Resources and References

• Skew Removal
  • Grayscale De-skew Implementations
  • Binary De-skew Implementations
  • Mechanical De-Skew Implementations
• Skew Measurement from Image Data

Skew Removal

Grayscale De-skew Implementations

• Picture Elements, Inc.
  
  • Imaging Subsystem Engine^tm (ISE^tm) Board
• BancTec, Inc.
  
  • S-Series Scanners
  • 5100/5300 Check Transports

Binary De-skew Implementations

This is a (likely incomplete) list of binary de-skew developers. Other companies may incorporate their products on a licensing basis.

• Accusoft
• Hypersoft / Log Cabin Software
• J&K Imaging
• Kofax Image Products
• Picture Elements, Inc.
• Seaport Imaging
• TMSSequoia
• VisionShape

Mechanical De-Skew Implementations

Many of the leading scanner manufacturers quietly incorporate mechanical de-skew functions into their feeders and transports. Those specifically discussed in this white paper are listed here.

• Bureau of the Census Technical Services Division
• Imaging Business Machines, LLC
• BancTec, Inc.

Skew Measurement from Image Data

As we note above, this technique is often computationally expensive and unnecessary, since working with the document's black border works so well. But it is interesting technically, so we include some references.

Three good surveys of image-based skew measurement papers exist.

• Witten, I. et al, 1994, Managing Gigabytes, Van Nostrand Reinhold, New York, pp. 326-327.
• O'Gorman, L. and R. Kasturi, 1995, Document Image Analysis, IEEE Computer Society Press, Los Alamitos, CA, pp. 161-165.
• Amin, A. et al, "Comparative study of skew detection algorithms," J. Electronic Imaging, 5:4, October 1996, pp. 443-451.

A list of some of the relevant papers follows.

• Postl,W., "Detection of linear oblique structures and skew scan in digitized documents," Proc. 8th Int'l. Conf. on Pattern Recognition, October, 1986, pp.687-689.
• Baird, H.S., "The skew angle of printed documents," Proc. Conf. Soc. Photographic Scientists and Engineers, 1987, pp. 14-21.
• Hinds, S.C., J.L. Fisher, and D.P. D'Amato, "A document skew detection method using run-length encoding and the Hough transform," Proc. 10th Int'l. Conf. Pattern Recognition (ICPR), June, 1990, pp. 464-468.
• J.L. Fisher, S.C. Hinds, and D.P. D'Amato, "A rule-based system for document image segmentation," Proc. 10th Int'l. Conf. Pattern Recognition (ICPR), June, 1990, pp. 567-572.
• Nakano, Y., et al, "An algorithm for the skew normalization of document image," Proc. 10th Int'l. Conf. Pattern Recognition (ICPR), June, 1990, pp. 8-13.
• Story, G., et al, "The RightPages image-based electronic library for alerting and browsing," IEEE Computer, Sept. 1992, pp. 17-26.
• O'Gorman, L., "The document spectrum for page layout analysis," IEEE Trans. Pattern Analysis and Machine Intelligence, 15:11, Nov. 1993, pp. 1162-1173.