title: opencv: Mat constructor from rect
body: <p>I am attempting to generate a subimage from a openCV matrix data structure as follows:</p>
  
  <pre><code>cv::Rect sub_image = cv::rect(10, 10, 200, 200);
  cv::Mat submat = original_image(sub_image);
  </code></pre>
  
  <p>My question is if I have some low level memcpy operations and I use submat.data as the source, will it be pointing to the correct subimage? I guess not as the documentation seems to allude that it all points to the same dataset.</p>
  
  <p>If so, how can I use the construct</p>
  
  <pre><code>cv::Mat submat = original_image(sub_image);
  </code></pre>
  
  <p>to actually copy the data as well?</p>