[fitsbits] BLANK keyword misinterpretation

[Arnold Rots]

Shouldn't you also flip the sign bit?
That's part of the traditional trick.

  - Arnold

Steve Allen wrote:
> ...
> Our data originate via a 16-bit AtoD conversion which produces bits
> corresponding to C "unsigned short" on modern big-endian processors.
> The pixel values are always offset such that all values are positive.
> We store the bits directly in the image arrays as unsigned short
> integers using the traditional trick of offsetting the physical data
> values using the keywords
> 
> BITPIX   = 16
> BZERO    = 32768
> BSCALE   = 1
> ...
> 
> --
> Steve Allen          UCO/Lick Observatory       Santa Cruz, CA 95064
> sla at ucolick.org      Voice: +1 831 459 3046     http://www.ucolick.org/~sla
> PGP: 1024/E46978C5   F6 78 D1 10 62 94 8F 2E    49 89 0E FE 26 B4 14 93
> 
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Arnold H. Rots                                Chandra X-ray Science Center
Smithsonian Astrophysical Observatory                tel:  +1 617 496 7701
60 Garden Street, MS 67                              fax:  +1 617 495 7356
Cambridge, MA 02138                             arots at head-cfa.harvard.edu
USA                                     http://hea-www.harvard.edu/~arots/
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