US 8,509,486 B2Granted

Vehicle license plate recognition method and system thereof

AssigneeNational Chiao Tung University

InventorsJun-Wei Hsieh, Sin Yu Chen

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Abstract

A vehicle license plate recognition method and a system thereof are disclosed. A region where a vehicle license plate image exists is detected according to the edge densities of an input image and a vehicle license plate specification. A text area of the vehicle license plate image is divided into a plurality of character images. The character images are binarized to obtain a plurality of binarized character images. A plurality of characters is recognized from the binarized character images. The characters are recombined to form a character string. The abovementioned steps are repeated to obtain a new character string from another image of the same vehicle, which is captured at a next time point. The character string is compared with the new character string character by character to obtain a comparison result for verifying reliability of recognition through a voting technique.

Claims17

Dependent claims

A vehicle license plate recognition method comprising:

Step (a):
converting an image of a vehicle into a gray-level image, calculating edge densities of said gray-level image, and defining a region from a plurality of regions where a vehicle license plate image exists according to said edge densities and a vehicle license plate specification, wherein regions having a higher value of said edge density are appointed as candidate license plate areas, and using a predetermined threshold edge density to exclude said candidate license plate areas having said edge density lower than said predetermined threshold edge density;
Step (b):
detecting a text area of said vehicle license plate image, partitioning said text area into a plurality of character images, and binarizing said character images to obtain a plurality of binarized character images;
Step (c):
recognizing a plurality of characters from said binarized character images;
Step (d):
recombining said characters into a character string of a vehicle license plate and outputting said character string;
and Step (e):
receiving a next image of said vehicle, which is captured at a different time point, and repeating Step (a) to said Step (d) to obtain a new character string from said next image;
comparing said character string with said new character string character by character to obtain a comparison result for verifying reliability of recognition.

8 more elements

A vehicle license plate recognition system comprising a license plate detection module detecting an image, converting said image into a gray-level image, calculating edge densities of said gray-level image, and defining a region from plurality of a regions where a vehicle license plate image exists according to said edge densities and a vehicle license plate specification, wherein regions having a higher value of said edge density are appointed as candidate license plate areas, and using a predetermined threshold edge density to exclude said candidate license plate areas having said edge density lower than said predetermined threshold edge density, a character partition module connected with said license plate detection module, partitioning said vehicle license plate image into a plurality of character images, and binarizing said character images to obtain a plurality of binarized character images;

a character recognition module connected with said character partition module, recognizing characters from said binarized character images;
a character recombination module connected with said character recognition module, recombining said characters into a character string of a vehicle license plate, and outputting said character string;
and a voting module connected with said character recognition module, obtaining a new character string generated in a next time point, comparing said character string with said new character string character by character to generate a comparison result for verifying reliability of recognition.

Dependencies are inferred from the claim text.