env/bin/imgresize.sh

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#!/bin/sh
# imgresize
# Written in 2019-2020 by Lucas
# CC0 1.0 Universal/Public domain - No rights reserved
#
# To the extent possible under law, the author(s) have dedicated all
# copyright and related and neighboring rights to this software to the
# public domain worldwide. This software is distributed without any
# warranty. You should have received a copy of the CC0 Public Domain
# Dedication along with this software. If not, see
# <http://creativecommons.org/publicdomain/zero/1.0/>.
usage()
{
cat - <<. >&2
Usage:
${0##*/} size in-file out-file
"size" is WxH or Wx or xH.
.
exit 1
}
err()
{
printf "%s: %s\n" "${0##*/}" "$*" >&2
exit 1
}
check_dimension_format()
{
printf "%s\n" "$1" | grep -q "^[0-9]*x[0-9]*\$" && [ "$1" != "x" ]
}
[ $# -eq 3 ] && check_dimension_format "$1" || usage
[ -n "$2" ] || err "input file name can't be empty"
[ -n "$3" ] || err "output file name can't be empty"
size=$1
w=${size%x*}
h=${size#*x}
infile=$2
outfile=$3
inprog=
case $infile in
*.jpg | *.jpeg)
inprog=jpegtopnm
;;
*.png) inprog=pngtopam
;;
*) err "unknown input format"
;;
esac
outprog=
case $outfile in
*.jpg | *.jpeg)
outprog=pnmtojpeg
;;
*.png) outprog=pamtopng
;;
*) err "unknown output format"
;;
esac
$inprog <"$infile" |
pamscale ${w:+-width "$w"} ${h:+-height "$h"} |
$outprog >"$outfile"