% Otsu image thresholding (for image thresholds > 0)
% Otsu, N., "A Threshold Selection Method from Gray-Level Histograms," IEEE Transactions on Systems, Man, and Cybernetics, Vol.
% 9, No. 1, 1979, pp. 62-66.
% Similar to MATLAB function graythresh.m
% input: image (IM)
% output: binary image (IM_OTSU) and optimal threshold value