title: Not getting correct subtraction result for difference of two images in python
body: <p>This is my python code where i want to find difference between two images. </p>
  
  <pre><code>import cv
  import numpy as np
  img1=cv.imread('/storage/emulated/0/a.jpg',0)
  print(img1[0:1])
  img2=img1
  img2[0:1994]=1
  print(img2[0:1])
  rows,cols=img1[0:1].shape
  print(rows)
  print(cols)
  rows,cols=img2[0:1].shape
  print(rows)
  print(cols)
  print(np.subtract(img1[0:1,0:1], img2[0:1,0:1]))
  </code></pre>
  
  <p>I am subtracting these numpy arrays but getting zero always. Kindly help regarding this matter. </p>