title: Change image channel ordering from channel first to last
body: <p>I want to change the ordering of this numpy images array to channel_last
  training_data : (2387, 1, 350, 350) to (2387,350,350,1)
  validation_data : (298, 1, 350, 350) to (298, 350, 350, 1)
  testing_data : (301, 1, 350, 350) to (301, 350, 350, 1)</p>
  
  <p>I tried this but it is not working</p>
  
  <pre><code>np.rollaxis(training_data,0,3).shape
  np.rollaxis(validation_data,0,3).shape
  np.rollaxis(testing_data,0,3).shape
  </code></pre>