[task #15878] SDSS RGB color conversion in ConvertType

[Mohammad Akhlaghi]

URL:
  <https://savannah.gnu.org/task/?15878>

                 Summary: SDSS RGB color conversion in ConvertType
                 Project: GNU Astronomy Utilities
            Submitted by: makhlaghi
            Submitted on: Mon 11 Jan 2021 11:42:37 PM UTC
         Should Start On: Mon 11 Jan 2021 12:00:00 AM UTC
   Should be Finished on: Mon 11 Jan 2021 12:00:00 AM UTC
                Category: ConvertType
                Priority: 5 - Normal
              Item Group: New feature
                  Status: Postponed
                 Privacy: Public
        Percent Complete: 0%
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
                  Effort: 0.00

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Details:

SDSS has an interesting algorithm to merge images from three filters into an
RGB-colored image (for example JPEG or PDF).

The algorithm is defined in Lupton et al. 2004
<https://ui.adsabs.harvard.edu/abs/2004PASP..116..133L/abstract>, with the
goal of showing the brightest parts of an image in logarithmic scale and the
fainter parts in linear scale (to show both).

An implementation of this is in Astropy
<https://docs.astropy.org/en/stable/visualization/rgb.html>, as the 
make_lupton_rgb
<https://docs.astropy.org/en/stable/_modules/astropy/visualization/lupton_rgb.html#make_lupton_rgb>
function. 

Fortunately implementing the basic function is easy in ConvertType to avoid
the huge dependency tree of Astropy and do it fast! It can be implemented in
an option like the example below. Where AAA is the Q parameter and BBB is the
"stretch" parameter.


astconvertt red.fits green.fits blue.fits --luptonrgb=AAA,BBB


Raul Infante-Sainz kindly provided the links above and this issue was
recommended by Ignacio Trujillo.




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