Equivalence of different methods for slant and skew corrections in word recognition applications

Normalization of slant and skew is often used in processing a word image before recognition. In this paper, we prove the theoretical equivalence of different methods for slant and skew corrections. In particular, we show that correcting first for skew by rotation and then for slant by a shear transformation in the horizontal direction is equivalent to first correcting for slant by a shear transformation in the horizontal direction and then for skew by a shear transformation in the vertical direction. Our proof can be easily modified to prove equivalence of other methods for correcting the slant and skew.