title: python matplotlib.pyplot imread
body: <p>I'm using <code>plt.imread</code> for reading big .tiff images.
  Because of the big dimensions, I would like to select just a part of the image to be loaded.
  I would like to do something like:</p>
  
  <pre><code>plt.imread(filename, [s1:s2, r1:r2])
  </code></pre>
  
  <p>choosing the initial and final pixel for both dimensions.</p>
  
  <p>Is there a way to do this?</p>
  
  <p>Many thanks</p>