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Sorry everybody, first time using GitHub.

CLA signed; can't add a "trivial" tag.

Why these changes are needed? This isn't a trivial issue, it need to be discussed on the bug tracker.

This new PNGs look fine to me. How much space is saved?

Sorry Raymond, I had to deal with some things and simply wasn't around…
If I recall properly, ≈ 5 to 50 % depending on the file.

I want reproducible compression step.