title: opencv morphological dilation filter as maximum filter
body: <p>Like the definition of median filter, I can define "maximum filter" as for a local window </p>
  
  <p>e.g. dst(x,y) = max(3x3 local window pixels)</p>
  
  <p>But I cannot find such a filter in opencv, the closest one is "dilate" function</p>
  
  <p>Then I use the default configuration of "dilate" function, but the result is incorrect
  compare to my brute force implementation of the maximum filter.</p>
  
  <p>I found that for 3x3 case, the equivalent dilate configuration is to use a 1x1 rectangular structure element, that is</p>
  
  <p><code>dilate(src, dst, getStructuringElement(MORPH_RECT, Size(1,1)))</code></p>
  
  <p>My questions are:</p>
  
  <ol>
  <li><p>It seemed counter-intuitive for me that I thought a structure element is equivalent to a local window. But now the local window's size is only 1x1 pixel?</p></li>
  <li><p>What if my maximum filter's local window expands(e.g. 5x5, 7x7)? Is there any relationship between the maximum filter and dilation filter?</p></li>
  </ol>