title: Transparent pixels in OpenCV C++ (when using GrabCut)
body: <p>I am using OpenCV 's implementation of GrabCut in order to remove the background from images. But for now the new background is black. Is there any way to make it transparent? 
  For now this part of the code looks like this:</p>
  
  <pre><code>Mat binMask( image.size(), CV_8UC1 );
  binMask = mask &amp; 1;
  image.copyTo( result, binMask );
  </code></pre>
  
  <p>Can I somehow fill the binMask with transparent pixels?
  I've read some tutorials for overlaying images, but I don't need a transparent image in front of my picture but behind.
  I hope someone could help.
  Many thanks!</p>