[fitsbits] Rendering FITS Data

[Grinder]

"Steve Allen" <sla at ucolick.org> wrote in message
news:mailman.1066254781.4389.fitsbits at listmgr.cv.nrao.edu...

Thanks for your response.  I can't say I'm a dedicated fan, but
enjoyed your appearance on "Homicide: Life on the Streets" a
few years ago.

> On Mon 2003-10-13T21:59:24 -0500, Grinder hath writ:
> > If you have a 2d array of 16-bit signed integer values, you
can
> > make a simple linear transformation to and 8-bit grayscale
> > palette.  I imagine log and poly transforms are of use as
well.
>
> In the absence of the experts (see below) I suppose that the
best
> (only?)  way to determine this is to survey the existing FITS
display
> programs.  I have encountered programs that map the image to
display
> using sqrt, square, log, linear, and various histogram
equalization
> and/or cutoff methods.

I've taken a look at ds9 and FITSView.  My rendering methods
match the output from ds9, but FITSView must mean something
different by "linear" than ds9, as it's output is radically
different.  For example:

Given a 16-bit integer data set, ds9 apparently maps the MSB of
each pixel to a linear 8-bit grayscale.  So values like, 0x0000
to 0x0400 appear essentially the same -- black.  FITSView,
though, has much better contrast for these low values even when
set to linear.  Examining a screenshot of the rendering shows
that it is not strictly using grayscale colors.  Small
variations in the RGB components are present, providing a
larger palette, but still appearing as a grayscale.

Any idea what they're doing?

> > Basically, I'm looking for a discussion of useful
techniques,
> > either here, or some existing web resources.  Thanks for
your
> > time and consideration.
>
> This parallels a question that has been bouncing around the
FITS
> community -- should there be various levels of FITS
conformance?  In
> this case perhaps what would help most is a class of FITS
documents
> which could have a status akin to the Internet (IETF) RFCs
that are
> known as Best Current Practice (BCP).  The problem with this
notion is
> that writing and approving any such documents are mostly
thankless
> tasks which subtract from the valuable time of the few who
are
> interested in implementing them.
>
> If these sorts of techniques are published it is likely that
many of
> their authors are currently at the ADASS conference, so this
> discussion is likely to take many days to finish.

That's good background.  Does the FITS community have any
collecting points on the web?