What is the best way to print maps/cartoons/text saved as a picture/etc., so pictures that are not photos? The standard routines seem to blur and soften the printed picture, which is probably reasonable for photos, but gives horrible results for pictures that have very sharp features.
See potrace to vectorize black and white images. It gives pretty good results for cartoon-type pictures (though you may need to tweak the parameters).
In the general case, I suppose you could use gimp to extract borders and then feed it to potrace, and then re-rasterize it at a higher resolution and add it as a layer on top of the enlarged original image.