title: Rotation using Bilinear Interpolation Backward Mapping Calculation?
body: <p>I just started learning Image processing.
  Could someone help me explain this <a href="https://i.stack.imgur.com/rxYkp.png" rel="nofollow noreferrer">Step3</a> how to calculate these column? i really don't understand it. So please explain it simply as possible.</p>
  
  <p>Rotation formula -> <a href="https://i.stack.imgur.com/XvHdF.png" rel="nofollow noreferrer">forward and backward mapping</a></p>
  
  <p>Flowchart diagram and equations <a href="https://i.stack.imgur.com/5qvZP.png" rel="nofollow noreferrer">Step1</a></p>
  
  <p>Forward mapping -> <a href="https://i.stack.imgur.com/CCilR.png" rel="nofollow noreferrer">Step2</a></p>
  
  <p>Backward mapping table1 <a href="https://i.stack.imgur.com/lHohc.png" rel="nofollow noreferrer">Step3</a>  &lt;-- here is my question </p>
  
  <p>Backward mapping table1(cont.) -> <a href="https://i.stack.imgur.com/Kd3y3.png" rel="nofollow noreferrer">Step4</a></p>
  
  <p>Forward mapping and Backward mapping result -> <a href="https://i.stack.imgur.com/ZtUZw.png" rel="nofollow noreferrer">Step5</a></p>