Method and apparatus for decoding unresolved complex multi-width bar code symbology profiles

• US 5,514,858 A
• Filed: 02/10/1995
• Issued: 05/07/1996
• Est. Priority Date: 02/10/1995
• Status: Expired due to Term

• Current Assignee: Intermec IP Corporation (Honeywell International Inc.)
• Original Assignee: Intermec Corporation (Honeywell International Inc.)
• Inventors: Ackley, H. Sprague
• Primary Examiner(s): Hajec, Donald T.
• Assistant Examiner(s): Le, Thien Minh
• Application Number:
  US08/386,745
• Time in Patent Office: 452 Days
• Field of Search: 235/462, 235/469, 235/454, 235/463
• US Class Current: 235/462.16
• 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 7/1486 Setting the threshold-width for bar codes to be decoded

Abstract

A method and apparatus for decoding profiles which fail to resolve narrow elements in complex multi-width symbols, first begins by identifying which elements in the profile are resolved. Second, the environments surrounding each resolved element are examined. Third, several closure boundaries are determined, and the widths of resolved elements are determined at a selected threshold. The size of each resolved element is determined based on its measured width at a threshold selected based on the environment surrounding the resolved element. Fourth, the distances between the centers of the resolved elements are determined. Thereafter, an X-dimension is determined for 1-wide narrow elements unresolved in the profile. Based on the X-dimension and known center distances, a matrix is constructed for determining the number of narrow elements unresolved between two resolved elements. Based on the measured center distances, the resolved element widths and the matrix, all of the elements are identified in the profile and the profile is subsequently decoded.

Claims

1. A method of decoding a bar code symbol representing encoded information, the bar code symbol including a plurality of relatively spaced bars having at least first, second and third widths, and spaces between the bars having at least first, second and third widths, the second and third widths being greater than the first width, the method comprising the steps of:

receiving light reflected from the bar code symbol and producing an output signal therefrom that represents the reflectance of the bars and spaces comprising the bar code symbol;

receiving the output signal and producing a wide feature signal resolving the bars and spaces having the second and third widths, but the wide feature signal having unresolved portions that fail to resolve at least some of the bars and spaces having the first width;

receiving the wide feature signal and determining which of the bars and spaces are resolved by defining a first threshold and identifying a plurality of resolved portions in the wide feature signal that extend beyond the first threshold, each of the plurality of resolved portions corresponding to one of the resolved bars and spaces;

determining an environment for each of the plurality of resolved portions based on whether a selected resolved portion is between two other of the plurality of resolved portions, between two unresolved portions, or between a resolved and an unresolved portion in the wide feature signal;

defining at least a second threshold;

measuring a width for each of the plurality of portions at one of the first and second thresholds depending upon the environment of the selected resolved portion;

determining a narrow width of the bars and spaces having the first width based on the measured widths;

determining a number and location of the bars and spaces having the first width based on the determined narrow width and the measured widths; and

determining the information encoded in the bar code symbol based on the determined number and location of bars and spaces having the first width and the measured width for each of the plurality of portions.

2. The method of claim 1, further comprising the steps of:

identifying a center for each of the plurality of portions; and

measuring distances between the centers of the plurality of portions.

3. The method of claim 2 wherein the step of determining a narrow width includes the steps of:

identifying a preselected center distance between the centers of the plurality of portions; and

dividing the preselected center distance by a first predetermined amount to determine the narrow width.

4. The method of claim 3 wherein the preselected center distance in the step of determining a narrow width is a smallest center distance.

5. The method of claim 3 wherein the bar code symbol includes one of a start and stop character, and the preselected center distance in the step of determining a narrow width is a center distance derived from one of the start and stop characters.

6. The method of claim 2 wherein the step of determining a number and location includes the steps of:

creating a lost element matrix that identifies a number of the bars and spaces having the first width that are unresolved between resolved bars and spaces, the lost element matrix being created based on estimated center distances between the resolved bars and spaces and the determined narrow width; and

determining the number and location of the bars and spaces having the first width by comparing the center distances measured with respect to the plurality of portions in the wide feature signal to the estimated center distances in the lost element matrix.

7. The method of claim 6, further comprising the steps of:

comparing a selected distance, measured between the centers of selected first and second portions in the plurality of portions, to the lost element matrix to determine a selected number of bars and spaces having the first width that are unresolved between the selected first and second portions;

examining the first and second portions to determine a parity; and

ensuring that the selected number of bars and spaces having the first width is correct by determining if the parity of the selected first and second portions correlates to a parity of a selected number of bars and spaces having the first width.

8. The method of claim 7, further comprising the steps of:

creating a decode matrix that identifies the number of bars and spaces having the first width that are unresolved between the resolved bars and spaces in the wide feature signal;

repeating the steps of comparing, examining and ensuring for all of the plurality of portions; and

filling in the decode matrix with the identified number of the bars and spaces having the first width if the parity correlates.

9. The method of claim 1 wherein the step of measuring a width includes the step of determining whether the measured width for each portion corresponds to the second width or the third width.

10. The method of claim 9 wherein the step of measuring a width includes the step of estimating a first range of widths of the bars and spaces having the second width and a second range of widths of the bars and spaces having the third width.

11. The method of claim 10 wherein the first and second ranges in the step of measuring a width are derived from the narrow width.

12. The method of claim 10 wherein the step of measuring a width includes the step of averaging a selected number of the widths measured for each portion.

13. The method of claim 9 wherein the step of measuring a width includes the step of estimating a first range of widths of the bars having a second width, a second range of widths of the spaces having a second width, a third range of widths of the bars having the third width, and a fourth range of widths of the spaces having the third width.

14. The method of claim 9 wherein the step of determining a number and location includes the steps of determining whether each portion correctly corresponds to the second width or the third width, and

adjusting the correspondence of each portion to the second width or the third width.

15. The method of claim 1 wherein the step of determining an environment includes the step of determining whether a selected unresolved portion corresponds to a single unresolved bar or space having the first width, or more than one bar or space having the first width.

16. The method of claim 15 wherein the step of determining an environment includes the step of examining a slope of the wide feature signal proximate to the selected resolved portion.

17. The method of claim 1 wherein the step of defining at least a second threshold includes the step of defining a plurality of thresholds between the first threshold and the second threshold, and wherein the step of measuring a width measures a width for each of the plurality of portions of one of the plurality of thresholds.

18. The method of claim 17 wherein the plurality of thresholds in the step of defining at least a second threshold are at a distance of 1/2ⁿ between the first and second thresholds, where n equals 0, 1, 2, 3 or 4.

19. The method of claim 17 wherein the step of measuring a width measures a width of the selected resolved portion at the first threshold if the selected resolved portion is between two unresolved portions, and at a threshold approximately halfway between the first and second thresholds if the selected resolved portion is between two other of the plurality of resolved portions.

20. The method of claim 1 wherein the step of determining a number and location includes the step of determining if all of the bars and spaces in the bar code symbol have been identified.

21. The method of claim 20 wherein the step of determining a number and location includes the step of performing a parity check on the bar code symbol after determining the number and location of the bars and spaces having the first width.

22. The method of claim 1 wherein the bar code symbol has a predetermined width, and wherein the step of determining a number and location includes the step of determining if the predetermined width is equal to a sum of the widths measured for the plurality of portions and the determined number of bars and spaces having the first width.

23. The method of claim 22 wherein the bar code symbol is from a symbology having a parity, wherein the step of measuring a width includes the step of determining whether the measured width for each portion corresponds to the second width or the third width, and wherein the step of determining a number and location includes the step of correcting a width determined for a given measured width based on the parity in the symbology if the sum of the widths is unequal to the predetermined width.

24. The method of claim 1 wherein the bar code symbol is from a symbology having a row identification parity and wherein the symbol has a predetermined width, wherein the step of measuring a width includes the step of determining whether the measured width for each portion corresponds to the second width or the third width, and

wherein the step of determining a number and location includes the steps of determining if the predetermined width is equal to a sum of the widths measured for the plurality of portions and the determined number of bars and spaces having the first width;

and

correcting a width determined for a given measured width based on the parity in the symbology.

25. The method of claim 1, further comprising the steps of:

identifying start or stop characters in the bar code symbol based on the wide feature signal; and

determining a type of symbology from which the bar code symbol was generated based on the identified start or stop characters in the bar code symbol.

26. The method of claim 1, further comprising the steps of:

identifying start or stop characters in the bar code symbol based on the wide feature signal;

determining if the wide feature signal includes an acceleration distortion by comparing a distance between the plurality of portions in the wide feature signal; and

applying a compensation factor to the wide feature signal to compensate for the acceleration distortion.

27. The method of claim 1 wherein the step of determining a narrow width comprises the steps of:

averaging at least a few of the widths measured for the plurality of portions that correspond to one of the bars and spaces having one of the second and third widths to produce an average value; and

dividing the average value by a predetermined amount to determine the width of the bars and spaces having the first width.

28. The method of claim 1, further comprising the steps of:

determining if all of the bars and spaces having a first, second and third widths are resolved in the wide feature signal, before the step of receiving the wide feature signal; and

decoding the wide feature signal if all of the bars and spaces having the first, second and third widths are resolved.

29. A method of decoding a machine-readable symbol representing encoded information, the symbol including a plurality of relatively spaced two-dimensional geometric shapes, the shapes and spaces between the shapes having sizes with at least first, second and third widths in at least one dimension, the second and third widths being greater than the first width, the shapes having a reflectivity less than a reflectivity of the spaces, the method comprising the steps of:

receiving light reflected from the symbol and producing an output signal therefrom that represents the reflectance of the shapes and spaces comprising the symbol;

receiving the output signal and producing a wide feature signal that resolves at least some of the shapes and spaces having the second and third widths, but which fails to resolve at least some of the shapes and spaces having the first width;

receiving the wide feature signal and determining which of the shapes and spaces are resolved by identifying a plurality of portions in the wide feature signal that correspond to the resolved shapes and spaces;

determining the size of each of the identified portions that correspond to the resolved shapes and spaces;

generating a lost element matrix in response to the wide feature signal and the sizes of the identified portions that correspond to the resolved shapes and spaces; and

determining the information encoded in the symbol based on the lost element matrix and the determined size of each of the identified portions.

30. The method of claim 29 wherein the step of determining a size includes the step of defining a plurality of thresholds and measuring a width of each of the plurality of portions in the wide feature signal at one of the plurality of thresholds.

31. The method of claim 30 wherein the step of determining a size includes the steps of:

determining a slope of the wide feature signal proximate to each of the plurality of portions; and

determining at which of the plurality of thresholds to measure the widths of each of the plurality of portions based on the determined slope.

32. The method of claim 31, further comprising the step of measuring a distance with respect to each of the plurality of portions in the wide feature signal.

33. The method of claim 32 wherein the step of generating a lost element matrix includes the steps of:

creating a lost element matrix that identifies a number of the shapes and spaces having the first width that are unresolved between the resolved shapes and spaces, the lost element matrix being created based on estimated distances between the plurality of portions in the wide feature signal; and

determining a number and location of the shapes and spaces having the first width by comparing the distances measured with respect to the plurality of portions in the wide feature signal to the estimated distances in the lost element matrix.

34. The method of claim 33 wherein the step of measuring a distance includes the steps of:

identifying a center for each of the plurality of portions; and

measuring distances between the centers of the plurality of portions.

35. The method of claim 33 wherein the symbol is from a symbology having parity, wherein the symbol has a predetermined width, and the method further comprising the steps of determining if all of the shapes and spaces in the symbol have been identified;

determining if the predetermined width is equal to a sum of the determined sizes for each of the identified portions and the determined number of shapes and spaces having the first width; and

correcting a size determined for a given identified portion based on the parity in the symbology.

36. The method of claim 29, further comprising the step of determining a width of the shapes and spaces having the first width based on the wide feature signal.

37. The method of claim 35 wherein the step of determining the width of the shapes and spaces having the first width includes the steps of:

measuring at least one distance with respect to the plurality of portions in the wide feature signal; and

dividing the measured distance by a predetermined amount to determine the width of the shapes and spaces having the first width.

38. The method of decoding a profile produced from a machine-readable symbol that represents encoded information, the symbol including a plurality of relatively spaced two-dimensional geometric shapes, the shapes and spaces between the shapes having sizes with at least first, second and third widths in at least one dimension, the second and third widths being greater than the first width, the profile resolving at least some of the shapes and spaces having the second and third widths, but failing to resolve at least some of the shapes and spaces having the first width, the spaces having a reflectivity higher than a reflectivity of the shapes, the method comprising the steps of:

determining which of the shapes and spaces are resolved by identifying a plurality of portions in the profile that correspond to the resolved shapes and spaces;

determining the size of the identified plurality of portions that correspond to the resolved shapes and spaces;

determining a number and location of the shapes and spaces having the first width based at least in part on the determined size of the identified plurality of portions that correspond to the resolved shapes and spaces; and

determining the information encoded in the symbol based on the determined size of the identified plurality of portions that correspond to the resolved shapes and spaces, and number and location of the shapes and spaces having the first width.

39. An apparatus for decoding a machine-readable symbol representing encoded information, the machine-readable symbol including a plurality of relatively spaced two-dimensional shapes, the geometric shapes and spaces between the shapes having sizes with first, second and third widths in at least one dimension, the second and third widths being greater than the first width, the apparatus comprising:

a sensor that receives light that is reflected from the machine-readable symbol and produces an output signal therefrom that represents the reflectance of the shapes and spaces comprising the symbol;

a receiver that receives the output signal and produces a large shape signal indicative of at least some of the shapes or spaces having the second or third widths, but failing to produce a signal indicative of at least some of the shapes and spaces having the first width; and

a processor for processing the large shape signal and producing a signal indicative of the information encoded in the symbol, the processor (i) determining which of the shapes and spaces are resolved by identifying a plurality of portions in the large shape signal that each correspond to one of the resolved shapes and spaces, (ii) determining the size of the resolved shapes and spaces, (iii) generating a lost element matrix in response to the large shape signal and the size of the resolved shapes and spaces, and (iv) producing a signal indicative of the information encoded in the symbol based on the lost element matrix and the determined size of the resolved shapes and spaces.

40. The apparatus of claim 39 wherein the processor defines a plurality of thresholds and measures a width of each of the plurality of portions in the large feature signal at one of the plurality of thresholds.

41. The apparatus of claim 40 wherein the processor determines a slope of the large feature signal proximate to each of the plurality of portions and determines at which of the plurality of thresholds to measure the widths of each of the plurality of portions based on the determined slope.

42. The apparatus of claim 39 wherein the processor measures distances between each of the plurality of portions in the large shape signal.

43. The apparatus of claim 42 wherein the lost element matrix identifies a number of the shapes and spaces having the first width that are unresolved between the resolved shapes and spaces, wherein the processor generates the lost element matrix based on estimated distances between the plurality of portions in the large shape signal, and wherein the processor produces the signal indicative of the information encoded in the symbol by determining a number and location of the shapes and spaces having the first width by comparing the distances measured with respect to the plurality of portions in the large shape signal to the estimated distances in the lost element matrix.

44. The apparatus of claim 42 wherein the processor measures distances by identifying a center for each of the plurality of portions in the large shape signal and measuring distances between the centers of the plurality of portions.

45. The apparatus of claim 39 wherein the processor determines a width of the shapes and spaces having a first width based on the large shape signal.

46. The apparatus of claim 45 wherein the processor determines the width of the shapes and spaces having the first width by measuring at least one distance with respect to the plurality of portions in the large shape signal, and dividing the measured distance by a predetermined amount to determine the width of the shapes and spaces having the first width.

47. The apparatus of claim 39 wherein the processor determines which of the resolved shapes and spaces have the second width and which of the shapes and spaces have the third width based on the measured widths of the plurality of portions.

48. An apparatus for decoding a machine-readable symbol representing encoded information, the machine-readable symbol including a plurality of relatively spaced two-dimensional shapes, the geometric shapes and spaces between the shapes having sizes with first, second and third widths in at least one dimension, the second and third widths being greater than the first width, the apparatus comprising:

a sensor that receives light that is reflected from the machine-readable symbol and produces an output signal therefrom that represents the reflectance of the shapes and spaces comprising the symbol;

a receiver that receives the output signal and produces a large shape signal indicative of at least some of the shapes or spaces having the second or third widths, but failing to produce a signal indicative of at least some of the shapes and spaces having the first width;

a detection circuit that determines which of the shapes and spaces are resolved by identifying a plurality of portions in the large shape signal that each correspond to one of the resolved shapes and spaces;

a first measuring circuit that generates a distance signal indicating distances between each of the plurality of portions in the large shape signal, and that generates a size signal that indicates the size of the resolved shapes and spaces; and

a decoding circuit that determines a number and location of the shapes and spaces having a first width by analyzing the distance signal and the width signal, and therefrom produces a signal indicative of the information encoded in the symbol.

49. The apparatus of claim 48, further comprising a slope detection circuit that generates a slope signal for each of the plurality of portions in the large shape signal.

50. The apparatus of claim 48, further comprising a thresholding circuit that defines a plurality of thresholds with respect to the large shape signal and identifies the sizes of the resolved spaces and shapes;

and

a second measuring circuit that measures a width for each portion at the threshold and produces a measuring signal, the measuring signal indicating which of the resolved shapes and spaces correspond to shapes and spaces having the second width and which of the resolved shapes and spaces have the third width.

51. The apparatus of claim 48 wherein the decoding circuit is a microprocessor.

52. The method of decoding a profile produced from a machine-readable symbol that represents encoded information, the symbol being from a symbology having new identification parity and including a plurality of relatively spaced two-dimensional geometric shapes, the shapes and spaces between the shapes having sizes with at least first, second and third widths in at least one dimension, the second and third widths being greater than the first width, the profile resolving at least some of the shapes and spaces having the second and third widths, but failing to resolve at least some of the shapes and spaces having the first width, the spaces having a reflectivity higher than a reflectivity of the shapes, the method comprising the steps of:

determining the size of the resolved shapes and spaces; and

determining the information encoded in the symbol based on the determined size of the resolved shapes and spaces, and the parity of the symbol.