title: Apply homography on contours as well as Mat
body: <p>Currently I am using the following sequence</p>
  
  <pre><code>vector&lt;vector&lt;Point&gt;&gt; contours
  1. findContours(srcMat, contours, ...)
  2. convert contours to Point2f
  3. findHomography(src, dst, RANSAC)
  4. warpPerspective(srcMat, destMat, homo)
  5. findContours
  </code></pre>
  
  <p>I would like to avoid step#4, while also transforming the Mat since I use some ROI relative to the contours from the transformed Mat.</p>