It does decompress the source PNG and build a new file from the pixels. You can see the source here. https://github.com/google/zopfli/blob/master/src/zopflipng

It does decompress the source PNG and build a new file from the pixels. You can see the source here. https://github.com/google/zopfli/blob/master/src/zopflipng/zopflipng_lib.cc https://github.com/google/zopfli/blob/master/src/zopflipng/z...