The upper image is the original image of the corridor. The lower left image is produced by projectively warping the original image so that the floor tiles map to squares. This is simply achieved by computing the plane projective transformation that maps four corners of the imaged square tiles to corners of a square. Similarly, the right image is produced by a projective warping that maps the four imaged corners of the door surround to a rectangle. Both mappings correspond to a synthetic rotation of the camera about the (fixed) camera centre.