Method and apparatus for accurately locating data regions in stored images of symbols

• US 5,811,776 A
• Filed: 02/26/1996
• Issued: 09/22/1998
• Est. Priority Date: 02/26/1996
• Status: Expired due to Term

• Current Assignee: Intermec IP Corporation (Honeywell International Inc.)
• Original Assignee: Intermec Corporation (Honeywell International Inc.)
• Inventors: Liu, Lingnan
• Primary Examiner(s): Hajec, Donald T.
• Assistant Examiner(s): TREMBLAY, MARK STEPHEN
• Application Number:
  US08/607,100
• Time in Patent Office: 939 Days
• Field of Search: 235/462, 235/463
• US Class Current: 235/462.27
• 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 7/1443 locating of the code in an image

Abstract

A method and apparatus locates multiple "bounding boxes" within an image of a symbol located within an image stored by a reader. The symbol preferably has a recognition pattern with an longitudinally extending bar and at least one vertically extending reference bar, such as in the Code One symbology. The method locates the positions of landmark points within the stored image. Landmark points include points at the end of the longitudinally extending bar, points at the corner or root formed between the longitudinally extending bar and the vertically extending bar, points at the ends of the vertically extending bars, and points at the intersection between the bars and blocks that extend transversely therefrom. Based on the locations of the landmark points, horizontal and vertical line functions are defined between collinear landmark points. Based on the intersection of the line functions, multiple bounding boxes are constructed to determine the periphery and all data areas of the symbol within the stored image.

Claims

1. A method for computing a location of data regions in a stored image of a symbol, the symbol including a plurality of symbol characters and a recognition pattern having an outermost bar and at least one vertical reference pattern extending perpendicularly from the recognition pattern, the method comprising the steps of:

locating a position of a first end portion and a second end portion of the outermost bar of the recognition pattern in the stored image, wherein the stored image may include distortions of the symbol;

locating a position of a root portion at an intersection between the at least one vertical reference pattern and the outermost bar in the stored image;

locating a position of an outermost portion at a free end of each of the at least one vertical reference pattern in the stored image;

determining a position of a first corner portion and a second corner portion for the symbol in the stored image by extending at least one line from the outermost portion of each at least one vertical reference pattern a predetermined distance in a predetermined direction; and

defining at least first and second areas enclosing at least some of the plurality of symbol characters in the data regions of the symbol, the first area being defined by the positions of the first end portion, the first corner portion, the root portion, and the outermost portion, and the second area being defined by the second end portion, the second corner portion, the root portion, and the outermost portion.

2. The method for computing a location according to claim 1 wherein the at least one vertical reference pattern has a foot at the free end and at least one block extending transversely therefrom, and wherein the step of locating the position of the outermost portion includes the steps of:

traveling along each of the at least one vertical reference pattern until an inner corner portion of the at least one block of the at least one vertical reference pattern is reached;

crossing the at least one block of the at least one vertical reference pattern to determine a location of an outer corner portion;

traveling along each of the at least one vertical reference pattern until an inner corner portion of the foot of the at least one vertical reference pattern is reached;

crossing the foot of the at least one vertical reference pattern to determine the location of the outermost portion; and

wherein the step of defining at least first and second areas defines first and second bounding boxes in the first area and third and fourth bounding boxes within the second area, the first bounding box being defined by at least the first end portion, the root portion, and the outer corner portion, and the second bounding box being defined by at least the outer corner portion, the outermost portion, and the first corner portion, the third bounding box being defined by at least the second end portion, the root portion, and the outer corner portion, and the fourth bounding box being defined by the outer corner portion, the outermost portion, and the second corner portion.

3. The method for computing a location according to claim 1 wherein the step of locating the position of the outermost portion includes the steps of:

traveling along each of the at least one vertical reference pattern until an inner corner of a foot of the at least one vertical reference pattern is reached; and

crossing the foot of the at least one vertical reference pattern to determine the location of the outermost portion.

4. The method for computing a location according to claim 3 wherein the step of locating a position of the root portion includes the steps of:

starting at one of the first end portion and the second end portion and incrementally advancing along the edge of the outermost bar from the one of the first and second end portion until an edge is no longer detected ahead of the advance and a direction of the edge changes by approximately 90°

; and

designating a termination of the advance along the outermost bar as the root portion of the at least one vertical reference pattern.

5. The method for computing a location according to claim 3 wherein the step of traveling along each of the at least one vertical reference pattern includes the steps of:

starting at one of the root portion of the at least one vertical reference pattern and incrementally advancing along the at least one vertical reference pattern until at least one of an edge is no longer detected ahead of the advance and a direction of the edge alters by more than approximately 90°

; and

designating a termination of the advance along the at least one vertical reference pattern as the inner corner of the foot of the at least one vertical reference pattern.

6. The method for computing a location according to claim 3 wherein the step of crossing the foot of the at least one vertical reference pattern includes the steps of:

taking a reading of an intensity at a present position;

comparing the intensity against a threshold intensity;

incrementally advancing the position along a crossing direction until an intensity at a current portion exceeds the threshold intensity; and

designating the current portion where the threshold intensity was exceeded as the outermost portion.

7. The method for computing a location according to claim 5 wherein the crossing direction is perpendicular to an entry boundary on the foot.

8. The method of computing a location according to claim 1 wherein the step of locating a position of the root portion includes the step of locating a plurality of root portions at an intersection between a plurality of vertical reference patterns and the outermost bar;

wherein the step of locating a position of the outermost portion locates a plurality of outermost portions at free ends of the plurality of vertical reference patterns and a plurality of corner points at an intersection between the plurality of vertical reference patterns and at least one block extending transversely from each vertical reference pattern; and

wherein the step of defining at least first and second areas includes the step of determining a plurality of vertical and horizontal linear functions wherein each vertical linear function includes the root portion and the outermost portion for one of the plurality of vertical reference patterns, wherein each horizontal linear function includes either the plurality of outermost portions or the plurality of corner portions, and wherein a plurality of areas enclosing the data regions are defined by an intersection of the plurality of horizontal and vertical linear functions.

9. The method of computing a location according to claim 8 wherein the step of determining a plurality of vertical and horizontal linear functions includes the step of determining if the plurality of outermost portions are collinear and whether the plurality of corner portions are collinear, and ignoring one or more of the outermost portions that are not collinear with remaining outermost portions, and ignoring one or more corner portions that are non-collinear with remaining corner portions.

10. The method for computing a location according to claim 1 wherein the step of determining a position of the first and second corner portions includes the steps of:

determining positions of first and second root portions respectively located at intersections between first and second vertical reference patterns and the outermost bar of the recognition pattern; and

calculating the predetermined distance based on a ratio defined by a distance between the first and second outermost portions of the first and second vertical reference patterns multiplied by a distance between one of the first and second root portions and one of the first and second end portions of the outermost bar divided by a distance between the first and second root portions.

11. The method for computing a location according to claim 1, further comprising the step of:

comparing an angle of a line connecting the first end point and the second end point with a line connecting first and second outermost points of first and second vertical reference bars, respectively, to determine a correction value; and

wherein the step of calculating the predetermined distance includes multiplying the ratio by the correction value.

12. A method for computing bounding boxes of a Code One symbol in a stored image of the symbol having a recognition pattern, including a top bar adjacent an upper data region and a lower bar adjacent a lower data region, and at least four vertical reference bars, each having a foot end away from the recognition pattern, a root portion and a block positioned therebetween, the four vertical reference bars including first and second vertical reference bars whose root portion is contiguous with the top bar, and third and fourth vertical reference bars whose root portion is contiguous with the lower bar, wherein the upper and lower data regions contain a plurality of symbol characters, the method comprising the steps of:

locating a position of a first end point and a second end point of the top bar in the stored image, wherein the stored image may include distortions of the symbol;

locating a position of root points at the root portions of the first and second vertical reference bars from at least one of the first and second end points in the stored image;

locating in the stored image an inner corner point of each of the block portions of the first and second vertical reference bars from the root points of the first and second vertical reference bars, respectively;

crossing the block portions of the first and second vertical reference bars to locate outer corner points of each of the blocks of the first and second vertical reference bars;

locating in the stored image inner corner points of the foot of the first and second vertical reference bars from the outer corner points of the first and second vertical reference bars, respectively;

crossing the foot of the first and second vertical reference bars to reach a top point of the first and second vertical reference bars;

projecting from the root points of the first and second vertical reference bars in a second predetermined direction along the recognition pattern;

determining the location of root points of the root portion of the third and fourth vertical reference bars in the stored image;

locating in the stored image an inner corner point of each of the block portions of the third and fourth vertical reference bars from the root points of the third and fourth vertical reference bars, respectively;

crossing the block portions of the third and fourth vertical reference bars to locate outer corner points of each of the blocks of the third and fourth vertical reference bars;

locating in the stored image the inner corner points of the foot of the third and fourth vertical reference bars from the outer corner points of the third and fourth vertical reference bars, respectively;

crossing the foot of the third and fourth vertical reference bars to reach bottom points of the third and fourth vertical reference bars;

determining a plurality of vertical line functions for each of the first, second, third and fourth vertical reference bars, based on the root points and top or bottom points of each vertical reference bar;

determining a plurality of horizontal linear functions, each linear function based on the top points, bottom points, corner points of the first and second vertical reference bars, and corner points of the third and fourth vertical reference bars; and

defining a plurality of upper and a plurality of lower bounding boxes based on intersections of the plurality of vertical line and horizontal linear functions, the plurality of bounding boxes enclosing the upper and lower data regions of the Code One symbol.

13. The method for computing according to claim 12 wherein the step of locating a position of the root points of the first and second vertical reference bars includes the steps of:

moving along the top bar in incremental steps from one of the first and second end points;

continuing to advance along the top bar until at least one of an edge is no longer detected ahead of the advance and a direction of the edge changes by approximately 90°

; and

designating a termination of the advance along the top bar as the root portion of the first and second vertical reference bars.

14. The method for computing according to claim 13 wherein the step of locating an inner corner point of the blocks of the first and second vertical reference bars, comprises the steps of:

starting at the root portion of the first and second vertical reference bars;

proceeding to incrementally advance along the at least one vertical reference pattern until at least one of an edge is no longer detected ahead of the advance and a direction of the edge alters by approximately more than 90°

; and

designating a termination of the advance along the first and second vertical reference patterns as the inner corner point of the blocks of the first and second vertical reference patterns.

15. The method for computing according to claim 13 wherein the steps of crossing the block portions and crossing the foot of the first and second vertical reference bars comprises the steps of:

taking a reading of an intensity at a preset position;

comparing the intensity against a threshold intensity;

incrementally advancing the position along a crossing direction until the intensity at that point exceeds the threshold intensity; and

designating the position where the threshold intensity was exceeded as one of the outer corner point and the top point of the first and second vertical reference bars.

16. An apparatus for decoding a machine-readable symbol representing encoded information, the symbol having a recognition pattern with an outermost bar and at least one vertical reference pattern extending approximately perpendicular from the recognition pattern, the apparatus comprising:

a sensor that receives light reflected from the symbol and produces an output signal therefrom;

a receiver that receives the output signal and produces a data signal indicative of the encoded information, the recognition pattern and the at least one vertical reference pattern, wherein the data signal may represent distortions of the symbol; and

a processor for decoding the encoded information encoded in the symbol, the processor being programmed to (a) locate a position of a first end point and a second end point of the outermost bar of the recognition pattern from the data signal, (b) locate a position of each of the vertical reference patterns and an outermost point of each of the at least one vertical reference patterns from the data signal, (c) determine a position of a first corner point and a second corner point for the symbol by calculating at least one line from the outermost points a predetermined distance in a predetermined direction, (d) define a plurality of bounding boxes using the positions of the first end point, the second end point, the first corner point, the second corner point, the outermost points and the positions of the at least one vertical reference patterns, and (e) decode the encoded information within the plurality of bounding boxes.

17. The apparatus of claim 16 wherein the processor is programmed to locate the position of the outermost point by (i) examining the outermost bar from at least one of the first end point toward the second end point until a root point at an adjacent base of the vertical reference pattern is located, (ii) traveling along each of the at least one vertical reference pattern until an inner corner of a foot of the at least one vertical reference pattern is located, and (iii) examining the foot of the at least one vertical reference pattern to determine the location of the outermost point.

18. The apparatus of claim 17 wherein the processor travels along the vertical reference pattern by (i) starting at one of the root point of the at least one vertical reference pattern, (ii) proceeding to incrementally advance along the at least one vertical reference pattern until at least one of an edge is no longer detected ahead of the advance and a direction of the edge alters by approximately more than 90°

, and (iii) designating a termination of the advance along the at least one vertical reference pattern as the inner corner of the foot of the at least one vertical reference pattern.

19. The apparatus of claim 18 wherein the processor crosses the foot by (i) taking a reading of a light intensity at a present position, (ii) comparing the light intensity against a threshold light intensity, (iii) incrementally advancing the position along a crossing direction until an intensity at a current point exceeds the threshold light intensity, and (iv) designating the current point where the threshold intensity was exceeded as the outermost point.

20. The apparatus of claim 16 wherein the processor is programmed to determine the position of the first and second corner points by (i) comparing an angle of a line connecting the first end point and the second end point with a line connecting the outermost point of each of the at least one vertical reference pattern to determine the predetermined direction, and (ii) calculate the predetermined distance based on the distance between the first and second end point and the at least one vertical reference pattern, as well as the distance between the outermost point of each of the at least one vertical reference pattern.

21. A method for computing a location of at least one data region in a stored image of a symbol, the symbol including a recognition pattern having an outermost bar and at least one vertical reference pattern extending perpendicularly from the recognition pattern, the method comprising the steps of:

locating the outermost bar and at least one vertical reference pattern of the recognition pattern; and

dividing the at least one data region of the stored image of the symbol into a plurality of regions based on the located position of the outermost bar and at least one vertical reference pattern.