title: cornerSubPix in OpenCV: purpose and application
body: <p>I tried to understand the <code>cornerSubPix</code> API in OpenCV for its idea behind and usefulness. I read the explanation in the <a href="http://docs.opencv.org/modules/imgproc/doc/feature_detection.html#cornersubpix" rel="nofollow">link</a> and can't understand how it works and how it is useful.
  Can somebody explain me how it works and how it is useful at corner refinement? I checked my corner detection application for without <code>cornerSubPix</code> and with <code>cornerSubPix</code>. Not much difference in output image, but it takes time to process.
  Thanks </p>