title: Difference between cv2.NORM_L2 and cv2.NORM_L1 in opencv python
body: <p>I am using sift algorithm from python extra modules for some feature matching.
  Although one thing I did not understand is the concept behind the normType passed to the BFMatcher. i.e Which ones have to be used in what case?</p>
  
  <p>Any help will be invaluable</p>