We've done further tests with Cleaver (still loving it :-) ) and we have noticed the following issue.

Feeding cleaver with a 30x30x30 cube with 2 label regions separated along a plane, please see below the generated mesh (the tets (red and blue) are intersected with a slice of the volume. Please disregard the odd looking intersections :-), nevertheless we can observe:

 - a) the generated tet mesh is coarse in the homogeneous areas

 - b) the generated tet mesh is detailed along the jagged green-cream labels boundaries.

 - c) the generated tet mesh is detailed along the smooth air(black)-green label boundaries.

I understand a) and b). I also understand that air is treated as a label (I know Ricardo previously mentioned it).

However, as a naive user, I would expect to have a coarser mesh along the smooth (!=jagged) label boundaries ? Would it be a hard feature to add into Cleaver ?

Thanks for your insights,

Julien.