title: Why scipy.ndimage.gaussian_filter doesn't have a kernel size?
body: <p>Why the function <code>scipy.ndimage.gaussian_filter</code> let choose a value of <code>sigma</code> but no the size of the kernel?
  Theoretically, the kernel size must increase with increasing σ to maintain the Gaussian nature of the filter.
  Does Scipy do this automatically? How?</p>