INTHIST = VL_INTHIST(LABELS) computes the integral histogram for
   the label maps LABELS.

   LABELS is a [M,N,L] UINT32 array containing L label maps (one for
   each MxN layer). Each label map associate to each pixel one of K
   labels (0 denotes no association).

   INTHIST is the [M,N,K] integral histograms obtaining by
   integrating the label maps. The total number of labels K is
   obtained as the maximum value of LABELS, and each enry in a label
   map contributes with unitary mass.

   VL_INTHIST(..., 'MASS', MASSES) specifies the mass MASSES for each
   entry of LABELS.

   VL_INTHIST(..., 'NUMLABELS, K) specifies the number of labels
   explicitly.

   Author