Hi, > ImageMagick's convert knows a -map option with which one can specify a > sample image from which it will take the colour palette and apply it > to the image to be converted. This should ensure uniform colors > across the map. The tradeoff is a potentially less optimal colour > conversion for each individual tile. But I think uniform colours are > more important.
I'm currently doing some work on OSM animations (with Mapnik rendered images). I have had good success by combining a number of wildly different tiles into one image and then running convert sample.png -depth 8 -colors 256 -unique-colors colormap.png on it. The resulting colormap.png has one pixel per color. It could still be tweaked manually if need be, and then you run convert tile.png -colors 256 -depth 8 -map colormap.png output.png on the payload images. The resulting file size is, in my case, slightly smaller than a corresponding GIF image, and running an extra pngcrush on the resultant file gives only one or two percent additional saving. Bye Frederik -- Frederik Ramm ## eMail [EMAIL PROTECTED] ## N49°00'09" E008°23'33" _______________________________________________ Tilesathome mailing list [email protected] http://lists.openstreetmap.org/listinfo/tilesathome
