EP1049064A2 - Traffic monitoring device with polarisation filters - Google Patents

Abstract

The device has an arrangement (20) for illuminating a target object (24) and an image acquisition arrangement (28) for stori traffic violation. There is an arrangement (22) for polarising the light illuminating the target object and an arrangement (30) polarising the light reflected from the object.

Description

Technical field

The invention relates to a traffic monitoring device for detecting Traffic violations, what means to illuminate a target object and Has image capturing means for storing the traffic violation. Furthermore concerns the invention a method for capturing target objects with a Traffic monitoring device, which means for illuminating the target object and Image acquisition means for storing the traffic violation of traffic violations having.

The basis of the state of the art

Traffic monitoring devices are used to detect traffic violations check. Such traffic violations are e.g. Exceeded speed or crossing intersections despite the red light. A sensor detects the respective traffic violation recorded. This sensor triggers the trigger with its signal a photo camera and then a flash. With the flash unit Illuminated area to be photographed. It is usually photographed either the front or rear side of the motor vehicle, since there the number plates are arranged. So far, it has been necessary for legal reasons, not only that License plate, but also to image the entire vehicle so that a Law enforcement can be instituted. The image captured by a camera becomes this either stored digitally in a digital image memory or as a photo on a film. In order to be able to identify the license plate later on the photograph, this has to be done License plate should still be clearly recognizable. A camera lens will therefore focused on the area where the license plate is at a trigger point should be located.

The license plate is coated with a highly reflective material around it to be able to recognize particularly well. So that the vehicle can also be recognized, a sufficiently strong flash should be installed, which illuminates the vehicle so that next to the License plate also the front or rear of the vehicle later in the picture is recognizable. Unfortunately this will make the recording necessary and relative high light intensity on the license plate due to the well reflective coating often no longer recognizable in the picture. The one reflected off the license plate Light is so intense that the signs are often no longer clearly defined are recognizable. Identification is often overexposed to the sign impossible. The vehicle is clearly identifiable, but the license plate is not.

Furthermore, not only is the light reflected by the coating absorbed, but also light from all other light sources. Street lights, illuminated windows or car lights etc. affect the quality of the images. The contrast and the Sharpness on the photo film is due to the "overexposure" and extraneous light sources blurred, so that the photos taken are sometimes unusable To be available. As a result, the number plates are not clearly recognizable are.

A scanner is often used for further image processing in order to scan the image with a Process data processing system. The scanner scans the image and stores it in digital form in the data processing system. On Font recognition program determines the characters of the from the digital image License plate, which is then used to track down the traffic offender can be.

With such traffic monitoring devices, it is disadvantageously noticeable that if overexposure and stray light prevent exact number plate recognition. This overexposure and the stray light have a negative effect on the image and Image editing. The number plates are in the pictures due to the Overexposure and the stray light not clearly recognizable. But if one License plate cannot be clearly identified, so tracking the Traffic offenders also do not take place for legal reasons.

From the German Offenlegungsschrift 2129 984 is a device and a Method for recording images by means of a traffic monitoring device known to suppress reflection of ambient light Polarization filter is arranged in front of the camera.

In the European patent DE 691 10 752 T2 a lighting and Display system for vehicles described in which a projector is an infrared Emits light bundle, which is polarized via a polarizer. That reflected Light is captured by a camera via a further polarizer, which captured the Feeds images to a processing and display arrangement. The driver of the vehicle This enables the areas captured by the camera to be viewed.

Disclosure of the invention

The object of the invention is to provide a traffic monitoring device in which the license plate is clearly and clearly visible on the picture with the camera, the problems of overexposure and stray light sources, as are known from the prior art Technology are known to be largely eliminated.

According to the invention the object is achieved in that a Traffic monitoring device of the type mentioned, means for polarizing of light that illuminates the target and means for polarizing that of the Has target object reflected light. The task continues through a process solved the type mentioned, in which the light to illuminate with a defined polarization plane is generated and only by the image capture device Light with this corresponding polarization plane is detected.

The invention is based on the surprising finding that through polarization overexposure of the image is avoided. Continue to be distracting Light influences from other light sources when registering license plates as far as possible Suppressed side effect. With polarization filters only light with a certain one arrives Direction of polarization through the filter. On this known physical phenomenon builds up the principle of the traffic monitoring device according to the invention. It will namely only processed polarized light with a predetermined polarization plane.

For this purpose, a light source first generates polarized light. You get polarized light e.g. by placing a polarization filter in front of a conventional light source. Conventional light sources produce light with arbitrary and different ones Polarization planes from which a preferred polarization filter Polarization plane is filtered out. In the present facility is suitable as conventional light source, in particular a flash device. Other known light sources such as LASER or other methods, for example via reflection with a "Brewster angles" for generating polarized light are for the invention Furnishings can also be used.

The light reflected from the target object now has the same polarization plane as that incident light. With an appropriately arranged polarization filter in front of one The camera only records the reflected light, which is the same Plane of polarization, like the incident polarized light. That way overexposure to the license plate area is prevented. It will continue achieved that essentially only the incident flash light and not light from sources of interference is recorded.

Further advantageous embodiments result from the subject of Subclaims.

An embodiment of the invention is described below with reference to FIG associated drawings explained in more detail.

Brief description of the drawings

Fig. 1

shows a sketch of an application of an inventive Traffic monitoring device.

Fig. 2

shows a traffic monitoring device according to the invention in three-dimensional representation.

Fig. 3

shows an example of how an overexposure with an inventive Traffic monitoring device is avoided.

Fig. 4

indicates how overexposure can affect an image.

Fig. 5

shows an example of an image in which an overexposure with a traffic monitoring device according to the invention was eliminated.

Preferred embodiment of the invention

1, 10 denotes a traffic monitoring device according to the invention, which is set up as an example at a suitable point of an intersection 12. At the A 12 traffic light 14 is also posted to regulate traffic. On Vehicle 16 has passed traffic light 14 in red. Contacts 18 are red the traffic light 14 is activated. The traffic monitoring device 10 triggers when activated State first a camera 28 and then a flash light with a flash lamp 20. In front the flash lamp 20 has a first polarization filter 22 mounted so that only light with one defined polarization direction the vehicle 16 with the license plate 24 of the Traffic offender reached. From the vehicle 16 is essentially only the flash light Flash lamp 20, i.e. polarized light, is reflected. This polarized flash will now via a second polarization filter 30, which is in front of an optic 26 of the camera 28 is filtered out. The polarization filters 22 and 30 are aligned so that they both only allow a certain plane of polarization of light to pass through. Through the Using polarized light to illuminate the vehicle 16 will Reduced light intensity.

As a side effect, all the disturbing ones in the area become Light sources largely suppressed by selecting a polarization direction.

A traffic monitoring device 10 shown in a three-dimensional view becomes shown in Fig. 2. The traffic monitoring device 10 is in a housing 32 arranged, which is mounted on a foot 34. The camera 28 is in the housing 32 provided, which is indicated by dashed lines. The camera 28 has one Film stage 36. From a film magazine 38, a film 40 is turned over the film stage 36 onto a Film roll 42 pulled. In front of the camera 28 is a lens 44 for focusing intended. Basically, such a camera 28 functions like conventional commercially available cameras, which is why a detailed description is omitted. That from The image captured by the camera is recorded as a photo on a film. But there are also Film, video and digital cameras for use in an invention Traffic monitoring device conceivable. With digital cameras, instead of one Photo film a digital image storage for use.

The lens 44 is screwed into a first opening 46 of the housing 32. Before the The objective 44 is the second polarization filter 30. The is in a second opening Flash lamp 20 mounted. The first polarization filter 22 is in front of the flash lamp 20 arranged. Both polarization filters 22 and 30 are with respect to their polarization planes aligned equally.

In Fig. 3 is shown in the form of a schematic diagram as an example, how an irradiation for the recording with the traffic monitoring device 10 is prevented. That through the polarization filter 22 polarized flash light of the flash lamp 20 strikes the rear or Front of the vehicle 16. Both the vehicle 16 and the License plate 24 illuminated. Dashed lines 50, 52 represent the Illumination of the vehicle 16 with polarized light. Line 54 represents accordingly Illumination of the license plate. Lines 56, 58 and 60 represent the analog light rays reflected from vehicle 16 and license plate 24. The reflected Light rays 56, 58 and 60 fall among other things in optics 26 the Traffic monitoring device 10, in front of which the polarization filter 30 is arranged. From there they arrive at the film 36 of the camera 28 which is in the housing 32 of the Traffic monitoring device is arranged.

The result is that, surprisingly, the overexposure of the recorded Image or film is avoided. The sharpness or the contrast becomes significant with the Image capture improved.

Fig. 4 shows a schematic diagram of a license plate of a vehicle as it is is available for evaluation if the image is taken out overexposed. The real contours of the signs of the license plate are as continuous lines drawn. The contrast of the characters becomes blurred due to the overexposure. The transition of the characters to the background finally proceeds in such a way that even the The characters merge, which means that the number plate characters no longer are clearly recognizable.

Fig. 5 shows a schematic diagram of a license plate of a vehicle as it is is available if due to an arrangement of polarization filters 22, 30 Overexposure of the image is avoided or suppressed. The contours of each Signs can be seen more clearly. The evaluation also by electronic Image processing for further processing can be done from such license plates make it much easier.

Claims (6)

Traffic monitoring device (10) for detecting traffic violations, which has means (20) for illuminating a target object (24) and image capturing means (28) for storing the traffic violation, characterized by means (22) for polarizing the light which illuminates the target object (24) , and by means (30) for polarizing the light reflected from the target. Traffic monitoring device (10) according to claim 1, characterized in that the means for polarizing the light are designed as reflecting and polarizing surfaces . Traffic monitoring device (10) according to Claim 1, characterized in that the means for polarizing the light are designed as optical polarization filters (22, 30). Traffic monitoring device (10) according to one of the preceding claims, characterized in that the means for illuminating a target object (24) are formed by a flash device (20). Traffic monitoring device (10) according to one of Claims 1 to 4, characterized in that the image acquisition means are formed by a photographic or digital camera (28) for recording the traffic violation. Method for detecting traffic violations of target objects (24) with a traffic monitoring device (10), which has means (20) for illuminating the target object (24) and image capturing means (28) for storing the traffic violation, characterized in that the light for illuminating with a defined polarization plane is generated and only light with this corresponding polarization plane is detected by the image capture device (28).

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