Abstract:
A system mounted on a vehicle for performing vehicle control applications and driver warning applications, the system including a camera configured to acquire a plurality of images of the environment in front of the camera. The camera includes a filter wherein the filter is installed at the focal plane of the camera and wherein designated portions of the filter transmit selective light wavelength. The preferred filter has a checkerboard pattern. The system further including an image processor capable of analyzing in real time a plurality of respective image sequences acquired from at least one of the portions of the filter and is capable of detecting yellow lane markings on a concrete road surface.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit under 35 USC 119(e) from U.S. provisional application 60/836,670 filed Aug. 10, 2006, the disclosure of which is included herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to driving assistant systems (DAS) in vehicles such as vehicle lane departure warning (LDW) systems and automatic headlight control (AHC) systems, and more specifically to the combination of multiple DAS systems being run in parallel including a camera with a filter with symmetric patterns, such as a checkerboard filter.  
       BACKGROUND OF THE INVENTION AND PRIOR ART  
       [0003]     As cameras become smaller and technology becomes more advanced, more processing can be done to assist a driver of a vehicle. There are various driving assistant systems (DAS) which are known in the industry including, lane departure warning (LDW), to notify a driver when a lane divider is accidentally crossed; lane change assist (LCA) to monitor vehicles on the side of the vehicle and notify the driver when the path is clear to change lanes; Forward collision warning (FCW), to indicate when a pending rear end collision might occur; and automatic headlight control (AHC), to lower the drivers high beams when an oncoming vehicle is detected. A DAS can be either a passive system, informing the driver about a detected item or event of interest, or an active system, whereas the system intervenes in the driving, for example activating the brakes. The terms “DAS system”, DAS application” and “control system” are used herein interchangeably.  
         [0004]     Some of the DAS applications maybe run in daytime or nighttime mode (LDW), whereas other applications are limited for nighttime applications (AHC). The camera requires different settings for daylight then it does for nightlight operation. Changing the camera settings between applications is not efficient—and both applications would suffer lose of imaging frames. To install multiple cameras in a vehicle is a costly and weighty solution.  
         [0005]     Therefore there is a need to be able to simultaneously run multiple driving assistant systems which require different camera settings.  
         [0006]     The system of the present invention performs in parallel a number of DAS applications. The system detects and classifies objects in real time, e.g. vehicles, pedestrians, oncoming vehicle headlights, leading vehicle taillights and streetlights, in a series of images obtained from a camera mounted on a vehicle. The images are used in parallel by a number of DAS applications including lane departure detection, forward collision control and headlight control systems. The classification of objects is preferably used by more than one of the vehicle DAS applications. In a headlight control system, the classification of objects is used to provide a signal for switching the headlights between high beams and low beams.  
         [0007]     Reference is now made to  FIGS. 1 and 1   a  (prior art) which illustrate a vehicle control system  100  including a camera or image sensor  110  mounted in a vehicle  50  imaging a field of view in the forward direction, having an optical axis  114 . Image sensor  110  typically delivers images in real time and the images are captured in a time series of image frames  120 . An image processor  130  is used to process image frames  120  to perform a number of prior art vehicle DAS applications. Vehicle  50  is, for example, following a lead vehicle  10 .  
         [0008]     The terms “object” and “obstacle” are used herein interchangeably.  
         [0009]     The terms “camera” and “image sensor” are used herein interchangeably.  
         [0010]     Exemplary prior art vehicle control sub-systems are: 
        Block  132 —a collision warning sub-system. A Collision Warning system is disclosed in U.S. Pat. No. 7,113,867 given to Stein, and included herein by reference for all purposes as if entirely set forth herein. Time to collision is determined based on information from multiple images  120  captured in real time using camera  110  mounted inside vehicle  50 .     Block  134 —a lane departure warning (LDW) sub-system. Camera based LDW systems perform tasks including detecting the road and lanes structure, as well as the lanes vanishing point. Such a system is described in U.S. Pat. No. 7,151,996 (&#39;996) given to Stein et al, the disclosure of which is incorporated herein by reference for all purposes as if entirely set forth herein. If a moving vehicle has inadvertently moved out of its lane of travel based on image information from images  120  from forward looking camera  110 , then system  100  signals the driver accordingly. Road geometry and triangulation computation of the road structure are described in patent &#39;996. The use of road geometry works well for some applications, such as forward collision warning (FCW) systems based on scale change computations, and other applications such as headway monitoring, adaptive cruise control (ACC) which require knowing the actual distance to the vehicle ahead, and lane change assist (LCA), where a camera is attached to or integrated into the side mirror, facing backwards.     Block  138 —an automatic vehicle headlight control sub-system. Automatic vehicle headlight control for automatically controlling the status of the vehicle&#39;s headlights. Automatic vehicle headlight control increases the safety as well as reduces the hazard caused by the occasional failure of the driver to deactivate the high beams which distract the other driver. U.S. application Ser. No. 11/689,523 (&#39;523) filed on May 22, 2007, the disclosure of which is incorporated herein by reference for all purposes as if entirely set forth herein, describes a system and methods for detecting on coming vehicles, preceding vehicles and street lights, and providing a signal to the headlight control unit of the car to switch from high beams to low beams or vise versa. Application &#39;523 includes using a red/clear checkerboard filter yielding a red image stream and a clear image stream for detecting the taillights and headlights of other vehicles.        
 
         [0014]     Vehicle control systems, such as disclosed in U.S. application Ser. No. &#39;523 which rely on changing exposure parameters (i.e., aperture, exposure, magnification, etc) of camera  110  in order to get optimal results for one application, e.g. detecting oncoming vehicles headlights, have a difficult time maintaining other control systems which rely on the same camera  110 , e.g. lane departure warning, forward collision warning, etc. As a result of changing exposure parameters half or more of the (possibly critical) frames may not be available for the other control systems. This greatly affects performance of the other control systems.  
         [0015]     It is advantageous to be able to use the same image sensor that is used for other applications such as LDW, FCW and headway monitoring. Bundling up multiple applications into the same hardware reduces cost but more importantly the space the hardware occupies is reduced. Since at least the camera unit of the systems is typically mounted on the windshield near the rear-view mirror, the camera unit must be small so as not to block the driver&#39;s view of the road.  
         [0016]     The lane detection algorithm (LDA), which is the core of the LDW system, can be performed on grayscale images in most cases. Black and white (B&amp;W) cameras have the advantage of being more sensitive than color cameras and thus work better on unlit roads on dark nights. But B&amp;W cameras also suffer from some deficiencies, including:  
         [0017]     1. The brightness of a lane marking in the image is sometimes the same as the brightness of the road surface even though the hue (or color) is different. As a result the lane marking is very clear to the driver but invisible in the camera image. For example, yellow markings on a concrete road often appear in a B&amp;W image with the same intensity, thus the lane marking is not distinguishable in the image and thus, cannot be distinguished from the road surface.  
         [0018]     2. In order for the camera to perform well on unlit roads on dark nights, but on bright sunny days, the images acquired are often saturated and the camera must be set with a very low exposure (typically 25-100 μSec, at pixel readout rate of 25 MHz). A camera “quantization problem” is aroused by the fact that an exposure time can be set only by “chunks” defined by an image line length (in pixels) and the time required to acquire a single pixel. This quantization makes it difficult to control the set an optimal exposure: if an image line is read in 25 μSec, image lines are read in 25 μSec chunks. Thus, 25 μSec might be too short but 50 μSec might be too long, but cannot specify a 37 μSec exposure time, for example, which is not a multiple of a chunk of 25 μSec. In some cases even an exposure of 25 μSec in duration is too long and the intensity image of the road surface becomes saturated.  
         [0019]     A color camera can be used to detect the color of various patches of the road and thus determine the lane markings in the color image. However conversion of the image to color space, and the handling the color image, requires significantly more memory and computation power which are always at a premium in embedded applications.  
         [0020]     It would also be possible to solve the problem of detecting yellow lines on concrete by adding a colored filter in front of the camera. For example, a yellow filter will cut out the blue light reflected off the road surface and thus darken the road surface relative to the yellow lane marks. But adding a colored filter in front of the camera reduces the brightness of the image (by about 30%), which might enhance the problem of the camera performance on unlit roads on dark nights. A red filter could also be used with similar deficiencies.  
         [0021]     Thus there is a need for and it would be advantageous to have a system performing multiple DAS applications such as LDW, Forward Collision Warning (FCW), headway monitoring and vehicle headlights control, using the same B&amp;W camera and capable of detecting yellow lanes on a concrete road and resolve saturation in images on bright days.  
         [0022]     The red/clear filter and the combination of obtained respective red image stream and the clear image stream can be used as input to two completely different DAS applications at the same time. Using the two image streams of the red/clear filter, multiple applications may be run on a color camera or a black and white camera.  
       SUMMARY OF THE INVENTION  
       [0023]     The term “respective images” is used herein to refer to two or more images acquired concurrently by a camera. In a camera using a filter installed at a focal plane of the camera, for example a checkerboard filter, the dark squares of the checkerboard preferentially transmit a pre selected color light, such as red light, and the other squares are, for example, comparatively clear and transmit white light. One image is formed from the colored/red light transmitted by the dark squares of the checkerboard and a respective image is formed concurrently from the white light transmitted by the light/white squares of the checkerboard filter. The term “colored/red image portion” is used herein to refer to images obtained from the portion of the single image transmitted by the clear portion of a filter. The term “clear image portion” is used herein to refer to images obtained from the portion of the single image transmitted by the colored/red portion of a filter.  
         [0024]     The term “symmetric images” is used herein to refer to two or more respective images having the generally same number of pixels (typically, ± one pixel) arranged in generally the same number of columns and rows and having substantially the same pixel size (typically, ± one column/row).  
         [0025]     The term “primary image” is used herein to refer to images obtained from the filter which is selected to perform the vehicle control and/or driver warning applications.  
         [0026]     The term “secondary image” is used herein to refer to images obtained from filters which are not currently selected to perform the vehicle control and/or driver warning applications and serve to support the respective symmetric primary image.  
         [0027]     It is the intention of the present invention to provide a system and method of use, the system mounted on a vehicle for performing vehicle control applications and driver warning applications including a camera typically mounted inside the vehicle, the camera configured to acquire a plurality of images of the environment in front of the camera, the camera further includes a filter wherein the filter is installed at the focal plane of the camera and wherein designated portions of the filter transmit selective light wavelength. The system further including an image processor capable of analyzing in real time a plurality of respective image sequences acquired from at least one of the portions of the filter.  
         [0028]     Preferably, the filter has a checkerboard pattern having two colors, thereby two images are acquired—one from each light color transmitted by each of the color squares of the checkerboard filter. Two respective images, acquired from each portion of the filter are substantially symmetric images, having substantially the same resolution and being distributed substantially symmetrically over the plane of the filter. The two colors of the checkerboard filter are preferably red and clear, whereas the red portion transmits red light and the clear portion transmits substantially all wave length of light (white light).  
         [0029]     It should be noted that the average intensity of a red image is lower by 35-50% of the average intensity a respective clear image, and thereby if a pixel in said clear image is saturated, the corresponding pixel in the respective red image is not saturated. Hence, in the day time with very bright days, red images are used as the primary images to prevent the saturation of images as typically occur in clear images.  
         [0030]     In embodiments of the present invention, the filter is a “stripe” filter wherein the colors of the stripes alternate cyclically. The structure of the filter is not limited to a checkerboard pattern or stripe pattern, and other shapes or geometric lattices may be similarly be used.  
         [0031]     In methods of using the system of the present invention, automatically select which stream of color (red/clear) images is used, depending on existing environment conditions such as day/night.  
         [0032]     In embodiments of the present invention the system uses both respective symmetrical images acquired from each of the portions of the filter, to detect objects in said images and an object is detected in both images or in the primary image only, the primary image stream is used by the system to further process the detected object.  
         [0033]     In embodiments of the present invention the system uses both respective symmetrical images acquired from each of the portions of the filter, to detect objects in said images and an object is detected in secondary images only, the secondary image stream is used by the system to further process the detected object. The detected object can be a yellow lane marked on a concrete road surface.  
         [0034]     In embodiments of the present invention the system uses concurrently performs two DAS different applications. For example: during night operation, the clear image stream is used as the primary image stream for an LDA application and the red image stream is used as the primary image stream an AHC application. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0035]     The present invention will become fully understood from the detailed description given herein below and the accompanying drawings, which are given by way of illustration and example only and thus not limitative of the present invention, and wherein:  
         [0036]      FIG. 1  is a prior art drawing of a conventional vehicle with a mounted camera for vehicle control systems;  
         [0037]      FIG. 1   a  is a drawing illustrating multiple prior art vehicle control outputs using a single hardware camera and hardware;  
         [0038]      FIG. 2  is a drawing according to an embodiment of the present invention of a vehicle control system using the same camera and hardware as in  FIG. 1   a;    
         [0039]      FIG. 2   a  is a drawing of a red/clear filter used in accordance with an embodiment of the present invention;  
         [0040]      FIG. 3  illustrates another filter, in accordance with embodiments of the present invention;  
         [0041]      FIG. 4  illustrates yet another filter, in accordance with embodiments of the present invention;  
         [0042]      FIG. 5  is a drawing according to an embodiment of the present invention of a vehicle control and/or warning system using the same camera and hardware as in  FIG. 1   a;  and  
         [0043]      FIG. 6  illustrates a monitor output of a lane departure warning system and a vehicle headlight control system, according to embodiments of the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0044]     The present invention is an improved system mounted on a vehicle for performing LDW and AHC applications and possibly for performing other vehicle control and driver warning applications. The system includes a camera mounted inside the cabin and configured to acquire images of the road in front of the camera. In a dark environment, upon detecting a leading vehicle or oncoming vehicles the system switches the headlights to low beam, otherwise the system switches the headlights to high beam. The camera of the present invention includes a filter preferably with a checkerboard pattern, the checkerboard pattern being a red and clear filter combination. The checkerboard filter yields a pair of symmetric respective images: a clear image and a red image, whereas both images have substantially identical resolutions. The system of the present invention can use either the clear image or the red image as the primary image, to perform the warning and control applications, whereas the other image is used to enhance the system performance capabilities.  
         [0045]     Before explaining embodiments of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the host description or illustrated in the drawings.  
         [0046]     Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art of the invention belongs. The methods and examples provided herein are illustrative only and not intended to be limiting.  
         [0047]     In an embodiment of the present invention there is provided an image sensor with a filter, which is placed in a focal plane of the camera or in contact with the light sensitive surface. The filter includes at least two groups of elements, each group of element allowing transmission of at least partially different frequencies, arranged, for example, in a checkerboard pattern.  
         [0048]     Referring now to the drawings,  FIG. 2  schematically illustrates a system  200  according to embodiments of the present invention. Image frames  120  are captured from image sensor or camera  110 . Methods according to different embodiments of the present invention analyze using an image processor  230  in real time one or more of shape, position and motion of spots of measurable brightness in image frames  220 . In U.S. application Ser. No. &#39;523, a red/clear filter such as “checkerboard” filter is used to distinguish between red and white lights and for classifying the lights.  
         [0049]     Reference is also made to  FIG. 2   a  which illustrates a checkerboard filter  250 , in accordance with embodiments of the present invention. In a camera  110 , using a checkerboard filter  250 , one stream of images  220   a  is formed from the light transmitted by dark squares  254  of the checkerboard which preferentially transmit red light and the other squares  252  are comparatively clear and transmit white light to form a second stream of respective images  220   b . The symmetry in resolution of the checkerboard pattern of checkerboard filter  250  makes images  220   a  acquired from the colored portion of checkerboard filter  250  and respective images  220   b  acquired from the clear portion of checkerboard filter  250  generally symmetric images, enabling a smooth switching of images acquired from one portion of checkerboard filter  250  to images acquired from another portion of checkerboard filter  250 .  
         [0050]     Red/clear filter  250  is installed at a focal plane  112  of image sensor  110  so that an imaged spot from an object, e.g. portions of a road surface, obstacles, headlights of an oncoming vehicle, streetlights, taillights of a leading vehicle, falls on multiple pixels both with and without red filtering of red/clear filter  250 . The imaged spot is correlated with the [spatial transmittance] profile, e.g. checkerboard of red/clear filter  250 . In day time, a spot, such as an image of a yellow lane marking on a cement road surface  20 , will have a high correlation with the checkerboard red pixels profile and a comparatively poor correlation with the checkerboard clear pixels profile of filter  250 . Thus, in daytime, the correlation with the red filter profile is preferably used to detect yellow lane marking on a cement road surface  20 .  
         [0051]     It should be noted that the red/clear filter is given here by way of example only and other colored filters combination can be used adaptive to the detecting application In certain scenes the image acquired from one color element is used as the primary image and in other scenes the image acquired from another color element is used as the primary image.  
         [0052]     The choice of a “checkerboard” is given by way of example only and other shapes or geometric lattices may be similarly used, such as stripes of red and clear.  FIG. 3  illustrates yet another example embodiment of a filter  260 , in accordance with the present invention. In filter  260 , two streams of corresponding symmetric images can be formed, each of which with preferably a different color element, one stream of images with pixels yield from color stripes  262 , a second stream of images with pixels yield from color stripes  274 . Each colored stream of images can serve a different application and/or support application performed by the system, in certain situations.  FIG. 4  illustrates yet another example embodiment of a filter  270 , in accordance with the present invention. In filter  270 , four streams of corresponding symmetric images can be formed, each of which with preferably a different color element, one stream of images with pixels yield from color element  272 , a second stream of images with pixels yield from color element  274 , a third image with pixels yield from color element  276  and a fourth image with pixels yield from color element  278 . Each colored stream of images can serve a different application and/or support application performed by the system, in certain situations.  
         [0053]     In one embodiment of the invention, a red/clear checkerboard filter  250  is used.  FIG. 5  is a drawing according to an embodiment of the present invention of a vehicle control and warning system  300 , using the same camera  110  and hardware as in  FIG. 1   a.  Camera  110  of system  300  also includes a checkerboard filter  200 , thereby producing at least two streams of respective image frames, for example, clear images  322  and red images  320 . Each of the at least two streams is analyzed in parallel by processing unit  330 .  
         [0054]      FIG. 6  illustrates an example of a monitor output of a system  300  having a lane departure warning sub-system  334  and a vehicle headlight control sub-system  338 , according to embodiments of the present invention, in a night scene. During night operation, the LDA will perform optimally with clear image stream  322 , which is used as the primary image stream. Taillight detection will perform optimally with red images  320  and thus red image stream  320  is used as the primary image stream for this application. System  300  detects an oncoming vehicle  40  and switches the headlight to low beam state. In daytime operation, system  300  also detects yellow lane markings  22  on concrete road surfaces  20 , other lane markings  24  and street lights  30 .  
         [0055]     System  300  is improved over prior art system  100 , having the choice of using two or more sets of symmetric image frames acquired from filters with different color elements, the filter is coupled with camera  110 . The improved system performance enables improving blocks  132 ,  134 , . . . ,  138 , respectively replacing blocks  332 ,  334 , . . . ,  338 .  
         [0056]     During night operation, clear images  322  are used as the primary images, as clear images  322  are more responsive to light. Red images  320  are used during daytime for lane detection since the red light enhances yellow lines  22  on concrete roads surface  20  thus solving the problems of B&amp;W cameras not utilizing a filter  250  (which can be thought of as if using an array of only clear pixels), where yellow lines  22  and concrete roads surface  20  yield in the acquired images substantially the same intensity. During day light operation, red image stream  320  is used as the primary image stream. Red images  320  yield an average intensity which is lower by 35-50% relative to respective clear images  322 . Thus, another problem of a B&amp;W image sensor is solved: preventing the saturation of images in very bright days. In the day time, when entering dark situations such as tunnels, the system can switch to using the clear image  322  as the primary image stream.  
         [0057]     Systems  200  or  300  switch between primary and secondary images can be triggered by the detected image brightness and camera  110  settings. For example, if system  200 / 300  uses the red images as the primary images and the automatic gain control (AGC) unit of camera  110  requests an exposure above a certain threshold, system  200 / 300  switches to using the clear image.  
         [0058]     Furthermore, in consideration of the “quantization problem” and in order to improve the exposure used, in case where the red image is for example 65% as bright as the clear image, if the red image with one image line of exposure (for example 25 μSec) is too dark but the red image with two image lines of exposure is too bright, the AGC algorithm, can choose to use the clear image with one image line of exposure, which is in between.  
         [0059]     At any time, if an object is not detected in the primary image but detected in the respective secondary image, system  300  will switch to use the secondary image. For example, if a lane markings  22  are not detected in the primary image, for example a clear image  322 , system  300  can switch to using a respective image from the secondary image stream, for example red image stream  320 , if the lane marking  22  is detected in the secondary image.  
         [0060]      FIG. 6  illustrates an example of a monitor output of a system  300  having a lane departure warning sub-system  134  and a vehicle headlight control sub-system  138 , according to embodiments of the present invention, in a night scene.  FIG. 6  exemplifies a concurrent use of system  300  in two DAS different applications: LDA application and AHC application. During night operation, the clear image stream is used as the primary image stream for the LDA application. The LDA will perform optimally with red images and thus the red image stream is used as the primary image stream for this application.  FIG. 6  also shows the AHC application as being active and uses the red image stream as the primary image stream to detect spots of light, and then the AHC application uses the relative brightness in the primary and secondary images to determine the color of the spot. In particular, the AHC application determines whether the spot is a red light which is indicative of leading vehicle taillights  12  ( FIG. 1 ).  
         [0061]     The invention being thus described in terms of embodiments and examples, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.