WO1997032237A2

WO1997032237A2 - System for photographing moving vehicles

Info

Publication number: WO1997032237A2
Application number: PCT/IL1997/000073
Authority: WO
Inventors: Shmuel Kedmi; Dror Lenger; Daniel Katz
Original assignee: Driver Safety Systems Ltd.
Priority date: 1996-02-28
Filing date: 1997-02-27
Publication date: 1997-09-04
Also published as: EP0883870A4; EP0883870A2; IL117311A0; AU1809297A; CA2247883A1; WO1997032237A3

Abstract

A system for producing still photographs of vehicles in motion comprising a camera (100) arranged to view moving vehicles (120, 160) and operative to record an image of a vehicle (160) and an exposure controller operative to control the exposure of the camera in accordance with light conditions known from at least one preceding image of a vehicle (120).

Description

SYSTEM FOR PHOTOGRAPHING MOVING VEHICLES

The present invention relates to camera systems in general, and in particular to camera systems for producing photographs of moving vehicles.

Systems for producing still photographs of moving vehicles are well known in the art.

Prior art systems for producing still photo^¬ graphs of moving vehicles suffer from a. number of short¬ comings. Exposure control is particularly difficult. Exposure control methods known in the art typically rely on the ambient light level when no vehicle is in the field of view in order to set the exposure. This method is inaccurate because vehicles tend to reflect light differently than other objects in the scene.

When illumination is provided by a flash, problems arise because vehicle license plates typically have a retroreflective background so that the camera, located near the flash, receives a high level of light from the license plate. The high level of light is typically received because the license plate has a high coefficient of reflectance compared to the body of the vehicle. As a consequence, the resulting picture will typically include either a clear image of the vehicle and an over-exposed picture of the license plate or, alterna¬ tively, a clear image of the license plate and an under¬ exposed or non-visible image of the vehicle.

The present invention seeks to provide an improved system for producing photographs of moving vehicles .

There is thus provided in accordance with a preferred embodiment of the present invention a system for producing still photographs of vehicles in motion including a camera arranged to view moving vehicles and operative to record an image of a vehicle, and an expo- sure controller operative to control the exposure of the camera in accordance with light conditions known from at least one preceding image of a vehicle.

Further in accordance with a preferred embodi¬ ment of the present invention the system also includes an image storage device operative to at least temporarily store at least one of a series of images of a series of vehicles, taken in sequence, wherein the at least one preceding image of a vehicle is stored in the image storage device.

The camera may include a CCD video camera.

Still further in accordance with a preferred embodiment of the present invention the exposure control¬ ler includes an aperture controller and an exposure time controlle .

Additionally in accordance with a preferred embodiment of the present invention the exposure control¬ ler includes a sample and hold circuit which receives an exposure input and drives an analog iris controller.

Moreover in accordance with a preferred embodi¬ ment of the present invention the system also includes a frame grabber receiving an output from the camera, proc¬ essing circuitry operative to obtain exposure information from the contents of the frame grabber relating to previ¬ ously recorded images of vehicles and to provide exposure control inputs to the exposure controller, and a frame grabber actuator operative to actuate the frame grabber when a vehicle is within a desired field of view of the camera thereby to record an image of the vehicle.

There is also provided in accordance with another preferred embodiment of the present invention a system for producing still photographs of vehicles in motion including a camera arranged to view moving vehi¬ cles and operative to record an image of a vehicle, and a flash illuminator disposed remote from the camera for illuminating the vehicle from a direction selected such that primary reflections from a vehicle number plate are not received by the camera, thus preventing saturation of the image by such reflection and permitting other parts of the vehicle to be seen in the image.

Additionally in accordance with a preferred embodiment of the present invention the system also includes an exposure controller operative to control the exposure of the camera and the operation of the flash illuminator in accordance with light conditions known from at least one preceding image of a vehicle.

Further in accordance with a preferred embodi¬ ment of the present invention the system also includes an image storage device operative to at least temporarily store at least one of a series of images of a series of vehicles, taken in sequence, wherein said at least one preceding image of a vehicle is stored in said image storage device.

Still further in accordance with a preferred embodiment of the present invention the system includes a frame grabber receiving an output from the camera, proc¬ essing circuitry operative to obtain exposure information from the contents of the frame grabber relating to previ¬ ously recorded images of vehicles and to provide exposure control inputs to the exposure controller as well as controlling the flash illuminator, and a frame grabber actuator operative to actuate the frame grabber when a vehicle is within a desired field of view of the camera thereby to record an image of the vehicle.

The camera may include a CCD video camera.

Further in accordance with a preferred embodi¬ ment of the present invention the system also includes a flash illuminator disposed remote from the camera for illuminating the vehicle during camera actuation from a direction selected such that primary reflections from a vehicle number plate are not received by the camera, thus preventing saturation of the image by such reflection and permitting other parts of the vehicle to be seen in the image .

There is also provided in accordance with another preferred embodiment of the present invention a method for producing still photographs of vehicles in motion including recording an image of a first vehicle, storing the image of the first vehicle, analyzing light conditions of the stored image, and recording an image of a second vehicle, wherein, in the step of recording an image of a second vehicle, exposure is controlled in accordance with a result of the analyzing step.

The present invention will be understood and appreciated from the following detailed description, taken in conjunction with the drawings in which:

Fig. 1 is a simplified pictorial illustration of a system for producing still photographs of vehicles in motion constructed and operative in accordance with a preferred embodiment of the present invention;

Figs. 2 and 3 are simplified pictorial illus¬ trations of the system of Fig. 1, showing the operation thereof under various stages of operation;

Fig. 4 is a simplified pictorial illustration of a system for producing still photographs of vehicles in motion constructed and operative in accordance with an alternative preferred embodiment of the present inven¬ tion;

Fig. 5 is a simplified block diagram illustra¬ tion of a preferred implementation of the system of Fig. 1 ; and

Fig. 6 is a simplified flowchart illustration of a preferred method of operation of the apparatus of Fig. 1.

Reference is now made to Fig. 1 which is a simplified pictorial illustration of a system for produc¬ ing still photographs of vehicles in motion, constructed and operative in accordance with a preferred embodiment of the present invention. It is appreciated that the system of Fig. 1 may have many uses, and may be particu¬ larly useful in monitoring and controlling vehicle use such as, for example, in aiding in enforcing traffic regulations or in monitoring vehicles entering or exiting a defined area.

The system of Fig. 1 preferably comprises a camera 100. The camera 100 may be any suitable type of camera, such as an electronic camera, appropriate for taking still photographs under electronic control. Typically, the camera 100 comprises a CCD video camera, such as, for example, a model XC-75 CE CCD camera commer¬ cially available from Sony, Japan.

Reference is now additionally made to Fig. 5, which is a simplified block diagram illustration of a preferred implementation of the system of Fig. 1. The apparatus of Fig. 5 comprises a processor 144, typically a microprocessor. The processor 144 is preferably opera¬ tive to actuate the camera 100 when a vehicle is within a desired field of view of the camera 100. The determina¬ tion that a vehicle is within a desired field of view may be made in any number of ways, as is well known in the art. For example, a traffic sensor, such as a radar unit or a pavement sensor, may be used to determine when a vehicle is within a desired field of view. Alterna¬ tively, as is well known in the art, the processor 144 may be operative to actuate the camera 100 only when a vehicle is within a desired field of view of the camera 100 and the vehicle has committed an apparent traffic violation such as, for example, proceeding through a stop light without stopping.

In Fig. 1 a vehicle 120 is shown within the desired field of view of the camera 100. A desired field of view generally comprises a field of view including a license plate of a vehicle, such as license plate 125, along with other parts of the vehicle. Referring to Fig. 5_ι i is seen that the appa¬ ratus of Fig. 5 also preferably comprises an image storage device, such as a frame grabber 140, associated with the camera 100. The frame grabber 140 may comprise any appropriate commercially available frame grabber, as is well known in the art. The frame grabber 140 prefera¬ bly acts as a buffer for capturing and storing a frame of the video image produced by the camera 100. The image storage device l4θ is preferably operative to receive images captured by the camera 100 and to store at least one of a series of images taken of a series of vehicles, such as an image of the vehicle 120 (Fig. 1) .

The camera 100 preferably comprises an exposure controller 150. The exposure controller 150 is operative to control the exposure of the camera 100, based on light conditions known from at least one preceding image of a vehicle, stored in the frame grabber l4θ. Typical¬ ly, the exposure controller 150 comprises an aperture controller such as an iris controller 220 and an exposure time controller 225- The exposure controller 150 may comprise a sample and hold circuit and an analog iris controller, controlling an iris associated with the camera 100.

In Fig. 1 a second vehicle l6θ having a second license plate 165 is shown, outside the field of view of the camera 100.

The vehicle 120 is shown illuminated by light from the sun 170. The system of Fig. 1 also optionally comprises a remote flash illuminator 180. The remote flash illuminator 180 provides additional illumination of the field of view of the camera 100 as needed. The remote flash illuminator 180 is optionally disposed remote from the camera 100 because primary reflections from a license plate such as the license plate 125 are generally reflected in the direction of the source of illumination. The remote flash illuminator 180 is pref- erably disposed at a direction selected to ensure that such primary reflections are not received by the camera 100, thus preventing the desired image from being satu¬ rated with the primary reflections and thus preventing problems with wash-out.

The operation of the apparatus of Fig. 1 is now briefly described. The camera 100, under control of the processor 144 (Fig. 5) . takes a picture of the vehicle 120, including the area of the license plate 125- The remote flash illuminator lδO is preferably actuated to illuminate the field of view during taking of the pic¬ ture. Reflected light 195 from the license plate 125 travels generally in the direction of the remote flash illuminator 180 and, because of the remote location chosen for the remote flash illuminator 180, not in the direction of the camera 100.

The image resulting from the picture taken by the camera 100 is stored in the frame grabber l4θ (Fig. 5) . The processor 144 (Fig. 5) preferably analyzes the light conditions of the stored image using techniques which are well-known in the art such as, for example, techniques used in commercially available automatic exposure-controlled cameras.

Reference is now additionally made to Figs. 2 and 3 which are simplified pictorial illustrations of the system of Fig. 1, showing the operation thereof under various stages of operation. In Fig. 2, the vehicle 120 of Fig. 1 is no longer shown as present, while the second vehicle l6θ is seen to have not yet entered the field of view of the camera 100. Because no vehicle is in the field of view of the camera 100, the processor 144 pref¬ erably does not actuate the camera 100.

In Fig. 3, the second vehicle 160 is seen to have entered the field of view of the camera 100. The camera 100, under control of the processor 144, takes a picture of the vehicle 160, typically including the area of the second license plate 165. During exposure of the picture, the exposure controller 150 (Fig. ) ₁ under control of the processor 144 (Fig. 5) preferably controls the exposure of the picture in accordance with the light conditions analyzed from the previously taken picture of the vehicle 120, as explained above with reference to Fig. 1.

The remote flash illuminator lδO is preferably actuated to illuminate the field of view during taking of the picture. Reflected light I96 from the second license plate I65 travels generally in the direction of the remote flash illuminator 180 and, because of the remote location chosen for the remote flash illuminator 180, generally not in the direction of the camera 100.

It is appreciated that the exposure controller 150 (Fig. 5) ₁ under control of the processor 144 (Fig. 5) may control the exposure of the current picture. based on light conditions from one previous picture or from more than one previous picture. . In the case when more than one previous picture was used, any appropriate weighting may be given to each of the plurality of previous pic¬ tures .

The image resulting from operation of the camera 100 is stored in the frame grabber l4θ (Fig. 5) - The processor 144 (Fig. 5) preferably analyzes the light conditions of the stored image, as described above, for use in controlling the exposure of future pictures.

Reference is now made to Fig. 4, which is a simplified pictorial illustration of a system for produc¬ ing still photographs of vehicles in motion constructed and operative in accordance with an alternative preferred embodiment of the present invention. The system of Fig. 4 is similar to the system of Fig. 1, described above, except as follows. The camera 100 is located so that the desired field of view thereof comprises a front license plate 197 and a driver 198 of the vehicle 120. Shown in Fig. 4 is reflected light 199 from the front license plate 197, similar to the reflected light 195 of Fig. 1. As with the reflected light 195 i Fig. 1, the reflected light 199 travels generally in the direction of the remote flash illuminator 180 and, because of the remote location chosen for the remote flash illuminator 180, generally not in the direction of the camera 100.

The operation of the system of Fig. 4 is simi¬ lar to that described above with reference to Figs. 1 3< It is appreciated that the system of Fig. 4 may be operated to photograph the front of a vehicle such as the vehicle 120, including an image of the face of the driver 1 8- It is appreciated that the embodiment of Fig. 4 may be preferable in order to capture an image of the face of the driver 198 and thus aid in identification of the driver 198 as well as identifying the vehicle 120 by means of the front license plate 197.

Reference is now made to Fig. 5. which is a simplified block diagram illustration of a preferred implementation of the system of Fig. 1. The system of Fig. 5 preferably comprises a camera unit 202. The camera unit 202 preferably includes a lens 203, which may be a fixed focus lens, and a CCD video camera 205-

The output of the CCD video camera 205, com¬ prising a video image, is received by the frame grabber l4θ, which captures a single frame from the video image and passes the captured frame to the processor 144.

The processor 144 may be any appropriately programmed processor, such as a microprocessor. The processor 144 analyzes light characteristics of the captured single frame. Based on the analyzed light characteristics the processor 144 operates to control exposure of the next image to be captured by sending signals to an iris controller 220 and an exposure time controller 225, which together constitute an exposure controller 150. Typically, under control of the proces- sor 144 the exposure controller 150 implements a sample and hold circuit, in that the captured image is sampled and then held for controlling exposure of the next image.

The iris controller 220 opens or closes an aperture (not shown) , as is well known in the art, and thus adjusts the amount of light entering the lens 203 • The exposure time controller 225 controls the exposure time of the CCD video camera 205.

The processor 144 is also preferably operative to send an appropriately timed signal to the remote flash illuminator lδO, causing the remote flash illuminator 180 to flash and to illuminate the scene to be photographed by the camera 100.

Reference is now made to Fig. 6 which is a simplified flowchart illustration of a preferred method of operation of the apparatus of Fig. 1. The method of Fig. 6 preferably includes the following steps:

A picture of a first vehicle is taken, and the image is stored, typically in the frame grabber 140 of Fig. 5 (step 250) . Light conditions of the stored image are analyzed, typically by the processor 144 of Fig. 5 (step 260) . A picture is then taken of a second vehicle, with exposure of the picture being based on the light conditions analyzed in step 260 (step 270) .

While the vehicles depicted in Figs. 1 - 4 are automobiles, it is appreciated that vehicles photographed by the system of the present invention may comprise any type of vehicles, including, for example, automobiles, motorcycles, and trucks.

It is appreciated that the software components of the present invention may, if desired, be implemented in ROM (read-only memory) form. The software components may, generally, be implemented in hardware, if desired, using conventional techniques.

It is appreciated that various features of the invention which are, for clarity, described in the con- texts of separate embodiments may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, de¬ scribed in the context of a single embodiment may also be provided separately or in any suitable subcombination.

It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention is defined only by the claims that follow:

Claims

C LA IMS

1. A system for producing still photographs of vehicles in motion comprising: a camera arranged to view moving vehicles and operative to record an image of a vehicle; and an exposure controller operative to control the exposure of the camera in accordance with light condi¬ tions known from at least one preceding image of a vehi¬ cle .

2. A system according to claim 1 and also compris¬ ing an image storage device operative to at least tempo¬ rarily store at least one of a series of images of a series of vehicles, taken in sequence, wherein said at least one preceding image of a vehicle is stored in said image storage device.

3- A system according to any of the preceding claims and wherein said camera comprises a CCD video camera.

4. A system according to claim 1 or claim 2 and wherein said exposure controller comprises an aperture controller and an exposure time controller.

5- A system according to claim 1 or claim 2 and wherein said exposure controller comprises a sample and hold circuit which receives an exposure input and drives an analog iris controller.

6. A system according to claim 1 or claim 2 and also comprising: a frame grabber receiving an output from said camera ; processing circuitry operative to obtain expo- sure information from the contents of the frame grabber relating to previously recorded images of vehicles and to provide exposure control inputs to said exposure control¬ ler; and a frame grabber actuator operative to actuate said frame grabber when a vehicle is within a desired field of view of said camera thereby to record an image of said vehicle.

7- A system for producing still photographs of vehicles in motion comprising: a camera arranged to view moving vehicles and operative to record an image of a vehicle; and a flash illuminator disposed remote from the camera for illuminating the vehicle from a direction selected such that primary reflections from a vehicle number plate are not received by the camera, thus pre¬ venting saturation of the image by such reflection and permitting other parts of the vehicle to be seen in the image .

8. A system according to claim 7 and also compris- ing: an exposure controller operative to control the exposure of the camera and the operation of the flash illuminator in accordance with light conditions known from at least one preceding image of a vehicle.

9- A system according to claim 8 and also compris¬ ing an image storage device operative to at least tempo¬ rarily store at least one of a series of images of a series of vehicles, taken in sequence, wherein said at least one preceding image of a vehicle is stored in said image storage device.

10. A system according to any of claims 7 and also comprising: a frame grabber receiving an output from said camera; processing circuitry operative to obtain expo¬ sure information from the contents of the frame grabber relating to previously recorded images of vehicles and to provide exposure control inputs to said exposure control¬ ler; and a frame grabber actuator operative to actuate said frame grabber when a vehicle is within a desired field of view of said camera thereby to record an image of said vehicle.

11. A system according to any of claims 7 " 9 and wherein said camera comprises a CCD video camera.

12. A system according to claim 1 or claim. 2 and also comprising: a flash illuminator disposed remote from the camera for illuminating the vehicle during camera actua¬ tion from a direction selected such that primary reflec¬ tions from a vehicle number plate are not received by the camera, thus preventing saturation of the image by such reflection and permitting other parts of the vehicle to be seen in the image.

13. A method for producing still photographs of vehicles in motion comprising: recording an image of a first vehicle; storing the image of the first vehicle; analyzing light conditions of the stored image; and recording an image of a second vehicle, wherein, in said step of recording an image of a second vehicle, exposure is controlled in accordance with a result of said analyzing step.