Abstract:
The present invention provides a headlight control apparatus which suppresses a feeling of strangeness given to a driver of an own vehicle by hunting due to reflector light while preventing a preceding vehicle and an on-coming vehicle from being dazzled, based on a video image obtained by a camera. The headlight is controlled by detecting the position of a light spot in the image captured by the camera to perform irradiation with a pattern which reduces the light quantity of a certain area above the detected light spot. Thereby, even if hunting occurs due to the reflector light, the irradiation light quantity of an entire irradiation area of the headlight does not vary, but only the irradiation light quantity for a partial area above a reflector varies, and therefore, the feeling of strangeness given to the driver can be suppressed.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a headlight control apparatus for an automobile.  
         [0003]     2. Description of Related Art  
         [0004]     There has been researched and developed an art of automatically switching a high beam and a low beam of a headlight by analyzing a video image of an on-vehicle camera.  
         [0005]     JP-B-6-55581 discloses an art of switching a headlight from a high beam to a low beam so as not to cause a driver of a preceding vehicle or an on-coming vehicle to be dazzled, by detecting tail light of the preceding vehicle or a headlight of the on-coming vehicle in a video image of a color camera.  
         [0006]     JP-A-2002-526317 discloses a technique of continuously controlling an irradiation area of a headlight by calculating a distance to a preceding vehicle or an on-coming vehicle on the basis of a state of a headlight and a tail lamp in an image of a camera to further improve the above art. According to this technique, it becomes possible to achieve more appropriate control as compared with the two-stage control of the high beam and the low beam.  
       BRIEF SUMMARY OF THE INVENTION  
       [0007]     In the above described prior arts, if the camera recognizes the reflection light from a reflector when the headlight of the own vehicle is switched to the high beam, the headlight of the own vehicle is changed to the low beam by erroneously recognizing the reflection light as a headlight beam of the on-coming vehicle. However, since the reflection light from the reflector becomes weak at the moment of switching the headlight to the low beam, it is determined that the headlight beam becomes absent, and the operation of switching the headlight to the high beam is repeated. That is, the high beam and the low beam are periodically switched, so that blinking is repeated. This is called hunting. There is the possibility that this hunting causes a feeling of strangeness of the driver of the own vehicle. Originally, the reflector is installed for the purpose of making it easy for a driver to recognize a road contour or the like at night, and the information of the reflector position is important in night driving.  
         [0008]     Accordingly, the present invention provides a headlight control apparatus which suppresses a feeling of strangeness given to a driver of an own vehicle by hunting due to reflector light while preventing a preceding vehicle and an on-coming vehicle from being dazzled, on the basis of a video image obtained by a camera.  
         [0009]     In the invention, a position of a light spot in an image captured by a camera is detected, and a headlight is controlled so as to perform irradiation with a pattern in which the light quantity is reduced in a certain area above the detected light spot.  
         [0010]     More preferably, there is provided a headlight control apparatus including a headlight for irradiating a front region of a vehicle, of which light quantity can be controlled in every partial area in the irradiated region, a camera mounted on the vehicle for capturing an image of the front region of the vehicle, and a control unit for detecting a position of a light spot in the image inputted from the camera to control an irradiation pattern of the headlight based on the position of the light spot, wherein the control unit is configured to control the headlight so as to reduce the light quantity in a certain area above the portion of the detected light spot.  
         [0011]     According to the invention, even if the reflector light causes the hunting, the irradiation light quantity of the entire irradiated area does not vary, but only the irradiation light quantity in a partial area above the reflector varies, and therefore, the feeling of strangeness given to the driver can be suppressed.  
         [0012]     Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0013]      FIG. 1  is a block diagram of a method of controlling light distribution of a headlight;  
         [0014]      FIG. 2  is a block diagram of a camera and an image analyzing unit;  
         [0015]      FIG. 3  is a detailed diagram of the inside of the camera;  
         [0016]      FIG. 4  is a processing flow for calculating the distance between two vehicles on that basis of two images differing in exposure amount;  
         [0017]      FIGS. 5A, 5B  and  5 C are explanatory views of a state ahead of a vehicle in the case that a preceding vehicle and an on-coming vehicle are present;  
         [0018]      FIGS. 6A and 6B  are explanatory views of a technique of detecting the positions of a headlight and a tail lamp;  
         [0019]      FIG. 7  is a view for explaining the constraint of the arrangement of the camera and the headlight;  
         [0020]      FIGS. 8A and 8B  are explanatory views showing the positions of mask areas on the basis of a detection result of the headlight and the tail lamp;  
         [0021]      FIGS. 9A and 9B  are explanatory views of a light distribution pattern video image, and a position where a light projection quantity is actually reduced;  
         [0022]      FIG. 10  is an explanatory diagram of the headlight and a headlight control unit; and  
         [0023]      FIG. 11  is an explanatory view showing an LED array. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]      FIG. 1  is a schematic diagram showing an entire configuration for achieving a method of controlling light distribution of a headlight, which is an embodiment according to the present invention. A cameral  101  is mounted on a vehicle so as to capture a field of view ahead of the vehicle, and a headlight  104  is mounted on the vehicle so as to illuminate a front region ahead of the vehicle.  
         [0025]     Regarding the arrangement, it is desirable that the camera  101  and the headlight  104  are installed as near to each other as possible. This leads to simplification of calibration of optical axis adjustment or the like. As shown in  FIG. 1 , it is convenient from the viewpoint of the optical axis adjustment to install both the camera  101  and the headlight  104  inside one headlight unit  105 . This is because the optical axis of the camera  101  and the optical axis of the headlight  104  can be aligned with each other within the range of a certain assembly tolerance, and therefore, by adjusting the installation angle of the headlight unit  105  to the vehicle, both optical axes of the camera  101  and the headlight  104  can be adjusted while maintaining correlation of the optical axes of the cameral  101  and the headlight.  
         [0026]     Further, as shown in  FIG. 7 , the optical axis  701  of the camera  101  and the optical axis  702  of the headlight  104  are made parallel with each other. This is because, if the optical axes are not parallel with each other, a gap is generated between a spatial position captured by the camera  101  and a spatial position to which the light is projected by the headlight  104 . The angle of view  703  of the camera is made equal to the light projection angle  704  of the headlight.  
         [0027]     However, if there is no room in the space of the headlight unit  105 , and the cameral  101  cannot be housed in the space, the camera  101  may be installed in a cabin, for example, in an inmost recess of an rearview mirror or the like, to be installed in the position where the camera  101  can take a front region ahead of the vehicle. In this case, a gap is generated between the center points of the image captured area by the camera  101  and the light projection area by the headlight  104 , and therefore, the image captured by the camera  101  is converted into an image seen from the position of the headlight  104 . Specifically, the coordinates which are set as a center point on the captured image data are slid, and zoom processing is performed based on the distance between the camera mounting position and the headlight mounting position.  
         [0028]     By performing similar processing, the configuration in which only one of the left and right headlight units  105  is loaded with the camera  101  and the other headlight unit  105  is not loaded with the camera  101  may be adopted. That is, the image captured by the camera  101  loaded on one of the headlight units  105  is converted into an image seen from the position of the headlight  104  on the opposite side, and the light distribution of the headlight can be controlled based on the image.  
         [0029]     The vehicle front region image captured up by the camera  101  is inputted into an image analyzing unit  102 . The image analyzing unit  102  obtains the positions of light spots estimated as a headlight of an on-coming vehicle and a tail light of a preceding vehicle based on the inputted image. Subsequently, the image analyzing unit  102  generates a light distribution pattern which reduces the light quantity of a part of an upper portion above the detected light spot portion areas, and transmits the light distribution pattern to a headlight control unit  103  as a video image signal. In the headlight control unit  103 , the received video image information is returned to the light distribution pattern of the headlight  104 , and a liquid crystal plate in the headlight  104  is controlled. Hereinafter, the processing in each units will be described in detail.  
         [0030]     Next, a method of detecting the headlight of the on-coming vehicle and the tail light of the preceding vehicle with a camera will be described.  FIG. 2  is a diagram showing an internal configuration of the camera  101  and the image analyzing unit  102 . A CCD  201  is an image capturing element which converts light into an electric charge. The CCD  201  converts the video image of the region ahead of the vehicle into an analogue image signal, and transfers the analog image signal to a camera DSP  202 . The camera DSP  202  includes an ADC (Analog-Digital Converter)  303  therein, converts the analogue image signal into a digital signal and transmits the digital signal to an image input I/F  205  of the image analyzing unit  102 . The image signal is continuously transmitted while a synchronous signal is included at the head thereof, so that it is possible to take in only the image of timing required for the image input I/F  205 . The image taken into the image input I/F  205  is written in a memory  206 , and processing and analysis are performed by an image processing unit  204 . Details of the processing will be described later. A series of steps is performed in accordance with a program  207  written in an FROM. Control and necessary calculation for taking in the image in the image input I/F  205  and for performing image processing in the image processing unit  204  are performed by a CPU  203 .  
         [0031]     Here, the camera DSP  202  contains an exposure control unit  301  for performing exposure control and a register  302  which sets exposure time, and the CCD  201  captures an image for the exposure time set in the register  302  of the camera DSP  202 . The register  302  can be rewritten by the CUP  203 , and the rewritten exposure time is reflected at the time of capturing an image in and after the next frame or the next field. The exposure time can be controlled by turning on and off the power supply of the CCD  201  by the camera DSP  202 , and the quantity of light exposed to the CCD  201  is restricted by the time during which the power supply is on. The exposure time control can be realized by an electronic shutter method as described above, and it can also be similarly realized by using a method of opening and closing a mechanical shutter. The exposure amount may be changed by adjusting an aperture. In the case of operating every other line as in the case of interlace, the exposure amount may be changed between the odd-numbered lines and the even-numbered lines.  
         [0032]      FIG. 4  is a flow chart showing the flow of the process of this embodiment. In steps from S 11  to S 14 , an image for detecting high luminance and an image for detecting low luminance are obtained from the camera  101 , and the image data is transferred to the image analyzing unit  102 . The transferred image data includes synchronizing signals, and the CPU  203  performs processing relating to the image input and output using the above described synchronizing signals as interruption timing. In steps S 15  and S 16 , the light spot position is detected from the image in the image analyzing unit  102 , and the light distribution pattern which reduces the light quantity of a part of the upper portion above the light spot portion area detected in step S 2  is determined. In step S 3 , the light distribution pattern projected by the headlight  104  is controlled by the headlight control unit  103 .  
         [0033]     Next, the detailed processing in each of the steps will be described. The steps from S 11  to S 16  enclosed by the dotted line S 1  are a step group for light source detection. In step S 11 , the CPU  203  in the image analyzing unit  102  sets the register  302  in the camera  101  at a high luminance detecting exposure time. This is the exposure time optimal for detecting a light spot with high luminance, and is selected to detect the headlight of the on-coming vehicle ahead or the light spot of the tail lamp in the relatively short distance. The exposure time is from about 1/120 seconds to 1/250 seconds, which depends on the sensitivity characteristics of the CCD  201  which is the image capturing element.  FIGS. 5A, 5B  and  5 C show examples of the captured image. When the state of  FIG. 5A  is captured for the high luminance detecting exposure time, the result is  FIG. 5B . Since the luminance of the headlight of an on-coming vehicle  501  is high, it is come out as light spots as shown in  FIG. 5B , but since the luminance value of the tail lamp of a preceding vehicle  502  is low, is not come out. In step S 12 , the digital image captured with the exposure time set in step S 1  is inputted from the image input I/F  205 , and stored in the memory  206 . In step S 13 , the register  302  in the camera  101  is rewritten to store the low luminance detecting exposure time by the CPU  203  in the image analyzing unit  102 . This is the exposure time optimal for detecting the light spot with low luminance, and is selected to detect the light spot of the tail lamp in a relatively long distance ahead. Therefore, the exposure time becomes longer than the one set in step S 11 , and is about 1/30 seconds to 1/60 seconds.  FIG. 5C  shows the image which is captured for the low luminance detecting exposure time. The low luminance light spot of the tail lamp of the preceding vehicle  502  can be captured, but since the headlight of the on-coming vehicle  501  is highly luminous, it causes blooming to saturate the peripheral pixels with white. In step S 14 , as with the case of step S 12 , the digital image captured with the exposure time set in step S 13  is inputted from the image input I/F  205  and stored in the memory  206 .  
         [0034]     In steps S 15  and S 16 , the image obtained from the camera is analyzed and the positions of the light spots are obtained. The processing is performed by the CPU  203  and the image processing unit  204 . In step S 15 , the position of a high luminance light spot  601  is detected from a high luminance detecting image  503 . The method for calculating the light spot position will be described in detail later. When the high luminance light spot position is obtained, a low luminance light spot position is detected by using a low luminance detecting image  504  in step S 16 . Here, the low luminance detecting image  504  includes the light spot of high luminance, and is likely to cause blooming. However, there is no problem because in step S 16  the position of a red light spot  602  is calculated from the low luminance detecting image. With the above procedure, the positions of the light spots  601  of the headlight of the on-coming vehicle, and the light spots  602  of the tail light of the preceding vehicle can be obtained respectively.  
         [0035]     Next, a method of determining the positions of mask areas  801  and  802  in which the light quantity is decreased, based on the detected positions of the light spots of the headlight and the tail light will be described by using  FIG. 8 . The mask areas  801  and  802  are provided so as not to dazzle the drivers of the on-coming vehicle  501  and the preceding vehicle  502 , respectively, and therefore, need to be set in portions where the drivers may exist. The headlights and the tail lights are generally mounted in positions lower than the positions of the drivers. Therefore, the positions of the mask areas  801  and  802  are set above the detected light spot  601  of the headlight and light spot  602  of the tail light. The sizes of the mask areas  801  and  802  are set so as not to be less than the sizes of the light spot  601  of the headlight and the light spot  602  of the tail light as shown in  FIG. 8  for achieving the object of not dazzling the drivers. When the sizes of the light spot  601  of the headlight and the light spot  602  of the tail light are large, the on-coming vehicle  501  and the preceding vehicle  502  may be close to the own vehicle correspondingly, and therefore, the sizes of the mask areas  801  and  802  are also made large. Since the light spot  602  of the tail light is darker as compared with the light spot  601  of the headlight, the color of the light spot is taken into consideration when determining the size, and if it is the red light of the tail light, the size of the mask area  802  needs to be changed. Specifically, the mask area  802  is set to be large with respect to the light spot having the same size, as compared with the case that the light spot is white (headlight). This is because as compared with the case of the headlight, the preceding vehicle may be in a position near the own vehicle even if the light spot is small. Considering that the on-coming vehicle  501  looks slant at the time of passing by the on-coming vehicle  501 , the driver does not always exist directly above the light spot  601  of the headlight and the light spot  602  of the tail light. Therefore, by making the shapes of the mask areas  801  and  802  oval shapes longer in the lateral direction as shown in  FIG. 8 , it is possible to irradiate a wide range as much as possible, while reducing the risk of dazzling the drivers. The shapes of the mask areas  801  and  802  may be rectangular considering the easiness of control of the headlight and the calculation amount, in addition to the oval shapes as illustrated in  FIG. 8 . Further, the light reduction ratios of the mask areas  801  and  802  can be set freely from 0% to 100%.  
         [0036]     Here, it is important that the mask areas  801  and  802  do not overlap the light source, and therefore, the reflector always reflects, which eliminates the phenomenon that projection light of the headlights exhibits hunching due to the reflector as in the conventional example.  
         [0037]     The mask areas  801  and  802  which are determined as above are transferred to the headlight control unit  103  in a video image form as a light distribution pattern video image  901  shown in  FIG. 9 . The light distribution pattern video image  901  is in the form of a gray scale video image of 8 bits. Specifically, the luminance value of the area desired to be irradiated other than the mask area  902  is set at  255 , and the luminance value of the mask area  902  is set in the range of 0 to 255 depending on the light reduction amount. For example, if no light is desired to be irradiated to the mask area, the luminance value is set at zero. If it is set at zero, the light is not projected to the mask area theoretically and the purpose of preventing a dazzle is achieved, but since there is the possibility that the drivers of the on-coming vehicle and the preceding vehicle do not recognize the existence of the own vehicle, a very small amount of light of about 10 to 20 is set to be irradiated for safety. As a signal when the light distribution pattern video image  901  is transferred to the headlight control unit  103 , a video image signal may be transferred. For this purpose, it may be possible to use a signal in any form such as analogue signals of NTSC, PAL and analogue RGB and the like, as well as digital signals of IEEE1394, a camera link, USB and the like. The analogue signal of NTSC is convenient when the camera and the headlight unit are away from each other. The digital signals of IEEE1394 and the like have the advantage of capable of transferring video images with high definition, and do not require AD/DA conversion.  
         [0038]     In  FIG. 10 , a video image input I/F  1006  receives the light distribution pattern video image  901  transferred to the headlight control unit, and a liquid crystal control unit  1005  controls the electric charge of a liquid crystal  1002  in the headlight. The liquid crystal  1002  shuts off the light when electric charges are applied to it, and transmits the light when electric charges are not applied to it, and therefore, the liquid crystal control unit  1005  conducts control so as to apply the electric charges to the portions of the mask area  902 . The headlight  104  is constituted of a light source  1004 , a condenser lens  1003 , the liquid crystal  1002  and a light projection lens  1001 , and changes the pattern to be projected by changing the pattern of the liquid crystal with the principle of the liquid crystal projector. As the light source  1004 , a halogen lamp, a xenon lamp, and a high pressure mercury lamp are cited, and any of those may be used.  
         [0039]     In this embodiment, the example of using the liquid crystal for light distribution pattern control of the headlight is described, but the light distribution pattern may be changed by using an LED array  1102  with high directivity as shown in  FIG. 11 . LEDs  1103  in  FIG. 11  are controllable independently of each other, and only the LEDs  1103  irradiating the portion of the mask area  901  are stopped or reduced in luminance.  
         [0040]     It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims.