title: Discarding alpha channel from images stored as Numpy arrays
body: <p>I load images with numpy/scikit. I know that all images are 200x200 pixels.</p>
  
  <p>When the images are loaded, I notice some have an alpha channel, and therefore have shape (200, 200, 4) instead of (200, 200, 3) which I expect.</p>
  
  <p>Is there a way to delete that last value, discarding the alpha channel and get all images to a nice (200, 200, 3) shape?</p>