[Maposmatic-dev] [task #9917] Apply optipng (or pngcrush) on generated PNG files

[Jeroen van Rijn]

Follow-up Comment #2, task #9917 (project maposmatic):

I've posed a question to the Cairo list to see if write_to_png could be
called with parameters to pass directly to libpng and its use of zlib.

http://lists.nongnu.org/archive/html/maposmatic-dev/2010-01/msg00463.html

Unfortunately it appears that Cairo's PNG output is a debug path never meant
for production use; I was advised to see about overloading write_to_png and
using a dedicated graphics library to do the actual png writing, which then
might also give more flexibility in telling libpng what to do.

My proposal is that I first pursue optimal parameters for optipng as intended
and add this support to maposmaticd, then instead of marking this task as
closed, direct the effort to finding a suitable python image library which if
present (as an optional dependency) allows to write png's (and possible other
raster graphics) from Cairo's image context while at the same time directly
allowing us to set libpng/zlib parameters for better compression.

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