Runs a directory of PNGs through a quantizer and optimizers and outputs to a compressed directory.

optimizepngs

#!/bin/sh
# adapted from: https://github.com/bingalls/webGraphicsMagick/blob/master/compressLossy.sh

COMPRESS_DIR='./compressed' #Creates compressed copies in $COMPRESS_DIR.

#Create dest dir for compressed copies of images
if [ ! -d $COMPRESS_DIR ];then
  mkdir $COMPRESS_DIR
else
  #read -t15 is bash for timeout of 15 seconds
  read -p "$COMPRESS_DIR/ already exists. 'y' to overwrite existing files: " proceed
  if [ "y" != $proceed ];then
    echo "Exiting, to preserve existing contents in ./$COMPRESS_DIR/"
    exit 1;
  fi
fi

if [ `find . -maxdepth 1 -name "*.png" | head -1` ]; then    #*.png exists
  mkdir $COMPRESS_DIR/tmp
  for i in *.png;do

    cp $i $COMPRESS_DIR/tmp/quant.png

    echo "quantizing $i"
    pngquant 32 -f --ext .png $COMPRESS_DIR/tmp/quant.png

    echo "compressing with optipng"
    optipng -quiet -o2 $COMPRESS_DIR/tmp/quant.png $COMPRESS_DIR/tmp/optipng.png

    echo "compressing with pngcrush"
    pngcrush -q -l9 -m0 $COMPRESS_DIR/tmp/quant.png $COMPRESS_DIR/tmp/crush.png

    echo "comparing compressions"
    
    file=`basename $i`
    smallest=`ls -1S $COMPRESS_DIR/tmp/*|tail -1`
    if [ `du $smallest|cut -f1` -lt `du $i|cut -f1` ];then
      mv -f $smallest "$COMPRESS_DIR/$file"
    fi
    #Insert a read here, to pause, and compare *magick to pngcrush, for benchmarking.
    rm $COMPRESS_DIR/tmp/*
  done
  rmdir $COMPRESS_DIR/tmp
fi    #*.png exists