[fitsbits] Image Extension Question

[Randall Thompson]

Hi Chris,
   Yes the Image extension like the primary HDU allows the use of
the "reserved" keywords BSCALE, BZERO, and BLANK. These keywords
are not "mandatory", but when used, must conform to the definition 
specified in the FITS standard. In general, I think the use of 
floating point data is preferred over scaled integers.

   The original Image extension paper can be found at:
http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1994A%26AS..105...53P

  A list of the reserved FITS keywords can be found in tables F.2 and
F.3
in Appendix F of the FITS standard:
http://archive.stsci.edu/fits/fits_standard/node89.html#SECTION0019

See also comments regarding the use of these keywords versus
floating point data at:
http://archive.stsci.edu/fits/fits_standard/node49.html#SECTION00103

Randy
 
 
Christopher Lawton wrote:
> 
> Hello,
> 
> I am in the process of writing a utility to read data from FITS files.  The
> FITS standard is very clear but I have one question about the Image
> Extension.  The standard doesn't define mandatory keywords to scale the
> image data, like the BZERO and BSCALE keywords for the primary data.  Is the
> convention to use BZERO and BSCALE to scale image data if needed?  Should I
> expect the BLANK  keyword to be used for undefined values or is there no
> convention for representing undefined values in Image Extension data?
> 
> Thanks,
> Chris Lawton
> clawton at mathworks.com