title: Scale imread matrix in python
body: <p>I am looking for a way to rescale the matrix given by reading in a png file using the matplotlib routine imread,
  e.g. </p>
  
  <pre><code>from pylab import imread, imshow, gray, mean
  from matplotlib.pyplot import show
  a = imread('spiral.png')
  #generates a RGB image, so do
  show()
  </code></pre>
  
  <p>but actually I want to manually specify the dimension of $a$, say 200x200 entries, so I need some magic command (which I assume exists but cannot be found by myself) to interpolate the matrix.</p>
  
  <p>Thanks for any useful comments : )</p>
  
  <p>Cheers</p>