This is where we put the original versions of images so that we can update them if needed.
_opt versions of the files are compressed/optimised and are the versions that are embedded in the Wiki.
Optimizing SVG files:
svgcleaner seems to be the best tool for reliably shrinkifying SVG files (does a better job of using groups to apply shared styles than scour):
Available in Arch as community/svgcleaner.
svgcleaner file.svg file_opt.svg
if you want the output in a human readable form rather than one massive line:
svgcleaner --indent=1 file.svg file_opt.svg
Optimising PNG files:
oxipng seems to be the best of the commonly available PNG optimisers. It has support for Zopfli which generally offers better compression than zlib.
Available in Arch as community/oxipng.
oxipng --strip safe --alpha --zopfli -o max --out file_opt.png file.png