Output 900x900 Real32 SKY coord image (e.g. mos1S001-bkgimsky-2000-7200.fits)
The user can input (the output file name via the param outimage, but if none is entered the program will derive a filename based on the instrument and expid from the input file, e.g. mos1S001-bkgimsky-2000-7200.fits)
