Vehicle license plate imaging and reading system for day and night

• US 20030174865A1
• Filed: 03/15/2002
• Published: 09/18/2003
• Est. Priority Date: 03/15/2002
• Status: Active Grant

• Current Assignee: Extreme CCTV, Inc. (Robert Bosch GmbH)
• Original Assignee: Extreme CCTV, Inc. (Robert Bosch GmbH)
• Inventors: Vernon, Mark William
• Granted Patent: US 7,016,518 B2
• Time in Patent Office: Days
• US Class Current: 382/105
• CPC Class Codes: G06V 10/143 Sensing or illuminating at different wavelengths
• 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

This invention provides an infrared illuminator and camera system for imaging of auto vehicle license plates. The system works in ambient light conditions, ranging from bright sunlight, to dim light, to dark, to zero ambient light. It yields high-contrast imaging of the letters and numbers on retro-reflective license plates. The images of the license letter and number combinations can be read manually by a remote operator. They can be converted to text format with optical character recognition computer hardware and software. The text data can then be compared to data files listing license numbers to provide further data about the owner of a licensed vehicle. A decision can be made quickly about whether to allow a vehicle to proceed through a gate, or whether to take other action. The system uses a mono camera that is enhanced for infrared sensitivity and combined with a high power infrared illuminator to maximize range at night, and with shutter speeds set up to capture clear license plate pictures even with fast moving vehicles and even with their headlights on and interfering with human observation of the license plates. Optical filtering to pass infrared in the range of the illuminator and to reduce light outside this range, combines with a lens set up, to avoid vertical smear and sensor overload caused by headlights at night and by highlight reflected glare from the sun in daytime.

Claims

1. A license plate reader system for all ambient light conditions, comprising a high power infrared illuminator for night and a camera that:

a) is enhanced for infrared sensitivity and resolution;

b) has shutter speeds set up to capture clear license plate pictures on vehicles moving at any speed up to a predicted speed limit for the vehicles, even with their headlights on;

c) has optical filtering of light wavelengths outside the range of light wavelength emitted by the high power infrared illuminator, in order to avoid sensor overload from headlights and reflected glare from sunlight.

2. The license plate reader system of claim 1, in which the camera is a monochrome camera that has high resolution and low inter-pixel leakage.

3. The license plate reader system of claim 1, in which the camera has a lens set up with a small aperture formed by an iris to avoid sensor overload, to increase depth of field for focused images of license plates on moving vehicles, and to avoid vertical smearing of images.

4. The license plate reader system of claim 1, in which the camera has a sunshield to avoid vertical smear from overhead ambient light on images captured by the camera.

5. The license plate reader system of claim 1, in which the high power infrared illuminator provides illumination of over a distance of at least 35 meters from the camera at an intensity to capture clear license plate pictures even with fast moving vehicles and even with their headlights on.

6. The license plate reader system of claim 1, in which the high power infrared illuminator has sufficient power to allow closed circuit television surveillance over a distance of at least 100 meters.

7. The license plate reader system of claim 6, in which the high power infrared illuminator comprises an infrared light source that is powered with an electrical voltage that is lower than the infrared light source'"'"'s normal voltage operating range in order to extend bulb life in the illuminator.

8. The license plate reader system of claim 1, in which the high power infrared illuminator emits wavelengths in the range of 830 to 1000 nanometers, and the optical filtering comprises a filter that passes infrared wavelengths in the range of 830 to 1000 nanometers, and restricts wavelengths of light below and above that range.

9. The license plate reader system of claim 1, in which the shutter speed is {fraction (1/1000)} of a second in order to capture license plate images from vehicles travelling at speeds in the range of 0 to 100 miles per hour.

10. The license plate reader system of claim 1, in which the camera and the illuminator are each contained in a weather-tight housing.

11. The license plate reader system of claim 1, further comprising an armoured cable for sending a video signal from the system to a remote location.

12. The license plate reader system of claim 1, in which images of license plates sent for processing by an automated optical character recognition module.

13. The license plate reader system of claim 1, in which alphanumeric characters read from a license plate of a vehicle are compared with data from license plate databases in preparation for a response to the vehicle.

14. The license plate reader system of claim 1, further comprising a second such system, each system located a measured distance apart, in order to capture separate and timed license plate images for use in speed monitoring.

15. The license plate reader system of claim 2, in which the camera is mounted in a camera housing and a heater is mounted within the housing to keep the camera within an operating temperature range.

16. The license plate reader system of claim 2, in which the illuminator is contained in a lamp housing with gaskets to seal against weather conditions, but in which the gasket has a bleed channel to allow vapour to escape from the interior of the housing.

17. The license plate reader system of claim 2, in which the camera is contained in a camera housing that is mounted with a U-bracket to a lamp housing for the illuminator in order to allow the angle of the camera to be adjusted with respect to the illuminator.

18. The license plate reader system of claim 2, in which the camera and the illuminator are each provided with a sunshield.

19. The license plate reader system of claim 2, in which:

a) the camera has a lens set up with a small aperture formed by an iris to avoid sensor overload, to increase depth of field for focused images of license plates on moving vehicles, and to avoid vertical smearing of images;

b) the camera has a sunshield to avoid vertical smear from overhead ambient light on images captured by the camera;

c) the high power infrared illuminator provides illumination of over a distance of at least 35 meters from the camera at an intensity to capture clear license plate pictures even with fast moving vehicles and even with their headlights on;

d) the high power infrared illuminator has sufficient power to allow closed circuit television surveillance over a distance of at least 100 meters;

e) the high power infrared illuminator comprises an infrared light source that is powered with an electrical voltage that is lower than the infrared light source'"'"'s normal voltage operating range in order to extend bulb life in the illuminator;

f) the high power infrared illuminator emits wavelengths in the range 830 to 1000 nanometers, and the optical filtering comprises a filter that passes infrared wavelengths in the range of 830 to 1000 nanometers, and restricts wavelengths of light below and above that range;

g) the shutter speed is {fraction (1/1000)} of a second in order to capture license plate images from vehicles travelling at speeds in the range of 0 to 100 miles per hour;

h) the system is contained in a weather-tight housing.

20. The license plate reader system of claim 19, further comprising an armoured cable for sending a video signal from the system to a remote location and a second such system located a measured distance apart, in order to capture, separate, and time license plate images for use in speed monitoring.

21. The license plate reader system of claim 19, in which images of license plates are hdownloaded for processing by an automated optical character recognition module.

22. The license plate reader system of claim 21, in which alphanumeric characters read from a license plate of a vehicle are compared with data from license plate databases in preparation for a response to the vehicle.

23. The license plate reader system of claim 19, in which:

a) the camera is mounted in a camera housing and a heater is mounted within the housing to keep the camera within an operating temperature range;

b) the illuminator is contained in a lamp housing with gaskets to seal against weather conditions, but in which the gasket has a bleed channel to allow vapour to escape from the interior of the housing;

c) the camera is contained in a camera housing that is mounted with a U-bracket to a lamp housing for the illuminator in order to allow the angle of the camera to be adjusted with respect to the illuminator;

d) the camera and the illuminator are each provided with a sunshield.