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Method for locating and reading a two-dimensional barcode

  • US 6,082,619 A
  • Filed: 12/16/1998
  • Issued: 07/04/2000
  • Est. Priority Date: 12/16/1998
  • Status: Expired due to Fees
First Claim
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1. A method of decoding randomized information printed on a human readable medium in the form of a bitmap of rows and columns of data pixels representing encoded data bits, each of said data pixels being either a first or second color, said bitmap having a predetermined size and surrounded by an outer region of pixels of predetermined substantially uniform color, comprising the steps of:

  • scanning said human readable medium to digitize said bitmap;

    formatting said bitmap to a pixel based grayscale representation;

    converting said pixel based grayscale representation to a pixel based binary representation by setting a threshold intensity level based on said grayscale representation and converting pixels to a first level or to a second level dependent on their relationship to said threshold;

    locating the row and column boundaries of a candidate region for said digitized bitmap by moving a window across said pixel based binary representation in stepwise fashion in a predetermined pattern, at each step testing a portion of said representation which is encompassed by said window to determine whether said portion conforms to one or more characteristics of said bitmap, and setting the boundaries of said candidate region as the boundaries of said window if said portion does conform to said one or more characteristics of said bitmap;

    determining the skew angle of said digitized bitmap within said candidate region;

    deskewing said digitized bitmap so that the skew angle is reduced to substantially zero;

    reading out binary data from said digitized bitmap to produce a one-dimensional array of digital data;

    derandomizing said one-dimensional array of digital data; and

    error-correcting the derandomized one-dimensional array of digital data to produce a substantially error-free digital representation of the encoded information.

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