Method and apparatus for reading under sampled bar code symbols

• US 20050145698A1
• Filed: 12/02/2004
• Published: 07/07/2005
• Est. Priority Date: 12/02/2003
• Status: Active Grant

• Current Assignee: Andrew Longacre Jr, Dennis W. Mcenery, Thomas Hawley, William H. Havens, Ynjiun Wang
• Original Assignee: Andrew Longacre Jr, Dennis W. Mcenery, Thomas Hawley, William H. Havens, Ynjiun Wang
• Inventors: Longacre, Andrew Jr., Havens, William H., Hawley, Thomas, Wang, Ynjiun, McEnery, Dennis W.
• Granted Patent: US 7,364,081 B2
• Time in Patent Office: Days
• US Class Current: 235/462.120
• 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 7/1465 using several successive scans of the optical code
• CPC Class Codes: G06K 7/1491 the method including a reconstruction step, e.g. stitching two pieces of bar code together to derive the full bar code

Abstract

The present invention is directed to a method for reading a bar code symbol with an optical reader. The method includes the step of scanning the bar code symbol to obtain a plurality of scan lines. Each of the plurality of scan lines includes a linear array of N-pixel values. Adjacent pixels in the linear array of N-pixel values are separated by a sample separation distance. A reconstructed scan line is generated that interleaves the N-pixel values from selected scan lines of the plurality of scan lines. A reconstructed pixel sample separation distance of adjacent interleaved pixels is an integer fraction of the pixel sample separation distance.

Claims

1. A method for reading a bar code symbol with an optical reader, the method comprising:

scanning the bar code symbol to obtain a plurality of scan lines, each of the plurality of scan lines including a linear array of N-pixel values, adjacent pixels in the linear array of N-pixel values being separated by a sample separation distance; and

generating a reconstructed scan line that interleaves the N-pixel values from selected scan lines of the plurality of scan lines, whereby a reconstructed pixel sample separation distance of adjacent interleaved pixels is an integer fraction of the pixel sample separation distance.

2. The method of claim 1, wherein the step of scanning includes the step of acquiring a plurality of linear scan lines images to obtain the plurality of scan line images.

3. The method of claim 1, wherein the step of scanning includes the step of acquiring a two-dimensional image of the bar code.

4. The method of claim 3, further comprising the step of selecting the plurality of lines from the two-dimension image.

5. The method of claim 3, wherein the two dimensional image is comprised of a 480×

640 array of pixels.

6. The method of claim 1, wherein the pixel sample separation on each of the plurality of lines being greater than or approximately equal to a width of the narrowest bar code symbol feature.

7. The method of claim 1, wherein the spatial frequency of the narrowest bar code symbol feature is approximately W per unit distance, W being an integer value.

8. The method of claim 7, wherein the pixel sample separation on each of the plurality of lines is greater than (W/2) times the unit distance.

9. The method of claim 7, wherein the step of scanning is performed at a spatial sampling rate of less than 2 W pixel samples per unit distance.

10. The method of claim 1, wherein the bar code symbol is a linear bar code symbol.

11. The method of claim 1, wherein the bar code symbol is a stacked linear bar code symbol.

12. The method of claim 1, wherein the bar code symbol is a two-dimensional bar code symbol.

13. The method of claim 1, wherein each of the plurality of scan lines is a row of pixels in a two-dimensional image of the bar code.

14. The method of claim 13, wherein each of the plurality of scan lines is separated by a vertical separation distance, the vertical separation distance being an integer multiple of a width of a pixel row.

15. The method of claim 1, further comprising the step of:

designating one of the plurality of scan lines as a reference scan line; and

inserting M-interpolated data points between each adjacent pixel pair in each of the plurality of scan lines at equally spaced sub-pixel positions to form an interpolated reference line and a plurality of interpolated scan lines, each interpolated line including N(M+1) sub-pixel values, the data point separation distance between sub-pixel values being substantially equal to the sample separation distance divided by M+1, wherein M is an integer value.

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

determining an optimum delay value for each interpolated scan line, the optimum delay value yielding a cross-correlation maximum for the cross-correlation calculation of the interpolated scan line and the interpolated reference line;

choosing M-selected interpolated scan lines from the plurality of interpolated scan lines;

selecting a spatial shift amount for each selected interpolated scan line, the spatial shift amount being the integer multiple of the sample separation distance that corresponds to the optimum delay value for the selected interpolated scan line; and

shifting each of the M-selected interpolated scan line relative to the interpolated reference line by its corresponding spatial shift amount to obtain (M+1) shifted scan lines.

17. The method of claim 16, wherein said generating step includes the step of adding the (M+1) shifted scan lines such that a pixel value and M data point values are added at each sub-pixel position to generate a composite pixel value at each sub-pixel position, the reconstructed scan line including N(M+1) composite pixel values that are separated by the data point separation distance.

18. The method of claim 16, wherein the generating step includes the step of interleaving the (M+1) shifted scan lines such that only pixel values are placed at each sub-pixel position, the reconstructed scan line including N(M+1) pixel values obtained during the step of scanning, the N(M+1) pixel values being separated by the data point separation distance.

19. A method for reading a bar code symbol with an optical reader, the optical reader including a two-dimensional imager, the method comprising:

scanning the bar code symbol to obtain a plurality of scan lines, each of the plurality of scan lines including a linear array of N-pixel values, adjacent pixels in the linear array of N-pixel values being separated by a sample separation distance;

designating one of the plurality of scan lines as a reference scan line;

inserting M-interpolated data points between each adjacent pixel pair in each of the plurality of scan lines at equally spaced sub-pixel positions to form an interpolated reference line and a plurality of interpolated scan lines, each interpolated line including N(M+1) sub-pixel values, the data point separation distance between sub-pixel values being substantially equal to the sample separation distance divided by M+1, wherein M is an integer value;

determining an optimum delay value for each interpolated scan line, the optimum delay value yielding a cross-correlation maximum for the cross-correlation calculation of the interpolated scan line and the interpolated reference line;

choosing M-selected interpolated scan lines from the plurality of interpolated scan lines;

selecting a spatial shift amount for each selected interpolated scan line, the spatial shift amount being the integer multiple of the sample separation distance that corresponds to the optimum delay value for the selected interpolated scan line; and

shifting each of the M-selected interpolated scan line relative to the interpolated reference line by its corresponding spatial shift amount to obtain (M+1) shifted scan lines.

20. The method of claim 19, wherein the step of reconstructing is performed by adding the (M+1) shifted scan lines such that a pixel value and M data point values are added at each sub-pixel position to generate a composite pixel value at each sub-pixel position, the reconstructed scan line including N(M+1) composite pixel values that are separated by the data point separation distance.

21. The method of claim 19, wherein the step of reconstructing is performed by interleaving the (M+1) shifted scan lines such that only pixel values are placed at each sub-pixel position, the reconstructed scan line including N(M+1) pixel values obtained during the step of scanning, the N(M+1) pixel values being separated by the data point separation distance.

22. A method for reading a bar code symbol with an optical reader, the optical reader including a two-dimensional imager, the method comprising:

acquiring a two-dimensional image of the bar code symbol;

selecting a plurality of lines from the two-dimension image, each of the plurality of scan lines including a linear array of N-pixel values, adjacent pixels in the linear array of N-pixel values being separated by a sample separation distance;

designating one of the plurality of scan lines as a reference scan line;

inserting M-interpolated data points between each adjacent pixel pair in each of the plurality of scan lines at equally spaced sub-pixel positions to form an interpolated reference line and a plurality of interpolated scan lines, each interpolated line including N(M+1) sub-pixel values, the data point separation distance between sub-pixel values being substantially equal to the sample separation distance divided by M+1, wherein M is an integer value;

determining an optimum delay value for each interpolated scan line, the optimum delay value yielding a cross-correlation maximum for the cross-correlation calculation of the interpolated scan line and the interpolated reference line;

choosing M-selected interpolated scan lines from the plurality of interpolated scan lines;

selecting a spatial shift amount for each selected interpolated scan line, the spatial shift amount being the integer multiple of the sample separation distance that corresponds to the optimum delay value for the selected interpolated scan line; and

shifting each of the M-selected interpolated scan line relative to the interpolated reference line by its corresponding spatial shift amount to obtain (M+1) shifted scan lines.

23. The method of claim 22, wherein the step of reconstructing is performed by adding the (M+1) shifted scan lines such that a pixel value and M data point values are added at each sub-pixel position to generate a composite pixel value at each sub-pixel position, the reconstructed scan line including N(M+1) composite pixel values that are separated by the data point separation distance.

24. The method of claim 22, wherein the step of reconstructing is performed by interleaving the (M+1) shifted scan lines such that only pixel values are placed at each sub-pixel position, the reconstructed scan line including N(M+1) pixel values obtained during the step of scanning, the N(M+1) pixel values being separated by the data point separation distance.

25. A system for reading a bar code symbol with an optical reader, the bar code symbol including a plurality of bar code features, the system comprising:

a imaging assembly configured to scan the bar code symbol to obtain a plurality of scan lines, each of the plurality of scan lines including a linear array of N-pixel values, adjacent pixels in the linear array of N-pixel values being separated by a sample separation distance; and

a processor coupled to the imaging assembly, the processor being programmed to generate a reconstructed scan line that interleaves the N-pixel values from selected scan lines of the plurality of scan lines, whereby a reconstructed pixel sample separation distance of adjacent interleaved pixels is an integer fraction of the pixel sample separation distance.

26. The system of claim 25, wherein the imaging assembly is configured to acquire a plurality of one-dimensional scan lines.

27. The system of claim 25, wherein the imaging assembly is configured to acquire a two-dimensional image of the bar code.

28. The system of claim 27, wherein the processor is configured to select the plurality of lines from the two-dimension image.

29. The system of claim 28, wherein the imaging assembly includes a 480×

640 imaging array.

30. The system of claim 25, wherein the imaging assembly does not have sufficient spatial resolution to capture all of the plurality of bar code features.

31. The system of claim 30, wherein the spatial frequency of the narrowest bar code symbol feature is approximately W per unit distance, W being an integer value.

32. The system of claim 31, wherein the pixel sample separation on each of the plurality of lines is greater than (W/2) times the unit distance.

33. The system of claim 32, wherein the step of scanning is performed at a spatial sampling rate of less than 2 W pixel samples per unit distance.

34. The system of claim 25, wherein each of the plurality of scan lines is a row of pixels in a two-dimensional image of the bar code.

35. The system of claim 34, wherein each of the plurality of scan lines is separated by a vertical separation distance, the vertical separation distance being an integer multiple of a width of a pixel row.

36. The system of claim 25, wherein the processor is further configured to:

designate one of the plurality of scan lines as a reference scan line; and

insert M-interpolated data points between each adjacent pixel pair in each of the plurality of scan lines at equally spaced sub-pixel positions to form an interpolated reference line and a plurality of interpolated scan lines, each interpolated line including N(M+1) sub-pixel values, the data point separation distance between sub-pixel values being substantially equal to the sample separation distance divided by M+1, wherein M is an integer value.

37. The system of claim 25, wherein the processor is further configured to:

determine an optimum delay value for each interpolated scan line, the optimum delay value yielding a cross-correlation maximum for the cross-correlation calculation of the interpolated scan line and the interpolated reference line;

choose M-selected interpolated scan lines from the plurality of interpolated scan lines;

select a spatial shift amount for each selected interpolated scan line, the spatial shift amount being the integer multiple of the sample separation distance that corresponds to the optimum delay value for the selected interpolated scan line; and

shift each of the M-selected interpolated scan line relative to the interpolated reference line by its corresponding spatial shift amount to obtain (M+1) shifted scan lines.

38. The system of claim 37, wherein the processor generates a reconstructed scan line by adding the (M+1) shifted scan lines such that a pixel value and M data point values are added at each sub-pixel position to generate a composite pixel value at each sub-pixel position, the reconstructed scan line including N(M+1) composite pixel values that are separated by the data point separation distance.

39. The system of claim 37, wherein the processor generates a reconstructed scan line by interleaving the (M+1) shifted scan lines such that only pixel values are placed at each sub-pixel position, the reconstructed scan line including N(M+1) pixel values obtained during the step of scanning, the N(M+1) pixel values being separated by the data point separation distance.