[fitsbits] Question(s) regarding development of proprietary FITS manipulation software. . .

[William Pence]

gberz3 wrote:
> Thanks Maren.  One question I suppose I've just forgotten to ask:  Is
> there anything particularly special about the actual graphics content
> of a FITS file?  Or is it perhaps simply a glorified TIFF or JPEG of
> some sort?
> 
> Regards,
> Michael

The FITS format is significantly different from other formats such as 
jpeg that are used to represent images.  The following text is copied 
from http://fits.gsfc.nasa.gov/fits_viewer.html, and comes originally 
from the FITS MIME-type document, RFC 4047:

----------------------------------------------------------------
  An application intended to render a FITS image for viewing by a user 
has significantly more responsibility than an application intended to 
handle other standard image formats (e.g., "jpg" or "gif" images). FITS 
data arrays contain elements which typically represent the values of a 
physical quantity at some coordinate location. Consequently they need 
not contain any pixel rendering information in the form of transfer 
functions, and there is no mechanism for color look-up tables. An 
application should provide this functionality, either statically using a 
more or less sophisticated algorithm, or interactively allowing a user 
various degrees of choice.

Furthermore, the elements in a FITS data array may be integers or 
floating point numbers. The dynamic range of the data array values may 
exceed that of the display medium and the eye, and their distribution 
may be highly nonuniform. Logarithmic, square-root, and quadratic 
transfer functions along with histogram equalization techniques have 
proved helpful for rendering FITS data arrays. Some elements of the 
array may have values which indicate that their data are undefined or 
invalid; these should be rendered distinctly.

The data array in a FITS image must have a dimensionality between 1 and 
999, the boundaries inclusive, indicated by the NAXIS keyword. The 
extent of any coordinate axis in a FITS data array may, however, consist 
of only a single element. Hence an algorithm designed to render 
two-dimensional images will be capable of displaying a three- or 
four-dimensional FITS array when one or two of the axes consist of a 
single pixel.
-- 
____________________________________________________________________
Dr. William Pence                       pence at milkyway.gsfc.nasa.gov
NASA/GSFC Code 662       HEASARC        +1-301-286-4599 (voice)
Greenbelt MD 20771                      +1-301-286-1684 (fax)