Patent Publication Number: US-9420151-B2

Title: Multi-lens camera system, vehicle mounting the multi-lens camera system, and range-finding method executed by the multi-lens camera system

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This patent application is based on and claims priority pursuant to 35 U.S.C. §119 to Japanese Patent Application Nos. 2012-063660, filed on Mar. 21, 2012 and 2013-001370, filed on Jan. 8, 2013 in the Japan Patent Office, the entire disclosures of which are hereby incorporated by reference herein. 
     BACKGROUND 
     1. Technical Field 
     The present invention relates to a multi-lens camera system capable of acquiring parallax information and a vehicle mounting the multi-lens camera system, and a range-finding method executed by the multi-lens camera system. 
     2. Related Art 
     Collision avoidance systems involving the use of in-vehicle stereo cameras have become widespread. A stereoscopic image of the area in front of the vehicle is generated using the stereo cameras, and an obstacle is detected and a distance to the obstacle is measured based on the generated stereoscopic image. The driver can then be alerted to take corrective action to avoid a collision or maintain a safe minimum distance between vehicles. Alternatively, the system can engage a control device such as the brakes and the steering. 
     Further, with improving sensor performance such as higher image resolutions, the focus of vehicle environment sensing has shifted from highway driving to city driving. In the city, the target sensing environment is much more diversified compared to the highway. The biggest problem for recognition processing in a complex sensing environment is that such diversity complicates processing, as a result of which the processing time lengthens and object misrecognition increases. 
     In recognition processing in the conventional in-vehicle stereo camera, initially, edges are detected over substantially the entire captured image and parallax is calculated for the edge-detected pixel position. Then, by executing clustering using the parallax information which is the calculation result and adding various types of information to the clustering result, the recognition target is finally detected. 
       FIG. 9  is a flow chart illustrating a general process of object recognition using parallax information. Herein, the recognition targets include a vehicle in front, a pedestrian, a motorbike, a bicycle, a traffic sign, and a traffic light as an object on a road. Initially, using a stereo camera including a reference camera unit and a comparison camera unit like that shown in  FIG. 1A , a captured image (stereo image) including a reference image and a comparison image is acquired at step S 201 . Then, using luminance information in the reference image, a dividing line (e.g., white lines and yellow lines, including stop line) on the road is recognized, at step S 208 . Along with this process, parallax is calculated based on the reference image and the comparison image at step S 202 , clustering is executed using the parallax information at step S 203 , and the clustering result is modified using the size of object, such as the vehicle, the pedestrian, the motorbike, the bicycle, the traffic sign, and the traffic light, at step S 204 . 
       FIG. 10  is an object-recognized image obtained by the processes executed at steps S 201  through S 204 . In  FIG. 10 , reference numeral  100  represents the clustering result recognized as the vehicle object size,  101  represents the clustering result recognized as the pedestrian, the motorbike, and bicycle size, and  102  represents the clustering result recognized as the traffic sign and the traffic light size. As is clear from the object-recognized image of  FIG. 10 , in particular, since the traffic sign and the traffic light are small, they are often misrecognized, as indicated by frames  102 ′. In addition, misrecognition of a pedestrian is also seen in an upper region of the image in  FIG. 10 , indicated by frame  101 ′. 
     Various conditional branch processes are executed on these object misrecognitions at steps S 205  and later shown in  FIG. 9 . For example, at step S 205 , a height of the road surface is calculated based on the dividing line (stop line) recognized at step S 208 , and the clustering result is modified using target model information for the pedestrian and the fallen object. In addition, at step S 206 , based on the luminance information in the reference image, a final determination is made regarding the target object for the region for which clustering is executed, using adaptive boosting (AdaBoost). Finally, the three-dimensional position of the recognized object is output at step S 207 . 
     In the processes of from steps S 201  through S 204 , if serious object misrecognition occurs or the target object cannot be separately recognized successfully, many complicated processes arise, for example, various conditional branch processing is needed subsequent recognition processing, or previous-stage processing must be revisited. Accordingly, it is important to improve the recognition success rate of the parallax calculation and the clustering, and to minimize misrecognition. 
     In order to recognize the objects in the images, for example, JP-2004-173195-A proposes a stereo camera system that captures scenery around the vehicle, calculates range data representing two-dimensional distribution of the distance between a camera that outputs color images and a target in a monitoring region, and recognizes another vehicle driving in front in the same lane or in an adjacent lane. Herein, a winker region having a predetermined dimension is set based on the vehicle position in the target-recognized image and a pixel constituting a color component of the winker is detected based on the color image. Accordingly, the winker and the near vehicle can be recognized simultaneously, using the color information and the parallax information. With this configuration, using a combination of the color information and the parallax information, multiple objects can be recognized accurately and simultaneously. 
     In the above-described method, as for the recognition objects whose color information is known in advance, by detecting the color components of the recognition objects based on the color image acquired by the color camera, the object can be detected accurately. However, it is necessary to provide the color camera in addition to the stereo camera, set the region where the color object is recognized in the image, and perform additional recognition processing using a different algorithm. In addition, in order to calculate the parallax in the entire image and the parallax in the setting region respectively, switching the parallax calculation algorithm and parameter is required. This operation complicates calculation processing and cannot solve the above-described problem. 
     SUMMARY 
     In one aspect of this disclosure, there is provided a novel multi-lens camera system includes multiple camera units and an image processor. The multiple camera units include respective optical filters and image sensors that acquire captured images via the optical filters. Each of the optical filters has multiple filter regions whose optical characteristics differ respectively. The image processor, operably connected to the multiple camera units, executes different types of image processing on the captured image to form an image that contains multiple image regions whose characteristics differ depending on the optical characteristics of the filter regions. 
     In another aspect of this disclosure, there is provided a vehicle including the above-described multi-lens camera system to recognize various types of targets positioned forward of the vehicle; and a vehicle drive control unit to control steering and braking in the vehicle based on the recognition result of the image processor. 
     In another aspect of this disclosure, there is provided a range-finding method in a multi-lens camera system that has multiple camera units including respective optical filters and image sensors that acquire captured images via the optical filters, each of the optical filters having multiple filter regions whose optical characteristics differ respectively. The method comprising the steps of: capturing images; dividing each of the captured images into multiple regions corresponding to the respective filter regions; calculating parallax information for a first image region in the captured image; performing clustering using the parallax information for the first image region; recognizing another target object for a second image region in the captured image while calculating parallax information and performing clustering using the parallax information for the first image region; modifying the clustering result; calculating parallax information only for the area where the target is recognized in the second image region, while modifying the clustering result for the first image region; and recognizing the target in the first image region and the second image region in the captured image in three dimensions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
         FIG. 1A  is a schematic view illustrating a stereo camera in a stereo camera system according to a present disclosure; 
         FIG. 1B  is an expanded diagram illustrating an image sensor and an optical filter in each of camera units shown in  FIG. 1A ; 
         FIG. 2  is a photograph of an image acquired by the stereo camera system shown in  FIG. 1B ; 
         FIG. 3  is a block diagram illustrating a configuration of an image processor in the stereo camera system shown in  FIG. 1A ; 
         FIG. 4  is a fundamental view illustrating the stereo camera shown in  FIG. 1A ; 
         FIG. 5  is a flow chart illustrating a process executed by the stereo camera system shown in  FIG. 1B ; 
         FIG. 6A  is a timing chart illustrating a comparative example of a stereo camera system in which the parallax is calculated for an entire captured image; 
         FIG. 6B  is a timing chart illustrating the stereo camera system shown in  FIG. 1B , in which the parallax is calculated for only a predetermined region in the captured image; 
         FIG. 7  is a parallax image after the parallax is calculated and clustering is executed in the comparative example shown in  FIG. 6A ; 
         FIG. 8  is a schematic diagram illustrating a vehicle mounting the stereo camera system shown in  FIG. 1A ; 
         FIG. 9  is a flow chart illustrating a related-art process of object recognition using parallax information; and 
         FIG. 10  is an object-recognized image obtained by processes executed at steps S 201  through S 204  shown in  FIG. 9 . 
     
    
    
     DETAILED DESCRIPTION 
     In describing preferred embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology so selected, and it is to be understood that each specific element includes all technical equivalents that have the same function, operate in a similar manner, and achieve a similar result. 
     Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views thereof, and particularly to  FIGS. 1A through 8 , a stereo camera system according to illustrative embodiments of the present disclosure is described. 
       FIGS. 1A and 1B  illustrate one example of a stereo camera device  1  in a stereo camera system (range-finding system)  1000  according to a present disclosure. In  FIG. 1A , the range-finding system  1000  includes the stereo camera device  1  and an image processor  30  operatively connected to the stereo camera device  1 . The stereo camera device  1  includes a reference camera unit  10  and a comparison camera unit  20 , each disposed on opposite sides of the stereo camera device  1 . The reference camera unit  10  includes an image sensor (image pickup element)  11 , an optical filter  12  disposed upon the image sensor  11 , and a lens  13  that concentrates light on the image sensor  11 . Similarly, the comparison camera unit  20  includes an image sensor (image pickup element)  21 , an optical filter  22  disposed upon the image sensor  21 , and a lens  23  that concentrates the light on the image sensor  21 . 
     In the range-finding system  1000 , the image processor  30  performs parallax calculation and image recognition based on a captured image (sensor image) acquired by the camera units  10  and  20 . The stereo camera system  1000  functions as a range-finding apparatus that captures the same object from different viewpoints, and measures a distance to the object and calculates a position of the object, using the fact that the focus on the sensor image changes depending on the distance to the object. 
       FIG. 1B  is an expanded diagram illustrating the image sensor ( 11 ) and the optical filter  12 ( 22 ) in the respective camera units  10 ( 20 ). In  FIG. 1B , the optical filter  12  of the reference camera unit  10  has an identical configuration to that of the optical filter  22  of the comparison camera unit  20 . Therefore, images acquired by the image sensors  11  and  21  have the same basic characteristics. Each of the optical filter  12  in the reference camera unit  10  and the optical filter  22  in the comparison camera unit  20  is a special kind of complex filter, which is divided into a color filter region  12   a ( 22   a ), a clear filter region  12   b ( 22   b ), and a neutral density (ND) filter region  12   c ( 22   c ). Accordingly, color information can be detected by using the color filter region  12   a , and luminance information can be detected by using the clear filter region  12   b  and the ND filter region  12   c.    
       FIG. 2  is a photograph of a stereo image (captured image)  40  acquired by the stereo camera system  1000  shown in  FIG. 1 . The stereo image  40  acquired by the stereo camera device  1  is divided into image regions  40   a ,  40   b , and  40   c , which reflect the characteristics of the respective filter regions  12   a ( 22   a ),  12   b ( 22   b ), and  12   c ( 22   c ). It is to be noted that, by providing the clear filter region  12   b ( 12   b ) in a central image region  40   b  of the image  40 , the other upper and lower regions can be formed by different filters, and the regions can be formed appropriately depending on the information to be detected. In addition, the division of the captured image is not limited to the horizontal direction; alternatively, the regions of the image can be divided in a vertical direction. 
     In  FIG. 2 , the image region  40   a  in the stereo image  40 , serving as a second image region, is a color filter corresponding region (color-filter image region) obtained by concentrating the light on the image sensor  11 ( 21 ) passing through the color filter region  12   a . The image region  40   b , serving as a first image region, is a clear filter corresponding region (clear-filter image region) obtained by concentrating the light on the image sensor  11 ( 21 ) passing through the clear filter region  12   b ( 22   b ). The image region  40   c , serving as a third image region, is an ND filter corresponding region (ND filter image region) obtained by concentrating the light on the image sensor  11 ( 21 ) passing through the ND filter region  12   c ( 22   c ). In the stereo image  40  having multiple different optical characteristics, the parallax calculation is performed for the clear-filter image region  40   b . The clear-filter image region  40   b  is the region where the sizes of the object (first target object), such as a vehicle in front  40   b - 0 , pedestrian, motorbike, and bicycle  40   b - 1  are detected. When the stereo camera system  1000  is mounted on a vehicle, the region  40   b  corresponding to the clear filter region  12   b  is determined in the captured image  40  by considering a slope, heights of the vehicle  40   b - 0  and pedestrian  40   b - 1  around the vanishing point in the captured image  40  in a vertical direction. 
     Parallax information is very effective to recognize the vehicle  40   b - 0  and the pedestrian  40   b - 1 , and by calculating the parallax (distance) with high image resolution, the object can be separated with a high degree of accuracy and long-range recognition becomes possible. In addition, in order to calculate collision with another vehicle  40   b - 0 , pedestrian, or bike  40   b - 1 , calculating the distance to the object is necessary. Accordingly, it is preferable that the clear filter  12   b  be set for this region (central region) and the parallax information be aggressively used for recognition processing. 
     On the other hand, objects (second target object) such as a traffic sign and a traffic light  40   a - 2  in the upper region  40   a  in the stereo image  40  are small, and for that reason are often falsely recognized based on the parallax information. Conversely, since the color of the traffic light and the traffic sign  40   a - 2  is determined, different from the color of vehicle, by using the color information aggressively more than the parallax information, the object  40   a - 2  can be recognized effectively. Therefore, the color filter  12   a  is provided in the upper region, and the camera units  10 ( 20 ) capture this upper image region  40   a  as color image. 
     Herein, when the parallax information is calculated using the color information, executing multiple dimensional parallax calculation is necessary, using RGB and YCRCR, and changing processing time and the algorithm is needed. Accordingly, initially, the traffic sign/traffic light  40   a - 2  is recognized based on the color-filter upper image region  40   a , and then the parallax calculation process using the color image is executed if needed. 
     In addition, for the lower image region  40   c , as a narrowest region, which is not used for the image recognition. In  FIG. 2 , a hook is seen in the lower image region  40   c  in the stereo image  40 . The ND filter  12   c  that targets only a light wavelength (luminance information) by emitting LED light is set in the lower image region  40   c . Therefore, raindrops  40   c - 4  can be detected using the unnecessary image region (ND filter image region)  40   c  in the stereo image  40 . Alternatively, if the lower image region  40   c  is used as the image recognition, a target is set at a very close range. In this case, since the object in the photograph (image) is big in this lower image region  40   c , parallax calculation is executed by setting image rough. 
     As described above, in the stereo camera device  1 , the parallax calculation process and use method is variable for the optically divided regions  40   a ,  40   b , and  40   c , and the other image information (color information, luminance information) is used actively. Accordingly, the object misrecognition can be alleviated, the recognition success rate is improved, and the cost and space of the stereo camera system  1000  and the vehicle control system can be decreased. 
       FIG. 3  is a diagram illustrating a configuration of the image processor  30  in the stereo camera system  1000 . As illustrated in  FIG. 3 , the image processor  30  includes a parallax calculator  31 , a random access memory (RAM)  32 , a central processing unit (CPU)  33 , and a RAM  34 . The RAM  32  functions as a frame buffer to which a reference image  10 A acquired by the reference camera unit  10  and a comparison image  20 A acquired by the comparison camera unit  20  are input. The parallax calculator  31  is constituted by field programmable gate array (FPGA) or application specific integrated circuit ASIC. The CPU  33  executes recognition processing based on color pixel components (RGB pixel components) in the reference image  10 A passed through the color filter region  12   a  and the color pixel components in the comparison image  20 A passed through the color filter region  22   a . The RAM  34  temporarily stores data and process data executed by the CPU  33 . 
     The process executed by the parallax calculator  31  can be executed by the CPU  33 . However, considering processing speed, it is preferable that the parallax calculation process be executed by the hardware configuration. In the process of the parallax calculator  31 , if serious object misrecognition occurs and the parallax calculator  31  cannot separate the object suitably, many complicated processes arise, for example, various conditional branch processing is needed subsequent recognition processes, or previous-stage processing must be revisited. Therefore, the next-stage CPU  33  becomes expensive, and the processing time lengthens. In order to response to this problem, it is very important to keep simple process in the parallax calculator  31 , improve the recognition success rate of the parallax calculation process, reduce object misrecognition, and then alleviate a processing load on the subsequent CPU  33 . 
     However, the importance of the parallax calculator  31  becomes more significant in the city where the vehicle  40   b - 0 , the pedestrian, motorbike, and bicycle  40   b - 1 , the traffic light/traffic sign  40   a - 2  are recognized as targets, than in the highway where only the vehicle in front is mainly detected. Accordingly, the parallax calculation process method is set variable, and using other method aggressively, the decrease in the object misrecognition and improve in the recognition success rate become practical, and the cost and space of the stereo camera system  1000  and the vehicle control system can be decreased. 
       FIG. 4  is a fundamental view illustrating the stereo camera device  1 . The image processor  30  computes a distance to the objects, using a baseline length (distance between the reference camera unit  10  and the comparison camera unit  20 ) B, a focal length f, a parallax (difference in the focus point from viewpoint) d, and a distance Z to the object. 
     The parallax (disparity) d is calculated based on following formula 1. 
     
       
         
           
             
               
                 
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     In the formula 1, a reference numeral d represents a corresponding position between the reference image  10 A acquired by the reference camera unit  10  and the comparison image  20 A acquired by the comparison camera unit  20 . The position d is generally calculated by block-matching using vicinity pixels around an attention pixel. For example, assuming that the block size of frame containing the vicinity pixels is set at 9×9 block, the parallax d is calculated based on sum of absolute difference (SAD) like that represented as a following formula 2. 
     
       
         
           
             
               
                 
                   
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     As for a block matching method, other than SAD, various methods, such as, Sum of Squared Differences (SSD), Normalized Cross Correlation (NCC), and Zero-mean Sum of Absolute Differences (ASAD) are proposed, and any method can be used for this disclosure. 
     Using this block-matching parallax calculation method, pixels in the comparison image (or decimal interpolated sub-pixel composite image) are calculated one by one for a target pixel in the reference image, and the most correlated position is computed as the parallax “d”. 
     As described above, to search the parallax about certain pixels, a process for the pixels corresponding to at least equal to or over the assumed parallax d is needed, and therefore, an enormous amount of time is required. For example, assuming that a search length (width) w where the parallax d is searched while the pixel is shifted per one pixel is 64 pixels, the processing time to execute parallax calculation for a certain image takes 64 times as long as the processing time for one pixel, even if a time period in which the parallax d is searched for 1 pixel is set at 1 clock cycle. However, in general, a setting that a time period in which correlation value is searched for 1 pixel is at 1 clock cycle is impossible, and the processing time is exponentially increased based on the block size used for calculating correlation value. Therefore, reducing the parallax calculation time is major issue. The parallax calculation is represented as a general forms, as following formula 3.
 
 T=N ×( t×w )  (3)
 
     In the formula, T represents a parallax calculation time for one image, N represents number of pixels of parallax calculation, t represents related calculation time per pixel, and w represents the search width. This calculation formula 3 corresponds to a process at step S 202  in  FIG. 9 , and shortening this processing time is one of solving way to the issue. In order to solve this issue, in the present embodiment, this parallax calculation is executed only for the clear-filter image region  40   b.    
       FIG. 5  is a flow chart illustrating a process in the stereo camera system  1  in the present disclosure. Initially, the reference camera unit  10  and the comparison camera unit  20  capture the reference image  10 A and the comparison image  20 A as stereo images (captured images) at step S 100 . Then, each of the reference image  10 A and the comparison image  20 A is divided based on the filter component of the filters  12  and  22  shown in  FIG. 1B  at step S 101 . By passing the respective filter regions  12   a ,  12   b , and  12   c , different processes are executed for the image regions  40   a ,  40   b , and  40  whose optical characteristics differ respectively. 
     &lt;Process in the Clear-Filter Image Region  40   b&gt;   
     In the image shown in  FIG. 2 , the two items of luminance information of the clear-filter image regions  40   b  in the reference image  10 A( 40 ) and the comparison image  20 A( 40 ) are input to the parallax calculator  31  shown in  FIG. 3 , the parallax calculation using the luminance image (luminance information) described with  FIG. 4  is executed at step S 102 . In particular, since the parallax calculation process at step S 102  needs much time, though the process is simple, executing the parallax calculation process by the hardware configuration is necessary. Then, in the parallax calculator  31 , using the clear-filter image region  40   b  in the reference image  10 A, to recognize the dividing line (stop line) in the road at step S 103   a , and to execute the clustering at step S 103   a , using the parallax information calculated at step S 103   b . The clustering results are modified based on the own vehicle size and the sizes of the objects such as vehicle  40   b - 0 , pedestrian, motorbike, and bicycle  40   b - 1 , at step S 104 . 
     Then, using target model information, the clustering results are modified at step S 105 . For example, the height of the road is calculated based on the data of the dividing line  40   b - 3  recognized at step S 103   a , and the objects  40   b - 0  and  40   b - 1  on the dividing line  40   b - 3  is used as the target model. Then, based on the luminance information of the reference image  10 A, final determination is made regarding the target object  40   b - 0  and  40   b - 1  for the region for which clustering is executed, using adaptive boosting (Adaboost), at step S 106 . With these processes, the parallax calculator  31  outputs three-dimensional positions of the recognized objects  40   b - 0  and  40   b - 1  at step S 107 . 
     &lt;Process in the Color-Filter Image Region  40   a&gt;   
     Herein, the process for the color-filter image region (central region)  40   a  is not executed in the parallax calculator  31 , but the data is transmitted to the CPU  33 , and the CPU  33  executes recognition processing of the traffic light and the traffic sign  40   a - 2  in the color-filter image region  40   a . Using the color-filter image region  40   a  of the reference image  10 A( 40 ) divided at the step S 101 , the CPU  33  recognizes the traffic light and the traffic sign  40   a - 2  at step S 110 . Then, the CPU  33  performs the parallax calculation only for the result area where at least one of the traffic light and the traffic sign  40   a - 2  is recognized, using the color information detected in both the reference image  10 A and the comparison image  20 A, at step S 111 . The CPU  33  outputs the three-dimensional positions about the recognized objects of the traffic light and the traffic sign  40   a - 2  at step S 112 . 
     As described above, the parallax calculator  31  performs the parallax calculation for the result area in the color-filter image region  40   a , recognized by the CPU  33 . At this time, the parallax calculator  31  is needed to perform the parallax calculation for the color-filter image region  40   a  whose type is different from that executed for the clear-filter image region  40   b.    
     Since the color image is represented as R, G, B, or YCnCr, the color information used for the parallax calculation is not one dimension, as the luminance information of the monochrome image. The parallax calculation for the color image is generally required to take over 3 times longer than that for the luminance image. 
     In addition, in the parallax calculation for the color image, although the object misrecognition can be alleviated because the matching process is performed based on the multiplex information, the parallax cannot be calculated for the entire pixels, unlike the clear-filter image region  40   b . In addition, the focused points passed through the lenses  11  and  21  are not uniform in the entire pixels, unlike the luminance image, and thus, measuring distance with a high degree of accuracy becomes impractical. Therefore, this color lens is not suit for calculating the parallax for the faraway objects. Accordingly, it is preferable that the parallax be calculated only for the recognized area in the color-filter image region  40   a  where the objects of the traffic light/traffic sign  40   a - 2  are recognized by using the color information. 
     In addition, when the parallax is calculated for the recognized portion in the color-filter image region  40   a , since purpose in use is different from the parallax calculation for the luminance information in the clear-filter image region  40   b , suitable algorithm and parameter of the parallax calculation for the color image is differ from that for the luminance image. 
     For example, when the color objects  40   a - 2  are detected in the image, it is necessary to calculate the parallax in the entire image initially and then to measure the distance to the object  40   a - 2 , considering the dispersion of the color parallax. Accordingly, it is preferable that the block matching be applied for the image where the image difference among the pixels or between the adjacent pixels is large, using more simple method. 
     By contrast, when it appears that a certain object is acquired in a certain portion in the reference image  10 A, the entirety of that portion is treated as a single lump and the comparison image  20 A is searched for a lump having characteristics identical to those of the acquired lump. As for these methods, not block matching but, for example, phase limitation correlation using spatial frequency characteristics is effective for this parallax calculation. 
     &lt;Process in the ND Filter Image Region  40   c&gt;   
     As for the ND filter image region  40   c , the data is not executed in the parallax calculator  31  but is transmitted to the CPU  33 , and the CPU  33  recognizes the raindrops  40   c - 4 . The CPU  33  does not execute the parallax calculation because the range to the raindrops  40   c - 4  need not be found. At step S 120 , the CPU  33  recognizes the raindrops  40   c - 4 , using the luminance image for the ND filter image region  40   c  in the reference image  10 A at step S 120 . Then, the CPU  33  outputs the detection results for the raindrops  40   c - 4  at step S 121 . 
       FIGS. 6A and 6B  are timing charts illustrating the elements of the distance measuring (ranging) process in the stereo camera system.  FIG. 6B  illustrates respective flows in the stereo camera system  1000  in which the parallax is calculated for only the regions  40   b  and the predetermined area of the region  40   a  in the captured image  40  shown in  FIG. 1B . 
       FIG. 6A  is a timing chart illustrating a comparative example of a stereo camera system in which the parallax calculator executes the parallax calculation and clustering for the entire images based on the luminance, at the process step S 300 , executes recognition processing for the color image acquired by the color camera set at separately at step S 301 , and modifies the process results at process at step S 303  based the recognition result of the process at step S 301 . In the flow shown in  FIG. 6A , the parallax calculation and the clustering are executed for the entire image based on the luminance, this process at step  300  takes 3 frames. The parallax image executed by the process at step  300  is illustrated in  FIG. 7 .  FIG. 7  is a parallax image after the parallax is calculated and clustering is executed in  FIG. 6A . To recognize the color image takes a long processing time and causes many object misrecognitions. 
     By contrast, in the present embodiment, the optical filters  12  and  22  are constituted by a special type of the optical filter (complex optical filter) as illustrated in  FIG. 1B , and the parallax calculation logic suitably to the respective regions is applied. Accordingly, the process of the color recognition and the parallax calculation can be executed by only single camera image  40 . In addition, the process method for the corresponding region are changed, and therefore, the process in the CPU  33  and the parallax calculator  31  can be effectively used, as illustrated in  FIG. 6B . That is, in the present embodiment, the clear-filter image region  40   b  is set at one-third in the entire image  40 , and the parallax calculation in the parallax calculator  31  can be executed within 1 frame that is one-third time of the parallax calculation process shown in  FIG. 6A . With reference to  FIG. 6B , after the processes at the steps S 102  and S 103  are executed within 1 frame, the process at step S 112  can be performed in the subsequent frame at step S 111 . 
     Along with these processes, the CPU  33  can perform the processes at steps S 110  and S 120  within one frame, and performs the processes at steps S 101  through S 106  within the subsequent frame. In the present embodiment, the efficiency in the process is greatly high. Further, adding the recognition for the color image, the ranging using the color information becomes possible. This is the reason why the color image suitable portion where the target of the traffic light/traffic sign  40   a - 2  is recognized in the color-filter image region  40   a  is detected as the recognized portion (recognized target area), and the then, parallax calculation is executed for only the recognized portion. It is to be noted that, in order to be made this process possible, switching in the parallax calculation algorithm, corresponding to the optical filter captured image and the recognition method, and switching in the parameter are needed. 
     In general, when the entirely-different parallax calculation logics are applied, different types of parallax calculation logics have to be implemented in the parallax calculation hardware (parallax calculator). Depending on the required accuracy of the recognized portion, general block-matching algorithm may be used. In this case, when the general block-matching algorithm is applied to the images whose optical characteristics are different, only changing the block size is not enough to calculate the parallax. 
     For example, in the color image region, since the image is focused on the pixels through the RGB color filter, when the primary image whose color is not interpolated is used, the search widths of the respective filter separated image regions are changed, or when the image whose color is interpolated is used, the amount of pixel information after the color is interpolated differs among the respective regions. 
     As described above, in the present disclosure, by dividing the filter and formed image into the central region  40   b  where the parallax calculation is executed based on the luminance, the upper region  40   a  where the image can be rather effectively recognized using the color image, depending on the application and the recognition target, the object misrecognition by the parallax calculator  31  can be alleviated and the recognition success rate can be improved. 
     In addition, the parallax calculation logic can be applied for the respective divided regions effectively, and unnecessary calculating can be reduced. Furthermore, since the region where the parallax calculation using the luminance information is executed can be limited, the processing load on the parallax calculator  31  can be minimized, thereby reducing the cost of the parallax calculator  31  and the CPU  33 . In addition, providing an additional sensor for detecting the raindrops  40   c - 4 , an additional color camera for recognizing the color information and constituting the color stereo camera whose processing load is great becomes unnecessary. Accordingly, the utility stereo camera can operate multiple applications, resulting in reduced cost and size of the stereo camera system. 
     In the present disclosure, the stereo camera system  1000  optically devises the optical filters  12  and  22  so that the (acquired) stereo image can be divided into multiple regions corresponding to the recognition targets, and the image sensors  11  and  21  can capture the image in a form suitable for recognition processing. 
     Accordingly, organizing the recognized target, arranging the regions to capture the target, constructing the special type of the optical filters (complex filters)  12  and  22  suitable for the recognition, changing the algorithm of the parallax calculation logic, and changing thinning out image rate and the position detected algorithm of the parallax calculation executed pixels in accordance with the image characteristics of the special type filter and the recognition method, the object misrecognition can be alleviated and the recognition target can be expanded. 
     Furthermore, with this improvement of the characteristics, the entire process can be sped up. In the above-described embodiment, the stereo camera system includes two camera lenses, similar configuration and basis can be applied, the stereo camera system can install over two distance measuring (ranging) cameras. 
     &lt;Vehicle&gt; 
       FIG. 8  is a schematic diagram illustrating a vehicle  50  mounting the present stereo camera system  1000  (range-finding device). An image processing system in the vehicle  50  includes a pickup unit  51  to acquire the image forward the vehicle  50  and an image analysis unit  52  that calculates the distance from another vehicle driving in front of the vehicle  50  based on the image captured in the pickup unit  51 . The image pickup unit  51  is positioned near a rearview mirror in the vehicle  50  so that the image pickup unit  51  can capture the image forward of the vehicle  50  containing another vehicle driving in front of the vehicle  50  and calculate a distance to another vehicle from the vehicle  50 . The image of the vehicle in front acquired by the image pickup unit  51  is input to and converted into the image signal for output to the image analysis unit  52 . The image analysis unit  52  analyses the output image signal from the image pickup unit  51 . As for the image pickup unit  51 , the stereo camera device  1  of the present embodiment composed of the reference camera unit  10  and the comparison camera unit  20  can be used. As a part of function of the image analysis unit  52 , the parallax calculator  31  and the CPU  33  can be applied. 
     A vehicle drive control unit  58  can control the steering and the brake of the vehicle  50  based on the distance from the vehicle in the front calculated by the image analysis unit  52 . 
     Numerous additional modifications and variations are possible in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the disclosure of this patent specification may be practiced otherwise than as specifically described herein.