Agglomerative Clustering Stopping Criteria
Clearly, 2 standard deviations beyond Omega is not the same as twice the mean.

Apparently, their process is this:


compute the distance matrix
compute the mean
compute the standard deviation
compute hierarchical clustering with maximum linkage
cut the tree at mu+2*sigma


Because complete linkage is in O(n^3), this approach will not scale to longer videos or higher frame rates.