title: How to make a new filter and apply it on an image using cv2 in python2.7?
body: <p>How to make a new filter and apply it on an image using cv2 in python2.7?</p>
  
  <p>For example:</p>
  
  <pre><code>kernel = np.array([[-1, -1, -1],
                     [-1,  4, -1],
                     [-1, -1, -1]])
  </code></pre>
  
  <p>i'm new to opencv so if you can explain that'd be great. thanks!</p>