title: Rotate, Scale and Translate around image centre in OpenCV
body: <p>I really hope this isn't a waste of anyone's time but I've run into a small problem. I am able to construct the transformation matrix using the following:</p>
  
  <pre><code>M = 
  s*cos(theta)        -s*sin(theta)       t_x
  s*sin(theta)        s*cos(theta)        t_y
  0                   0                   1
  </code></pre>
  
  <p>This works if I give the correct values for theta, s (scale) and tx/ty and then use this matrix as one of the arguments for cv::warpPerspective. The problem lies in that this matrix rotates about the (0,0) pixel whereas I would like it to rotate about the centre pixel (cols/2, rows/2). How can incoporate the centre point rotation into this matrix?  </p>