title: how to fill borders when rotating images?
body: <p>I'm using the following code to rotate images in opencv. However, afterwards the corners are colored in black. I thought when I set <code>borderMode</code> to <code>BORDER_CONSTANT</code> I can specify the color. But whatever color I set (the last parameter), the result is always black. </p>
  
  <pre><code>cv::Mat rotated; 
  float rotation = 3.0f; 
  cv::warpAffine(img, 
                rotated, 
                rotation, 
                img.size(),  
                cv::INTER_CUBIC, 
                cv::BORDER_CONSTANT, 
                cv::Scalar(1.0, 1.0, 1.0, 0.0));
  cv::imshow("rotated", rotated); 
  </code></pre>
  
  <p>Could someone please explain me, what I am doing wrong here? </p>
  
  <p>I know I could use <code>cv::floodFill</code> afterwards, but somehow it should be possible to do using only <code>warpAffine</code>. </p>