[iaufwg] FITS conventions

[Steve Allen]

On Fri 2006-02-10T15:59:55 +0100, Francois Ochsenbein hath writ:
> 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.

I remain unmotivated, but not immovable.

There are plenty of graphics formats for color images.  They are well
supported by existing software.  Some of them (TIFF, the EXIF
extensions to JPEG) have rich metadata contructs akin to, and in some
ways surpassing, the conventions already established for FITS (even to
the point of rivaling the WCS conventions).  TIFF has mechanisms for
registering new metadata tags which are at least as functional as the
IAUFWG is for FITS.  These image formats inherently have functional
schemes for compression.

If amateurs are motivated only by stunning color pictures then let
them discard FITS.  I feel that our job should be to encourage the
development of new rich conventions, but to do so without practical
need is to add complexity which may be misguided.
If members of the astronomical community develop a tool that takes
multiwavelength FITS data with WCS metadata and an interface that
makes stunning color images then yes, we should act, but maybe
not directly to add color images to FITS per se.

I do not hesitate to point out that the EXIF extensions to JPEG work
by embedding a TIFF file within the JPEG.  I suppose this is because
of the rich metadata tag structure inherent in TIFF.  If there is a
desire to pass around pretty color images while at the same time
passing around the FITS files with the numerical data then I suggest
we simply define a new extension HDU types something like

XTENSION = 'MIME; image/jpeg; charset=us-ascii'

Note that this is quite similar to the concept developed at NOAO
by Nelson Zarate.

If there is a desire to preserve some coordinates in a pretty picture,
then the image can be encoded into GeoTIFF with its WCS tags.  Then
the resulting TIFF can be loaded into any GIS software system.

--
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