The present invention relates to an image recording system.
An image recording system may be used, for example, in motor vehicles to obtain images of the vehicle surroundings and, in conjunction with assistance systems, to facilitate the driver in guiding the vehicle. In particular, such an image recording system also picks up vehicles which are moving in the same traffic lane or adjacent traffic lanes in front of the host vehicle. An image recording system of this type includes at least one image sensor and an optical system that is assigned to this image sensor and images a photo field of the vehicle surroundings onto the image sensor. A task of such assistance systems is the precise measurement of distance, since optical traffic-lane monitoring systems and vehicle-to-vehicle distance monitoring systems function only with sufficient reliability if precise distance values are known. Furthermore, such image recording systems are being used increasingly for a function called “Night Vision”, in which the scene illuminated by infrared high-beam headlamps is recorded via a camera also sensitive in the infrared range, and represented on a display for the driver in order to permit a greater visual range. The image sensors used in such image recording systems are usually CCD or CMOS cameras. Since these cameras do not expose continuously, thus during the complete frame phase, but only in certain time intervals (e.g., shutter time in the case of CCD cameras), there is the risk that pulsed light sources picked up by the image recording system will be distortedly represented. In this connection, distortedly represented means that the light sources are picked up and reproduced with too low an intensity, with too high an intensity or, in the worst case, are not picked up and reproduced by the image recording system at all. For example, the pulsed light sources may be brake lights or taillights of preceding vehicles implemented using LED technology, or oncoming vehicles having pulsed LED front lighting. The distorted representation comes about because the ON phases of the pulsed light sources do not coincide with the exposure phases of the camera. However, the faulty sensing and representation of the pulsed light sources can give rise to dangerous situations. One risk comes about, for example, because the driver of the host vehicle, upon glancing at his/her night vision display, no longer recognizes that the preceding vehicle is braking. At this point, there is a threat of a rear-end collision. When driving at night, preceding or oncoming vehicles cannot be recognized as well on the display, since the pulsed light sources are no longer clearly represented.
German Patent No. DE 100 33 103 A1 describes an infrared imaging system that has at least one IR light source and at least one IR display device for representing a relief able to be illuminated by the IR light source, an IR detector for recognizing an external IR pulse additionally being provided. This patent starts from the assumption that the indicated imaging systems are used in motor vehicles, and encountering motor vehicles are also equipped with them. The additionally provided IR detector detects interfering IR light pulses from another vehicle which could blind the imaging system of the host vehicle. Furthermore, the IR detector controls the inherent pulse frequency in such a way that it is adjusted to the external pulse frequency. For example, the adjustment is made in such a way that in the absence of an external IR lamp, the relief is illuminated the entire time, and if one or more external lamps are present, the radiating time of the IR system in the host vehicle is set so that a maximum illumination time remains.
U.S. Patent Application No. 2003/0043280 A1 also describes an image recording system having an infrared camera and an infrared lamp which illuminates the coverage range of the infrared camera. In addition, the image recording system includes a sensor which, upon detection of an external pulsed light source in the coverage range of the image recording system, controls the infrared camera in such a way that, to the greatest extent possible, the external pulsed light source is not picked up by the camera.
The present invention may permit substantially improved sensing of pulsed light sources, to thus improve the recognition of pulsed light sources and thereby to increase traffic safety. To this end, the image recording system may advantageously include a radiation sensor having generally identical intensity dynamics, having a generally identical opening angle and a generally identical direction of view as the camera, for sensing pulsed light sources. The image recording system also includes a control device which ascertains the discrepancy based on the signals from the camera and the radiation sensor. In one example embodiment, as a function of the discrepancy determined, a warning signal is generated which indicates deficiencies in the display representation to the driver. Additionally, the display may be controlled to the dark state temporarily, or perhaps switched off. In more complex embodiment variants, the exposure phase of the camera is synchronized with the ON phase of the light source as a function of the discrepancy. In another example embodiment variant, the image recording system is operated in a linear mode on one hand, and in a non-linear mode on the other hand. Recorded images are compared. In response to the appearance of pulsed light sources, at least partial areas of the images acquired in the non-linear mode are replaced by corresponding partial areas of the images acquired in the linear mode.
Below, the present invention is explained in greater detail based on the example embodiments shown in the figures.
In the following, exemplary embodiments of the present invention are described. A first exemplary embodiment is explained with reference to
Radiation detector 3 quasi continuously ascertains an average brightness level of entire image scene 6 which is picked up by image recording system 1. From the histogram of the camera image, which is formed for an exposure control, an average brightness is likewise formed by calculating back with the aid of the known exposure parameters for this histogram. If these two brightness levels deviate significantly from each other, it may be deduced that pulsed light sources 7 are in the coverage range of image recording system 1 which are not completely picked up by camera 2, since its exposure phase at least partially coincides with the dark phases of pulsed light sources 7. This situation is denoted hereinafter as discrepancy. In one example embodiment variant of the present invention, in response to the existence of such a discrepancy, a warning is output on display 5 of image recording system 1.
For example, this warning may prompt the driver to pay particularly close attention to the road, and to at least temporarily disregard the representation on display 5. In an alternative embodiment variant, possibly in conjunction with such a warning, display 5 may be switched off at least temporarily since it no longer correctly represents the surroundings of the vehicle, particularly pulsed light sources 7 present there.
If image recording system 1 includes a camera 2 capable of a restart, in a further exemplary embodiment of the present invention, it may be attempted to shift the exposure phase of camera 2 in such a way that the exposure phase of camera 2 and the ON phase of pulsed light source 7 are synchronized in correct phase relation. This is clarified with reference to
This relationship is explained again in the following with reference to
In another example embodiment variant of the present invention, a camera 2 is provided which is not capable of any restart. Cameras of this kind are relatively widespread. In this embodiment variant, the exposure time of camera 2 is altered in such a way that the ON phases of pulsed light source 7 are completely detected. To that end, first of all there is a switch to maximum exposure time, which corresponds to the frame duration. Additionally, camera 2 is switched over from a non-linear to a linear photographic mode. This means that no unexposed phases come about due to a non-linear knee characteristic curve. At the same time, the amplification is reduced in order to keep an overexposure in bright areas of the coverage range of camera 2 as little as possible. These measures ensure that pulsed light sources 7 are completely detected. The image thus obtained is calculated back to absolute brightness and compared with the previously recorded, likewise calculated back but not completely exposed image. Significant differences between the two images are apparent at the places at which there are pulsed light sources. These places are then replaced in the original image by the intensities ascertained in a linear photographic mode, which means pulsed light sources are now also picked up and become visible in their actual intensity.
This relationship is explained again in the following with reference to
In the event the host vehicle is equipped with pulsed front headlights (e.g., with LED or laser headlights) which are synchronized with the exposure phases of the camera, then the illumination phases of the front headlights in the host vehicle are also shifted, analogous to the exposure phases of the camera.
Number | Date | Country | Kind |
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102005033863.1 | Jul 2005 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP2006/062806 | 6/1/2006 | WO | 00 | 9/30/2009 |