[OSM-dev] .bpg tiles

[Jukka Rahkonen]

Hi,

There is also experimental support for BPG in GDAL. Only documentation 
by now is in these two mails 
http://thread.gmane.org/gmane.comp.gis.gdal.devel/39440

-Jukka Rahkonen-

andrzej zaborowski wrote 2015-03-17 13:21:
> Hi,
> 
> BPG is an image format by Fabrice Bellard that was in the news a few
> months ago as "the JPEG replacement".  Its lossy compression mode
> seems to work well for OSM tiles because the artifacts are of a
> different type than in JPEG.  Here are some results for a small test
> area for different compression ratios (percentages of size saved
> against PNG).
> 
> 51% at default level (-q 28) -- I could see no artifacts in the test 
> area
> 
> 62% at -q 32 -- minor deterioration can be seen, you can browse a
> small area at c.tile.openstreetmap.pl/viewer.bpg.xhtml
> 
> 89% at -q 40 -- linear features and labels still readable but
> low-contrast elements disappear, ugly but no problems at tile seams.
> 
> Unfortunately the stock encoder is slow when compared to PNG.  I'm not
> sure if it makes sense to use for tiles rendered on-demand because the
> compression time adds to the rendering time.  It would work well for
> static or low-zoom tiles though.  I imagine compression would also be
> improved with bigger tiles but I'm not sure if 8x8 metatiles at
> 512x512 pixels is not too heavy for a tileserver -- is anyone
> generating such tiles with mod_tile?
> 
> You can use this Leaflet plugin to support .bpg tiles:
> https://github.com/balrog-kun/Leaflet.bpg
> 
> There's also a hacky integration attempt for mod_tile:
> https://github.com/balrog-kun/mod_tile/commit/3188147ff207fb4e47c7d0af4d0ee6fd7f159c56
> 
> Cheers
> 
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