A bash script to run PNGs through both pngcrush and opticrush using unreasonably zealous settings.

pngfix.sh

#!/bin/bash
# This script attacks either all file arguments given to it, or all png's in a subtree (if 
# a directory or no argument is given), and runs both pngcrush and optipng on them with liberal settings.
CRUSH=$(which pngcrush)
OPTI=$(which optipng)
OPTS1='-rem cHRM -rem gAMA -rem iCCP -rem sRGB -q'
OPTS2='-quiet -fix -o4'
TEMP="/tmp/temp.png"

BEFORE=0
AFTER=0
MAXDIFF=0

FILES=("$@")

# if argument is a directory, then run on all pngs in it's subtree
# if no argument is supplied then run in current working directory 
if [[ $# -lt 2 ]] && [ -d $FILES ]; then 
  if [[ $# -eq 0 ]]; then FILES='.'; fi
  OLDIFS=$IFS
  IFS=$'\n' 
  FILES=($(find -x $FILES -iname '*.png' -type f))
  IFS=$OLDIFS
fi

# find the sum of all file sizes
LEN=${#FILES[@]}
for (( i=0; i<${LEN}; i++ )); do
  FILESIZE=$(stat -f%z "${FILES[$i]}")
  BEFORE=$(( $BEFORE + $FILESIZE ))
done

# crush all files
for (( i=0; i<${LEN}; i++ )); do

  FILEBEFORE=$(stat -f%z "${FILES[$i]}")
  # crush
  $CRUSH $OPTS1 -- "${FILES[$i]}" $TEMP
  $OPTI $OPTS2 -- $TEMP
  
  # stats
  FILESIZE=$(stat -f%z "$TEMP")
  DIFF=$(( $FILEBEFORE - $FILESIZE ))
  AFTER=$(( $AFTER + $FILESIZE ))

  # replace if $DIFF is > 0
  if [[ $DIFF -gt 0 ]]; then
    cp $TEMP "${FILES[$i]}"
  fi

  echo "> ${FILES[$i]}"
  echo "> before:" ${FILEBEFORE} "- after:" ${FILESIZE} "= saved:" ${DIFF} "bytes"
  
done

rm -f $TEMP

echo '--------------------------'
echo 'total size before:' ${BEFORE}
echo 'total size after:' ${AFTER}
echo 'reduction:' $( echo "scale=4; (($BEFORE - $AFTER) / $BEFORE) * 100" | bc ) "%"
echo '--------------------------'