[fitsbits] Re: Reading floating point FITS files

[Rob Seaman]

Don Wells says:

> There is another way that we could support inclusion of color imagery
> in FITS files: we could agree to permit XTENSION='JPEG', XTENSION='TIFF',
> XTENSION='GeoTiff', XTENSION='PNG', etc.  The XTENSION mechanism enables
> FITS to wrap up any data object[*] and declare its type.

NOAO implemented a general purpose foreign file encapsulation scheme
several years ago.  The interest in this has been very minimal.  The
reality is that FITS is already general enough to permit the storage
of all the graphics formats mentioned above.  Adding additional
functionality (explicit typing and presumably a keyword to convey
the size of the embedded object) only makes it more likely that
somebody will actually use this feature.  Are we really ready to see
FITS turned into some poor man's XML to be used only as a wrapper to
provide access to somebody else's data format?

On the other hand, the original discussion focused on the exact opposite
feature - how to use native FITS to provide color handling (and perhaps
other features) similar to the various non-astronomical picture formats.
It might help if somebody could provide a use case for why this might be
a requirement of some astronomical project.

Mark Calabretta says:

> it still doesn't make much sense to me that as the last step in
> producing a composite image, after regridding each input FITS image
> onto a common coordinate system, you have to resort to writing it out
> in GeoTIFF simply because FITS can't handle colour.

I would think this is obvious.  The final step isn't to write the result
as non-FITS because FITS doesn't provide some feature - the final step
is to write non-FITS because we are in some sense publishing the result
to a wider audience.  FITS isn't used because printers and web browsers
and the plug-ins and helper applications that are available to the
general internet community (including astronomers) don't speak FITS.

Imagine some truly lovely implementation of a color model in FITS.  A
FITS color model could be a semantic color model, unlike those provided
by the generally available "photographic" formats like GIF or JPEG.
Each separate color plane could retain its original meaning - and the
sum of the information across all the color planes could be much more
expressive than any plane taken alone.  For one thing, a FITS color
model could include narrow band or non-visible colors (extending into
radio and gamma spectra) - and could include more than the three colors
arising from human perception theories and trichromatic printer/display
color mixing technologies.  That said - is this a standard that would
be adopted and supported outside of astronomy?  And in the absence of
commercial support, how useful would this methodology be to astronomers?

It is possible to imagine extending FITS in both directions - to
implement color support within FITS or to permit foreign formats to be
accessed from within FITS.  Both directions would require software to
be developed - and to be widely adopted - before the extensions would
be useful.  Before we put resources into what would be a daunting task,
there should be a motivation stronger than purely a sense of esthetics.

Rob Seaman
NOAO/SDS