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Method of imaging a coding pattern with data elements encoding by pulse-position modulation

  • US 7,913,923 B2
  • Filed: 02/05/2008
  • Issued: 03/29/2011
  • Est. Priority Date: 02/08/2007
  • Status: Expired due to Fees
First Claim
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1. A method of imaging a coding pattern disposed on a surface of a substrate, said method comprising the steps of:

  • (a) capturing an image of a portion of said coding pattern, said coding pattern comprising;

    a plurality of target elements defining a target grid, said target grid comprising a plurality of cells, wherein neighboring cells share target elements;

    a plurality of data elements contained in each cell; and

    a plurality of tags, each tag being defined by a plurality of contiguous cells, each tag comprising respective local tag data encoded by a respective set of said data elements,wherein said data elements encode data values by pulse position modulation;

    (b) low-pass filtering said captured image so as to obscure said data elements and preserve said target elements;

    (c) observing a perspective distortion of said preserved target elements due to a 3D orientation of said reader relative to said surface; and

    (d) calculating a 2D perspective transform using said target elements.

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