB (the differences in the image would be small anyway).


I am doing the spectrum to CIE(x,y) processing in my PhD work, but the command 'splot ... with rgbimage' or 'splot ... with rgbalpha' will do all I need, and the data processing will be done separately, as well as the CIE diagram data generation can be.

To conclude, 'splot ... with rgbimage' is enough to do the job. 

Thanks again for the ideas.

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