[fitsbits] Re: Reading floating point FITS files

[Mark Calabretta]

On Fri 2003/11/28 14:51:53 -1000, Thierry Forveille wrote
in a message to: Mark Calabretta <Mark.Calabretta at atnf.CSIRO.AU>
and copied to: Thierry Forveille <forveill at cfht.hawaii.edu>,
     seaman at noao.edu (Rob Seaman), fitsbits at fits.cv.nrao.edu

>Sure, but how many users are there that care about the data values/detailed 
>coordinate information and that would not want to play with their own
>colour tables?

Currently, there is not even a way to indicate in FITS that a particular
image (e.g. the crab nebula multispectral composite) is meant to have a
colour interpretation.

> My guess is that there are large constituencies for each
>capability but that they are mostly disjoint. They might even be the same
>person by the way, just not at the same time: I am glad to use nicely
>prepackaged pictures for my classes, but for my research where I use the
>full data I'd play with the colours anyways to look for additional 
>structure.

Does this mean that you store the image data as jpeg, FITS, or both?

Of course, you would still be able to twiddle the colours in a colour
FITS dataset; I have in mind upper- and lower-threshholding and power
law correction at least.  These would allow a reasonable transform from
intensity/luminance varying linearly with pixel value (a non-linear
perceptual scale) to a more-or-less linear scale of lightness (a linear
perceptual scale).  Colour FITS would probably also include a CIE-based
colour space to record true (device-independent) colour.  I don't
believe this is possible in any of the common computer graphics image
formats.

> Most astronomical datasets have more information than can be
>displayed on a screen no matter how smart the lookup table choice, so
>we'd just make one particular reasonable choice. That's fine if it
>can be done (very) simply, but otherwise I'd rather stick to jpeg (or
>postscript, or whatever) stored next to the fits file on the web site.

You would almost always want to do that anyway because the general public
cannot be expected to have ready access to FITS viewers.  However, that
is not the point.

Mark Calabretta
ATNF