How to convert BGR to Grayscale in OpenCV Python?

If you want to convert an image to black and white, then pass cv2.COLOR_BGR2GRAY flag to the cv2.cvtColor() function.

import cv2

img = cv2.imread('/home/mohit/cardiff.jpg')
if img is None:
  print('Image is not present.')
else:
  img = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
  cv2.imshow(img)
  cv2.destroyAllWindows()
  cv2.waitKey(0)

Output

Original Image