numpy 计算矩阵中指定元素的个数

import numpy as np
import cv2 as cv

img = np.zeros((200,200)).astype(np.uint8)
img[100:200,100:200] = 128
img[:100,:100] = 255
img[:10,:10] = 9
print(np.sum(img==0))
cv.imshow('img',img)
cv.waitKey()