use array enumeration to simplify for loops

simplify-loops.py

import numpy as np

img = np.arange(6).reshape(2, 3)

# looping over all elements like this ...
for x in range(img.shape[0]):
    for y in range(img.shape[1]):
        print(img[x, y])

# ... is easier and more readable with numpy
for (x, y), value in np.ndenumerate(img):
    print(value)