[TASS] hot pixels

["Arne A. Henden" <aah@NOFS.NAVY.MIL>]

Chris gave the URL for the iraf function cosmicray.
Thinking about the problem, cosmicray will remove
what it says -- cosmic rays -- but will not remove
hot pixels since by definition they appear at the
same place on sequential images and therefore cannot
be rejected.  The normal approach for hot pixels
is to take dark frames and subtract.  This works
as long as the pixels are 'hot' because of high
dark current, and the dark frames are of the same
length and temperature as the science frames.  If
the pixels are 'hot' because they are just bad,
then the normal approach is to locate the pixels
and create a mask file.  This mask file is then
used by a routine such as iraf's fixpix to go in
and replace the bad pixels in all images
by interpolation from surrounding pixels, or just
marking them as really bad (such as setting them
to a large negative value) and ignoring them in
subsequent processing.
Arne