Small bash script that optimize jpeg images by their PSNR metrics. Compress original file in variety quality from low to high and compare PSNR. If it greater then threshold and size less, copy tmp file to working dir and go to next file. On big files slow, cant find ImageMagick alternative. Any suggestions, ideas?

Optimize JPEG bash

#!/bin/bash

TMPDIR="/tmp/psnr_tmp"
PSNR_LEVEL=39

mkdir $TMPDIR

ls *.jpg | while read file; do
	echo $file
	echo "-----------------"
	name=${file%%.*}
	actualsize=$(du -b "$file" | cut -f 1)
	for q in {60..90..1} ; do
		echo -ne "Process quality: $q"\\r
		convert -quality $q $file $TMPDIR/$file
		compare $file $TMPDIR/$file $TMPDIR/$name_diff.png
		psnr=$(compare -metric PSNR $file $TMPDIR/$file $TMPDIR/$name_diff.png 2>&1 >/dev/null)
		if [ $(echo "$psnr>=$PSNR_LEVEL" | bc) -eq 1 ]; then
			jpegtran -copy none -optimize -outfile $TMPDIR/$file $TMPDIR/$file
			compressedsize=$(du -b "$TMPDIR/$file" | cut -f 1)
			if [ $compressedsize -lt $actualsize ]; then
				mv $TMPDIR/$file .
				echo "Quality: $q Result: filesize $actualsize => $compressedsize"
			else
				echo "Can't be more lossy comressed with current PSNR level: $PSNR_LEVEL"
			fi
			break
		fi
	done
done

rm -r $TMPDIR