title: converting a Mat object to double arr (OpenCV)
body: <p>I wish to preforme an anistropic diffusion on a Mat object in opencv.
  The anistropic is implemented in C and accepts the following:</p>
  
  <pre><code>applyFilter(double* I, Size sz, double theta, double scale, double eta)
  </code></pre>
  
  <p>I've searched in the documentation and online but havent found a sufficiant answer, how to convert my <code>Mat</code> object to <code>double[][]</code>, so i can run it through the function.</p>
  
  <p>Regards,</p>