title: OpenCV displaying a 2-channel image (optical flow)
body: <p>I have optical flow stored in a 2-channel 32F matrix. I want to visualize the contents, what's the easiest way to do this?</p>
  
  <p>How do I convert a <code>CV_32FC2</code> to RGB with an empty blue channel, something <code>imshow</code> can handle?  I am using OpenCV 2 C++ API.</p>
  
  <h3>Super Bonus Points</h3>
  
  <p>Ideally I would get the angle of flow in hue and the magnitude in brightness (with saturation at a constant 100%). </p>