Cascade plate recognition system

• US 20070292029A1
• Filed: 01/22/2007
• Published: 12/20/2007
• Est. Priority Date: 06/16/2006
• 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:
  US11/655,930
• Publication Number:
  US 20070292029A1
• Time in Patent Office: Days
• US Class Current: 382/181
• CPC Class Codes: G06V 20/62 Text, e.g. of license plates, overlay texts or captions on TV images
• CPC Class Codes: G06V 30/10 Character recognition
• CPC Class Codes: G06V 30/148 Segmentation of character regions

Abstract

The present invention discloses a cascade plate recognition system, wherein a compact plate region detection module receives an image, detects the plate area candidates of the image, picks out the sequences having continuous identical pixels from the plate area candidates, performs smearing and filtering on the sequences, extracts connected components from the plate area candidates to obtain compact plate regions, verifies the compact plate regions and outputs the verified compact plate regions; a plate character segmentation and recognition module receives the verified compact plate regions, extracts independent-character regions from each verified compact plate regions, verifies the independent-character regions and recognizes the verified independent-character regions to obtain the information of the plate characters. Thereby, the present invention has the advantages of high accuracy, learning capability and fast realtime operation.

Claims

1. A cascade plate recognition system, comprising:

a compact plate region detection module, further comprising;

a plate-like area generation module, receiving an input image and detecting plate area candidates in said image;

a one-pass plate region extraction module, utilizing a one-pass image scanning process to detect compact plate regions from said plate region candidates, and performing an integrated process implying two functions, non-plate candidates suppression and plate candidates smearing, to obtain all candidates of said compact plate regions without altering the original source via predetermining thresholds, the width and the height of a character and the number of the plate characters; and

a plate verification module, verifying said candidates of compact plate regions and outputting verified compact plate regions; and

a plate character segmentation and recognition module, further comprising;

a histogram segmentation module, receiving said verified compact plate regions and segmenting each said verified compact plate region into independent-character regions and connected-character regions;

a projection segmentation module, defining the boundaries of each said connected-character region and segmenting said connected-character region into said independent-character regions to obtain all said independent-character regions from each said verified compact plate region; and

a character verification module, verifying said independent-character regions and recognizing said verified independent-character regions to obtain the information of the plate characters.

2. The cascade plate recognition system according to claim 1, wherein a low-level feature analysis method is used to filter out non-plate regions and obtain said plate area candidates.

3. The cascade plate recognition system according to claim 2, wherein said low-level feature analysis method utilizes a vertical-gradient operation to obtain a vertical-gradient image and utilizes a thresholding method to perform a binarization operation on said vertical-gradient image to obtain said plate area candidates.

4. The cascade plate recognition system according to claim 1, wherein said one-pass plate region extraction module is used to extract all compact plate regions, which are bound the top and bottom of plate characters, directly.

5. The cascade plate recognition system according to claim 1, wherein said plate verification module is trained to automatically learn a plurality of features of said compact plate regions before performing verification and utilizes said features to verify said compact plate regions.

6. The cascade plate recognition system according to claim 4, wherein said plate verification module is trained with a statistical learning method.

7. The cascade plate recognition system according to claim 4, wherein said features are Harr-like features.

8. The cascade plate recognition system according to claim 1, wherein said histogram segmentation module obtains the histogram of each said verified compact plate region and performs a histogram-segmentation process on said histogram to obtain said independent-character regions and said connected-character regions.

9. The cascade plate recognition system according to claim 8, wherein after said histogram segmentation module obtains said histogram, the Otsu'"'"'s method and a peak-valley analysis method are used to obtain promising thresholds and then obtain said the independent-character regions and said connected-character regions from each said verified compact plate region.

10. The cascade plate recognition system according to claim 7, wherein said peak-valley analysis method obtains said promising thresholds via a mode initiation process and a peak-valley decision process of said histogram.

11. The cascade plate recognition system according to claim 1, wherein said projection segmentation module utilizes a peak-valley analysis method to define the boundaries of said connected-character regions.

12. The cascade plate recognition system according to claim 11, wherein said projection segmentation module further utilizes a hypothesis rule to form the candidates of said independent-character regions.

13. The cascade plate recognition system according to claim 1, wherein said character verification module is trained to automatically learn a plurality of features of said independent-character regions before performing verification and utilizes said features to verify said independent-character regions.

14. The cascade plate recognition system according to claim 11, wherein said character verification module is trained with a statistical learning method.

15. The cascade plate recognition system according to claim 1, wherein said character verification module utilizes the OCR (Optical Character Recognition) technology to recognize said verified independent-character regions and obtains the information of said plate characters.

16. The cascade plate recognition system according to claim 1, further comprising a condition-filtering module, which has multiplex filtering conditions and filters the information of said plate characters with said filtering conditions.

17. The cascade plate recognition system according to claim 1, wherein at least one image-capturing device is used to obtain said images and send said images to said plate-like area generation module.