title: Gaussian filter in scipy
body: <p>I want to apply a Gaussian filter of dimension 5x5 pixels on an image of 512x512 pixels. I found a scipy function to do that:</p>
  
  <pre><code>scipy.ndimage.filters.gaussian_filter(input, sigma, truncate=3.0)
  </code></pre>
  
  <p>How I choose the parameter of sigma to make sure that my Gaussian window is 5x5 pixels?</p>