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EP0561334A2
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Method and apparatus for decoding two-dimensional bar code using CCD/CMD camera
Assignee: Symbol Technologies LLC
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Filing: 1993-03-15
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Granted: —
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Expires: 2013-03-15
Abstract
Abstract A method and apparatus for decoding a two-dimensional bar code symbol using a charge-coupled device (CCD) camera or a charge-modulation device (CMD) camera. The CCD/CMD camera takes pictures of the symbol and the picture is converted into digital data. The location and orientation of the two-dimensional bar code symbol is determined and verified. Defects and damages on the symbol are detected and corrected. The symbol is scanned to read the codewords of the two-dimensional bar code symbol.
Inventors
- 👤 Stephen J. Shellhammer
- 👤 Ming-Hua Chen
- 👤 Arman Nikzad
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-30 18:06
CPC Classifications
G; G06; G06K; G06K7/00; G06K7/10; G06K7/10544; G06K7/10821; G06K7/1093; G06K19/00; G06K19/06; G06K19/06009; G06K19/06037; G06K7/01; G06K7/016; G06K7/0166; G06K7/14; G06K7/1404; G06K7/1408; G06K7/1417; G06K7/1439; G06K7/1443; G06K7/1456
Claims Analysis
Total Claims: 27
Claim 1
Independent Claim
122 words
A method of decoding a two-dimensional bar code symbol (20) having rows of bar coded information in codewords including a start and a stop codeword, the codewords being formed of a plurality of modules, the method being characterised by: taking a picture of the two-dimensional bar code symbol (20), converting the picture to lines of image data, and storing the image data in a memory; determining the orientation of the two-dimensional bar code symbol (20) in the image data by locating at least one of the start and stop codewords; determining a sequence of lines passing through the rows of the bar code symbol (20); and scanning the two-dimensional bar code symbol (20) along the sequence of lines to read the codewords.
Claim 2
Dependent Claim
59 words
A method of decoding a two-dimensional bar code symbol according to Claim 1, wherein the orientation determining comprises scanning the lines of image data to determine edge locations of the symbol; searching for one of the start and stop codewords along the edge of the symbol; and determining a plurality of control points adjacent the start and stop codewords.
Claim 3
Dependent Claim
26 words
A method of decoding a two-dimensional bar code symbol according to Claim 1 or Claim 2, including verifying the orientation of the two-dimensional bar code symbol.
Claim 4
Dependent Claim
25 words
A method of decoding a two-dimensional bar code symbol according to Claim 2 or Claim 3 wherein the image data scanning includes a horizontal scan.
Claim 5
Dependent Claim
28 words
A method of decoding a two-dimensional bar code symbol according to Claim 2 or Claim 3 or Claim 4 wherein the image data scanning includes a vertical scan.
Claim 6
Independent Claim
39 words
A method of decoding a two-dimensional bar code symbol according to any one of Claims 2 to 5 wherein the image data scanning includes skipping a predetermined number of lines while searching for the said start or stop codeword.
Claim 7
Independent Claim
35 words
A method of decoding a two-dimensional bar code symbol according to any one of Claims 2 to 6, wherein the searching is repeated until a predetermined number of start and stop codewords have been found.
Claim 8
Dependent Claim
35 words
A method of decoding a two-dimensional bar code symbol according to Claim 7, further comprising selecting the best two start and best two stop codewords from the predetermined number of located start and stop codewords.
Claim 9
Dependent Claim
129 words
A method of decoding a two-dimensional bar code symbol according to Claim 3 or any one of the preceding claims when dependent upon Claim 3, wherein the image data scanning determines the edge locations, the image data scanning including selecting two end points to find edge locations therebetween; traversing a line between the two end points; calculating the slope of the line; comparing a gray level of a first pixel position to a second pixel position on the line; determining the first pixel position to be an edge location when the comparison is greater than or equal to a first predetermined threshold value; incrementing the first and second pixel positions along the line according to the slope; and repeating the comparing step until the last end point is reached.
Claim 10
Dependent Claim
65 words
A method of decoding a two-dimensional bar code symbol according to Claim 3 or any one of the preceding claims when dependent upon Claim 3, wherein the control point determining step comprises determining a line passing through a first bar of each of the start and stop codewords; and locating points both on the line and at the edge of the two-dimensional bar code symbol.
Claim 11
Dependent Claim
51 words
A method of decoding a two-dimensional bar code symbol according to Claim 4 of any one of the preceding claims when dependent upon Claim 4, wherein the verifying step includes checking whether the two-dimensional bar code symbol forms a rectangle having a shape meeting requirements of a first predefined acceptable condition.
Claim 12
Dependent Claim
74 words
A method of decoding a two-dimensional bar code symbol according to Claim 11, wherein said checking comprises connecting the control points to form a rectangle; calculating a slope for each line of the rectangle; comparing the slopes of intersecting lines at each corner of the rectangle; and concluding that the symbol has the acceptable rectangular shape when each of the comparisons determines that the intersecting lines are perpendicular to within a predefined error limit.
Claim 13
Independent Claim
37 words
A method of decoding a two-dimensional bar code symbol according to any one of the preceding claims, including detecting defects on the two-dimensional bar code symbol; and amending the scanning procedure in dependence upon the defects detected.
Claim 14
Dependent Claim
79 words
A method of decoding a two-dimensional bar code symbol according to Claim 13, wherein the detecting comprises determining a control line at top and bottom edges of the symbol; forming a first and second neighbouring lines adjacent and at opposite sides of each of the control lines; searching for the start and stop codewords on each said neighbouring line; and determining the symbol to have a defect when each said control line fails to meet a second predetermined condition.
Claim 15
Dependent Claim
42 words
A method of decoding a two-dimensional bar code symbol according to Claim 14, wherein the second predefined condition includes the first neighbouring line having both start and stop codewords and the second neighbouring line having neither of the start and stop codewords.
Claim 16
Dependent Claim
57 words
A method of decoding a two-dimensional bar code symbol according to Claim 14 or Claim 15 including correcting for one defective control line with the other control line being a valid control line, the correcting comprising adjusting the defective control line to be parallel with the valid control line and to include one of the control points.
Claim 17
Dependent Claim
95 words
A method of decoding a two-dimensional bar code symbol according to Claim 16, further comprising validating the adjusted control line by forming two neighbouring lines adjacent and at opposite sides of the adjusted control line; searching for one of the start and stop codewords on each said neighbouring line; and determining the valid correction of the defective control line by testing whether the adjusted control line meets a condition of having one neighbouring line having one of the start and stop codewords and the other neighbouring line having neither of the start and stop codewords.
Claim 18
Independent Claim
69 words
A method of decoding a two-dimensional bar code symbol according to any one of the preceding claims, wherein the sequence of lines is determined by forming rascan start and rascan stop lines; selecting virtual scan head and corresponding virtual scan tail points on the rescan start and scan stop lines, respectively; and retrieving a pair of head and corresponding tail points and forming a line connecting the two points.
Claim 19
Dependent Claim
76 words
A method of decoding a two-dimensional bar code symbol according to Claim 18 in which the bar code symbol is scanned by computing gray-level differences between successive pixels on the line connecting the head and tail points; finding extrema of the computed differences; comparing each extremum to a third predetermined threshold value; determining the extremum to be an edge when the comparison is greater than the third predetermined threshold value; and calculating distances between adjacent edges.
Claim 20
Dependent Claim
34 words
A method of decoding a two-dimensional bar code symbol according to Claim 19, further comprising optimizing the scanning to reduce the scanning time and overhead by reducing the number of head and tail pairs.
Claim 21
Dependent Claim
76 words
A method of decoding a two-dimensional bar code symbol according to Claim 1, wherein the sequence of lines is determined by defining an interval having a beginning point and an end point at a centre of each row of the two-dimensional bar code symbol and forming a line connecting the beginning and end points; partitioning the defined interval into a predetermined unit sub-intervals; and approximating width of the modules to correspond to a nearest unit sub-interval.
Claim 22
Dependent Claim
50 words
A method of decoding a two-dimensional bar code symbol according to Claim 21, wherein the scanning comprises summing gray-level values for each module interval; comparing the sum to a fourth predetermined threshold value; and determining the module to be one of a plurality of predefined values corresponding to the comparison.
Claim 23
Dependent Claim
33 words
A method of decoding a two-dimensional bar code symbol according to Claim 1, further comprising detecting and correcting damage due to destruction of one of the start and stop codewords of the symbol.
Claim 24
Dependent Claim
123 words
Apparatus for decoding a two-dimensional bar code symbol having rows of bar coded information in codewords including a start and a stop codeword, the codewords being formed of a plurality of modules, the apparatus comprising: means for taking a picture of the two-dimensional bar code symbol, converting the picture to lines of image data, and storing the image data in a memory; means for determining an orientation of the two-dimensional bar code symbol in the image data by locating at least one of the start and stop codewords; means for determining a sequence of lines passing through the rows of the bar code symbol; and means for scanning the two-dimensional bar code symbol along the sequence of lines line to read the codewords.
Claim 25
Dependent Claim
36 words
The apparatus for decoding a two-dimensional bar code symbol according to claim 24, further comprising means for detecting defects on the two-dimensional bar code symbol and correcting the detected defects on the two-dimensional bar code symbol.
Claim 26
Dependent Claim
67 words
The apparatus for decoding a two-dimensional bar code symbol according to claim 24, wherein the orientation determining means comprises: means for scanning the lines of image data to determine edge locations of the symbol; means for searching for one of said start and stop codewords along the edge locations of the symbol; and means for determining a plurality of control points adjacent the start and stop codewords.
Claim 27
Dependent Claim
26 words
The apparatus for decoding a two-dimensional bar code symbol according to claim 26, further comprising means for verifying the orientation of the two-dimensional bar code symbol.
References Cited (Backward Citations)
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