[Mug Funky]

i've never seen undot produce an artefact...?

removedirt can be a bit agressive as far as removing objects rather than just noise, but for compressibility gain versus detail it can't be beaten. if used with motion compensation (especially the new stuff being developed lately) it can give a practically artefact-free compressibility boost.

degrainmedian is also very good - doesn't give blocks like removedirt can if not used judiciously, and still gives a handy compressibility gain.