[iaufwg] FITS conventions

[William Pence]

This issue of color images in FITS is probably of interest to many FITS 
users, so it would be good for someone to move this discussion to 
fitsbits at nrao.edu so more people can participate.  If the FITS community is 
able to agree on some new conventions, then these could eventually be added 
to the FITS Standard after going through the formal approval process.  If 
desired, a separate email list could be set up for this purpose, to allow 
interested persons to work out the details of the new convention.

The technical group that we have talked about appointing to clarify the 
current FITS standard would not be the appropriate group to develop major 
new FITS conventions. It might be appropriate however for this technical 
group to suggest adding a short section to the FITS Standard that summarizes 
the current situation, i.e.,  that FITS was not originally designed to 
support color images, and currently there is no recognized standard for how 
to represent color information (although there have been some suggestions).

Bill


Francois Ochsenbein wrote:
> Dear Bill & IAUFWG members,
> 
> About the FITS conventions which should be clarified, there is
> the long-standing convention about color images which was discussed
> several times, but which never reached an agreement. FITS can be
> discarded (e.g. by amateur astronomers) as an interesting format 
> just for this lack of a definition, which I feel is a pity.
> 
> The two approaches for storing RGB images in FITS files are, either to
> store one color as the main 2D matrix and other colors in FITS extensions,
> or to use a 3D 'matrix' with a convention specifying which 'axis' contains
> the color information (e.g. via CTYPE='RGB' as proposed many years ago). 
> I know that several discussions occured about these alternatives and the 
> usage of 'pseudo-dimensions', but a recommendation of the FITS authorities 
> on how to write color images in FITS would avoid to see a proliferation of
> contradictory conventions about this issue.
> 
> One immediate help could be to add to the FITS documents a list of
> the "official" CTYPEs . This list should contain, in addition to 
> the WCS conventions, at least the "STOKES" convention which is 
> widely used, and the "RGB" convention which was discussed many times.
> 
> Does this sound impossible ?
> 
> Cheers, francois
-- 
____________________________________________________________________
Dr. William Pence                       pence at milkyway.gsfc.nasa.gov
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