A few days ago Ulli merged a huge piece of code into the vigra master. I don’t know much about most of the contents, but one thing will be rather helpful: the UnionFind data structure was reworked. Before these changes you could only use the makeContiguous method once. After that, the structure was only a hash table and could not be used for labeling any more. With the changes however it should be possible to generate contiguous labelings whenever needed without breaking the structure itself. This could be really hepful, because I am using a rather hacky way right now (see this entry point). I’m gonna try this out and see if it works for me.