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Method of detection document alteration by comparing characters using shape features of characters

  • US 8,331,670 B2
  • Filed: 03/22/2011
  • Issued: 12/11/2012
  • Est. Priority Date: 03/22/2011
  • Status: Active Grant
First Claim
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1. A method implemented in a data processing apparatus for detecting alterations between an original image and a target image, the original and target images being binary bitmap images, the method comprising:

  • (a) defining a plurality of bounding boxes in the original image and the target image, each bounding box enclosing one or more connected groups of pixels of one character;

    (b) identifying a plurality of matching pairs of bounding boxes in the original image and the target image, wherein each matching pair of the bounding boxes have substantially the same locations in the original image and the target image, respectively;

    (c) for each matching pair of bounding boxes;

    (c1) calculating a plurality of shape features including (1) a Euler number of each of the pair of characters enclosed by the pair of bounding boxes, and (2) a Hausdorff distance between the pair of characters; and

    (c2) determining whether the pair of characters enclosed by the pair of bounding boxes are the same character or different characters by evaluating (1) whether the Euler numbers of the pair of characters are equal, and (2) whether the Hausdorff distance between the pair of characters is smaller than a first predefined threshold.

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