title: low-pass filter in opencv
body: <p>I would like to know how I can do a low-pass filter in opencv on an IplImage.
  For example <strong>"boxcar"</strong> or something similar.</p>
  
  <p>I've googled it but i can't find a clear solution.
  If anyone could give me an example or point me in the right direction on how to implement this in opencv or javacv  I would be grateful.</p>
  
  <p>Thx in advance.</p>