License Plate Recognition

• US 20190066492A1
• Filed: 08/22/2017
• Published: 02/28/2019
• Est. Priority Date: 08/22/2017
• Status: Active Grant

• Current Assignee: Q-Free Netherlands BV (Q-Free ASA)
• Original Assignee: Q-Free Netherlands BV (Q-Free ASA)
• Inventors: Nijhuis, Jos A. G.
• Granted Patent: US 10,950,124 B2
• Time in Patent Office: Days
• CPC Class Codes: G06V 20/52 Surveillance or monitoring of activities, e.g. for recognising suspicious objects recognising microscopic objects G06V20/69
• CPC Class Codes: G06V 20/62 Text, e.g. of license plates, overlay texts or captions on TV images
• CPC Class Codes: G06V 20/625 License plates
• CPC Class Codes: G08G 1/0175 by photographing vehicles, e.g. when violating traffic rules
• CPC Class Codes: G08G 1/054 photographing overspeeding vehicles

Abstract

A license plate recognition and secondary image review system and processes are described. The system supplements optical character recognition with a secondary image review process that matches an acquired image with either images in a trusted database of historic confirmed identification or with fingerprint data derived from the images compared with confirmed fingerprint data from prior identifications contained in a trusted data base. The system provides an alternative to manual reviews in a selected subset of OCR identifications, while maintaining a preselected accuracy and risk of misidentification.

Claims

1. A method for identifying characters on license plates said method comprising:

a) a learning process comprising;

i) acquiring a plurality of images of vehicles on a roadway, said images including the license plates,

ii) identifying, solely by optical character recognition, the characters on the license plates in the plurality of images, and grouping the images identified as the same license plate, thereby providing a plurality of first identification groups,

iii) determining if all of the images in each of the plurality of first identification groups are the same license plate,

b) an identification process, used subsequent to the learning process, the identification process comprising;

i) acquiring a plurality of images of vehicles on a roadway, said images including the license plates,

ii) identifying, solely by optical character recognition, the characters on the license plates in the plurality of images, and grouping the images identified as the same license plate, thereby providing a plurality of second identification groups,

iii) matching the identified characters of the second identification groups with the identified characters of the first identification groups, and, if the matched first identification groups included only one license plate confirm the optical character recognition of the second identification group, and, if the first identification groups included more than one license plate comparing pairwise each image in the second identification group with a confirmed image of each image in the first identification group, the comparison providing a confidence estimate for the match of each pairwise compared images, and, the confirmed image including an associated license plate characters, and,

iv) assigning the characters of the license plate in the second identification group as the associated licenses plate characters that are associated with the confirmed image that had the highest confidence estimate.

2. The method for identifying characters on license plates of claim 1 wherein the comparing pairwise each image in the second identification group with a confirmed image of each image in the first identification group compares fingerprint data extracted from the image in the second identification group with fingerprint data extracted from the confirmed image in the first identification group.

3. The method for identifying characters on license plates of claim 1 wherein a confirmed image is one where an owner of a license plate is associated with the characters on the license and the owner of the license plate is billed on the basis of the identified characters on the license plate and the owner paid the bill.

4. The method for identifying characters on license plates of claim 1 wherein a confirmed image is one that has been manually reviewed.

5. A method for identifying characters on license plates of vehicles on a roadway, said method comprising:

a) creating groups of license plates that are confusingly similar, the groups including a plurality of images of vehicles having license plates that are confusingly similar and an associated license plate number, and,

b) acquiring images of the vehicles on a roadway, and,

c) identifying the characters on the licenses plates of the vehicles on a roadway using optical character recognition, and,

d) if the characters identified by optical character recognition match the characters of a group of licenses plates that are confusingly similar, pairwise match the acquired image of the vehicle on a roadway with the plurality of images of vehicles having plates that are confusingly similar, the pairwise matching producing a confidence estimate, the confidence estimate having a high estimate for images that match and a low estimate for images that do not match, and,

e) selecting the pairwise match that has the highest confidence estimate, and,

f) assigning the associated license plate number from the image of vehicles having license plates that are confusingly similar to the acquired image of the vehicle on the roadway.

6. The method of claim 5 wherein the creating groups of license plates that are confusingly similar is done by assigning license plates to the group that have confusingly similar characters in a same sequential location on the license plate.

7. The method of claim 5 wherein the creating groups of license plates that are confusingly similar is done by billing an owner associated with the license plate of vehicle on a roadway, the owner identified by the optical character recognition of the license plate in the image, and, if the owner, in response to the billing, identifies a true value of the character on the license plates of his vehicle, and the true value is not the characters on the license plate of the vehicle on the roadway identified by optical character recognition, assign both the true value of the characters on the license plate and the characters identified by optical character recognition to a group of confusingly similar license plates.

8. A method for identifying characters on a license plate on a vehicle, the method comprising:

a) acquiring an image of a vehicle, the image including an image of the license plate, and,

b) using optical character recognition make a first estimate of the characters on the license plate, and,

c) compare pairwise the image of the vehicle with images of vehicles previously identified on the roadway, the vehicles previously identified having an associated license plate number, the pairwise matching producing a confidence estimate, the confidence estimate having a high estimate for images that match and a low estimate for images that do not match, and,

d) selecting the image of vehicles previously identified on the roadway that has the highest confidence estimate, and,

e) if the associated license plate number of the selected image of vehicles previously identified on the roadway is the same as the first estimate of the characters on the licenses plate identify the characters on the license plate of the vehicle as the first estimate of the characters, and,

f) if the associated license plate number of the selected image of vehicles previously identified on the roadway is not the same as the first estimate of the characters on the licenses plate identify the characters on the license plate of the vehicle as the associated license plate number.

9. The method of claim 8 wherein the pairwise matching of the images is pairwise matching of fingerprint data derived from the images.