title: Why does this order of the Gaussian filter in scipy give the x and y derivative?
body: <p>I'm using a Gaussian filter with Scipy and I saw this code online which I'm curious about. </p>
  
  <pre><code>imx = zeros(im.shape)
  filters.gaussian_filter(im, (sigma,sigma), (0,1), imx)
  imy = zeros(im.shape)
  filters.gaussian_filter(im, (sigma,sigma), (1,0), imy)
  </code></pre>
  
  <p>For the first Gaussian filter call, the order is (0,1) and according to <a href="https://www.hdm-stuttgart.de/~maucher/Python/ComputerVision/html/Filtering.html#id1" rel="nofollow noreferrer" title="this document">this link</a>, that should give the the first order derivative of a Gaussian in y-direction. However, on running the code, I can see that the Gaussian is along the X direction.</p>
  
  <p>The same thing applies to imy. Why does the code work that way?</p>
  
  <p>For reference, running:</p>
  
  <pre><code>filters.gaussian_filter(im, (sigma, sigma), (0, 1), output= imx)
  </code></pre>
  
  <p>on this array:</p>
  
  <pre><code>[[0 3 2]
  [1 4 1]
  [3 4 2]]
  </code></pre>
  
  <p>Returns:</p>
  
  <pre><code>[[0.00071801 0.00148952 0.00077151]
   [0.0006947  0.00144284 0.00074815]
   [0.00067141 0.00139622 0.00072482]]
  </code></pre>
  
  <p>Which is a Gaussian in the x direction, even though the order (0, 1) suggests that it should be in the y direction. I think I might be missing something.</p>