Abstract:
In order to obtain a low-cost stereo camera which can decrease the load of software-based calibration, a stereo camera is provided with a first vehicle-mounted camera which comprises a first lens unit and a first imaging element, and a second vehicle-mounted camera which comprises a second lens unit and a second imaging element. This stereo camera is characterized in that the first imaging element has a first sensitivity value recording unit in which sensitivity values of the first imaging element are recorded, and the second imaging element has a second sensitivity value recording unit in which sensitivity values of the second imaging element are recorded, wherein the sensitivity variation width between the sensitivity values of the first imaging element recorded in the first sensitivity value recording unit and the sensitivity values of the second imaging element recorded in the second sensitivity value recording unit is within a preset reference width.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a stereo camera mounted on a vehicle. 
       BACKGROUND ART 
       [0002]    In recent years, mounting of an image processing system in a vehicle has been greatly expanded. It is especially significant for a stereo camera for image processing to match sensitivity of the right and left cameras to each other, for ensuring performance. 
         [0003]    For example, technologies of a compound-eye imaging device for adjusting signal levels of each imaging element so as to be identical when imaging an identical subject with the plurality of imaging elements are disclosed in PTL 1. The compound-eye imaging device disclosed in PTL 1 includes a sensitivity adjustment mechanism (diaphragm) driven by a motor, which is adjusted after the factory shipment. 
       CITATION LIST 
     Patent Literature 
       [0004]    PTL 1: JP 2010-135984 A 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0005]    In a vehicle-mounted stereo camera, the provision of the sensitivity adjustment mechanism causes an increase in costs, and the operation of adjustment mechanism (motor) may cause parallelization and sensitivity of right and left images to be out of adjustment, so that it is difficult to ensure accuracy in parallax calculation. 
         [0006]    However, a purchase of an expensive lens and imaging element or complicated calibration in software-base are needed when lenses having diaphragms with same aperture values in the right and left sides and the imaging elements having the same sensitivity are selected for use. 
         [0007]    The present invention has an object to provide a low-cost stereo camera which can decrease the load of software-based calibration. 
       Solution to Problem 
       [0008]    In order to solve the above-described problem, for example, a configuration described in claims is employed. The present disclosure includes a plurality of means for solving the above-described problem. As an example thereof, there is provided a stereo camera that includes a first vehicle-mounted camera including a first lens unit and a first imaging element configured to perform imaging via the first lens unit, a second vehicle-mounted camera including a second lens unit and a second imaging element configured to perform imaging via the second lens unit. The stereo camera is characterized in that the first imaging element includes a first sensitivity value recording unit in which a sensitivity value of the first imaging element is recorded, the second imaging element includes a second sensitivity value recording unit in which the sensitivity value of the second imaging element is recorded, and a sensitivity variation width between the sensitivity values of the first imaging element recorded in the first sensitivity value, recording unit and the sensitivity values of the second imaging element recorded in the second sensitivity value recording unit is within a predetermined reference width. 
       Advantageous Effects of Invention 
       [0009]    According to the present invention, the load of software-based calibration can be decreased at low cost. Any issues, configurations, and effects other than those described above will become apparent by reference to the following description of embodiments. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0010]      FIG. 1  is a perspective view for describing arrangement of a substrate of a stereo camera. 
           [0011]      FIG. 2  is a diagram viewed from a direction of arrow A in  FIG. 1 . 
           [0012]      FIG. 3  is a diagram viewed from a direction of arrow B in  FIG. 1 . 
           [0013]      FIG. 4  is a diagram viewed from a direction of arrow C in  FIG. 1 . 
           [0014]      FIG. 5  is a diagram illustrating an exemplary method for storing a sensitivity value in a sensitivity value recording unit of an image sensor. 
           [0015]      FIG. 6  is a diagram illustrating an exemplary method for recording optical information in an optical information recording unit of a lens unit. 
           [0016]      FIG. 7  is a diagram illustrating a method for selecting combination of the image sensor and the lens unit. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0017]    Hereinafter, one embodiment of the present invention is described with reference to the attached drawings. When a configuration of a stereo camera is described hereinafter, description of a component having common parts in the right and left may be made by omitting “R” and “L” after reference numeral, As the configuration, the same applies to the one to which “R” and “L” are appended. 
         [0018]    The stereo camera according to the embodiment is a vehicle-mounted stereo camera, and captures images of an area in front of a vehicle via a windshield of the vehicle. 
         [0019]      FIG. 1  is a perspective view for describing arrangement of a substrate of the stereo camera.  FIG. 2  is diagram viewed from a direction of arrow A in  FIG. 1 .  FIG. 3  is a diagram viewed from a direction of arrow B in  FIG. 1 .  FIG. 4  is diagram viewed from a direction of arrow C in  FIG. 1 . 
         [0020]    As illustrated in  FIG. 4 , a stereo camera  1  includes two vehicle-mounted cameras  11  forming a pair of right and left. The stereo camera  1  includes a first vehicle-mounted camera  11 R arranged at a right side in a vehicle width direction and a second vehicle-mounted camera  11 L arranged at a left side in the vehicle width direction. The first vehicle-mounted camera  11 R and the second vehicle-mounted camera  11 L are housed in a single case  2 , while being integrally fixed to each other. The first vehicle-mounted camera  11 R includes a first lens unit  12 R and a first image sensor  13 R capturing images via the first lens unit  12 R. The second vehicle-mounted camera  11 L includes a second lens unit  12 L and a second image sensor  13 L capturing images via the second lens unit  12 L. 
         [0021]    The first lens unit  12 R includes a first lens  21 R, a first diaphragm  22 R having a fixed aperture value, and a first lens case  23 R housing the first lens  21 R and the first diaphragm  22 E. Similarly, the second lens unit  12 L includes a second lens  21 L, a second diaphragm  22 L having a fixed aperture value, and a second lens case  23 L housing the second lens  21 L and the second diaphragm  22 . 
         [0022]    The first lens unit  12 R includes a first optical information recording unit  24 R in which optical information of the first lens unit  12 R is recorded. The second lens unit  12 L includes a second optical information recording unit  24 L in which the optical information of the second lens unit  12 L is recorded. The optical information recording units  24 R and  24 L are disposed on the cases  23 R and  23 L of the lens units  12 R and  12 L and can be read from outside. The optical information contains information such as a focus value, a sensitivity value (transmittance), and shading of the lens unit  12 . 
         [0023]    The first image sensor  13 R and the second image sensor  13 L include imaging elements  32 R and  32 L in two imaging substrates  31 R and  31 L separately arranged on the right and left sides, respectively. The first imaging element  32 R includes a first sensitivity value recording unit  33 R (see reference numeral  33  in  FIG. 5 ) in which the sensitivity values of the first imaging element.  32 R are recorded, and the second imaging element  32 L includes a second sensitivity value recording unit  33 L (see reference numeral  33  in  FIG. 5 ) in which the sensitivity values of the second imaging element  32 L are recorded. The first sensitivity value recording unit  33 R and the second sensitivity value recording unit  33 L only need to be capable of readably recording the sensitivity value, and include such as a RAM, an EPROM, and an EEPROM. The sensitivity value of the lens unit  12  and the sensitivity value of the imaging element  32  according to the embodiment are a relative value that indicates luminosity. 
         [0024]    The imaging substrate  31 R of the first image sensor  13 R and the imaging substrate  31 L of the second image sensor  13 L are coupled to a main substrate  41  via communication connection units  34 R and  34 L, respectively. External information which is captured through the lens units  12 R and  12 L into the first imaging element.  32 R and the second imaging element  32 L, is transmitted from the imaging substrates  31 R and  31 L via the respective communication connection units  34 R and  34 L to the main substrate  41 . 
         [0025]    The main substrate  41  includes a power source unit  42 , a video processing unit  43 , and a recognition processing unit  44 . The video processing unit  43  optically corrects signals from the imaging substrates  31 R and  31 L, and performs stereo matching processing to obtain three dimensional information (hereinafter, parallax image). The recognition processing unit  44  extracts necessary information using the videos corrected with the video processing unit  43  and the obtained parallax image. 
         [0026]      FIG. 5  is a diagram illustrating an exemplary method for storing a sensitivity value in a sensitivity value recording unit of an imaging element. 
         [0027]    Operations for recording the sensitivity value in the sensitivity value recording unit  33  of the imaging element  32  may be performed in a manufacturer of the imaging element  32  before the factory shipment, for example. More specifically, a light source  61  which emits uniform amount of light over a predetermined range, is imaged with the imaging element  32 . The sensitivity value of the obtained image is measured with a computer PC. Subsequently, the own sensitivity value as a measurement result is recorded in the sensitivity value recording unit  33 . 
         [0028]    Therefore, when the stereo camera  1  is assembled, it is possible to select a pair of imaging elements  32  forming a pair by reading the sensitivity value by communicating with the imaging element  32 . More specifically, the two imaging elements  32  are selected such that a sensitivity variation width between the sensitivity values of one imaging element  32  and the sensitivity values of the other imaging element  32  is within a predetermined reference width. 
         [0029]    For the stereo camera  1  that employs the two imaging elements  32  selected in this manner, the sensitivity variation width between the sensitivity values of the first imaging element  32 R recorded in the first, sensitivity value recording unit  33 R and the sensitivity values of the second imaging element  32 L recorded in the second sensitivity value recording unit  33 L is within a predetermined reference width. That is, when the vehicle -mount e a camera  11 R in the right side and the vehicle-mounted camera  11 L in the left side each receive light from the predetermined light source  61 , a difference between a first signal level output from the imaging element  32 R in the right side and a second signal level output from the imaging element  32 L in the left side falls within a predetermined specified range. Therefore, this has an advantage of not causing a loss of operation time in comparison with the case of an evaluation of the sensitivity after assembly. 
         [0030]    For example, when each of imaging elements  32  has the sensitivity variation width of about ±20%, combinations to upper and lower limit values of the sensitivity variation width are conceivable in a case of combining the right and left with no consideration of the selection. This may result in a sensitivity difference between right and left of up to 40%. On the other hand, in the present invention, the two imaging elements  32  are each selected to be combined based on the sensitivity value recorded in the sensitivity value recording unit  33 , and accordingly it is possible to reduce the sensitivity variation width to keep the sensitivity variation within a predetermined reference width. For example, when upper and lower limit widths of sensitivity properties of the imaging element  32  are classified into two levels, the sensitivity variation width based on the combination of the right and left vehicle-mounted cameras  11 R and  11 L may be equal to or less than 50% in comparison with the sensitivity variation width before classification. 
         [0031]      FIG. 6  is a diagram illustrating an exemplary method for recording optical information in an optical information recording unit of a lens unit. 
         [0032]    Operations for recording the optical information in the optical information recording unit, of the lens unit  12  may be performed in a manufacturer of the lens unit  12  before the factory shipment, for example. More specifically, a predetermined chart  51  is captured through the lens unit  12  into imaging equipment  52 . The optical information containing information such as the focus value, the sensitivity value, and the shading is obtained with the computer PC. Subsequently, the own optical information as a measurement result is recorded in the optical information recording unit  24 . The recording of the optical information in the optical information recording unit  24  is performed by marking on the case  23  of the lens unit  12  with a laser  53 . The optical information is read by an assembly operator, a reader or the like. 
         [0033]    Therefore, when assembling the stereo camera  1 , it is possible to read the optical information from the optical information recording unit  24  and appropriately select each of the right and left lens units  12  such that, the sensitivity value of combined the lens unit  12  and the image sensor  13  becomes identical in the right and left vehicle-mounted cameras  11  and a desired sensitivity value. Accordingly, there is no loss of operation time in comparison with the case of performing an evaluation of the sensitivity after assembly. The optical information may be converted into a bar code or the like to be recorded. 
         [0034]    Hereinafter, an exemplary method for selecting combination of the image sensor and the lens unit is described with reference to  FIG. 7 . 
         [0035]    For the stereo camera  1 , it is significant to adjust signal strength of the videos from the right and left imaging substrates  31 R and  31 L in the video processing unit  43 . There are two methods for adjusting. One method (1) is to adjust the signal strength by digital signal processing of the obtained video information. The other method (2) is to adjust the sensitivity properties such as transmittance and the sensitivity values in whole optical system up to output ting the imaging element. 
         [0036]    For the former method (1), any stereo camera having inherently lower signal level causes performance to be limited by its signal level, and thus causes problems for mass produced products. In the present invention, therefore, the latter method (2), in other words, the method for adjusting the sensitivity properties of the optical system or the imaging element is selected, thereby performing stereo matching processing with higher performance. 
         [0037]    The lens units  12  are classified into an A rank a B rank, or the like based on the optical information and are arranged in equipment for each rank. The lens unit  12  compatible with the imaging element  32  is selected based on the sensitivity value read from the sensitivity value recording unit  33  of the imaging element  32  with the computer PC and is removed from the equipment classified in the ranks to be allocated. 
         [0038]    For example, when the sensitivity value of the second lens unit  12 L is higher than that of the first lens unit  12 R, the second imaging element  32 L having the sensitivity value equal to or less than the sensitivity value of the first imaging element  32 R is combined. When the sensitivity value of the second lens unit  12 L is lower than that of the first lens unit  12 R, the second imaging element  32 L having the sensitivity value equal to or more than that the sensitivity value of the first imaging element  32 R is combined. Accordingly, it is possible to absorb, by a simple mechanism, the variations in the sensitivity values obtained by combining the sensitivity value of the optical system of the stereo camera  1  and the sensitivity value of the imaging element  32 . 
         [0039]    In the embodiment described above, the optical information of the lens unit  12  is read from the optical information recording unit  24 . Alternatively, adjusting an aperture diaphragm diameter of the diaphragm  22  implemented within the lens unit  12  to be ranked, intentionally may be considered. In this case, it is enough to only record the aperture diaphragm diameter as ranked information. This results in simplification of measuring the single lens unit  12  and cost reduction. 
         [0040]    Although the case where the sensitivity value recording unit  33  is disposed in the imaging element  32  has been described as an example in the above-described embodiment, the embodiment is not limited to this structure. For example, the sensitivity value recording unit  33  may be included in the imaging substrate  31 . The sensitivity value recording unit  33  is not limited to the one which records signals with such as a ROM, and may be r the one which displays on the imaging substrate  31  with a bar code or the like. 
         [0041]    That is the detailed description of embodiments of the present invention. Note here that the present invention is not limited to the above-described embodiments, and may include various modification examples without departing from the spirit of the present invention recited in claims. For instance, the embodiments are described above in detail for explanatory convenience and the present invention is not always limited to the entire configuration described above. A part of one embodiment may be replaced with the configuration of another embodiment, or the configuration of one embodiment may be added to the configuration of another embodiment. In the configuration of each embodiment in part, other configurations may be added, deleted or replaced. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           1  stereo camera 
           11 R first vehicle-mounted camera 
           11 L second vehicle-mounted camera 
           12 R first lens unit 
           12 L second lens unit 
           32 R first imaging element 
           32 L second imaging element 
           33 R first sensitivity value recording unit 
           33 L second sensitivity value recording unit