I Forward this from OSM-dev because i didnt get any response there... I noticed that you can see the different colours in the background even on openstreetmaps main map... http://www.openstreetmap.org/?lat=47.01&lon=3.777&zoom=11&layers=B00FTF
The tile with "Moulis-Engilbert" and the one above have different background colours... bye falstaff -------- Original-Nachricht -------- Betreff: Re: [OSM-dev] PNG type for Mapnik map Datum: Tue, 27 May 2008 17:58:54 +0200 Von: Stefan Agner <[EMAIL PROTECTED]> An: [EMAIL PROTECTED] Hello, I found this E-Mail OSM-dev history: > > I tried it out and the png256 stuff in Mapnik doesn't do the right > > thing. You'll end up with tiles not fitting together because the > > colors > > as slightly off. The change is large enough to see in some places. > > > > Yes, I had the same experience. Not very often, but there'll be some > tiles that don't match (background colour usually) > > > Imagemagick convert seems to better with this. The algorithm it > > uses is > > described on http://www.imagemagick.org/script/quantize.php . But I > > could imagine that there are pathological cases where it also breaks. > > > > Yes, as with any quantization. AFAIK ImageMagick is using some kind > of octree algorithms and so is Mapnik. > Thanks for the link and I'll check it out. > > > I haven't looked into the algorithm that Mapnik uses, but maybe it can > > be improved by making sure that all colors mentioned in the Map file, > > i.e. all colors that we explicitly asked for, are retained. That way > > only the "artificial" colors created by the antialiasing will be > > changed. > > This should make sure that tiles will always fit together because all > > the larger colored areas will use the same colors. > > The above is pretty much what I'm thinking of trying. We can collect > colours distribution from *.xml file. > It would easy for solid strokes and fills and not so easy for image > based symbols, which might have thousands of colours. > I guess we can quickly quantize them as well. Also, we can just have > a predefined set of colours, might work even better. There is > probably some kind of cartographic rule - good map should have no > more then 24 different prime colours or something. > > Another thing I'd like to investigate is using different colour > spaces. I had more correct (visually on macbook) palette while > quantizing in YCbBr. > > Anyways, could you send me those tiles, where colours don't much, > please ? With original RGBA versions if possible. > > Cheers > Artem Im using now Mapnik 0.5.1 and trying to work without Imagemagick. I still have this different colours described above. The difference is very small, but its not just different between Imagemagick/Mapnik, with Mapnik there are also differences between area with roads and emtpy areas... I found nothing on Mapnik Trac about this. Is there a solution on the way? I've here some tiles made with Imagemagick and the same tile made with Mapnik itself, if needed... Bye falstaff -- cya stefan deheime.ch Bifangstrasse 20 6048 Horw Tel. +41 41 340 08 56 [EMAIL PROTECTED] http://www.deheime.ch/ _______________________________________________ dev mailing list [EMAIL PROTECTED] http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/dev -- cya stefan deheime.ch Bifangstrasse 20 6048 Horw Tel. +41 41 340 08 56 [EMAIL PROTECTED] http://www.deheime.ch/ _______________________________________________ Mapnik-users mailing list [email protected] https://lists.berlios.de/mailman/listinfo/mapnik-users
