title: Can copyMakeBorder() alter the source bits?
body: <p>Looking at the <a href="http://docs.opencv.org/2.4/doc/tutorials/imgproc/imgtrans/copyMakeBorder/copyMakeBorder.html" rel="nofollow noreferrer">basic example for <code>copyMakeBorder()</code></a>, we have the code:</p>
  
  <pre><code>copyMakeBorder( src, dst, top, bottom, left, right, borderType, value );
  </code></pre>
  
  <p>Are there any circumstances where the bits in <code>src</code> do not equal the bits in <code>dst(top, left, dst.height - top - bottom, dst.width - left - right)</code>, or in other words is the <code>src</code> always unmodified within <code>dst</code>?</p>
  
  <p>I ask because I've inherited some code that adds a border with <code>cv::BORDER_REFLECT + cv::BORDER_ISOLATED</code> but then extracts the <code>src</code> from inside the borders, so I'm suspicious that this is all unnecessary work.</p>
  
  <p>Furthermore, I've used <a href="https://stackoverflow.com/a/11905590/1270789">the code here</a> to convince myself that for the current code the <code>src</code> and the centre of the <code>dst</code> are equal, but I'd still like confirmation that my assumptions are correct.</p>