#!/bin/sh
set -e
t=.tmp.$$
xpmtoppm -alphaout="$t.pbm" "$1" > "$t.pnm"
pnmcomp -alpha="$t.pbm" "$t.pnm" "$t.pbm" "$t.2.pnm"
pnmtopng -alpha "$t.pbm" "$t.2.pnm" > "$2"
rm "$t.pnm" "$t.pbm" "$t.2.pnm"