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



 
 
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Old August 20th 07, 10:59 PM posted to sci.astro.fits
William Pence
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Default [fitsbits] Question(s) regarding development ofproprietary FITS manipulation software. . .

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
NASA/GSFC Code 662 HEASARC +1-301-286-4599 (voice)
Greenbelt MD 20771 +1-301-286-1684 (fax)


 




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