[iaufwg] FITS conventions

[Clive Page]

I have read Mark's document with interest.  Colour representation is a 
complex subject, and I suspect that if the FITS community tries to find a 
way of solving it completely, it might take a long time.

Lucio Chiapetti said:

> I do not feel at all the lack of a fixed or mandatory colour
> representation for a standard (NAXIS=2) FITS image, since I can obtain
> whatever look I want with a display program like ds9 (incidentally, after
> having written in the past some homegrown stuff [not to talk of IHAP and
> MIDAS], and done some use of IDL, I would say I've personally now settled
> on almost exclusive use of ds9).

I agree that ds9 now does nearly all that users want when displaying FITS 
images.  The problem is that having selected a sensible way to display 
one's image, there isn't any standard way of preserving that choice in the 
image file.  In high energy astronomy at least, we are not interested in 
the problems of true colour represenation (since there isn't one), what we 
want is a false colour representation which shows the important features 
of the image.  Having found that it would be nice to preserve it somehow.

So I wonder if we could start off by just defining a simple conversion 
from the intensity (or flux or whatever) from the primary FITS image array 
to some common colour representation, such as RGB.  A simple look-up table 
may be enough - and I guess that's what programs such as ds9 do internally 
and certainly what formats such as GIF store. I think this would make it 
easier to use programs like ds9 (as there would be a default look-up 
table) and also to use image conversion utilities like xv automatically.


-- 
Clive Page
Dept of Physics & Astronomy,
University of Leicester,    Tel +44 116 252 3551
Leicester, LE1 7RH,  U.K.   Fax +44 116 252 3311