[fitsbits] Any bad pixel mask convention?

[Eric Greisen]

Richard J. Mathar wrote:
> Is there something like a bad pixel mask FITS standard that stores bad pixels
> with a boolen value or perhaps a float where 1=good, NaN=bad in FITS images?
> Should one use a BLANK value combined with a byte or integer image or is
> it best to invent a private ASCII format for this purpose?

Internally AIPS uses a magic value with its floating image data.  But we 
do once in a blue Moon hit a real value that is exactly the magic value.

For FITS files we change this magic value into a NaN when we write out 
the files in floating point.  I doubt that integer is ever used now, but 
when it does we declare a blank value (e.g. -32767 in 16 bit) and scale 
the image to -32766 to +32766 and use -32767 for blanked pixels.

Eric Greisen