title: Convert an image shown in python, into an OpenCV image.
body: <p>So, I would like to simply take an existing plot that I have made via <code>plt.plot(x,y)</code>, convert it into an "image", so that I can then give it to OpenCV's video writer via:</p>
  
  <pre><code>cv2.VideoWriter('myMovie.avi', fourcc, 20.0, (640,480))
  writer.write(image)
  </code></pre>
  
  <p>My problem is, given the figure I have already plotted, how do I get "image"?</p>
  
  <p>Thanks.</p>