title: overlay image mask equivalent in CV2
body: <p>I want to plot two images on top of each other. In matplotlib this is easily done:</p>
  <pre><code>import matplotlib.pyplot as plt
  
  fig = plt.figure()
  plt.imshow(img, cmap=&quot;gray&quot;)
  plt.imshow(mask, cmap=&quot;jet&quot;, alpha = 0.3)
  plt.show()
  </code></pre>
  <p>what is the equivalent in cv2?.</p>