Integral Ratio: A New Class of Global Thresholding Techniques for Handwriting Images

  • Authors:
  • Yan Solihin;C. G. Leedham

  • Affiliations:
  • Nanyang Technological Univ., Singapore;Nanyang Technological Univ., Singapore

  • Venue:
  • IEEE Transactions on Pattern Analysis and Machine Intelligence
  • Year:
  • 1999

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Abstract

In this paper, we propose a new class of histogram based global thresholding techniques called Integral Ratio. They are designed to threshold gray-scale handwriting images and separate the handwriting from the background. The following tight requirements must be met: 1) all the details of the handwriting are to be retained, 2) the writing paper used may contain strong colored and/or patterned background which must be removed, and 3) the handwriting may be written using a wide variety of pens such as a fountain pen, ballpoint pen, or pencil. A specific application area which requires these tight requirements is forensic document examination, where a handwritten document is often considered as legal evidence and the handwriting must not be tampered with or modified in any way. The proposed class of techniques is based on a two stage thresholding approach requiring each pixel of a handwritten image to be placed into one of three classes: foreground, background, and a fuzzy area between them where it is hard to determine whether a pixel belongs to the foreground or the background. Two techniques, Native Integral Ratio (NIR) and Quadratic Integral Ratio (QIR), were created based on this class and tested against two well-known thresholding techniques: Otsu's technique and the Entropy thresholding technique. We found that QIR has superior performance compared to all the other techniques tested.