Quote - Mitchel filter? Are you talking in Luxrender or in Poser before export?

Well, I don't know if bagginsbill's latest GUI takes this in account (most likely), but the most simple is to add it yourself in the .lxs file, by hand (use Notepad). The advantage is that you can reuse your last export files.

Add:
PixelFilter "gaussian"

Before:
Sampler "metropolis"

(For those who haven't read the thread, this is supposed to remove the dark rings you get on light highlight/reflections)