OK, and it seems that those algorithms only take the grayscale into account. Compare http://paste.fulltxt.net/:gh http://paste.fulltxt.net/:gh (your output) wi

OK, and it seems that those algorithms only take the grayscale into account. Compare http://paste.fulltxt.net/:gh http://paste.fulltxt.net/:gh (your output) with http://paste.fulltxt.net/h-,:wiS http://paste.fulltxt.net/h-,:wiS (aalib's output). This probably isn't the best choice of image, but you can still see how aalib approximates the edges of the drawing with all sort of characters.