Skew and slant correction for document images using gradient direction

Abstract

A fast algorithm is presented for skew and slant correction in printed document images. The algorithm employs only the gradient information. The skew angle is obtained by searching for a peak in the histogram of the gradient orientation of the input grey-level image. The skewness of the document is corrected by a rotation at such an angle. The slant of characters can also be detected using the same technique, and can be corrected by a shear operation. A second method for character slant correction by fitting parallelograms to the connected components is also described. Document images with different contents (tables, figures, and photos) have been tested for skew correction and the algorithm gives accurate results on all the test images, and the algorithm is very easy to implement.