IL107931A - System and method for image acquisition - Google Patents

Description

A SYSTEM AND METHOD FOR IMAGE ACQUISITION mm:, won^ nu»en roiyn The present invention relates to a system and a method for image acquisition of an identifying indicia of a vehicle, and more particularly, the invention is concerned with a vehicle license plate reading system for automatic vehicle identification.

There are known in the art many systems for automatic vehicle identification essentially consisting of a camera, a device for illuminating the front or rear portion of a moving vehicle and an image processor. One of the problems which users of such systems are faced with when utilizing such systems is the difficult analysis of all information of the recorded image including the background information. More specifically, the difficulty lies in sorting out, from amongst the various alphabetical and numerical information present as background, as well as on the front and rear portions of the vehicles, such as common window and bumper stickers exhibiting slogans and advertising material, including vehicle manufacturer's name and car model and information concerning the numbers and/or letters depicted on the license plate. This task of information sorting and only thereafter processing the relevant sought after information displayed on the vehicle's license plate, is not simple and becomes even more difficult when the indicia displayed on the license plate is smaller than, and/or otherwise not as legible as, other alpha-numerical indicia present on the photographed image.

Among the many aspects related to solving the above problems, the present invention is concerned with the aspect of improving the image acquisition itself, rather than the improvement of the processing of the image acquired by the common methods, so as to diminish the efforts which must be invested in the retrieval of the sought after information.

It is therefore a broad object of the present invention to ameliorate the disadvantages of the prior art systems and methods of image acquisition of a vehicle's identifying indicia and to provide an improved system therefor.

It is a further object of the present invention to provide an improved system and method for automatically reading license plates of vehicles.

In accordance with the present invention there is therefore provided a system for image acquisition of an identifying indicia of a vehicle moving along an interrogation zone defined by substantially linearly extending length and a substantially constant width, said system comprising an optical imaging unit having an effective field of view of a width smaller than the width of said interrogation zone, said unit being located alongside or above said interrogation zone and oriented so that the field of view traverses said zone, at least two detectors positioned in spaced-apart relationship to each other in proximity to and along said zone for detecting vehicles moving therealong, and circuit means for synchronizing said imaging unit with said detectors and for triggering the imaging unit in response to said detectors.

The invention further provides a method for image acquisition of an identifying indicia of a vehicle moving along an interrogation zone defined by substantially linearly extending length and a substantially constant width, said method comprising providing an optical imaging unit, at least two detectors positioned in spaced-apart relationship to each other in proximity to and along said zone for detecting vehicles moving therealong, and circuit means for synchronizing said imaging unit with said detectors and for triggering the imaging unit in response to said detectors, adjusting the width of the effective field of view of said imaging unit to a width smaller than the width of said interrogation zone, positioning said unit alongside or above said interrogation zone in an orientation so that the field of view traverses said zone, and causing the triggering of said unit upon the identifying indicia entering said imaging zone.

The invention will now be described in connection with certain preferred embodiments with reference to the following illustrative figures so that it may be more fully understood.

With specific reference now to the figures in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.

In the drawings: Fig. 1 is a schematic representation of a prior art system for photographing license plates of a moving vehicle; Fig. 2 is a schematic representation of a system for image acquisition of an identifying indicia of a vehicle according to the present invention; Fig. 3 is a schematic representation of a modification of the system of Fig. 2 for image acquisition, according to the present invention, and Fig. 4 is a more detailed block diagram of part of the system of Fig. 3.

Referring first to Fig. 1, there is shown a commonly used (prior art) system for automatic photographing of a license plate of a vehicle 2 travelling along a road 4. The road 4 has two lanes, A and B, separated by a hatched line 6. Alongside the road 4 , there is positioned a camera 8 operationally triggered by a detector 10, situated at a distance 1 in the direction of travel from the camera. Both the camera 8, as well as the detector 10 are connected electronically to a control unit 12. As further seen, in order to assure the capability of photographing vehicles passing at any place across the entire width , along the lane A, the camera 8 has to be activated when a vehicle is located at the distance 1 therefrom, where the width of the field of view of the camera substantially equals the width W of the lane A. It can thus be readily understood that the information perceived by the camera is deficient from two aspects: a) it is photographed from a relatively large distance, and b) it, of necessity, encompasses the image of a multi-lane roadway, including a vast quantity of undesired information, from which the information sought with respect to the license plate indicia, must then be extracted.

Furthermore, in case a single camera is used to cover the two lanes A and B, the distance of photography is even greater, the field of view a of the camera and consequently the images obtained, require a much greater, costly and time consuming effort to process with a view to achieve a clear license plate image .

In contradistinction thereto, and with reference now to Fig. 2, there is illustrated an image acquisition system according to the present invention, wherein the system includes an optical imaging unit 14, a plurality of e.g., three vehicle detectors 15, 16 and 17 located alongside or above an interrogation zone, e.g., the lane A of a road 4 at a spaced-apart relationship to each other "downstream" the lane A. The unit 14 and the detectors 15, 16, and 17 are electronically operationally inter- connected by a controller 20 which triggers the imaging unit 14 in response to the signals of the detectors 15, 16 and 17. The effective imaging field of an angle of the unit 14 has a width w , w2 or w3 (rectangle or diameter) smaller than the width W of the lane A, as opposed to the field of view a of the prior art system of Fig. 1, having a width (rectangle or diameter) which equals the width W of the lane A. Hence, upon the detection of a vehicle passing by the detector 15 at a distance from the unit 14, there is recorded an image of the passing vehicle in a narrow field instead of an image of a wide field, thus obtaining a relatively larger image, of the real information sought and a greater and improved information separation capability, resulting in a higher indicia identification capability and a decrease in processing time.

The same operation and similarly improved results are also obtained upon the detection of a passing vehicle by the detector 17. Naturally, a certain overlap between the detection strips of width w^ w2 and w3 , should be established. Preferably, the width of the overlap should be about the width of the sought-after identifying indicia. Also, as understood, more than the illustrated three detectors 15, 16 and 17 can be positioned along the road, thereby enabling the further narrowing of the field of view for obtaining even better results .

Turning to Fig. 3, there is shown a modification of the system of Fig. 2, wherein there are provided two spaced-apart detectors 22 and 24 and a transceiver 26, all being electronically interconnected with a controller 28. This arrangement is suitable for measuring the speed of a passing vehicle, as well as its location inside the lane A, i.e., whether the vehicle travels along a path traversing the width indicated by w_^ or, e.g., along a path traversing the width indicated by w2« In accordance with this measured information, the imaging unit 14 is triggered.

Fig. 4 illustrates a more detailed block diagram of part of the system shown in Fig. 3. Signals from the detectors 22 and 24, which are spaced apart by a predetermined distance and which are adapted to furnish a vehicle's presence identification and a vehicle's disappearance identification, are fed to circuits 30 and 32, respectively. Upon the identification of a passing vehicle's front edge, a signal, optionally an ultrasound signal, is transmitted by the transmitter 34. The echo returning from the vehicle is received by the receiver 36, amplified and applied to the range finder 38. The time period elapsing from the instance of transmission to the instance of reception is determined and in accordance with this determination of time, it is fed to one of a multiplicity of output terminals, e.g., 40a, 40b and 40c, each representing a precalculated range of periods of time. A signal produced by the circuit 32, identifying the vehicle's rear edge, effects the closing of one of the analog switches 42a, 42b and 42c. The signal fed to either of the terminals 40a, 40b or 40c is thus transferred either directly, or via a corresponding delay circuit 44a or 44b, to a gate 46 producing a triggering signal to the imaging unit 14 (Fig. 3) .

It should be understood that while it is not specifically shown, the system according to the present invention also includes many other devices, per-se known in the art and utilizable for the same and similar purposes. For example, the image acquisition unit includes in addition to the camera 14 itself, a flash or a strobe 50 (Fig. 3) , synchronized to function in concert with the camera's shutter, as well as, e.g., peripheral devices such as a display unit 52, printers (not shown) , character recognition and processor unit 54 and the like.

It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims (9)

107,931/2 - 10 - WHAT IS CLAIMED IS:

1. A system for image acquisition of an identifying indicia of a vehicle moving along an interrogation zone defined by substantially linearly extending length and a substantially constant width, said system comprising: an optical imaging unit having an effective field of view of a width smaller than the width of said interrogation zone; said unit being located alongside or above said interrogation zone and oriented so that the field of view traverses said zone at an angle with respect to the longitudinal axis of said zone; at least two detectors positioned in spaced-apart relationship to each other in proximity to and along said zone for detecting vehicles moving therealong, and circuit means for synchronizing said imaging unit with said detectors and for triggering the imaging unit in response to said detectors.

2. The system as claimed in claim 1, further comprising a transceiver located in proximity to, and for projecting a beam across said zone for determining the travelling path of said vehicle relative to the width of said zone.

3. The system as claimed in claim 2, further comprising circuit means for calculating the vehicle's speed of travel and for triggering said imaging unit with respect thereto. 107,931/2 - 11 -

4. The system as claimed in claim 1, further comprising image processing means for analyzing, recording and displaying identifying indicia acquired by said unit.

5. The system as claimed inclaim 1, further comprising a flash or strobe unit arranged to illuminate the indicia on a vehicle in synchronization with the operation of said unit.

6. A method for image acquisition of an identifying indicia of a vehicle moving along an interrogation zone defined by substantially linearly extending length and a substantially constant width, said method comprising: providing an optical imaging unit, at least two detectors positioned in spaced-apart relationship to each other in proximity to and along said zone for detecting vehicles moving therealong, and circuit means for synchronizing said imaging unit with said detectors and for triggering the imaging unit in response to said detectors; adjusting the width of the effective field of view of said imaging unit to a width smaller than the width of said interrogation zone; positioning said unit alongside or above said interrogation zone in an orientation so that the field of view traverses said zone at an angle with respect to the longitudinal axis of said zone, and causing the triggering of said unit upon the identifying indicia entering said imaging zone. 107,931/2 - 12 -

7. The method as claimed in claim 6 further comprising providing a transceiver located in proximity to, and for irradiating across, said zone for determining the travelling path of said vehicle relative to the width of said zone, and circuit means for calculating the vehicle's speed of travel, and triggering said imaging unit with respect to the vehicle's travelling path and speed.

8. A system for image acquisition of an identifying indicia of a vehicle moving along an interrogation zone according to claim 1, substantially as hereinbefore described and with reference to the accompanying drawings.

9. A method for image acquisition of an identifying indicia of a vehicle moving along an interrogation zone according to claim 6, substantially as hereinbefore described and with reference to the accompanying drawings. FOR THE APPLICANT WOLFF, BREGMAN AND GOLLER