file1.fits and (if specified) file2.
A constant offset can be specified optionally.
The computed difference is stored in file1.fits.
The number of rows and columns in file1.fits
must be equal to those in file2.fits.
The subtracted image is put in file1.fits unless overridden by the
outfile= option.
const= subtracts the numerical constant specified.
factor= mutiplies file2 by factor before subtracting.
sub alphalyr dark factor=.7dark.fits
from the file alphalyr.fits.
storing the difference in alphalyr.fits.
sub alphalyr const=45
-
subtracts 45 from each pixel in file alphalyr.fits.