perform arithmetic on two portable anymaps
see also :
pbmmask - pnmpaste - pnminvert
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portable anymaps as input. Performs the specified arithmetic
operation, and produces a portable anymap as output. The two
input anymaps must be the same width and height.
is performed between corresponding pixels in the two
anymaps, as if maxval was 1.0, black was 0.0, and a linear
scale in between. Results that fall outside of [0..1) are
-difference calculates the absolute value of
pnmarith -subtract pnmfile1 pnmfile2, i.e. no
truncation is done.
All flags can
be abbreviated to their shortest unique prefix.
pnmpaste , pnminvert , pnm
1989, 1991 by Jef Poskanzer. Lightly modified by Marcel