Obstacle display device, especially for automotive vehicle.

The present invention relates to an obstacle display device and, more particularly, to such a device designed for displaying a present obstacle on the trajectory of a motor vehicle, this obstacle reflecting or emitting a radiation of a predetermined spectral range .

To view obstacles in the field to open the path of a motor vehicle, particularly when visibility is poor, it was proposed to install in the vehicle one or more video cameras equipped with CCD sensors or targets to load and coupling filters adequate to capture images of this field, and to electronically process images captured by (the) camera (s) to bring out certain characteristics of these images corresponding to obstacles such as vehicles present in the field. Complex algorithms applied to optical characteristics of the different pixels of the image are then required to extract the image contour of the floor for example and those vehicles traveling on that road. Such calculations require to be executed in real time, memories of large capacities and high computing power, allowing the execution of hundreds of millions of instructions per second, for example. Such processing means are a cost too high to qualify in a motor vehicle, from the perspective of economics.

The present invention therefore aims to provide a device for displaying obstacles either a cost as its incorporation in a motor vehicle is possible.

This object of the invention, as well as others which will emerge in the remainder of the present description, with an onboard device for displaying a present obstacle on the trajectory of a motor vehicle, this obstacle reflecting or emitting a radiation of a predetermined spectral domain, the device comprising a) a first means sensitive to radiation of a spectral domain covering the area predetermined and wider than this, to capture an image video of the field open to the growth in vehicle its trajectory, b) a second means of entry of another image of this field, sensitive to radiation of a spectral domain completing the predetermined area to cover substantially all the area of ​​sensitivity of the first medium, and c) means electronic treatment by difference of the two video images thus obtained to form a third image of the video field open to the vehicle, containing only an image contrast record of the obstacle.

The electronic means used to deal with difference, pixel by pixel, the two video images, are much smaller than those required for contour extraction and / or pattern recognition, operations that implement algorithms for processing complex as is known to the specialist. According to the invention, it is possible to visualize a barrier with electronic processing of reasonable cost, embeddable in a motor vehicle.

In one implementation of the invention, usable when the predetermined spectral domain in which radiates the obstacle is that infrared radiation, the area spectral sensitivity of the first means of entry covers the area visible and infrared field, the spectral domain of the second input sensitivity means covering the only visible area.

According to one embodiment of the invention, the first means of entry consists of a video camera with CCD sensor, possibly equipped with an infrared filter. The second gripping means is constituted by a CCD video camera equipped with a filter transmitting radiation alone visible range.

According to a second embodiment of the invention, the first and second video image capturing means comprises first and second lens units forming part of a CCD video camera sensor and equipped with optical deflector means for successively projecting on this sensor images of the same field, formed by the first and second objectives.

According to a third embodiment of the invention, the first and deuxièmme video capture means comprises a single lens forming part of a CCD video camera equipped with filter means arranged to ensure that two image frames successive video captured by the camera correspond to the filtered images in the visible range and in the infrared range, respectively.

In all embodiments, the electronic means of processing images captured video provide subtracting video signals pixel by pixel in frames of such signals corresponding to two images of the same field, consisting of two areas spectral radiation exhibiting at least one non-common portion to form a frame of video signals containing the image of the obstacle only. These electronic processing means may further comprise means for modifying histograms of captured video images prior to the subtraction pixel by pixel image representative of these video signals, to increase the contrast of the final image obtained.

The device of the invention is designed in particular to see a barrier consisting of a motor vehicle in the open field to the progress of the vehicle in which the device is shipped. The device then further comprises a source of infrared radiation illuminating the field, the obstacle of the vehicle should be in the field being viewed by the reflectors images of this radiation placed on the vehicle forming an obstacle.

Other features and advantages of the device according to the invention appear on reading the following description and on examining the accompanying drawing in which:<ul><li>Figure 1 is a diagram of a first embodiment of the display device according to the invention,</li><li>2 schematically represents an embeddable video camera to the device of Figure 1,</li><li>3 shows the graphs of the spectral transmittances of filters and the graph of the spectral sensitivity of CCD video cameras fitted to sensors used in the device according to the invention,</li><li>Figure 4 is a diagram of a variant of a video device with two cameras according to the invention,</li><li>Figure 5 is a diagram of a second embodiment of the device according to the invention, and</li><li>Figure 6 is a diagram of a third embodiment of the device according to the invention.</li></ul>

Referring to Figure 1 of the attached drawing where it appears that the device according to the invention, in this first embodiment, includes first and second gripping means of images formed by the video cameras 1 and 2 respectively. Preferably these cameras are the type that include CCD (charge coupled device). These sensors being constituted by components "solid state", the camera comprising such sensors are less fragile than conventional video cameras Vidicon tube, for example. The video cameras CCD sensors and are best suited to be embedded in a vehicle that is expected to undergo shocks depending on road conditions.

In Figure 3, there is shown at 28 the graph of the spectral sensitivity curve of a typical CCD camera. It appears from this figure that this spectral sensitivity extending over a wide range which covers both the visible (between 400 and 700 nanometers) and infrared (between 700 and 1200 nanometers). In the same figure 3, there is shown at 29 the graph of the spectral transmittance of an optical bandpass filter covering the visible range between 400 and 700 nanometers.

According to the present invention, the camera team 2 of the device according to the invention of such a filter 5 covering objective 4 of this camera with the lens 3 of the other camera is equipped with any filter. Of course the filter 5 may also be located behind the lens 4. The two goals 3 and 4 have the same characteristics optics.

The two cameras 1 and 2 are synchronized via a synchronization wire 6. The video signals from the cameras 1 and 2 are directed to image memories 7, 8 respectively, are optionally provided with conversion tables of grayscale LUT 1 and LUT 2 (English look-up table). These conversion tables are used to modify the histogram of each image, for a purpose which will be explained further. The thus treated two captured images are then stored in the frame memories 9 and 10. A CPU 11 coordinates the operation of memories 7, 8, 9, 10 and controls the subtraction pixel by pixel of the video frames contained in the memories 9 and 10, signals representative of frames of "difference" thus being available on a line 12 for a viewing these frames on a display device (not shown).

Now we explain the operation of the device of Figure 1 in conjunction with the examination of the graphs shown in Figure 3. In this figure, it is clear that the camera 2, provided with the band-pass filter 5 transmitting only the radiation visible area, not "see" objects whose reflectance or albedo is the upper range of the band spectral camera video 1 range that corresponds substantially to the field infrared between 700 and 1200 nanometers, these objects being well understood received by the first camera 1 that is not equipped with the filter. The objectives of the two cameras being oriented to cover the same field, as shown in Figure 1, it is understood that the subtraction in real time the images delivered by the two cameras provides an image resulting comprising only objects radiating or reflecting in the beach not covered by the filter 5, be in the infrared range.

Treatments per share images on their histograms are well known. These may be used (in 7 and 8) to decrease the contrast of the image captured through the filter 5 which transmits the radiation from the visible range. Similarly modifying the histogram of the image captured by the camera 1 without filter, can enhance contrast parts of the image that correspond to objects reflecting or infrared emitting. These measures enhance the contrast of the image obtained by difference of the images captured by the cameras 1 and 2.

So we can according to the invention, visualize and identify motor vehicles present in the field of the cameras 1 and 2. In fact, these vehicles have, at the rear, the lights of "stop" and, in front of projectors, all equipped with reflectors. An infrared radiation source is then mounted to the front of the vehicle equipped with the device according to the invention to project a beam of infrared radiation in the field open to the vehicle's trajectory, field monitored by cameras 1 and 2. If a vehicle progresses in this field, in the same direction as the vehicle equipped with the device according to the invention, the reflectors associated with these brake lights to reflect the cameras 1 and 2 part of the infrared radiation emitted by the source mounted at the before the vehicle equipped with such cameras. The image formed by the camera 1, unequipped filter, thus comprise portions of images corresponding to these reflectors brake lights. If a vehicle progresses in the field of the cameras in the opposite direction to that of the vehicle equipped with the device according to the invention are the reflectors of headlamps placed in front of the first vehicle that return an infrared radiation to the cameras 1 and 2. in both cases, the image obtained by subtraction of the images produced by these cameras contains the reflectors of the vehicle forming an obstacle in the field.

Such visualization of these reflectors s'avère particularly useful in driving at night, when visibility is poor.

Moreover, one can exploit the fact that automobiles are equipped with pairs of lights or projectors arranged horizontally in a fixed position relative to the other for additional information visualization obtained from these fires. Indeed, the variation of the distance images associated reflectors on the filtered and differentiated image obtained using the device according to the invention can detect if an obstacle is approaching (the distance images increases ) or away (the distance images decreases) and to measure the speed of the obstacle. Such information can be extracted by means of electronic image processing and additional communicated to the driver of the vehicle which can evaluate at any time the vicinity of the obstacle. The association of such treatment a detection form of the images of reflectors, used to distinguish the cars traveling in the opposite direction of cars which circulate in the same direction as the vehicle equipped with the device according to the invention, that the reflectors associated with the brake lights and headlights are a different shape.

Note that the use of a source of infrared radiation invisible to the naked eye, in front of the vehicle equipped with the device according to the invention, is not likely to interfere with other drivers.

Can further improve the image of the reflectors of a vehicle forming an obstacle in the image obtained by subtraction, by placing an infrared filter 13 on the optical axis of the camera 1, as shown in Figure 2 where the filter 13 is placed between the objective 3 and a CCD sensor 14. such a filter having a spectral transmittance conforms to the graph 30 of Figure 3, improves the elimination of objects reflecting or emitting in the visible, in the image final obtained.

A variant of the device of Figure 1 is shown in Figure 4. This embodiment comprises two optical paths formed by objective 1 ', 2', filters 15, 25, targets or CCD sensors 31, 32, and preamplifiers 33 34, respectively, in series in that order. The filter 15 passes in the visible range (400-700 nanometers) and the filter 25 transmits in the infrared range (700-1200 nm).

The device comprises a processing unit and input 36 common to both paths. Switching at a frequency of 50 Hz, for example, between each of these channels and this unit 36 ​​is provided by a control logic unit 35. Thus, a frame image in two is entered in the infrared spectrum, the other frame is input in the visible spectrum. The video output 37 of the unit 36 ​​is connected to a unit of image processing that performs a pretreatment on the gray levels and the differentiation according to the invention between two successive image frames.

There is shown in Figure 5 a second embodiment of the device according to the invention. This device takes the form of a video camera provided with two objectives ˝ 1, 2 ˝ and one CCD sensor 44. Filters 45 and 46 with transmission in the visible range and in the infrared field, respectively, are placed behind the 1˝ and 2˝ objectives respectively, on the optical axis thereof. Means optical deflectors 38, 39, 41 provide switching between each of the channels and the optical sensor 44. These optical means conprennent mirrors 38 and 39 defining between them an optical path 40, at 90 ° to the optical axis of the target 13 ', and a prism 41 mounted for rotation about an axis 43 perpendicular to the plane of the sensor 44. in a first position, the prism reflects light received from the mirror 39, from objective 1 ˝, to switch 44 and to a second position spaced from the first 180 °, the prism 41 illuminates the sensor 44 with the light from the objective 2˝ via the optical axes 42 and 43. the oscillating rotation of the prism to return 41 is synchronized with the signal "frame sync" on frequency of 50 Hz for example emitted by an electronic control associated with the CCD sensor 44. the motor means (not shown) ensure that oscillating in synchrony rotation with these signals . In this configuration, the device of the invention comprises a single electronic processing of the video signals detected by the sensor 44.

in Figure 6 there is shown a third embodiment of the display device according to the invention. This takes the form of a video camera to a single objective 47, this camera being modified to comprise a disc filter holder 48 placed in front of a CCD sensor 44 '. The disc filter holder may comprise two half circular sectors 49 and 51 respectively constituting a filter transmitting visible in the field and a filter transmitting infrared. A motor 52 drives the disc 48 in rotation via a toothed rim. The motor 52 is controlled to rotate the disc at a speed of 50 revolutions per second in synchronism with the signal "Frame Sync" emitted by control electronics associated with the sensor 44 '. Thus, during two successive frames of the video signal, two filters 49, 51 are sequentially interposed on the optical axis 53 of the objective 47 so as to filter successively in the visible and in the infrared, the light received by the sensor 44 '. And an image frame in two is formed in the infrared spectrum, the other field is formed in the visible spectrum. The processing of the image frames obtained is identical to that carried out when the two frames of images are captured by different cameras.

The various embodiments of the invention described above are likely to provide a visualization of obstacles reflecting or radiating in the infrared, allowing to happen treatments image costly, contour extraction or recognition form, of the prior art. They work perfectly in real time with electronic image processing power with a reasonable calculation.

Naturally, the invention is not limited to the described and illustrated embodiments that have been given by way of example. In particular, the choice of contiguous ranges of the spectral sensitivity band of the CCD sensor used could be modified to be suitable for radiating or reflecting obstacles in other spectral ranges. It could, in other applications, for example, use filters to bring out not only objects whose albedo corresponds to a range of the spectral band of the CCD sensor other than the infrared range, such as the beach below domain of wavelengths to which the CCD is sensitive (300 to 500 nanometers for example).

In addition, the presence of infrared radiation of the headlamp on a vehicle equipped with the device according to the invention is not necessary if the vehicles to identify as barriers themselves are equipped with infrared radiation rather than reflectors of this radiation.