alpha=1, all labels are implicitly weighted by their volume. This may not be desirable as smaller labels may represent a greater registration or segmentation challenge. Two alternative choices are to set alpha either to (i) the inverse mean volume of the current label pair to give all labels equal weighting or (ii) the inverse mean volume squared of the current label pair to weight by the inverse volume."
w=0): The volume columns are the overlap for default (implicit) weighting. Larger labels have more weight in the accumulated overlap
w=1): All labels treated equally
w=2): Unlike volume-weighting
w=3): The complexity of the labels
shuffle radius = 1.5)