LICENSE PLATE RECOGNITION SYSTEM USING SPATIAL-TEMPORAL SEARCH-SPACE REDUCTION AND METHOD THEREOF

• US 20090208060A1
• Filed: 04/23/2008
• Published: 08/20/2009
• Est. Priority Date: 02/18/2008
• Status: Abandoned Application

• Current Assignee: National Chiao Tung University (Government of The Republic of China)
• Original Assignee: National Chiao Tung University (Government of The Republic of China)
• Inventors: Wang, Shen-Zheng, Lee, Hsi-Jian
• Application Number:
  US12/107,882
• Publication Number:
  US 20090208060A1
• Time in Patent Office: Days
• US Class Current: 382/105
• CPC Class Codes: G06V 20/625 License plates
• CPC Class Codes: G06V 20/63 Scene text, e.g. street names

Abstract

The present invention discloses a license plate recognition system by utilizing spatial-temporal search-space reduction and method thereof. The license plate recognition system can selects a pixel with character edge feature from the inputted image and a plurality of candidate regions from the image; and detect if the candidate region of the inputted image has been appeared in a preceding image. Then the recognition system in the present invention separates the candidate region into a plurality of blocks, calculates the repeated block based on a current image and a preceding image, and determines whether the candidate region is repeated according to the repeated block. Thus, by discarding the repeated regions, the license plate recognition system in the present invention can avoid redundant calculation and improve the efficiency and performance for recognition of real plate character in the image.

Claims

1. A license plate recognition method by utilizing spatial-temporal search-space reduction, said method comprising:

(a) capturing a plurality of candidate regions from an inputted image, and placing said candidate regions in a candidate area;

(b) detecting whether said candidate regions of a current image has been appeared on at least a preceding image, if yes, then discarding said candidate regions from said candidate area; and

(c) outputting said candidate regions from said candidate area.

2. The license plate recognition method of claim 1, wherein said step (a) further comprises:

capturing a plurality of said candidate regions from a image.

3. The license plate recognition method of claim 1, wherein said step (b) further comprises:

comparing a similarity of said candidate regions based on different timing.

4. The license plate recognition method of claim 1, wherein said step (b) further comprises:

comparing said similarity of said candidate regions by separating said inputted image into a plurality of blocks, and making an image distance comparison with said blocks which overlapping with said candidate regions.

5. The license plate recognition method of claim 4, wherein said blocks is defined as a repeated block if said image distance is less than a threshold value, and said candidate region is defined as a repeated region based on an overlapping degree between said repeated block and said candidate regions.

6. The license plate recognition method of claim 4, wherein said image distance is got from one-side tangent distance of said image.

7. The license plate recognition method of claim 4, wherein if said blocks of said candidate regions has been defined as a non-repeated block previously, extract feature of said blocks.

8. The license plate recognition method of claim 1, wherein each candidate region is calculated and transformed to a character edge region according to vertical gradient, and then acquires a plurality of plate character candidate regions according to a bi-level one-pass plate extraction (BOPE) algorithm.

9. The license plate recognition method of claim 8, wherein said plate character candidate regions are defined as regions that bound top and bottom of plate characters tightly.

10. The license plate recognition method of claim 8, wherein said plate character candidate region has a predetermined height and a predetermined width, and if a height of said plate character candidate region is greater than said predetermined height or the width of said plate character candidate region is greater than said predetermined width, reducing said plate character candidate region in order to conform to said predetermined height and width.

11. The license plate recognition method of claim 1, wherein said step (a) is performed by a character edge detecting module and a plate character candidate region detecting module.

12. The license plate recognition method of claim 1, wherein said step (b) is performed by a repeated region detecting module.

13. The license plate recognition method of claim 1, wherein said inputted image is captured by an image captured device.

14. A license plate recognition system by utilizing spatial-temporal search-space reduction, said device comprising:

a character edge region detecting module for selecting a pixel with character edge feature from an inputted image;

a plate character candidate region detecting module for selecting a plurality of candidate regions from said pixel, and if said candidate regions comprise at least a plate character, said candidate regions is defined as a region that bound top and bottom of said plate characters tightly; and

a repeated region detecting module for detecting if said candidate regions of said inputted image has been appeared in a preceding image.

15. The license plate recognition system of claim 14, wherein each candidate region is calculated from character edge regions according to vertical gradient, and then acquires a plurality of plate character candidate regions according to a bi-level one-pass plate extraction (BOPE) algorithm.

16. The license plate recognition system of claim 14, wherein said repeated region detecting module separates said candidate regions into a plurality of blocks, calculates said repeated block based on a current image and a preceding image, and determines whether said candidate region is repeated according to said repeated block.

17. The license plate recognition system of claim 14, wherein said repeated region detecting module further compares a similarity of said candidate regions by separating said image into a plurality of blocks, and making an image distance comparison with said blocks said blocks which overlapping with said candidate regions.

18. The license plate recognition system of claim 17, wherein said block is defined as a repeated block if said image distance is less than a threshold value, and said candidate region is defined as a repeated region based on an overlapping degree between said repeated block and said candidate regions.

19. The license plate recognition system of claim 17, wherein said image distance is got from one-side tangent distance of said inputted image.