DEVICE AND METHOD FOR DETECTING VEHICLE LICENSE PLATES

• US 20130050493A1
• Filed: 08/23/2012
• Published: 02/28/2013
• Est. Priority Date: 08/30/2011
• Status: Active Grant

• Current Assignee: Kapsch TrafficCom AG (Datax Handelsgmbh)
• Original Assignee: Kapsch TrafficCom AG (Datax Handelsgmbh)
• Inventors: Mitic, Sladjan
• Granted Patent: US 9,025,028 B2
• Time in Patent Office: Days
• US Class Current: 348/148
• 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 30/1444 Selective acquisition, locating or processing of specific regions, e.g. highlighted text, fiducial marks or predetermined fields
• CPC Class Codes: G08G 1/0175 by photographing vehicles, e.g. when violating traffic rules
• CPC Class Codes: H04N 23/667 Camera operation mode switching, e.g. between still and video, sport and normal or high- and low-resolution modes
• CPC Class Codes: H04N 25/443 by reading pixels from selected 2D regions of the array, e.g. for windowing or digital zooming

Abstract

A system and method for detection of vehicle license plates including a video camera that has a first operating mode in which it generates a first image sequence of a small, strip-shaped section of its optical camera image at a high frame rate, and a second operating mode in which a second image sequence of its entire optical camera image is generated at a lower frame rate. In the first operating mode, at the time of the detection of a license plate in the first image sequence, the video camera is switched to the second operating mode to generate an image, which contains the license plate in or near the mentioned section.

Claims

1. A device for detecting vehicle license plates comprising:

a video camera configured to aim on a street section with passing vehicles including license plates to record an optical camera image and convert said camera image to an electronic image sequence,

wherein the video camera has a first operating mode in which the video camera is configured to generate a first image sequence of a small strip-shaped section of the optical camera image at a first frame rate, and a second operating mode in which the video camera is configured to generate a second image sequence of the entire optical camera image at a second frame rate, the first frame rate being higher than the second frame rate, and wherein

the video camera is configured by a control signal to switch between the first and the second operating modes; and

a detector unit coupled to the video camera, wherein upon detection of at least a portion of a license plate in the first image sequence, the detector unit is configured to send the control signal to the video camera, so that the video camera generates at least one electronic image which contains the license plate in or near said strip-shaped section, in the second image sequence.

2. The device according to claim 1, wherein the video camera is configured to scan the images of the first and of the second image sequences line by line, and wherein the strip-shaped section lies parallel to the scan lines.

3. The device according to claim 1, further comprising at least one light source which is aimed on the road section to illuminate said section differently in the first operating mode than in the second operating mode of the video camera.

4. The device according to claim 3, wherein the at least one light source illuminates said section more strongly or in a different wavelength range in the first operating mode than in the second operating mode

5. The device according to claim 1, wherein the video camera has different exposure parameters in the first operating mode than in the second operating mode.

6. The device according to claim 5, wherein the video camera has a different shutter speed, gain, or gamma correction in the first operating mode than in the second operating mode.

7. The device according to claim 5, wherein, in the second operating mode, the exposure parameters of the video camera are set depending on the reflectivity of the license plate portion detected in the first image sequence.

8. The device according to claim 1, wherein the video camera is a CMOS or CCD camera.

9. A method for detecting a vehicle license plate in the optical camera image of a traffic monitoring camera that is aimed on a street section, the method comprising:

electronically scanning a strip-shaped section of the optical camera image line by line for the generation of an electronic scanning signal, the electronic scanning signal being checked continuously for occurrence of a signal indicating a license plate; and

when said signal is detected, electronically scanning the entire optical camera image line-by-line and for at least one-time to generate an electronic scanning image of the entire optical camera image, which contains the license plate in or near the mentioned section.

10. The method according to claim 9, wherein said signal extends over several successive scan lines of the entire strip-shaped section.

11. The method according to claim 10, wherein said signal is a sequence of bursts, a length of which corresponds to a width of a vehicle license plate to be detected.

12. The method according to claim 9, wherein when electronically scanning the strip-shaped section, the road section is illuminated differently than when electronically scanning the entire optical camera image.

13. The method according to claim 12, wherein when electronically scanning the strip-shaped section, the road section is illuminated more strongly or in a different wavelength range than when electronically scanning the entire optical camera image.

14. The method according claim 9, wherein when electronically scanning the strip-shaped section, the camera is operated with different exposure parameters than when electronically scanning the entire optical camera image.

15. The method according claim 14, wherein when electronically scanning the strip-shaped section, the camera is operated with a different shutter speed, gain or gamma correction than when electronically scanning the entire optical camera image.

16. The method according to claim 14, wherein the exposure parameters of the camera when electronically scanning the strip-shaped section are set depending on said detected signal