Opencv image basic operation (III) -- image feature extraction (corner detection)

The code is as follows ：

import cv2 
import numpy as np

img = cv2.imread('test_1.jpg')
print ('img.shape:',img.shape)
gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
# gray = np.float32(gray)
dst = cv2.cornerHarris(gray, 2, 3, 0.04)    #  Perform focus detection 
print ('dst.shape:',dst.shape)
print ('dst',dst)
img[dst>0.01*dst.max()]=[0,0,255]
cv2.imshow('dst',img) 
cv2.imwrite("dst.png",img)
cv2.waitKey(0) 
cv2.destroyAllWindows()