Method and apparatus for decoding two-dimensional bar code

• US 5,635,697 A
• Filed: 06/03/1994
• Issued: 06/03/1997
• Est. Priority Date: 03/01/1989
• Status: Expired due to Term

• Current Assignee: Symbol Technologies, Inc. (Zebra Technologies Corporation)
• Original Assignee: Symbol Technologies, Inc. (Zebra Technologies Corporation)
• Inventors: Shellhammer, Stephen J., Nikzad, Arman, Swartz, Jerome
• Primary Examiner(s): Dolinar, Andrew M.
• Application Number:
  US08/253,694
• Time in Patent Office: 1,096 Days
• Field of Search: 235/462, 235/470, 235/471
• US Class Current: 235/462.11
• CPC Class Codes: G06F 3/002 Specific input/output arrangements not covered by G06F3/01 - G06F3/16 other optical apparatus G02B27/00
• CPC Class Codes: G06K 1/126 by photographic or thermographic registration recording apparatus for measuring instruments G01D15/00
• CPC Class Codes: G06K 19/06037 multi-dimensional coding
• CPC Class Codes: G06K 2019/06253 for a specific application
• CPC Class Codes: G06K 7/0166 by means of clock-signals derived from the code marks, e.g. self-clocking code
• CPC Class Codes: G06K 7/10722 Photodetector array or CCD scanning
• CPC Class Codes: G06K 7/1093 sensing, after transfer of the image of the data-field to an intermediate store, e.g. storage with cathode ray tube
• 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 7/1417 2D bar codes
• 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

A method and apparatus for decoding a two-dimensional bar code symbol using a charge-coupled device (CCD) camera, charge-modulation device (CMD) camera, or other bar code reading device such as a hand-held reader, light pen or wand, scan mouse, or stationary laser scanner. The CCD/CMD camera or reading device optically images the bar code symbol to obtain digital image data, which is stored in a memory. The location and orientation of the two-dimensional bar code

Claims

1. A system for reading and decoding a two-dimensional bar code symbol having rows of bar-coded information in which data is represented in each row by a plurality of codewords, each row including a predetermined control codeword, the codewords being formed of a plurality of modules, comprising:

a two-dimensional imaging camera for optically imaging the bar code symbol to obtain lines of image data corresponding to a field of view including the bar code symbol;

a memory for storing the lines of image data;

means for determining an orientation of the two-dimensional bar code symbol in the field of view by locating control codewords in at least two positions in the image data;

means for determining a sequence of lines passing through the rows of the bar code symbol in the image data from the orientation determined from the positions of the control codewords; and

means for scanning the two-dimensional bar code symbol in the image data along the sequence of lines line to read the codewords.

2. The system according to claim 1, wherein each row of the symbol includes two predetermined control codewords, one control codeword being a start codeword at the beginning of each row and the other control codeword being a stop control codeword at the end of each row.

3. The system according to claim 1, further comprising means for detecting defects in the two-dimensional bar code symbol and correcting the detected defects in the two-dimensional bar code symbol.

4. The system according to claim 1, further comprising a host computer for decoding the codewords obtained by scanning the two-dimensional bar code symbol in the image data.

5. The system according to claim 1, further comprising a frame grabber for converting analog signals from the camera into digital signals.

6. The system according to claim 1, wherein the bar code symbol contains a plurality of modes in which data is stored.

7. A method for reading and decoding a two-dimensional bar code symbol having rows of bar-coded information in which data is represented in each row by a plurality of codewords, each row including a predetermined control codeword which is the same for each row, the codewords being formed of a plurality of modules, the method comprising the steps of:

optically imaging the two-dimensional bar code symbol using a two-dimensional imaging camera to obtain lines of image data corresponding to a field of view including the bar code symbol;

storing the lines of image data in a memory;

determining an orientation of the two-dimensional bar code symbol in the field of view by locating control codewords in at least two positions in the image data;

determining a sequence of lines passing through the rows of the bar code symbol in the image data from the orientation derived from the positions of the control codewords; and

scanning the two-dimensional bar code symbol in the image data along the sequence of lines to read the codewords.

8. The method according to claim 7, wherein each row of the symbol includes two predetermined control codewords, one control codeword being a start codeword at the beginning of each row and the other control codeword being a stop control codeword at the end of each row.

9. The method according to claim 7, further comprising the steps of

detecting defects in the two-dimensional bar code symbol;

and

scanning the two-dimensional bar code symbol despite the presence of defects.

10. The method according to claim 7, further comprising the step of decoding in a host computer the codewords obtained by scanning the two-dimensional bar code symbol in the image data.

11. The method according to claim 7, further comprising the step of converting analog signals from the camera into digital signals using a frame grabber.

12. The method according to claim 7, wherein the bar code symbol contains a plurality of modes in which data is stored.