RESTORE_LOW8 will combine a compressed image with a low 8-bit image to restore
the full 12 bits of resolution. The images need to be taken relatively
close in time (less than hours apart), and it must be for the same
PFI location. A sample call is
IDL> out = restore_low8(low8, comp)
where low8 is the SXT image taken with the low 8 bits, and
comp is the comparable compressed image (ideally, acquired
at nearly the same time).