otsu threshold

otsu.jl

using StatsBase

function otsu_threshold(img, bit_depth = 256)
    counts = fit(Histogram, img[:], nbins = bit_depth).weights
    const total = prod(size(img))
    current_max, threshold = 0, 0
    weightB, sumB = 0, 0
    sumT = sum([i * counts[i] for i in 1:bit_depth])
    for (i, count) in enumerate(counts)
        weightB += count
        weightF = total - weightB
        if weightF == 0 break end
        sumB += i * count
        meanB = sumB / weightB
        meanF = (sumT - sumB) / weightF
        varBetween = weightB * weightF
        varBetween *= (meanB - meanF) * (meanB - meanF)
        if varBetween > current_max
            current_max = varBetween
            threshold = i
        end
    end
    return threshold
end