On 17 March 2015 at 12:48, Martin Koppenhoefer <dieterdre...@gmail.com> wrote: > 2015-03-17 12:21 GMT+01:00 andrzej zaborowski <balr...@gmail.com>: >> 62% at -q 32 -- minor deterioration can be seen, you can browse a >> small area at c.tile.openstreetmap.pl/viewer.bpg.xhtml > > I can see some aliasing e.g. in the casing, but am not sure if this is from > the rendering or the compression, it would be useful to have a direct > comparison (i.e. the same tiles in png and bpg and maybe also jpeg).
Good point, I set up this style comparison type page: http://bl.ocks.org/balrog-kun/raw/e37b92b537860c77e463/ with PNG vs. BPG. This took me a while.. The aliasing is probably from the rendering because the only difference I see is blurring of very low contrast lines. That said such comparisons of lossy formats are a little pointless because they compare arbitrary compression settings. If you wanted to compare to PNG at matching filesizes you'd need to use a BPG compression ratio where there wouldn't be any artifacts. > > This is announced as jpeg replacement, so I guess lots of colours are not a > problem? When using sat-images, hillshading or other kinds of gradients > (e.g. from blurring or rastersymbolizer) you will get a lot of shades and > png will compress worse compared to the relatively few colours you get for > instance with the standard style. So far it seems like this is not a problem, I'll convert a small sample if you can point me to one. > > Generally I think loosing image quality but saving 50% of space is likely > not a tradeoff that OSM wants to accept, or the tiles would already be > compressed in jpeg and not png. I agree but it depends on how you define quality. The thing with lossy compression is that it is designed to drop the elements that you don't notice anyway (or you notice the least). If you apply JPEG to a type of input it wasn't designed for it will drop the wrong parts of the data and then you definitely lose quality. There may be a format that actually does for map tiles what JPEG is supposed to do for photos and then it's harder to tell. With BPG it seems the compression time is a blocker with the current encoder. Cheers _______________________________________________ dev mailing list dev@openstreetmap.org https://lists.openstreetmap.org/listinfo/dev
