Hi,
this Sun bug: http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6357416
is preventing us to get antialiased 256 color images the simple and fast
way.
We're working on alternative ways (thanks Simone) but it would be nice
if the straight route would be wide open.
If you're interested in 8bit images and have a Sud id handy, please
vote for that bug 
Cheers
Andrea