Point correspondences
We estimate the projective transformation by matching features
1. Point correspondences. We try to
find blocks in the first image which
can easily be found in the second
image. We use blocks which have
substantial intensity changes in both
2. Point/normal correspondences. In
the case of blocks that have
substantial intensity changes in only
one direction, we encounter the
aperture problem: we can only
accurately estimate the motion of
a block in the direction of its normal.