METHOD FOR DECODING A LINEAR BAR CODE

• US 20120256001A1
• Filed: 12/21/2009
• Published: 10/11/2012
• Est. Priority Date: 12/21/2009
• Status: Active Grant

• Current Assignee: Datalogic IP Tech S.r.l. (Datalogic S.p.A.)
• Original Assignee: Datalogic IP Tech S.r.l. (Datalogic S.p.A.)
• Inventors: Zocca, Rinaldo, Deppieri, Francesco
• Granted Patent: US 8,915,443 B2
• Time in Patent Office: Days
• US Class Current: 235/462.41
• CPC Class Codes: G06K 7/14 using light without selection of wavelength, e.g. sensing reflected white light G06K7/10831 - G06K7/1097 take precedence

Abstract

A barcode decoding method includes obtaining a plurality of scanning lines defining a second set of scanning lines which also comprises a predetermined scanning line. Each scanning line has a first set of pixels, each identified by a first and by a second index. The pixels that are part of the second set of scanning lines define a third set of pixels and, from the pixels of the third set of pixels, it is possible to select a fourth set of pixels to construct an oversampled profile of the barcode, ordering intensity values calculated from the intensity values of the pixels of the fourth set. The pixels of the fourth set include pixels of the predetermined scanning line and further pixels of the third set that do not belong to the predetermined scanning line, to obtain a subpixel resolution that is able to decode the barcode.

Claims

1. A method for decoding a linear barcode in an image, by a sensor having a set of pixels, the method comprising:

a) selecting a predetermined scanning line, comprising a first ordered set of pixels, in which each pixel is identified by a first index and has a respective intensity value;

b) decoding said barcode by constructing a profile of said barcode from intensity values of said pixels of said predetermined scanning line;

c) obtaining a second set of scanning lines, which also comprises said predetermined scanning line, in which said scanning lines are ordered according to a second index and each scanning line comprises a respective first set of pixels for defining a third set of pixels, each identified by said first index and by said second index; and

d) selecting a fourth ordered set of pixels from said third set of pixels and constructing an oversampled profile of said barcode by ordering intensity values calculated from intensity values of said pixels of said fourth set, said fourth set of pixels comprising pixels of said predetermined scanning line and further pixels of said third set that do not belong to said predetermined scanning line, to obtain a subpixel resolution that is able to decode said barcode.

2. The method according to claim 1, wherein said selecting a fourth ordered set of pixels comprises:

e) calculating, for each pixel of said third set a corresponding shift value depending on the value of said first index and of said second index of said pixel;

f) processing said shift values thus obtaining an ordered fifth set of said shift values, each shift value of said fifth set being associated with a respective pixel of said third set; and

g) each pixel of said fourth set of pixels being selected and ordered according to the order indicated by said fifth set of shift values.

3. The method according to claim 2 wherein said processing said shift values comprises ordering said shift values in ascending order to obtain said fifth ordered set of shift values.

4. The method according to claim 2, wherein said calculating intensity values from intensity values of said pixels of said fourth set comprises assigning to each pixel of said fourth set the intensity value of said pixel and associating said intensity value with the respective shift value of said fifth set.

5. The method according to claim 2, wherein said method further comprises defining a sixth predetermined set of equidistant reference shift values and assigning to each equidistant shift value a respective intensity value calculated from intensity values of said pixels of said fourth set.

6. The method according to claim 5, wherein said method further comprises comparing each of said equidistant shift values with the shift values of said fifth set for identifying a first shift value of said fifth set having a minimum excess difference with respect to said equidistant shift value and a second shift value of said fifth set having a minimum defect difference with respect to said equidistant shift value.

7. The method according to claim 6, wherein said assigning a respective calculated intensity value to each equidistant shift value comprises interpolating the intensity value of a first pixel of said fourth set corresponding to said first shift value and a second intensity value of a second pixel of said fourth set corresponding to said second shift value and assigning said interpolated intensity value to said equidistant shift value.

8. The method according to claim 7, wherein said interpolating said first intensity value and said second intensity value comprises performing a weighted average, the weights of which derive from said minimum excess difference and from said minimum defect difference.

9. The method according to claim 1, wherein said obtaining said second set of scanning lines comprises acquiring a two-dimensional set of pixels by means of a reader using a two-dimensional sensor, said first index being a column index and said second index being a row index.

10. The method according to claim 9, wherein said method further comprises, after said obtaining said second set of scanning lines, calculating the tilt of said barcode with respect to a reference axis, before selecting said fourth set of pixels from said third set.

11. The method according to claim 10, wherein calculating said tilt comprises calculating a first parameter associated with the tilt of said barcode with respect to said reference axis, said reference axis being in particular a vertical reference axis.

12. The method according to claim 11, wherein calculating said first parameter comprises calculating the tangent of α

, α

being the angle between said barcode and said reference axis and wherein said parameter is the tangent of α

.

13. The method according to claim 12, wherein said calculating a corresponding shift value for each pixel of said third set is equivalent to multiplying said row index to the tangent of α

and adding the result to said column index.

14. The method according to claim 10, wherein said method further comprises analysing said two-dimensional set of pixels to determine a first black bar of said code.

15. The method according to claim 14, wherein calculating said tilt of said barcode comprises calculating the tilt between said first black bar and said reference axis, said reference axis being in particular a vertical reference axis.

16. The method according to claim 9 wherein selecting said first set of pixels further comprises selecting any of said pixel inside said barcode and considering said selected pixel as the initial pixel of said predetermined scanning line, assigning a value equal to 0 to said row index and to said column index of said selected pixel.

17. The method according to claim 16, wherein said method further comprises analysing said two-dimensional set of pixels to determine a first black bar of said code and calculate the height of said barcode as the distance between a first end vertex and a second end vertex of said first black bar.

18. The method according to claim 17, wherein said method further comprises selecting said initial pixel substantially halfway along the height of said first black bar.

19. The method according to claim 9, wherein said row index increases by one unit moving upwards in said third set of pixels.

20. The method according to claim 9, wherein said column index increases by one unit moving to the right in said first set of pixels.

21. The method according to claim 1, wherein said barcode is arranged tilted in said image with respect to a reference axis, and forms an angle equal to 0°

, 45°

, 90°

, 135°

, 270°

, 315° and

360°

with respect to said reference axis, and wherein said method further comprises changing the reciprocal position between said image and said sensor having said set of pixels.

22. The method according to claim 1, wherein said barcode is arranged tilted in said image with respect to a reference axis, and said barcode forms an angle comprised between 0°

and 45°

, between 45° and

90°

, between 90° and

135°

, between 135° and

270°

, between 270° and

315° and

between 315° and

360°

with respect to said reference axis.

23. The method according to claim 1, wherein said obtaining said second set of scanning lines comprises acquiring from the barcode each scanning line by means of a linear pixel sensor at various instants.

24. The method according to claim 23, wherein each acquired scanning line is processed by means of a correlation with said predetermined scanning line and from said correlation a second correlating parameter is calculated that is associated with said scanning line.

25. The method according to claim 24, wherein each pixel of each scanning line is identified by said first index, that corresponds to an ordering index of said pixel in said respective scanning line, and by said second index, which corresponds to said second correlating parameter.

26. The method according to claim 2, wherein said obtaining said second set of scanning lines comprises acquiring from the barcode each scanning line by means of a linear pixel sensor at various instants, and wherein said calculating for each pixel of said third set a corresponding shift value is the equivalent of adding said second index to said first index.

27. A barcode reader comprising a sensor having a set of pixels, the barcode reader being programmed with code for decoding a barcode comprising:

first code for selecting a predetermined scanning line, comprising a first ordered set of pixels, in which each pixel is identified by a first index and has a respective intensity value;

second code for decoding said barcode by constructing a profile of said barcode from intensity values of said pixels of said predetermined scanning line;

third code for obtaining a second set of scanning lines, which also comprises said predetermined scanning line, in which said scanning lines are ordered according to a second index and each scanning line comprises a respective first set of pixels for defining a third set of pixels, each identified by said first index and by said second index; and

fourth code for selecting a fourth ordered set of pixels from said third set of pixels and constructing an oversampled profile of said barcode by ordering intensity values calculated from intensity values of said pixels of said fourth set, said fourth set of pixels comprising pixels of said predetermined scanning line and further pixels of said third set that do not belong to said predetermined scanning line, to obtain a subpixel resolution that is able to decode said barcode.

28. The barcode reader according to claim 27, wherein said sensor having a two-dimensional set of pixels and wherein said third code comprises code for obtaining said second set of scan lines by acquiring the two-dimensional set of pixels using the sensor, said first index being a column index and said second index being a row index.

29. The barcode reader according to claim 27, wherein said sensor having a linear set of pixels and wherein said third code comprises code for acquiring from the barcode each scanning line by means of the sensor at various instants.

30. Computer-readable media tangibly embodying a programme that comprises code for decoding a barcode when the programme is run in a barcode reader, the computer-readable media comprising code to:

select a predetermined scanning line, comprising a first ordered set of pixels, in which each pixel is identified by a first index and has a respective intensity value;

decode said barcode by constructing a profile of said barcode from intensity values of said pixels of said predetermined scanning line;

obtain a second set of scanning lines, which also comprises said predetermined scanning line, in which said scanning lines are ordered according to a second index and each scanning line comprises a respective first set of pixels for defining a third set of pixels, each identified by said first index and by said second index; and

select a fourth ordered set of pixels from said third set of pixels and constructing an oversampled profile of said barcode by ordering intensity values calculated from intensity values of said pixels of said fourth set, said fourth set of pixels comprising pixels of said predetermined scanning line and further pixels of said third set that do not belong to said predetermined scanning line, to obtain a subpixel resolution that is able to decode said barcode.