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PNG + xz ?PNG + xz ?Posted Mar 5, 2013 12:21 UTC (Tue) by endecotp (guest, #36428)In reply to: PNG + xz ? by tialaramex Parent article: Google releases a better compression algorithm
> Filter type 0, method 0 is the unfiltered data. Yes,
> pngcrush tries this
You are right; I was confused. I was misled by the fact that the pngcrush output lists a whole series of "methods" that start with method 1:
IDAT length with method 1 (fm 0 zl 4 zs 0) = 38507
but this "method" is not the same as the "filter method", which is the "fm" number inside the ().
It remains true that for these images the PNG pre-processing does not help. If you're curious, I have put an example tile here: http://chezphil.org/tmp/maptile.png .
> I'd guess you've fed a bunch of more or less totally blank map tiles
No.
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PNG + xz ? Posted Mar 7, 2013 18:34 UTC (Thu) by huftis (subscriber, #58900) [Link]
Pngcrush just isn’t a very good PNG optimizer. Using OptiPNG or TruePNG, I managed to reduce the file size of your example PNG file by about 26% (from 33.5 KiB to 24.6 KiB).
PNG + xz ? Posted Mar 7, 2013 18:50 UTC (Thu) by huftis (subscriber, #58900) [Link]
And running PNGZopfli on the result of the TruePNG output gives a file size of only 23.4 KiB. Note that this is with the various max settings of both TruePNG and PNGZopfli, and running this takes a long time, but even with the (very fast) default settings we get a comparable file size – 23.5 KiB.
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