Hi Greg:

I think you mean the "--ic-weight" option in warp and warpx, not reformat?

Anyway, I would advise against using that. It never really worked as well as I was hoping, and I vaguely recall it will disappear altogether in the upcoming CMTK 2.3 release (which, sadly, isn't really making much progress right now).

So for lack of better options, I would recommend computing one direction and then using the explicit (numerical) inversion for the other direction.

As for speed - if you need to apply the same inverse often, you can compute a deformation field using the xform2dfield tool, which also accepts the "--invert" option for each transformation you give it. This way, you invert the deformation once, sample it, and henceforth use the sampled version.

Another option, which isn't implemented yet unfortunately, would be to fit a B-spline to the inverse of whatever transformation you would like to invert. This was planned for the next CMTK release (did I mention it's not making much progress?)

Hope this helps.

Torsten