Efficient and fault tolerant license plate matching method

• US 8,798,325 B2
• Filed: 02/21/2012
• Issued: 08/05/2014
• Est. Priority Date: 02/21/2012
• Status: Active Grant

• Current Assignee: Conduent Business Services, LLC (Conduent, Inc.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Wu, Wencheng, Kozitsky, Vladimir
• Primary Examiner(s): Mehta, Bhavesh
• Assistant Examiner(s): Harandi, Siamak
• Application Number:
  US13/401,142
• Publication Number:
  US 20130216101A1
• Time in Patent Office: 896 Days
• Field of Search: None
• US Class Current: 382/105
• CPC Class Codes: G06F 18/00 Pattern recognition
• CPC Class Codes: G06V 20/625 License plates
• CPC Class Codes: G06V 20/63 Scene text, e.g. street names
• CPC Class Codes: G06V 30/10 Character recognition
• CPC Class Codes: G06V 30/268 Lexical context

Abstract

A method and system for identifying a matching license plate. A pair of full or partial plate numbers to be matched can be received. The pair includes a target plate made up of a first set of characters and a suspect plate made up of a second set of characters. A set of number-order preserved sub-plates can be generated by adding and subtracting a single character from the second set of characters. Utilizing a site specific license plate matching table (P-table), a matching score between each of the sub-plates and the target plate may be calculated as part of a string correlation calculation. A maximum value for each of the sub-plate matching scores can then be calculated. The maximum value can be normalized to a 0˜100 scale and used as a final matching score. When the final matching score exceeds a predetermined threshold, an alert may be issued.

Claims

1. A method for identifying a matching license plate, said method comprising:

identifying a target plate comprising a first set of characters and a candidate plate comprising a second set of characters;

generating a set of sub-plates by adding or subtracting at least one character from the second set of characters;

computing a matching score between said candidate plate and said target plate;

computing a matching score between each of said sub-plates and said target plate; and

computing a maximum for each of said matching scores in order to thereafter normalize said maximum to obtain a final matching score for each of said matching scores.

2. The method of claim 1 further comprising issuing an alert if said final matching score exceeds a predetermined threshold.

3. The method of claim 1 further comprising calculating said matching score from a license-plate match table.

4. The method of claim 1 wherein a number order is preserved in each of said sub-plates.

5. The method of claim 1 further comprising computing said matching score utilizing a string convolution.

6. The method of claim 3 wherein said license-plate match table is specific to a site in which an image capture device is located.

7. The method of claim 6 wherein said license-plate match table is generated from heuristic rules regarding image similarity, site-specific mistakes in character recognition, and a plate simulation module.

8. A non-transitory computer-readable medium having computer-executable instructions for performing steps, said steps comprising:

identifying a target plate comprising a first set of characters and a candidate plate comprising a second set of characters;

generating a set of sub-plates by adding or subtracting at least one character from the second set of characters;

computing a matching score between said candidate plate and said target plate;

computing a matching score between each of said sub-plates and said target plate; and

computing a maximum for each of said matching scores in order to thereafter normalize said maximum to obtain a final matching score for each of said matching scores.

9. The non-transitory computer-readable medium of claim 8 wherein said steps further comprise issuing an alert if said final matching score exceeds a predetermined threshold.

10. The non-transitory computer-readable medium of claim 8 wherein said steps further comprise calculating said matching score from a license-plate match table.

11. The non-transitory computer-readable medium of claim 8 wherein a number order is preserved in each of said sub-plates.

12. The non-transitory computer-readable medium of claim 8 wherein said steps further comprise computing said matching score utilizing a string convolution.

13. The non-transitory computer-readable medium of claim 8 wherein said license-plate match table is specific to a site in which an image capture device is located.

14. The non-transitory computer-readable medium of claim 13 wherein said license-plate match table is generated from heuristic rules regarding at least one of image similarity, site-specific mistakes in character recognition, and a plate simulation module.

15. A system for identifying a matching license plate, said system comprising:

an image capture device;

a central processing unit operably connected to a database; and

a non-transitory computer-usable medium embodying computer code, said non-transitory computer-usable medium being coupled to said data bus, said computer program code comprising instructions executable by said processor and configured for;

identifying a target plate comprising a first set of characters and a candidate plate comprising a second set of characters;

generating a set of sub-plates by adding or subtracting at least one character from the second set of characters;

computing a matching score between said candidate plate and said target plate;

computing a matching score between each of said sub-plates and said target plate; and

computing a maximum for each of said matching scores in order to thereafter normalize said maximum to obtain a final matching score for each of said matching.

16. The system of claim 15 further comprising issuing an alert if said final matching score exceeds a predetermined threshold.

17. The system of claim 15 wherein said instructions are further configured for calculating said matching score from a license-plate match table.

18. The system of claim 15 wherein said instructions are further configured to preserve a number order in each of said sub-plates.

19. The system of claim 17 wherein said license-plate match table is specific to a site in which the image capture device is located.

20. The system of claim 19 wherein said license-plate match table is generated from heuristic rules regarding at least one of image similarity, site-specific mistakes in character recognition, and a plate simulation module.