DESCRIPTION:

Fill the connected area starting at x,y,z using a priority
queue. All connected voxels belonging to the same set as
x,y,z are remarked to targetset iteratively, filling areas
of high NLC first. Fill will either stop at "thresh", or you
can use ESC to break out of this command, or it will fill the
whole connected component.
Use -1 as greylevel to estimate it by a local gaussian blur.
Use -2 as greylevel to estimate it by an inverted local
gaussian blur.