Hi,
the achieved compression rates of png images created by python-imaging
are really bad, programs like optipng or pncrush can compress these
images much better, often only to 30-50% of the size generated by pil.
Looking into the code I found these lines in libImaging/ZipEncode.c:
// err = deflate(&context->z_stream, Z_NO_FLUSH);
/* FIXME: temporary workaround for problem with recent
versions of zlib -- 990709/fl */
err = deflate(&context->z_stream, Z_SYNC_FLUSH);
Reverting this to:
err = deflate(&context->z_stream, Z_NO_FLUSH);
/* FIXME: temporary workaround for problem with recent
versions of zlib -- 990709/fl */
// err = deflate(&context->z_stream, Z_SYNC_FLUSH);
improves the compression (close) to the desired optimum. I think the
mentioned bug in zlib is fixed, it is ten years ago.
For me it works fine, can somebody who understands more of this topic,
confirm this?
Flynn
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