NES-ish image color reduction

nes-ize

#!/bin/bash

if ! [ "$#" = 1 ]
then
  echo "Usage: $0 FILE"
  exit 1
fi

d="$(identify "$1" | cut -d' ' -f3)"
width="${d/x*/}"
height="${d/*x/}"
width_d="$(echo -n "$width" | wc -c)"
height_d="$(echo -n "$height" | wc -c)"
basename="${1/.*/}"

# https://commons.wikimedia.org/wiki/File:NES_palette.png#/media/File:NES_palette.png
convert "$1" -dither FloydSteinberg -remap nes-palettes.png -colors 25 ",$basename-palettes.png"

for x in $(seq 0 16 $((width - 1)))
do
  for y in $(seq 0 16 $((height - 1)))
  do
    # convert "$1" -crop "16x16+$x+$y" +dither -colors 4 -remap ",$basename-palettes.png" "$(printf ",$basename-sprite-%0${width_d}d-%0${height_d}d.png" $x $y)"
    convert "$1" -crop "16x16+$x+$y" -dither FloydSteinberg -colors 4 -remap ",$basename-palettes.png" "$(printf ",$basename-sprite-%0${width_d}d-%0${height_d}d.png" $x $y)"
  done
done

for x in $(seq 0 16 $((width - 1)))
do
  x="$(printf "%0${width_d}d" "$x")"
  convert ,$basename-sprite-$x-*.png -append ,$basename-sprite-v-$x.png
done
convert ,$basename-sprite-v-*.png -flatten $basename-nes.png
rm ,$basename-*