Script to Convert PNG Images to Indexed Color

toidx.sh

#!/usr/bin/env bash

## Creative Commons Zero (CC0) public domain dedication
#
#  To the extent possible under law, the author has
#  waived all copyright and related or neighboring
#  rights to this work. This work is published from:
#  The United States.
#
## For more information see: https://creativecommons.org/publicdomain/zero/1.0/

## Script to convert PNG images to indexed color.
#
#  Requires pngquant (https://pngquant.org/) &
## ImageMagick (https://imagemagick.org/).


argv=("$@")
argc="${#argv[@]}"

# check for pngquant executable
which pngquant > /dev/null 2>&1; res=$?
if [[ ${res} -gt 0 ]]; then
  echo "ERROR: 'pngquant' executable not found. Please install pngquant: https://pngquant.org/"
  exit 1
fi

# check for identify executable from ImageMagick
which identify > /dev/null 2>&1; res=$?
if [[ ${res} -gt 0 ]]; then
  echo "ERROR: 'identify' executable not found. Please install ImageMagick: https://imagemagick.org/"
  exit 1
fi

showUsage() {
  echo
  echo "$(basename $0) [-f] [-q min-max] path/to/image1 [path/to/image2...]"
  echo
}

force=0
pngq_params=("-v" "-f")
images=()

parsed_args=()
checkDuplicateArgs() {
  first=$1
  for second in "${parsed_args[@]}"; do
    if [[ "${first}" == "${second}" ]]; then
      return 1
    fi
  done
  return 0
}

args_done=0
for ((idx=0; idx < ${argc}; idx++)); do
  param="${argv[${idx}]}"
  if [[ ${args_done} -eq 0 ]] && [[ "${param}" == -* ]]; then
    checkDuplicateArgs "${param}"; res=$?
    if [[ ${res} -gt 0 ]]; then
      echo "ERROR: duplicate argument: ${param}"
      exit 1
    elif [[ "${param}" == "-h" ]] || [[ "${param}" == "--help" ]]; then
      showUsage
      exit 0
    elif [[ "${param}" == "-f" ]]; then
      force=1
    elif [[ "${param}" == "-q" ]]; then
      if [[ ${argc} -le ${idx}+1 ]]; then
        echo "ERROR: -q (quality) parameter requires a value: -q min-max"
        showUsage
        exit 1
      fi
      idx=${idx}+1
      pngq_params+=("--quality" "${argv[${idx}]}")
    fi
    parsed_args+=("${param}")
  else
    # done parsing arguments
    args_done=1
    images+=("${param}")
  fi
done

imagec="${#images[@]}"
if [[ ${imagec} -eq 0 ]]; then
  echo "ERROR: no images specified"
  showUsage
  exit 1
fi

for img in "${images[@]}"; do
  if [[ ! -f "${img}" ]]; then
    echo "ERROR: file not found or taget is not a file: ${img}"
    exit 1
  fi

  mimetype=$(file --mime-type "${img}" | sed "s|^${img}: ||")
  if [[ "${mimetype}" != "image/png" ]]; then
    echo "ERROR: file is not a PNG image: ${img}"
    exit 1
  fi

  colors=$(identify -verbose -unique "${img}" | grep "  Colors: " | sed -e 's/^.*Colors: //')
  if [[ -z ${colors} ]]; then
    echo -e "\nImageMagick: Error reading file ${img}"
    exit 1
  fi

  echo -e "\n${img}: found ${colors} colors"
  if [ ${force} -eq 0 ] && [ ${colors} -gt 256 ]; then
    echo "Image has more than 256 colors, not optimizing"
    exit 0
  fi

  pngquant "${pngq_params[@]}" -o "${img}" "${img}"
done