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 _______________________________________________ dev mailing list [email protected] https://lists.openstreetmap.org/listinfo/dev
