title: opencv VideoCapture.set greyscale?
body: <p>I would avoid to convert each frame taken by video camera with <code>cvtColor(frame, image, CV_RGB2GRAY);</code><br>
  Is there anyway to set <code>VideoCapture</code> to get directly in greyscale?</p>
  
  <p>Example:</p>
  
  <pre><code>VideoCapture cap(0);
  
  cap.set(CV_CAP_PROP_FRAME_WIDTH,420);
  cap.set(CV_CAP_PROP_FRAME_HEIGHT,340);
  cap.set(CV_CAP_GREYSCALE,1); //&lt; ???
  </code></pre>