title: Enlarge and restrict a quadrilateral polygon in opencv 2.3 with C++
body: <p>I can't find this answer anywhere, I hope somebody could help me.</p>
  
  <p>I have an image (all black) with a white generic quadrilateral polygon inside it, and the correspondent 4 corners coordinates of such polygon.</p>
  
  <p>I need to find the corners of a slightly enlarged quadrilateral and the same for a slightly reduced one (the shape must be the same, just a resize of the quadrilateral inside the image).</p>
  
  <p>Is there a function which allows me to do that, or should I compute manually some geometry?</p>
  
  <p>Thank you for your help.</p>