Method of detecting two-dimensional codes

• US 20030009725A1
• Filed: 05/14/2002
• Published: 01/09/2003
• Est. Priority Date: 05/15/2001
• Status: Active Grant

• Current Assignee: Sick AG (Sick)
• Original Assignee: Sick AG (Sick)
• Inventors: Reichenbach, Juergen
• Granted Patent: US 7,107,506 B2
• Time in Patent Office: Days
• US Class Current: 714/804
• 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 7/1473 error correction

Abstract

A method is described of detecting two-dimensional codes, in particular matrix codes, which include a plurality light and dark data bits arranged two dimensionally, in particular in matrix form. In the method, the code is detected as a gray scale value image; the detected gray scale value image is split into image areas corresponding to the individual data bits and a binarizing threshold representing a specific gray scale value is determined for the image areas. A respective binarizing of the gray scale value of the individual image areas is carried out by means of the binarizing threshold to produce a bit sequence which represents the data bits and consists of the values 0 and 1. The bit sequence is subsequently supplied to an error correction algorithm to recognize and/or correct bit errors within the bit sequence. In accordance with the invention, those so-called uncertain image areas are determined whose gray scale values each lie close to the binarizing threshold. Furthermore, these uncertain image areas are taken into special account in the error correction.

Claims

1. A method of detecting two-dimensional codes, in particular matrix codes, which include a plurality of light and dark data bits arranged two dimensionally, in particular in matrix form, wherein the code is detected as a gray scale value image;

wherein the detected gray scale value image is split into image areas corresponding to the individual data bits;

wherein a binarizing threshold representing a specific gray scale value is determined for the image areas;

wherein a respective binarizing of the gray scale value of the individual image areas is carried out by means of the binarizing threshold to produce a bit sequence which represents the data bits and consists of the values 0 and 1; and

wherein the bit sequence is supplied to an error correction algorithm to recognize and/or correct bit errors within the bit sequence,

characterized in that those so-called uncertain image areas are determined whose gray scale values each lie close to the binarizing threshold; and

in that these uncertain image areas are taken into special account in the error correction.

2. A method in accordance with claim 1, characterized in that the special taking into account of the uncertain image areas is carried out in that, for at least one of the uncertain image areas, a different value is assigned to the corresponding data bit than is pre-determined by the ratio of the detected gray scale value of the image area to the binarizing threshold.

3. A method in accordance with claim 1, characterized in that an error correction algorithm is used for the error correction which also allows the value “

indefinite”

for a certain number of bits of the bit sequence in addition to the values 0 and 1; and

in that at least some of the so-called uncertain bits of the bit sequence associated with the uncertain image areas are supplied to the error correction algorithm with the value “

indefinite”

.

4. A method in accordance with claim 1, characterized in that the Reed-Solomon algorithm is used for the error correction.

5. A method in accordance with claim 1, characterized in that a plurality of different bit sequences are produced in that the values of at least some of the so-called uncertain bits associated with the uncertain image areas are inverted in different variations or are set to “

indefinite”

.

6. A method in accordance with claim 5, characterized in that the different bit sequences are supplied to the error correction algorithm until a successful error correction can be carried out.

7. A method in accordance with claim 5, characterized in that, to produce the different bit sequences, the uncertain bits are inverted in the order of their uncertainty or are set to “

indefinite”

, i.e. in that first that bit is inverted or set to “

indefinite”

for which the gray scale value of the image area associated with it lies closest to the binarizing threshold.

8. A method in accordance with claim 5, characterized in that, to produce the bit sequences, no, one or multiple uncertain bits are inverted or set to “

indefinite”

.

9. A method in accordance with claim 5, characterized in that the number of uncertain bits to be inverted or set to “

indefinite”

is limited to a maximum value.

10. A method in accordance with claim 1, characterized in that those image areas are classified as uncertain image areas whose gray scale values each fall below a specific, in particular an adjustable, distance from the binarizing threshold.

11. A method in accordance with claim 1, characterized in that the positions of the uncertain image areas in the gray scale value image are detected.

12. A method in accordance with claim 11, characterized in that, for detecting the positions of the uncertain image areas, the respective position of the so-called uncertain bit associated with the uncertain image area in the bit sequence produced is detected.

13. A method in accordance with claim 1, characterized in that the binarizing threshold is determined using pre-set data bits in the code.

14. A method in accordance with claim 1, characterized in that a pre-determined value is used as the binarizing threshold.

15. A method in accordance with claim 1, characterized in that the binarizing threshold is determined dynamically, in particular continuously, in dependence on the gray scale value development over the detected image areas.

16. A method in accordance with claim 1, characterized in that only such image areas are used for determining the dynamic binarizing threshold whose gray scale values have a respective specific minimum distance from the current binarizing threshold.

17. A method in accordance with claim 1, characterized in that the respective gray scale value of the geometrical center of the image area is used as the gray scale value of an image area.

18. A method in accordance with claim 1, characterized in that for the grey scale value of an image area there is used a respective mean gray scale value determined over the surface of the image area.

19. A method in accordance with claim 1, characterized in that the maximum number of the bit errors which can be corrected by the error calculation algorithm can be set.

20. A method in accordance with claim 1, characterized in that the code Datamatrix ECC 200, the QR code or the Maxicode are used as the code.

21. A method in accordance with claim 1, characterized in that the error correction algorithm either supplies an error-corrected bit sequence or produces an error signal if an error correction was not possible.

22. A method in accordance with claim 21, characterized in that the error-corrected bit sequence is decoded.