Subject: BSCALE/BZERO

From: teuben at lynx.astro.umd.edu (Peter Teuben)
Date: 28 Jul 92 15:27:13 GMT

The NOST fits panel report states that for BITPIX < 0 (i.e. when
the data is stored in IEEE floating point format) the usage of
BSCALE and BZERO not recommended. We never (wanted to) forbid 
or explicitly state that it should or should not be applied
in section 6.3 (though section 5.2.2.5 does state this).

The FITS users guide (also published by NOST) does explicitly
states that BSCALE and BZERO  be applied in the BITPIX<0 case, with
the danger of producing overflows/underflows of course (hence the 
reason that BSCALE and BZERO should not be present).

I've indeed noted that the AIPS and MIRIAD readers 'correctly' apply
BSCALE and BZERO in the floating point cases, but the problem arose
when we imported a FITS file generated by IDL. The idl procedure
'WRITEFITS' seems to write images with BSCALE not 1.0, which has
caused some readers to read in the wrong datavalues.
Perhaps Wayne Landsman can comment on this.

Has anybody seen fits readers which skip BSCALE and BZERO if BITPIX < 0?

	Peter

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