Optimize all png files in history of repository with "git filter-branch" command

optimize.sh

#!/bin/sh

FILENAME="$1"
HASH=$(md5sum "${FILENAME}")
HIT=$(grep -c "${HASH}" /tmp/hash.txt)

echo "${FILENAME}"

if [ "${HIT}" -eq 0 ];then
  optipng -o7 -clobber "${FILENAME}"
  HASH=$(md5sum "${FILENAME}")
  echo "${HASH}" >> /tmp/hash.txt
else
  echo "SKIP"
fi

start.sh

#!/bin/sh

CMD="find . -iname '*\.png' -type f -print0 | xargs -0 -L 1 -P 4 --no-run-if-empty /tmp/optimize.sh"
git filter-branch --prune-empty --tree-filter "${CMD}" --force HEAD