SYSTEM FOR DECODING TWO DIMENSIONAL CODE AND METHOD THEREOF

• US 20150090792A1
• Filed: 12/12/2013
• Published: 04/02/2015
• Est. Priority Date: 09/29/2013
• Status: Active Grant

• Current Assignee: Peking University Founder Group Company Limited (Beijing Peking University Asset Management Company Limited), Founder Mobile Media Technology Beijing Company Limited
• Original Assignee: Peking University Founder Group Company Limited (Beijing Peking University Asset Management Company Limited), Founder Mobile Media Technology Beijing Company Limited
• Inventors: ZHANG, Ling, Guan, Chao, Liu, Zhenhua, Liu, Gezhang, Che, Wanyi
• Granted Patent: US 9,135,489 B2
• Time in Patent Office: Days
• US Class Current: 235/462.04
• CPC Class Codes: G06K 7/1417 2D bar codes
• CPC Class Codes: G06K 7/1478 adapting the threshold for pixels in a CMOS or CCD pixel sensor for black and white recognition

Abstract

Method and system for decoding a two dimensional code is disclosed. In the binarization process of a two dimensional code image, through performing a dividing operation on the two dimensional code image, each block region has a different grayscale threshold. For each block region, whether a pixel in the block region is determined as black or white is not solely based on the grayscale value of the pixel itself, but also an average grayscale value of a predetermined area set for the block region where the pixel locates. When the predetermined area in which the block region locates has a larger grayscale value as a whole, the grayscale threshold corresponding to the block region may become larger, and vice versa.

Claims

1. A method for decoding a two dimensional code, the method comprising:

performing a binarization process on a two dimensional code image to obtain a binary image, the binarization process comprising;

dividing the two dimensional code image into a plurality of block regions;

obtaining grayscale values of all pixels in each block region, and obtaining a grayscale value for each block region according to the grayscale values of all the pixels;

determining, a grayscale threshold for each block region according to an average grayscale value of a predetermined area where the block region locates;

binarizing pixels in the block region to obtain a binary image, according to a grayscale threshold corresponding to each block region;

decoding the binary image to obtain information content contained in the two dimensional code.

2. The method of claim 1 where the binarization process further comprises:

constructing a contrast factor according to the relationship between grayscale values of pixels in the two dimensional code image, wherein the contrast factor is proportional to the difference between a maximum grayscale value and a minimum grayscale value of the two dimensional code image;

the step of obtaining grayscale values of all pixels in each block region, and obtaining a grayscale value for each block region according to the grayscale values of all the pixels comprises;

determining a grayscale value for a block region, according to the relationship between the contrast factor and the difference between a maximum grayscale value and a minimum grayscale value in the block region, in conjunction with grayscale values of other block regions adjacent to the block region.

3. The method of claim 2 wherein determining a grayscale value for a block region according to the relationship between the contrast factor and the difference between a maximum grayscale value and a minimum grayscale value in the block region, in conjunction with grayscale values of other block regions adjacent to the block region, a grayscale value y_ij is obtained for a block region (i, j) according to the following equation:

4. The method of claim 2 wherein the contrast factor C is constructed according to the following equation:

5. The method of claim 1 wherein determining, a grayscale threshold for each block region according to an average grayscale value of a predetermined area where the block region locates:

the predetermined area comprises n×

n block regions, wherein n is an integer larger than 1.

6. The method of claim 1 wherein decoding the binary image to obtain information content contained in the two dimensional code comprises:

determining an initial coordination system and a correction coordination system in which a corrected image locates, wherein each point in the correction coordination system corresponds to a point in the initial coordination system; and

determining coordinates of central points of detection patterns and a corrected pattern in the initial coordinate system and the correction coordinate system respectively, wherein the detection patterns comprise a first detection pattern, a second detection pattern, and a third detection pattern;

correcting the binary image according to the coordinates of the central points of each detection pattern and the correction pattern in the initial coordinate system and the correction coordinate system to obtain a corrected pattern;

obtaining information contained in the corrected pattern.

7. The method of claim 6 wherein determining coordinates of central points of the detection patterns, the step of determining a central point of each detection pattern comprises:

detecting the binary image along a first direction to detect a first line segment having a length ratio of black;

white;

black;

white;

black meeting a first predetermined ratio, and determining the central point of the first line segment;

detecting along a second direction a line running through the central point of the first line segment to get a second line segment having a length ratio of black;

white;

black;

white;

black meeting the first predetermined ratio, and using the central point of the second line segment as the central point of the detection pattern.

8. The method of claim 7 wherein determining coordinates of the central point of each detection pattern further comprises:

setting a detection step size for detecting the binary image along the first direction, wherein the detection step size is less than or equal to the number of pixels in one module of the binary image in the first direction.

9. The method of claim 8 wherein setting a detection step size for detecting the binary image along the first direction, the detection step size is obtained according to the number of pixels in the binary image in the first direction and the number of pixels in the one module in the first direction.

10. The method of claim 8 wherein setting a detection step size for detecting the binary image along the first direction, the detection step size is obtained through the following equation:

L=Max(M×

N/Mod,Min)

wherein, M is the number of pixels contained in the binary image in the first direction, N is an adjustment coefficient and 0<

N≦

1, Mod is the preset number of modules contained in the binary image in the first direction, Min is the number of pixels contained in one module of the binary image in the first direction.

11. The method of claim 6 wherein determining coordinates of the central point of the correction pattern in the initial coordinate system comprises:

obtaining reference coordinates based on the relative location relationship between the central point of the correction pattern and the central points of the detection patterns;

locating the correction pattern precisely in a predetermined area with respect to the reference coordinates to obtain coordinates of the central point of the correction pattern.

12. The method of claim 11 wherein obtaining reference coordinates based on the relative location relationship between the central point of the correction pattern and the central points of the detection pattern comprises:

obtaining a horizontal reference coordinate according to the horizontal distance between the central point of the correction pattern and the central point of the first detection pattern;

obtaining a vertical reference coordinate according to the vertical distance between the central point of the correction pattern and the central point of the first detection pattern, wherein the horizontal distance and the vertical distance are determined according to the following equations;

the horizontal distance is ε

_h=ε

(X_R−

X_A)

the vertical distance is ε

_z=ε

(Y_R−

Y_A)

wherein, X_R=X_B−

X_A+X_C, Y_R=Y_B−

Y_A+Y_C, (X_B, Y_B) is the coordinates of the central point of the second detection pattern;

(X_C, Y_C) is the coordinates of the central point of the third detection pattern;

ε

is an offset factor of the correction pattern, and ε

=(N−

3)/K, K is the number of modules contained in the binary image in the first direction.

13. The method of claim 11 wherein locating the correction pattern precisely in a predetermined area with respect to the reference coordinates to obtain coordinates of the central point of the correction pattern:

the predetermined area is a square region including the reference coordinates, wherein the square region includes at least 64 modules.

14. The method of claim 11 wherein locating the correction pattern precisely in a predetermined area with respect to the reference coordinates to obtain coordinates of the central point of the correction pattern comprises:

detecting, in the predetermined area along the first direction, a third line segment having a length ratio of white;

black;

white meeting a second predetermined ratio, and determining the central point of the black portion of the third line segment;

taking the central point of the black portion of the third line segment as a reference to obtain a line perpendicular to the third line segment, detecting along the line a fourth line segment having a length ration of white;

black;

white meeting the second predetermined ratio, and taking the central point of the black portion of the fourth line segment as the central point of the correction pattern.

15. The method of claim 6 wherein correcting the binary image according to the coordinates of the central point of each detection pattern and the correction pattern in the initial coordinate system and the correction coordinate system to obtain a corrected pattern comprises:

obtaining conversion coefficients according to coordinates of the central point of each detection pattern and coordinates of the central point of the correction pattern in the initial coordinate system and the correction coordinate system;

according to the conversion coefficients, for each point in the correction coordinate system, finding out a module of the binary image in which its corresponding point in the initial coordinate system locates, and assigning the grayscale value of that module to the point to realize correction of the binary image.

16. The method of claim 15 wherein according to the conversion coefficients, for each point in the correction coordinate system, finding out a module of the binary image in which its corresponding point in the initial coordinate system locates, and assigning the grayscale value of that module to the point to realize correction of the binary image,

the grayscale value of the module is the grayscale value of the central pixel of the module.

17. The method of claim 15 wherein obtaining conversion coefficients according to coordinates of the central point of each detection pattern and coordinates of the central point of the correction pattern in the initial coordinate system and the correction coordinate system,

the conversion coefficients are obtained following a rule of perspective transformation.

18. A system for decoding a two dimensional code, the system comprising:

a binarization module for performing a binarization process on a two dimensional code image to obtain a binary image, further comprising;

a dividing unit for dividing the two dimensional code image into a plurality of block regions;

a grayscale value obtaining unit for obtaining grayscale values of all pixels in each block region, and obtaining a grayscale value for each block region according to the grayscale values of all the pixels;

a grayscale threshold obtaining unit for determining, a grayscale threshold for each block region according to an average grayscale value of a predetermined area where the block region locates;

a binary image obtaining unit for binarizing pixels in the block region to obtain a binary image, according to a grayscale threshold corresponding to each block region;

a decoding module for decoding the binary image to obtain information content contained in the two dimensional code.

19. The system of claim 18, characterized in that the binarization module further comprises:

a contrast factor construction module for constructing a contrast factor according to the relationship between grayscale values of pixels in the two dimensional code image, wherein the contrast factor is proportional to the difference between a maximum grayscale value and a minimum grayscale value of the two dimensional code image;

wherein the grayscale value obtaining unit is further configured to determine a grayscale value for a block region, according to the relationship between the contrast factor and the difference between a maximum grayscale value and a minimum grayscale value in the block region, in conjunction with grayscale values of other block regions adjacent to the block region.

20. The system of claim 19 wherein the contrast factor construction module obtains a grayscale value y_ij for a block region (i, j) in according to the following equation:

21. The system of claim 19 wherein the contrast factor C is constructed in the contrast factor construction module according to the following equation:

22. The system of claim 18 wherein in the grayscale threshold obtaining unit, the predetermined area is set to comprise n×

n block regions, wherein the n is an integer larger than 1.

23. The system of claim 18 wherein the decoding module comprises:

a coordinate determination unit, for determining an initial coordination system and a correction coordination system in which a corrected image locates, wherein each point in the correction coordination system corresponds to a point in the initial coordination system; and

comprising;

a detection pattern coordinate obtaining subunit for determining coordinates of central points of detection patterns in the initial coordinate system,

a correction pattern coordinate obtaining subunit for determining coordinates of the central points of the correction pattern in the initial coordinate system;

a correction coordinates obtaining subunit for determining the coordinates of the central points of the detection patterns and the correction patterns in the correction coordinate system;

a correction pattern obtaining unit for correcting the binary image according to the coordinates of the central points of each detection pattern and the correction pattern in the initial coordinate system and the correction coordinate system to obtain a corrected pattern;

an information obtaining unit for obtaining information contained in the corrected pattern.

24. The system of claim 23 wherein the detection pattern coordinate obtaining subunit is configured to detect the binary image along a first direction to detect a first line segment having a length ratio of black:

white;

black;

white;

black meeting a first predetermined ratio, and determining the central point of the first line segment; and

detect along a second direction a line running through the central point of the first line segment to get a second line segment having a length ratio of black;

white;

black;

white;

black meeting the first predetermined ratio, and using the central point of the second line segment as the central point of the detection pattern.

25. The system of claim 24 wherein the detection pattern coordinate obtaining subunit is further configured to set a detection step size for detecting the binary image along the first direction, wherein the detection step size is less than or equal to the number of pixels in one module of the binary image in the first direction.

26. The system of claim 25 wherein the detection pattern coordinate obtaining subunit is further configured to obtain the detection step size according to the number of pixels in the binary image in the first direction and the number of pixels in the one module in the first direction.

27. The system of claim 25 wherein the detection pattern coordinate obtaining subunit obtains the detection step through the following equation:

L=Max(M×

N/Mod,Min)

wherein, M is the number of pixels contained in the binary image in the first direction, N is an adjustment coefficient and 0<

N≦

1, Mod is the preset number of modules contained in the binary image in the first direction, Min is the number of pixels contained in one module of the binary image in the first direction.

28. The system of claim 23 wherein the correction pattern coordinate obtaining subunit is configured to obtain reference coordinates based on the relative location relationship between the central point of the correction pattern and the central points of the detection patterns, and locate the correction pattern precisely in a predetermined area with respect to the reference coordinates to obtain coordinates of the central point of the correction pattern.

29. The system of claim 28 wherein the correction pattern coordinate obtaining subunit is further configured to obtain a horizontal reference coordinate according to the horizontal distance between the central point of the correction pattern and the central point of the first detection pattern;

and obtain a vertical reference coordinate according to the vertical distance between the central point of the correction pattern and the central point of the first detection pattern, wherein the horizontal distance and the vertical distance are determined according to the following equations;

the horizontal distance is ε

_h=ε

(X_R−

X_A)

the vertical distance is ε

_z=ε

(Y_R−

Y_A)

wherein, X_R=X_B−

X_A+X_C, Y_R=Y_B−

Y_A+Y_C, (X_B, Y_B) is the coordinates of the central point of the second detection pattern;

(X_C, Y_C) is the coordinates of the central point of the third detection pattern;

ε

is an offset factor of the correction pattern, and ε

=(N−

3)/K, K is the number of modules contained in the binary image in the first direction.

30. The system of claim 28 wherein in the correction pattern coordinate obtaining subunit, the predetermined area is set as a square region including the reference coordinates, wherein the square region includes at least 64 modules.

31. The system of claim 28 wherein the correction pattern coordinate obtaining subunit is further configured to detect, in the predetermined area along the first direction, a third line segment having a length ratio of white:

black;

white meeting a second predetermined ratio, and determine the central point of the black portion of the third line segment; and

take the central point of the black portion of the third line segment as a reference to obtain a line perpendicular to the third line segment, detecting along the line a fourth line segment having a length ration of white;

black;

white meeting the second predetermined ratio, and taking the central point of the black portion of the fourth line segment as the central point of the correction pattern.

32. The system of claim 23 wherein the correction pattern obtaining unit comprises:

a conversion coefficient obtaining subunit for obtaining conversion coefficients according to coordinates of the central point of each detection pattern and coordinates of the central point of the correction pattern in the initial coordinate system and the correction coordinate system;

a correction subunit for according to the conversion coefficients, for each point in the correction coordinate system, finding out a module of the binary image in which its corresponding point in the initial coordinate system locates, and assigning the grayscale value of that module to the point to realize correction of the binary image.

33. The system of claim 32 wherein the correction subunit, the grayscale value of the central pixel of the module is set as the grayscale value of the module.

34. The system of claim 32 wherein in the correction subunit, the conversion coefficients are obtained following a rule of perspective transformation.

35. A system for decoding two dimensional code, the system comprising;

a processor, the processor is configured to

performing a binarization process on a two dimensional code image to obtain a binary image, the binarization process comprising;

dividing the two dimensional code image into a plurality of block regions;

obtaining grayscale values of all pixels in each block region, and obtaining a grayscale value for each block region according to the grayscale values of all the pixels;

determining, a grayscale threshold for each block region according to an average grayscale value of a predetermined area where the block region locates;

binarizing pixels in the block region to obtain a binary image, according to a grayscale threshold corresponding to each block region;

decoding the binary image to obtain information content contained in the two dimensional code.