[Tilesathome] color-reducing

[Matthias Julius]

Frederik Ramm <frederik at remote.org> writes:

> 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.

This is good to know.

And if we user perlmagick we can save a couple thousand process starts
per tileset.

If there is some agreement that this is useful I would take a look
implementing this.

Matthias