The number of rows and columns in file1 must be equal to those in file2.
The subtracted image is put in file1 unless overridden by the outfile option.
sub alphalyr dark
-subtracts the dark frame from the file `alphalyr'.
sub alphalyr const=45
-
Subtracts 45 from each pixel in file `alphalyr'.
sub alphalyr const=2*sky box=1
-
subtracts twice the variable SKY from file alflyr over the range specified in
box number 1. It is assumed that the variable SKY was set by a prior SKY
command.