Now that - for each camera - the rectifying PPM is known, we want to compute the linear transformation (in projective coordinates) that maps the retinal plane of the old PPM, , onto the retinal plane of .

We will see that this transformation is the matrix .

For any 3-D point **w**
we can write

We know from Eq. (10) that the equation of the optical ray associated to is

hence

Assuming that rectification does not alter the optical centre ( ), we obtain:

The transformation is then applied to the original image to produce a rectified image, as in Fig. 3. Note that the pixels (integer-coordinate positions) of the rectified image correspond, in general, to non-integer positions on the original image plane. Therefore, the gray levels of the rectified image are computed by bilinear interpolation.

Tue Feb 3 17:18:41 MET 1998