im = cv2.imread("1.jpg", 0)
width=im.shape[1]
heigt= im.shape[0]
mean = cv2.mean(im)[0]
print(mean)
(mean , stddv) = cv2.meanStdDev(im)
print(mean)
print(stddv)

输出：

102.40612538655598
[[102.40612539]]
[[12.17683064]]