[OSM-dev] PNG type for Mapnik map

[Robert (Jamie) Munro]

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Jochen Topf wrote:
> Hi!
> 
> http://svn.openstreetmap.org/applications/rendering/mapnik/generate_tiles.py
> uses a call to the external 'convert' program to reduce the number of colors
> for tiles rendered by Mapnik to 255. Since version r571 Mapnik supports
> writing to 8 bit palette PNGs. Palette PNGs are generally smaller than
> normal PNGs.
> 
> Is there any reason NOT to change the code to use Mapniks function to
> write out the image directly as 8bit paletted PNG, make the images
> smaller and save the call to 'convert'? (If nobody comes up with a
> reason, I'll change the code.)

AFAIK, the main reason the feature was added to mapnik was that /we/
needed it because the external convert was really slow (about the same
amount of time as the whole rest of the render).

So no, there is no reason not to change the code. Please do & make
mapnik run at twice the speed. Also, if you can make mapnik render
on-demand first, and only render the backlog when it's not busy, that
would probably be a great improvement.

Robert (Jamie) Munro

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