You may notice that
the stacked image
in one filter will be offset by integer amounts from the
stacked images in another filter.
We use the WCS to determine these shifts,
and imshift to then reshift them, using the
philtrans.cl script:
files WLM*.fits > dstack
philtrans dstack WLMU.fits
Will shift all of the stacked images so they line up with the reference
image "WLMU.fits", in this case. The way we've executed this, the
new images will replace the old.
One of the wonderful, wacky things about how IRAF handles the WCS is that the bad pixel mask creating in the stacking operation are unaffected. Furthermore, we can now imcopy the sections of the shifted, stacked images to keep just the good stuff, and the bad pixel masks are STILL appropriate!