Subject: IMAGE extension

From: [email-masked] (William Thompson)
Date: Mon, 22 Jun 92 16:01:35 -0400

Doug Tody ([email-masked]) quotes me as saying:

> > To my mind, the extension name IMAGE is *deceptively* simple.  It
> > implies something that just isn't necessarily true, i.e. that the
> > extension contains a picture.
> 
> It doesn't imply that to me.  I suppose you are right that people in
> other fields might be confused by the terminology but I think FITS should
> be oriented towards astronomy.  In any case, I don't see any problem with
> generalizing the concept of "image" (or "data image") to mean something
> more complex than a picture.
>  
> > Are we going to have to have another extension, which is exactly the same
> > except that XTENSION='SPECTRUM'?
> 
> A simple spectrum is a one dimensional image.  (there are also 2 and 3
> dimensional spectra).  The proposed IMAGE extension could be used to
> store spectra.
>  
> > There are, however, people who do think that FITS is only for images,
>                                                                 ^^^^^^
> you mean pictures...
> 
> > and who are surprised when they discover that it doesn't include
> > support for those features which are common for standard raster image
> > formats like GIF, TIFF, etc., e.g. embedded color tables, or RGB color
> > separation.  I've seen this confusion in people both on the
> > (alt.)sci.astro.fits newsgroup, and in support personnel who have been
> > working with us in developing hardware and software for astronomical
> > observations.
> 
> FITS doesn't have to try to be all things to all people - I don't think
> it would be successful it if did.  It was developed for astronomical
> data, and the terminology should be oriented towards astronomy.  In current
> astronomical use, "image" refers to a complex object (N-dimensional data
> array with associated header etc.).  The terms array and picture refer
> to simpler things.
> 
> This issue was discussed at both the European FITS meeting last May, and
> again at the WGAS.  At the European meeting no one objected to the name
> "IMAGE" for this extension, and in fact most people there preferred the
> term.  The issue wasn't discussed explicitly at the WGAS meeting; if I
> recall correctly the IMAGE extension was brought up for discussion and
> there were no objections raised.

I just did an informal poll of nine astronomers here at the NASA
Goddard Space Flight Center.  I asked them if they could draw a
distinction between the terms "picture" and "image".  Not one of them
could, at least in any way applicable to the digital storing of data.
Only one of them had ever heard of the term "image" being applied in
the way you use it, but only after I brought it up.

I don't intend to produce a flame, but I do want to get the facts
straight.  The most cogent reason for sticking with the name "IMAGE" is
that it is already in use, and I can live with that.

Bill Thompson

---

From: [email-masked] (Archie Warnock)
Date: Mon, 22 Jun 92 16:22:44 -0400

> that it is already in use, and I can live with that.

 I agree with Bill here.  What prompted my original note was that the
 adoption of the name IMAGE does, in fact, blur the distinction between
 data structure and data interpretation.  We (the FITS community) are, of
 course, free to do this.  We should also make sure we understand that we
 _are_ blurring that distinction, and that it is something we are doing
 intentionally. 

 It makes me uncomfortable to use IMAGE in this way.  It would make me
 even more uncomfortable if someone were to seriously propose to use
 SPECTRUM in a similar way.  You could, after all, store a 1-D spectrum as
 ordered pairs, as pairs of vectors, as a single flux vector and two
 scalars.  They're all spectra.  If we decide to continue to ignore the
 distinction between structures and interpretation, they'd all need
 different names.  My contention is that they should all be referred to
 as "SPECTRUM", with some additional syntax to indicate (to the software,
 not necessarily to the end user) how they have been stored.

 Do I object to the name IMAGE enough to vote to reject the proposal on
 that basis alone?  No, of course not.  It's not something that's
 necessarily wrong.  It's just an issue to be addressed and discussed.
 It's a bit glib and perhaps naive to dismiss the discussion simply
 because it hasn't been raised until now.

----------------------------------------------------------------------------
-- Archie Warnock                   Internet:  [email-masked]
-- Hughes STX                       "Unix --- JCL For The 90s"
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