[mapserver-users] File size of generated PNG

[thomas bonfort]

On Sat, Jun 9, 2012 at 6:56 AM, Jackey Cheung <cheung.jackey at gmail.com> wrote:
> Some background first. I'm currently using MapServer + TileCache, and
> planning to try out the new MapCache stuff. While using MS+TC, there was a
> headache bothers me. Although not specific to MS, I'm not sure where to
> start, so posting here in hope of getting some pointers.
>
> The problem is the file size of PNG images genereated by MS. They are
> relatively much larger than we want. Now we have one lengthy process that
> runs stuffs like pngcrush after seeded a cache with TC. This is a painfully
> lengthy proccess, which takes months to finish due to the coverage of map.
>
> Just wondering, how to make MS generates minimum size PNG, or how to make TC
> to slice images with minimum file size? Or is using "post-process" the only
> way to achieve it? We are not talking about the absolute minimum, just want
> to have the smallest size in average.

Mapcache itself does a png recompression after having chopped up a
metatile into individual tiles, so the actual png compression done by
mapserver is irrelevant in that case. As for the png compression used
by mapcache itself, you can set it to use quantization (png8 format),
ymmv depending on the actual image data you are rendering.

--
thomas

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