Floyd-Steinberg in order to avoid the energy level getting locally stuck
around error diffusion structure artifacts.
git-svn-id: file:///srv/caca.zoy.org/var/lib/svn/libpipi/trunk@2672 92316355-f0b4-4df1-b90c-862c8a59935f
dithering methods as of today, though extremely slow.
git-svn-id: file:///srv/caca.zoy.org/var/lib/svn/libpipi/trunk@2651 92316355-f0b4-4df1-b90c-862c8a59935f