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[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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