[Image-SIG] Patch: improved PNG saving speed

[Eli Golovinsky]

Hi,

I'm working on a screen capturing program and I noticed that it takes
quite a while for PIL to save PNG images. I ran a profiler on the
library and saw that the code that filters the PNG data (lines 133 to
234 in ZipEncode.c) takes about half of the entire compression time.
Removing it speeded up the saving considerably and only increased the
resulting files by about 25%.

I added an option to the save method called 'no_filter' that prevents
the filter code from running. I'm attaching a patch made against the
1.1.6 source kit (http://effbot.org/downloads/Imaging-1.1.6.tar.gz).

Maybe somebody will find it useful someday.

-- 
Eli Golovinsky
www.testuff.com
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