title: Getting array from imshow without plotting it
body: <p>I'm using <code>matplotlib.pyplot.imshow(img, cmap=cm.jet)</code>. <code>img</code> is a 2D matrix. The 
  resulting image is with color so I think the colormap add 3 color channels to the image.</p>
  
  <p>How can I retrieve the image as a numpy array (including the 3 color channels) without first saving the image or plotting the image using <code>imshow</code>?</p>