Converts an image to grayscale using the crude average of the r, g, and b

def to_gray(image):
  # image is a 3d numpy array
  (x, y, z) = image.shape
  gray = np.zeros((x, y))
  for i in range(x):
    for j in range(y):
      gray[i][j] = (image[i][j][0] + image[i][j][1] + image[i][j][2]) / 3
  return gray
  
img = np.zeros((2, 2, 3)) # blue image, 2x2

to_gray(img)