Techniques for reading two dimensional code, including MaxiCode

• US 6,340,119 B2
• Filed: 03/26/2001
• Issued: 01/22/2002
• Est. Priority Date: 10/22/1998
• Status: Expired due to Term

• Current Assignee: Symbol Technologies, LLC (Zebra Technologies Corporation)
• Original Assignee: Symbol Technologies, Inc. (Zebra Technologies Corporation)
• Inventors: Hunter, Kevin, He, Duanfeng, Joseph, Eugene
• Primary Examiner(s): Pitts, Harold I.
• Application Number:
  US09/816,173
• Publication Number:
  US 20010023896A1
• Time in Patent Office: 302 Days
• Field of Search: 235/494, 235/454, 382/202
• US Class Current: 235/494
• CPC Class Codes: G06K 7/14 using light without selection of wavelength, e.g. sensing reflected white light G06K7/10831 - G06K7/1097 take precedence
• CPC Class Codes: G06K 7/1443 locating of the code in an image
• CPC Class Codes: G06K 7/1456 determining the orientation of the optical code with respect to the reader and correcting therefore

Abstract

The disclosure relates to techniques for determining the presence, orientation and location of features in an image of a two dimensional optical code. The techniques are adapted for use in mapping data in an image pixel plane with grid locations in a grid-based two dimensional code to account for size, rotation, tilt, warping and distortion of the code symbol. Where such a code is a MaxiCode, techniques are disclosed for determining the presence and location of the MaxiCode bulls-eye, orientation modules, primary data modules and secondary data modules.

Claims

1. A method for associating pixel data in a pixel plane, obtained by an optical code reader from an image of a two dimensional grid-based symbol, with corresponding modules in the grid, comprising the steps of:

identifying subsets of the pixel data having a known association with plural seed modules;

determining the coefficients of a mathematical transform using the identified association between the pixel data subsets and the seed modules; and

using the mathematical transform to perform a two-dimensional mapping to associate other locations in the pixel plane with additional symbol modules.

2. The method of claim 1, wherein more than six seed modules are employed.

3. The method of claim 1, wherein the symbol is a MaxiCode symbol and the seed modules are the 18 orientation hexagon modules of the MaxiCode symbol.

4. The method of claim 1, wherein the grid-based symbol is located, at least in part, outside of any single plane perpendicular to the optical axis of the optical code reader.