python 计算并绘制灰度直方图

其灰度直方图为：

其灰度直方图为：

代码如下：

def calHistogram(img):
    if(len(img.shape) != 2):
        print("img size error")
        return None
    histogram = {}
    for i1 in range(img.shape[0]):
        for i2 in range(img.shape[1]):
            if histogram.get(img[i1][i2]) is None:
                histogram[img[i1][i2]] = 0
            histogram[img[i1][i2]] += 1
    #cal max value
    maxValue = 0.0
    maxKey = -1
    for key in histogram:
        if histogram[key] > maxValue:
            maxValue = histogram[key]
            maxKey = key
    print(maxValue)
    print(maxKey)

    # normalize
    for key in histogram:
        histogram[key] = float(histogram[key]) / maxValue
    return histogram

def drawHistoGram(histogram):
    pyplot.figure()
    #设置x轴的最小值，最大值。y轴的最小值，最大值
    pyplot.axis([0, 256, 0, 1])
    #显示网格线
    pyplot.grid(True)
    #key正好就是灰度
    keys = histogram.keys()
    #value是灰度的像素数量，这里是归一化之后的
    values = histogram.values()
    #这里正式绘制直方图
    pyplot.bar(tuple(keys), tuple(values))
    pyplot.show()
def testHistogram():
    test = cv.imread("test2.jpg")
    histogram = calHistogram(test)
    drawHistoGram(histogram)
    cv.imshow("test",test)
    cv.waitKey(0)

testHistogram()