Shell script to recursively optimize all image in the current directory. WARNING: THIS OVERWRITES YOUR ORIGINALS AND REMOVES METADATA!

optimizeimages.sh

#!/bin/sh
set -o errexit

PNGS=`find . -iname "*.png"`
JPGS=`find . -iname "*.jpg"`
TMP1="_TMP1.PNG"
TMP2="_TMP2.PNG"

echo "Optimizing PNG"
for PNG in ${PNGS}
do
	BEFORE=`stat -c %s ${PNG}`
	echo -n "	${PNG}: ${BEFORE} "
	cp ${PNG} ${TMP1}
	COLORS=`pngtopnm ${PNG} | ppmhist -noheader | wc -l`

	if [ "$COLORS" -lt 2 ]; then
		COLORS=2
	fi

	if [ "$COLORS" -lt 257 ]; then
		cat ${PNG} | pngquant ${COLORS} > ${TMP1}
	fi

	pngcrush -q -l 9 -brute -rem alla ${TMP1} ${TMP2}
	rm ${TMP1}
	optipng -quiet -o7 -out ${TMP1} ${TMP2}

	AFTER=`stat -c %s ${TMP1}`
	if [ "$AFTER" -lt "$BEFORE" ]; then
		mv ${TMP1} ${PNG}
		echo "--> ${AFTER}"
	else
		echo "(Already optimal)"
	fi

	rm -f ${TMP1} ${TMP2}
done

echo "Optimizing JPG"
for JPG in ${JPGS}
do
	BEFORE=`stat -c %s ${JPG}`
	echo -n "	${JPG}: ${BEFORE} "
	jpegtran -optimize -copy none ${JPG} > ${TMP1}
	AFTER=`stat -c %s ${TMP1}`

	if [ "$AFTER" -lt "$BEFORE" ]; then
		mv ${TMP1} ${JPG}
		echo "--> ${AFTER}"
	else
		echo "(Already optimal)"
	fi
	rm -f ${TMP1}
done

These are the same optimizations as implemented in Assetgraph-builder

assetgraph/assetgraph#49 (comment)

For those that don't read shell script fluidly (I know I don't), here is an explanation of what the script does.

It runs recursively through all directories under your current one and optimizes the pngs with the following tools:

pngquant in case the image has 256 or less colors. This converts the png to an 8bit png with a smaller palette, which makes each pixel be less bytes.
pngcrush for removing ancillary png chunks, like the tedious gamma chunk that always screws up browsers.
optipng for further efficiency in compressing the png file.

Then it overwrites your original pngs, so keep a backup, or even better, version control your files so you can see the difference.
Not that you should be able to see much difference other than on file size, since these optimizations are lossless.

I hope this helps you.

Just added jpeg optimization with jpetran, which is also lossless

Cheers, but pngquant had a bad affect on my alpha channel png files. They ended up looking terrible. pngquant is apparently lossy.

Please consider quoting every argument, especially with destructive commands like rm, so as to prevent space-in-file-name-related issues:

rm -f "$TMP1" "$TMP2"

Also, there are two mainstream extensions for JPEG files: jpg and jpeg.

I made an updated version of this with significant changes (including multi-threading) here:
https://github.com/mjc/optimizeimages.sh