function I = mi(nxy)
    pxy = nxy / sum(nxy(:));
    px = sum(nxy, 2) / sum(nxy(:));
    py = sum(nxy, 1) / sum(nxy(:));
    pi = pxy .* log2(pxy./(px*py));
    pi(nxy == 0) = 0.0;
    I = sum(pi(:));
end