Optimize images in the current dir with Zopfli (for PNGs), Guetzli (for JPEGs), WebP (for both lossy and lossless conversions). Keeps the smaller file of those.

optimg.sh

#!/bin/bash

# Optimize images for talk slides
# Run in directory with images, it does the following:
# 1. runs zopfli on all PNGs
# 2. runs guetzli on all JPEGs
# 3. creates lossy and lossless WebP, keeps the smaller one
# 4. keeps the WebP if smaller than original

GREEN=$(tput setaf 2)
NORMAL=$(tput sgr0)

echo "${GREEN}Running Zopfli on all PNGs${NORMAL}"
for I in *.png; do /opt/zopfli/zopflipng --iterations=50 --splitting=3 --lossy_8bit --lossy_transparent -y $I $I; done;
echo "${GREEN}Running Guetzli on all JPEGs${NORMAL}"
for I in *.jpg; do /opt/guetzli/guetzli $I $I; done;


for I in *.{png,jpg}; do

	FILE_LOSSY=${I%.*}-lossy.webp
	FILE_LOSSLESS=${I%.*}-lossless.webp

	echo -e "\n* ${GREEN}Converting ${I} to lossy WebP${NORMAL}"
	/opt/webp/bin/cwebp -m 6 -mt -noalpha $I -o $FILE_LOSSY;
	echo "* ${GREEN}Converting ${I} to lossless WebP${NORMAL}"
	/opt/webp/bin/cwebp -m 6 -mt -noalpha -lossless $I -o $FILE_LOSSLESS;

	SIZE_ORIG=$(wc -c <"$I")
	SIZE_LOSSY=$(wc -c <"$FILE_LOSSY")
	SIZE_LOSSLESS=$(wc -c <"$FILE_LOSSLESS")

	if [[ "$SIZE_LOSSLESS" -le "$SIZE_LOSSY" ]]; then
		echo "* ${GREEN}Lossless WebP is smaller than lossy, deleting lossy${NORMAL}"
		BEST_WEBP=$FILE_LOSSLESS
		rm $FILE_LOSSY
	else
		echo "* ${GREEN}Lossy WebP is smaller than lossless, deleting lossless${NORMAL}"
		BEST_WEBP=$FILE_LOSSY
		rm $FILE_LOSSLESS
	fi

	SIZE_WEBP=$(wc -c <"$BEST_WEBP")
	if [[ "$SIZE_ORIG" -le "$SIZE_WEBP" ]]; then
		echo "* ${GREEN}Original ${I} is smaller than WebP, deleting WebP${NORMAL}"
		rm $BEST_WEBP
	else
		echo "* ${GREEN}WebP is smaller than the original, keeping both WebP and the original${NORMAL}"
		mv $BEST_WEBP ${I%.*}.webp
	fi
done;