Homography

Homograhy

Python code to calc Homograpy matrix from each 4 points of source and
destination.

# 4つの点からホモグラフィ行列(平面射影変換行列)を求める
http://www.gistlog.org/gist/887734

See the link, great example of ImageMagick , how 4 point perspective
distortion works.
http://www.imagemagick.org/Usage/distorts/#perspective

Any destination points are calculated by next.

x' = Hx (x : source, x' : dest, H : homography)

     x'         x
s * ( y' ) = H ( y )
      1          1