[数据结构与算法]大津算法（python实现）

def ostu(im):
    a = im.shape[0]
    b = im.shape[1]
    total = a * b  # 总像素数
    histogram = [0 for i in range(256)]  # 灰度直方图
    for i in range(a):
        for j in range(b):
            histogram[im[i][j]] += 1
    sum1 = 0
    for i in range(256):
        sum1 += i * histogram[i]
    wB = 0
    sumB = 0
    max_var = 0
    threshold = 0
    for i in range(256):
        wB += histogram[i]
        if wB == 0:
            continue
        wF = total - wB
        if wF == 0:
            break
        sumB += i * histogram[i]
        mB = sumB / wB
        mF = (sum1 - sumB) / wF
        var1 = wB * wF * (mB - mF) ** 2
        if var1 >= max_var:
            threshold = i
            max_var = var1
    return threshold

具体算法描述参见大津算法 - 万维百科