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Anonymous
>>224109 That is only because png uses gzip to compress....
And 7zip uses LZMA which is far superior to GZIP.
PNG does this: bitmap data -> "filters" that make it compress better -> gzip
What OP has done is: bitmap data -> 7zip
The problem is is that you have missed out on the clever PNG "filters" that can GREATLY increase compressibility.
So what you want is a compressor that will handle the special case of png files, by ungzipping them, then compressing them. Such things DO exist, some compressors have a "media mode" which does this sort of thing.
some versions of PAQ should have it, and i think winrar might aswell (not sure).
OR you could save an uncompressed but filtered PNG, so when you save the PNG set the compression level to 0 and 7zip that, then save it as BMP, compress that, and see which is smaller.
If PNG is still not smaller, then unfortanetly you'd have to make your own command-line program that uses libpng to run the filters but not actually apply any compression.
Its the shitty gzip that is screwing things up, once it is compressed with the inferior format, it looks like it is random data to 7zip (random data cannot be compressed at all).
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