title: Plot Red Channel from 3D Numpy Array
body: <p>Suppose that we have an RGB image that we have converted it to a Numpy array with the following code:</p>
  
  <pre><code>import numpy as np
  from PIL import Image
  
  img = Image.open('Peppers.tif')
  arr = np.array(img) # 256x256x3 array
  </code></pre>
  
  <p>If we are interested in visualizing only the red channel, i.e. <code>arr[:,:,0]</code>, how can we plot this 2D Numpy array?</p>