stacking images

[<aah@nofs.navy.mil>]

Tom,
  I stacked several set of pretty-picture images from ARNE,
and it was a chore.  You don't just have offset in x and y,
but also rotation if you are not aligned to the pole.
  Stacking requires calculation of the offsets, rotation and
possible scale change, and then for each image you have to
create a temporary copy that has been properly aligned (it
has to be sub-pixel, so there are 4M operations).  Then you
read the images back in, add them in a memory buffer and
write the result out (which will no longer be a 2kx2k image).
  It is certainly possible to stack images; I do it all the
time in the GRB arena since I need to go deep on the bigger
telescopes and remove artifacts like cosmic rays.  However,
as a routine operation that you would do on every field every
night, it might be challenging.
Arne