Two Phase Data Reduction for Hough Transformation to Detect Skew

An important pre-processing task in an automated document image processing system is detection of skew in the image. Skew detection and correction is the first step in the document analysis and understanding processing steps. Correction the skewed scanned document image is very important, because it has a direct effect on the reliability and efficiency of the segmentation and feature extraction stages. It is desirable to have a fast, all-purpose skew detector. This paper proposes a novel two phase method. This two phase method reduces the skewed data before applying the skew detection and correction methods. A combination of the two phase method and the Hough Transformation can quickly and accurately detect skew on a wide variety of document images. Results of a test of the new algorithm and a comparison against the simple Hough transformation algorithm on 100 pages show the new algorithm to be much faster. Keywords-Skew detection; Hough Transformation; Two phase data reduction; Projection Profile; Least Squares method; and Principal Component analysis.