A data reduction method for efficient document skew estimation based on Hough transformation

Document recognition usually requires several preprocessing steps in which skew estimation and correction are critical to get a useful system. This paper proposes an efficient data reduction method to enhance the performance of document skew estimation by using a Hough transformation. The time complexity of the Hough transformation is O(ΘN), where N is the number of black pixels in a document and Θ is the skew estimation range divided by Δθ. We might enhance the performance by reducing N or Θ. The proposed method uses an efficient data reduction method called the modified version of divided horizontal histograms, which reduces the number of black pixels N, while retaining the skewness of document. In order to show the superiority of the proposed method, we have also performed experiments with scanned documents, comparing the result with those of the usual data reduction methods: vertical run-length and connected component methods