[Tilesathome] Colour resolution

[Kai Krueger]

Hello,

I have had the impression, that the osmarender/tah layer feels slower to browse 
than e.g. the mapnik layer, so I tried to find out what may be the cause for 
that. One of the things I have noticed is that the osmarender tiles are much 
bigger than the mapnik tiles, often on the order of 3 to 4 times bigger. Given 
that the difference between a single 100kb tile and a 27kb tile (e.g. z12 of 
Karlsruhe) can be noticed even over a reasonably fast dsl connection and 
definitely over slower links, it might be a good idea to try and reduce the tile 
size. This would also reduce up and download bandwidth needed by the server.

It seems one of the reasons for the bigger tiles is that the osmarender tiles 
use 24bit colours, whereas mapnik uses a 8 bit colour pallet. Would it be 
possible to convert the osmarender tiles to 8 bit colour pallet too? From a 
quick test, that roughly halved the size of the tiles and didn't make any a 
noticeable visual difference. Although the tiles are then still nearly double 
the size of the mapnik ones, this seems like a good start.

Is there any reason not to do this (other than that some one needs to code up 
the client side changes)? Has there been a discussion about this before?

Kai