title: How to expand / dilate a numpy array?
body: <p>I'm performing a image analysis and generated seeds in the form of a boolean <code>array</code> :</p>
  
  <pre class="lang-py prettyprint-override"><code>import numpy as np
  
  # Example output array
  a = np.array([[False, False, False], [False, True, False], [False, False, False]])
  
  &gt;&gt;&gt; a
  array([[False, False, False],
         [False,  True, False],
         [False, False, False]])
  </code></pre>
  
  <p>As I want to do a subsequent analysis on the area surrounding the <code>True</code> value, I want to expand it (by a certain number, say pixels). This would result in the following:</p>
  
  <pre class="lang-py prettyprint-override"><code>&gt;&gt;&gt; a
  array([[False, True, False],
         [True, True, True],
         [False, True, False]])
  </code></pre>
  
  <p>Is there any <code>function</code> or simple way of solving my 'radial expansion' problem?</p>
  
  <p>Thanks in advance,
  BBQuercus</p>