title: Image processing filters
body: <p>I am implementing the Box filter and I wonder if I should allow
  filter mask sizes like 3 X 5 or whatever, where the width is different
  than the height.</p>
  
  <p>So far I have implemented only filters with mask sizes like 3x3 or 5x5.
  Is it valid to allow width to be different than height? I guess I could 
  allow the user to specify such mask but if he gets wierd results it is his
  fault?</p>
  
  <p>Thanks</p>