title: How to rotate an image about the image center using homography?
body: <p>I am using opencv <code>warpPerspective</code> to generate images with different rotation to evaluate my feature point detection algorithm.</p>
  
  <p>In homography matrix, the up-left 2x2 matrix is the rotation matrix, <a href="https://stackoverflow.com/questions/6087241/opencv-warpperspective">as referred here</a>.</p>
  
  <p>But the result is a rotation about the origin( the up-left corner), how can I modify the homography matrix to rotate the image about its center?</p>
  
  <p>Regards.</p>