[vtkusers] ray casting, segmentation

[Lyubomir Zagorchev]

I use volume rendering to clip a volume in an arbitrary fashion using image stencil.
It works great, but after clipping I would like to keep only the visible structures that are displayed on the screen. I understand that volume rendering creates a 2D projection from the 3D volume using color and opacity lookup. Is there any way I can apply that same lookup to the original data voxels so that I can *segment* out the structures of interest in the volume? 

Thanks,
Lyubomir