System for simultaneously imaging vehicles and their license plates

• US 6,650,765 B1
• Filed: 01/11/2000
• Issued: 11/18/2003
• Est. Priority Date: 01/11/2000
• Status: Expired due to Term

• Current Assignee: Pulnix America Incorporated (JAI A/S)
• Original Assignee: Pulnix America Incorporated (JAI A/S)
• Inventors: Alves, James Francis
• Primary Examiner(s): Boudreau, Leo
• Assistant Examiner(s): Akhavannik, Hussein
• Application Number:
  US09/481,132
• Time in Patent Office: 1,407 Days
• Field of Search: 382/105
• US Class Current: 382/105
• CPC Class Codes: G08G 1/0175 by photographing vehicles, e.g. when violating traffic rules

Abstract

A vehicle video imaging system comprises a white-light LED array for illuminating retro-reflective painted parts of a vehicle'"'"'s license plate, a powerful flash with a visual spectrum cutout filter and a polarizing filter for illuminating any non-retro-reflective license plate paint and the vehicle itself. A video camera with a polarizing filter turned 90° relative to the one in front of the flash receives the illuminated image of the vehicle and its license plate. The retro-reflective paint of a license plate will return polarized light as it is received, so the white-light LED array will provide all the illumination needed by the camera to get a good high-contrast picture of the license plate. The polarizing filters will combine to block out most of the light from the flash that was returned still-polarized by the retro-reflective-paint license plate. All other surfaces that do not have retro-reflective paint will bounce-back and scatter the light from both the polarized flash and non-polarized light.

Claims

1. A vehicle and license plate imaging system, comprising:

a video camera for providing an image of a vehicle and a license plate in the dark and at night, and in which it is unknown if said license plate will be non-retro-reflective or retro-reflective;

a first polarizing filter mounted in front of the video camera and having a first polarizing orientation;

a low-level floodlight for providing an illumination of said vehicle and license plate for the video camera;

a flash lamp providing for a flash illumination of said vehicle and license plate for the video camera;

a visual-spectrum cutout filter placed between the flash lamp and said vehicle, and providing for a blockage of human-visible light spectra that would otherwise reach said vehicle, and providing for a combination of a first light with wavelengths less than 400 nanometers and a second light with wavelengths more than 700 nanometers at the fringes of the visible spectrum to contrast a variety of color combinations used in said license plate;

a second polarizing filter placed between the flash lamp and said vehicle, and having a second polarizing orientation that is orthogonal to said first polarizing orientation and providing for cross Polarization of said flash illumination;

wherein, a reflected light from the flash lamp with said second polarizing orientation that is returned from said vehicle and license plate is blocked by the first polarizing filter; and

wherein, the low-level floodlight is able to provide sufficient illumination for the camera if said license plate is a retro-reflective type.

2. The system of claim 1, wherein:

the visual-spectrum cutout filter blocks visible-spectrum light with wavelengths in the range of 400-700 nanometers.

3. The system of claim 1, wherein:

the floodlight comprises a white-light light-emitting-diode (LED) array.

4. The system of claim 1, further comprising:

a computer system connected to the video camera for providing automatic optical character recognition of any alphanumeric characters that are imaged from said license plate.

5. The system of claim 1, further comprising:

a computer system connected to the video camera for determining and issuing traffic citations for any vehicle law violations involving said vehicle.

6. A vehicle and license plate imaging system, comprising:

a video camera for providing an image of a vehicle and a reflective-paint license plate;

a first polarizing filter mounted in front of the video camera and having a first polarizing orientation;

a white-light light-emitting-diode (LED) array for providing a non-polarized illumination of said vehicle and reflective-paint license plate for the video camera;

a flash lamp for providing a flash illumination of said vehicle and reflective-paint license plate for the video camera;

a visual-spectrum cutout filter placed between the flash lamp and said vehicle and providing for a blockage of human-visible light spectra from the flash lamp that would otherwise reach said vehicle, and providing for a combination of a first light with wavelengths less than 400 nanometers and a second light with wavelengths more than 700 nanometers at the fringes of the visible spectrum to contrast a variety of color combinations used in said license plate; and

a second polarizing filter placed between the flash lamp and said vehicle, and having a second polarizing orientation that is orthogonal to said first polarizing orientation;

wherein, any light from the flash lamp with said second polarizing orientation that is returned from said vehicle and said retro-reflective-paint license plate is substantially blocked by the first polarizing filter, and light with no particular polarization that is returned from said vehicle and said retro-reflective-paint license plate can substantially pass by the first polarizing filter; and

wherein, the white-light LED array is able to provide sufficient illumination for the camera if said license plate is a retro-reflective type.

7. A method of simultaneously imaging a vehicle and its license plate when such license plate may or may not be painted with reflective paints and can comprise any number of contrasting colors, the method comprising the steps of:

flood-illuminating a vehicle and its license plate with a non-polarized light sufficient to return a usable visible image from a retro-reflective-paint license plate;

flash-illuminating said vehicle and its license plate with a polarized light sufficient to return a usable visible image from said vehicle and any non-retro-reflective-painted license plate, and providing for a combination of a first light with wavelengths less than 400 nanometers and a second light with wavelengths more than 700 nanometers at the fringes of the visible spectrum to contrast a variety of color combinations used in said license plate;

filtering out any of said polarized light returned from said vehicle and its license plate before it reaches a camera;

imaging said vehicle and its license plate with a camera; and

wherein, the non-polarized light is able to provide sufficient illumination for the camera if said license plate is a retro-reflective type.

8. The method of claim 7, wherein:

the step of filtering is such that a polarizing filter is used that is orthogonally oriented to said polarized light.

9. The method of claim 7, wherein:

the step of flood-illuminating uses a white-light light-emitting-diode (LED) array.

10. The method of claim 7, wherein:

the step of flash-illuminating includes the use of a visible-light filter that blocks light with wavelengths in the range of 400-700 nanometers.

11. The method of claim 10, wherein:

the step of flash illuminating includes simultaneously illuminating said vehicle and its license plate with two different colors.

12. The method of claim 7, wherein:

the step of flash illuminating includes using a first non-visible light filter and a second non-visible light filter so two different polarized light colors help contrast said license plate.