Patent Publication Number: US-10775497-B2

Title: Object detection device and object detection method

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This patent application is a national stage application under 35 U.S.C. § 371(c) of PCT Application No. PCT/JP2017/013835, filed on Mar. 31, 2017, which claims priority to Japanese Patent Application No. 2016-074643 filed on Apr. 1, 2016 in the Japan Patent Office, the entire disclosure of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to an object detection device that detects an object based on an image captured by an imaging means, and an object detection method. 
     BACKGROUND ART 
     For example, PTL 1 discloses a device that includes a radar sensor in a vehicle and acquires the lateral width of an object as a lateral dimension from a reflection point on the object by the radar sensor. The device described in PTL 1 determines that the true value of the lateral width is not detected when the object is positioned at an end of the probe range of the radar sensor or when another object exists in front of the target object. When determining that the object is not detected, the device corrects the current lateral width by a past lateral width recorded in a history. 
     According to PTL 1, even when the lateral width of an object is not correctly detected, the lateral width is corrected based on the past history information to suppress a problem that a warning or the like is given due to a failure to acquire the correct lateral width. 
     CITATION LIST 
     Patent Literature 
     [PTL 1] JP 2002-296350 A 
     SUMMARY OF THE INVENTION 
     When the lateral width of an object is acquired based on an image captured by an imaging means such as a camera or the like, the acquired lateral width of the object may incorrectly be smaller than in reality. The incorrect acquisition of lateral width of an object can occur regardless of the position of the object relative to the imaging means or whether another object exists in front of the target object. Therefore, according to the disclosure of PTL 1, even though the acquired lateral width of an object is smaller than in reality, it may be determined that the lateral width of the object is correctly detected. 
     The present disclosure has been conceived to solve the aforementioned problem. An object of the present disclosure is to provide an object detection device that correctly acquires the lateral width of an object positioned around a subject vehicle, and an object detection method. 
     According to the present disclosure, an object detection device detects an object existing around a vehicle based on an image captured by an imaging means. The object detection device includes: a lateral width acquisition unit that acquires a dimension of the object in a lateral direction with respect to an imaging direction of the imaging means as a lateral width; a determination unit that compares the current lateral width acquired by the lateral width acquisition unit with a past lateral width to determine whether the current lateral width is smaller than the past lateral width; and a correction unit that, when the current lateral width is smaller than the past lateral width, corrects right and left end positions of the current lateral width based on whichever is smaller, the deviation amount of the right end position of the object or the deviation amount of the left and position of the object. 
     The lateral width of an object may incorrectly be acquired to be smaller than in reality depending on the shape and pattern of outer surface of the object, attachments to the object, and the like. In this case, both the right and left end positions of the object are displaced. The deviation amounts of the right and left end positions of the lateral width are compared in magnitude relationship, under the concept that the end position with the smaller deviation amount more likely to have been correctly acquired than the end position with the larger deviation amount. Then, when the current width is smaller than the past lateral width, the right and left end positions of the lateral width are corrected based on the smaller one of the deviation amount of the right end position of the object or the deviation amount of left end position of the object. Accordingly, the right and left end positions of the lateral width can be corrected by the same deviation amount to suppress significant displacements of the right and left end positions of the lateral width and acquire the proper object width. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other objects, features, and advantages of the present disclosure will be more clarified by the following detailed description with reference to the attached drawings: 
         FIG. 1  is a configuration diagram of a PCSS; 
         FIG. 2  is a diagram describing positional information of a target object Ob detected by a controller; 
         FIG. 3  is a diagram describing PCS performed by a driving support ECU; 
         FIG. 4  is a diagram describing detection of width of an object; 
         FIG. 5  is a diagram describing deviation amounts DV; 
         FIG. 6  is a flowchart of a lateral width correction process performed by the driving support ECU; 
         FIG. 7  is a diagram describing the directions of displacements of right and left end positions; and 
         FIG. 8  is a diagram describing correction of an object width WO according to a second embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiments of an object detection device and an object detection method according to the present disclosure will be described below with reference to the drawings. In the embodiments described below, identical or equivalent components are given the same reference signs and descriptions of the components with the same reference signs are incorporated by reference. 
     First Embodiment 
       FIG. 1  illustrates a pre-crash safety system (hereinafter, called PCSS)  100  to which an object detection device and an object detection method are applied. The PCSS  100  is an example of a vehicle system installed in a vehicle, for example, which detects an object in front of the vehicle. When there is a risk of a collision between the detected object and the vehicle, the PCSS  100  performs processes for avoiding a collision of the subject vehicle with the object or mitigating the collision. In the following description, the vehicle equipped with the PCSS  100  will be called subject vehicle CS, and the object as a target of detection will be called target object Ob. 
     As illustrated in  FIG. 1 , the PCSS  100  includes various sensors, a driving support ECU  20 , a brake device  40 , a warning device  50 , and a seat belt device  60 . In the embodiment illustrated in  FIG. 1 , the driving support ECU  20  functions as an object detection device. 
     The various sensors are connected to the driving support ECU  20  to output detection results of the target object Ob to the driving support ECU  20 . Referring to  FIG. 1 , the various sensors include a camera sensor  31  and a radar sensor  37 . 
     The camera sensor  31  is formed from a CCD camera, a CMOS image sensor, or a near infrared sensor, for example. The camera sensor  31  is arranged on the front side of the subject vehicle CS to recognize the object Ob in front of the subject vehicle CS. The camera sensor  31  includes an imaging unit  32  that captures an image of the area in front of the subject vehicle, a controller  33  that performs known image processing on the image acquired by the imaging unit  32 , and an ECU I/F  36  that allows communications between the controller  33  and the driving support ECU  20 . The imaging unit  32  functions as an imaging means. 
     The imaging unit  32  includes a lens part that functions as an optical system and an imaging element that converts light collected through the lens part into an electrical signal. The imaging element can be a known imaging element such as a CCD or a CMOS. The electrical signal converted by the imaging element is stored as a captured image in the controller  33  through an ECU I/F  36 . 
     The controller  33  is formed from a known computer including a CPU, ROM, and RAM. The controller  33  includes functionally an object recognition unit  34  that recognizes the target object Ob seen in the captured image and a positional information calculation unit  35  that calculates positional information of the recognized object. The object recognition unit  34  recognizes the target object Ob from the captured image using dictionary information. The positional information calculation unit  35  calculates the relative position of the recognized target object Ob to the subject vehicle CS. 
     Specifically, the object recognition unit  34  acquires image data from the imaging unit  32 , and determines the kind of the target object Ob in front of the subject vehicle based on the image data and prepared dictionary information for object identification. The dictionary information for object identification is prepared for the individual kinds of objects such as automobile, two-wheel vehicle, and pedestrian, for example, and is stored in advance in the memory. The dictionary information for automobile is preferably prepared for at least a front part pattern and a rear part pattern. The dictionary information for two-wheel vehicle is preferably prepared to differentiate between bicycle and motorcycle. The object recognition unit  34  determines the kind of the target object Ob by comparing the image data with the dictionary information and conducting pattern matching. The dictionary information may include not only dictionary information for moving objects but also dictionary information for stationary objects such as guard rails, utility poles, road signs, and others. 
     As illustrated in  FIG. 2 , the positional information calculation unit  35  acquires positional information indicating the right and left relative positions of the target object Ob in a lateral direction D 2  with respect to the imaging direction of the camera sensor  31 . The positional information includes a lateral position X (Xl and Xr) indicating the right and left side positions of the target object Ob as seen in the lateral direction D 2  and an azimuth angle θ indicating the direction from the subject vehicle CS to the target object Ob. For example, the positional information calculation unit  35  calculates the azimuth angle θ using the lateral position X and the position of the subject vehicle CS. 
     The radar sensor  37  detects an object in front of the subject vehicle using directive electromagnetic waves such as millimeter waves or laser beams. The radar sensor  37  is installed in the front part of the subject vehicle such that its optical axis faces the area in front of the subject vehicle. The radar sensor  37  scans the area expanding in front of the vehicle within a predetermined scope with transmitted waves at predetermined time intervals, and receives reflected waves reflected by the surface of the object in front to acquire the distance to the object in front and the relative velocity to the object in front as object information. The radar sensor  37  inputs the acquired object information to the driving support ECU  20 . 
     The brake device  40  includes a brake mechanism that changes braking force of the subject vehicle CS and a brake ECU that controls the operation of the brake mechanism. The brake ECU is communicably connected to the driving support ECU  20  and controls the brake mechanism under control of the driving support ECU  20 . The brake mechanism includes, for example, a master cylinder, a wheel cylinder that applies braking force to the wheels, and an ABS actuator that adjusts the distribution of pressure (hydraulic pressure) from the master cylinder to the wheel cylinder. The ABS actuator is connected to the brake ECU and adjusts the hydraulic pressure from the master cylinder to the wheel cylinder under control of the brake ECU to regulate the amount of operation on the wheels. 
     The warning device  50  warns the driver about the presence of the target object Ob in front of the subject vehicle under control of the driving support ECU  20 . The warning device  50  is formed from a speaker provided in the cabin and a display unit that displays an image, for example. 
     The seat belt device  60  is a pretensioner that draws in a seat belt provided in each seat of the subject vehicle. When there is an increasing probability of a collision between the subject vehicle CS and the target object Ob, the seat belt device  60  performs a preliminary action of drawing in the seat belt. If the collision is inevitable, the seat belt device  60  draws in the seat belt to take the slack out of the seat belt, thereby securing the passenger such as the driver in the seat to protect the passenger. 
     The driving support ECU  20  is formed from a known microcomputer including a CPU, a ROM, and a RAM. The driving support ECU  20  refers to arithmetic programs and control data in the ROM to control the subject vehicle CS. The driving support ECU  20  also detects the target object Ob based on the image captured by the camera sensor  31 , and performs PCS on at least one of the devices  40 ,  50 , and  60  based on the detection result. 
     The driving support ECU  20  performs programs stored in the ROM to function as a lateral width acquisition unit  21 , a history calculation unit  22 , a determination unit  23 , a correction unit  24 , and a collision determination unit  25 . 
     First, the PCS performed by the driving support ECU  20  will be described with reference to  FIG. 3 . The collision determination unit  25  determines the probability of a collision between the subject vehicle CS and the target object Ob. In the embodiment, the collision determination unit  25  determines the probability of a collision using the lateral position of the target object Ob relative to the subject vehicle CS.  FIG. 3  illustrates the timings for actions of the PCS with TTC on the vertical axis and the lateral position on the lateral axis, with respect to the subject vehicle CS. The TTC decreases with a value on the vertical axis increasing proximity to the subject vehicle CS, which means that the time before the target object Ob collides with the subject vehicle CS is shorter. 
     The collision determination unit  25  determines the probability of a collision with the target object Ob using overlap ratio RR of an object width WO indicating the lateral dimension of the target object Ob and a collision determination area CDA virtually set in front of the subject vehicle. The collision determination area CDA is a virtual area that has a predetermined width Wcda in the lateral direction of the vehicle and extends in an imaging axial direction (imaging direction) D 1 . The overlap ratio RR refers to the amount of the object width WO overlapping the width Wcda of the collision determination area CDA, which is calculated by the following equation (1):
 
Overlap ratio  RR=WO/Wcda   (1)
 
     The inclination of the collision determination area CDA with respect to the imaging axial direction D 1  is set based on the movement path of the target object Ob. 
     When the overlap ratio RR is equal to or higher than a predetermined value, the collision determination unit  25  calculates a time to collision (TTC) indicating the time before the target object Ob collides with the subject vehicle CS. The collision determination unit  25  performs the individual actions of the PCS according to the TTC. In the embodiment, for example, at TTC1, the collision determination unit  25  controls the warning device  50  to warn the driver about the presence of the target object Ob in front of the subject vehicle in the traveling direction. At TTC2, the collision determination unit  25  controls the brake device  40  to perform automatic braking to gently decelerate the subject vehicle CS by a predetermined amount. At TTC3, the collision determination unit  25  decelerates the subject vehicle CS under control of the brake device  40  and performs a preliminary action to increase the tension of the seat belt device  60 . At TTC3, the collision determination unit  25  strongly decelerates the subject vehicle CS by a larger deceleration amount than that at TTC2. 
     If the object width WO is recognized to be smaller than in reality at the determination of the overlap ratio RR, the calculated overlap ratio RR becomes lower so that collision avoidance control may not be correctly performed even through there is actually a high probability of a collision with the target object Ob. Specifically, when the camera sensor  31  calculates the lateral position X based on the captured image and the dictionary information and calculates the object width WO based on the lateral position X, the calculated object width WO may incorrectly be smaller than in reality depending on the shape and pattern of the outer surface of the target object Ob and attachments to the target object Ob. In addition, when the target object Ob is a vehicle running in front of the subject vehicle, the rear part of the vehicle has projections and depressions, and lamps different among vehicle types, and thus at the calculation of the object width WO, the object width WO may be recognized as smaller than the real lateral width. 
     Referring to the vehicle illustrated in  FIGS. 4( a ) and 4( b ) , the real object width WO ranges from an end point a 1  to an end point a 2  of the rear part of the vehicle. However, the rear part of the vehicle in front has tail lamps, and the dictionary information is considered as being assigned to the shape and pattern of the tail lamps. That is, the rear part of the vehicle has appearance change points b 1  and b 2  due to the tail lamps, for example, in addition to the end points a 1  and a 2 , and the change points b 1  and b 2  may be recognized as end points of the rear part of the vehicle body. In this case, the object width WO is calculated from a lateral width W 1  between the change points b 1  and b 2  and a lateral width W 2  between the change point b 1  and the end point a 2  in the image, and recognized as being smaller than in reality. Although not illustrated, it is considered that the object widths WO of objects other than vehicles could be similarly recognized as being smaller than in reality. 
     Accordingly, when the object width WO may be recognized as being smaller than in reality, the driving support ECU  20  extends and corrects the lateral position X. Next, the functions of the driving support ECU  20  for correcting the object width WO will be described. 
     Returning to  FIG. 1 , the lateral width acquisition unit  21  acquires the object width WO. The lateral width acquisition unit  21  acquires the lateral position X and the azimuth angle θ from the positional information output from the camera sensor  31 , and uses the acquired lateral position X to calculate the object width WO indicating the dimension of the target object Ob in the lateral direction D 2 . 
     The history calculation unit  22  records the lateral position X acquired by the lateral width acquisition unit  21  as an acquisition history. In the case where the lateral position X is acquired at predetermined time intervals, the lateral position X is recorded by the kind of the target object Ob in the acquisition history. In addition to the lateral position X, the azimuth angle θ is recorded in the acquisition history. 
     The determination unit  23  determines whether the current object width WO acquired by the lateral width acquisition unit  21  is small by comparison to the acquisition history. Hereinafter, the latest lateral position X recorded in the acquisition history will be called current lateral position XC, and the object width WO calculated by the lateral width acquisition unit  21  from the latest lateral position XC will be called current object width WC. The determination unit  23  also calculates an estimated lateral width WE indicating the dimension of the target object Ob in the lateral direction D 2  based on the acquisition history, and compares the current object width WC with the estimated lateral width WE to determine whether the current object width WC is smaller. Specifically, the determination unit  23  uses the largest one of the object widths WO calculated from the lateral positions X recorded in the acquisition history as the estimated lateral width WE. 
     When it is determined that the current object width WC is smaller than the estimated lateral width WE, the correction unit  24  corrects the current lateral position XC based on a smaller deviation amount DV of the deviation amounts DV of the lateral position X of the target object Ob. According to the correction of the current lateral position XC by the correction unit  24 , the object width WO is extended and corrected in the lateral direction D 2 . 
     The deviation amounts DV have values indicating the variation in a right end point Xr and a left end point Xl of the current lateral position XC in the lateral direction D 2 . In the embodiment, the correction unit  24  calculates the deviation amounts DV from the differences from the current lateral position XC with respect to the estimated lateral width WE (the maximum value of the object width WO) recorded in the acquisition history as expressed in the following equation (2):
 
 DVr=|Xmr−Xr| 
 
 DVl=|Xml−Xl|   (2)
 
where DVr and DVl represent respectively right and left deviation amounts of the lateral position X. In the embodiment, Xr and Xl represent the current lateral position XC, and Xmr and Xml represent the lateral position X with the maximum object width WO recorded in the acquisition history.
 
     The deviation amounts DV have values including zero. For example, when either the right end point Xr or the left end point Xl of the current lateral position XC is not changed in the lateral direction D 2 , the deviation amounts DV become zero. 
     For example, object widths (t) illustrated in  FIG. 5  correspond to the object widths WO calculated by the lateral width acquisition unit  21  at times t 1  to t 5 . In the order of t 5  to t 1 , the object widths WO are represented at earlier times t. Among them, the object width WO (t 5 ) at time t 5  is the current object width WC. The object width WO (t 1 ) at time t 1  is the maximum object width WO, which constitutes the estimated lateral width WE. In this example, with respect to the object width WO (t 1 ), the current object width WC has the deviation amount DVl of the left end point Xl larger than the deviation amount DVr of the right end point Xr. 
     The correction unit  24  corrects the current lateral position XC using the smaller deviation amount DV as a correction value ADV. In the example of  FIG. 5 , the deviation amount DVr of the right end point Xr is smaller than the deviation amount DVl of the left end point Xl, and the deviation amount DVr of the right end point Xr constitutes the correction value ADV. Then, the correction unit  24  corrects the current lateral position XC by the correction value ADV. The thus corrected current lateral position XC is used by the collision determination unit  25  to determine the probability of a collision between the subject vehicle CS and the target object Ob as described above. 
     Next, a correction process of the object width WO performed by the driving support ECU  20  will be described with reference to the flowchart of  FIG. 6 . This process is repeatedly performed by the driving support ECU  20  at predetermined time intervals. 
     In step S 11 , the driving support ECU  20  calculates the current object width WC. The driving support ECU  20  acquires the latest lateral position X recorded in the history information as the current lateral position XC, and calculates the current object width WC based on the lateral position XC. Step S 11  functions as a lateral width acquisition step. 
     In step S 12 , the driving support ECU  20  calculates the estimated lateral width WE using the acquisition history. In the first embodiment, the driving support ECU  20  acquires from the acquisition history the lateral position X that is the same in kind as the current object width WC calculated in step S 11  and has the maximum object width WO. Then, the driving support ECU  20  uses the acquired lateral position X to calculate the estimated lateral width WE. 
     In step S 13 , the driving support ECU  20  determines whether the current object width WC is equal to or less than the estimated lateral width WE. For example, the driving support ECU  20  compares the current object width WC acquired in step S 11  to the estimated lateral width WE calculated in step S 12 . Step S 13  functions as a determination step. 
     When determining that the current object width WC is larger (step S 13 : NO), the driving support ECU  20  proceeds to step S 20 . In this case, the driving support ECU  20  determines that the current lateral position XC is proper, and updates the current lateral position XC as the lateral position X of the target object Ob in step S 20 . 
     On the other hand, when determining that the current object width WC is smaller than the estimated lateral width WE (step S 13 : YES), the driving support ECU  20  determines in step S 14  whether the current lateral position XC is displaced in the lateral direction D 2  with respect to the estimated lateral position XE. When the current lateral position XC and the estimated lateral position XE have the same right end point Xr and left end point Xl, it can be determined that the object width WO is correctly acquired. Accordingly, when not determining in step S 14  that the current lateral position XC is displaced in the lateral direction D 2  with respect to the estimated lateral position XE (step S 14 : NO), the driving support ECU  20  proceeds to step S 20  to update the current lateral position XC as the lateral position X of the target object Ob. 
     When determining that the current lateral position XC is displaced in the lateral direction D 2  (step S 14 : YES), the driving support ECU  20  calculates the correction value ADV according to the smaller deviation amount DV of the current lateral position XC in step S 15 . The driving support ECU  20  uses the foregoing equation (2) to calculate the respective deviation amounts DV of the right end point Xr and the left end point Xl. Then, the driving support ECU  20  determines the smaller deviation amount DV from a comparison between the calculated displacement volumes DV, and calculates the correction value ADV corresponding to the determined deviation amount DV. In the embodiment, the correction value ADV is identical to the value of the smaller deviation amount DV. 
     In step S 16 , the driving support ECU  20  determines whether the right end point Xr and the left end point Xl of the current lateral position XC are displaced in the same direction. The driving support ECU  20  determines the displacement directions of the right end point Xr and the left end point Xl by a comparison in the right end point Xr and the left end point Xl between the estimated lateral position XE and the current lateral position XC. 
       FIG. 7( a )  illustrates a case with different displacement directions of the object width WC. When the current object width WC is equal to or less than the estimated lateral width WE and the target object Ob is not moved in the lateral direction D 2 , the current lateral position X is located inside the estimated lateral position XE. 
       FIG. 7( b )  illustrates a case with the same displacement direction of the right end point Xr and the left end point Xl. When the current object width WC is equal to or less than the estimated lateral width WE and the relative positions of the subject vehicle CS and the target object Ob change in the lateral direction D 2 , the current lateral position XC has both the right end point Xr and the left end point Xl displaced in the relative movement direction of the subject vehicle CS and the target object Ob as compared to the estimated lateral position XE. For example, when the target object Ob moves in the lateral direction D 2  or the subject vehicle CS moves in the lateral direction D 2 , the right end point Xr and the left end point Xl are displaced in the same direction. 
     When determining that the right end point Xr and the left end point Xl are displaced in different directions (step S 16 : NO), the driving support ECU  20  uses the correction value ADV calculated in step S 15  to shift and correct the right end point Xr and the left end point Xl of the current lateral position XC at the azimuth angle θ in step S 17 . Referring to  FIG. 7( a ) , the deviation amount DVr of the right end point Xr is smaller than the deviation amount DVl of the left end point Xl, and the right end point Xr is located inside the right end point Xr of the estimated lateral position XE. Accordingly, the driving support ECU  20  moves the right end point Xr and the left end point Xl of the estimated lateral position XE toward the central side by the correction value ADV calculated according to the deviation amount DVl of the right end point Xr to calculate corrected right end point AXr and left end point AXl. 
     On the other hand, when determining that the right end point Xr and the left end point Xl are displaced in the same direction (step S 16 : YES), in step S 18 , the driving support ECU  20  uses the correction value ADV calculated in step S 15  to shift and correct the right end point Xr and the left end point Xl of the current lateral position XC in the movement direction of the target object Ob. Referring to  FIG. 7( b ) , the right end point Xr of the current lateral position XC is located outside the right end point Xr of the estimated lateral position XE to generate movement in the lateral direction D 2 . Accordingly, the driving support ECU  20  shifts the right end point Xr and the left end point Xl of the estimated lateral position XE to the right by the correction value ADV to calculate the corrected right end point AXr and left end point AXl. Steps S 17  and S 18  serve as correction steps. 
     In step S 19 , the driving support ECU  20  uses the corrected right end point AXr and left end point AXl calculated in step S 17  or S 18  to recalculate the azimuth angle θ output from the camera sensor  31 . For example, the driving support ECU  20  calculates the azimuth angle θ using the corrected right end point AXr and left end point AXl and the current position of the subject vehicle CS. 
     In step S 20 , the driving support ECU  20  updates the lateral position X of the target object Ob. In this case, the driving support ECU  20  updates the corrected right end point AXr and left end point AXl and the azimuth angle θ calculated in step S 19  as the right end point Xr, the left end point Xl, and the azimuth angle θ of the corrected object width WO. 
     As described above, in the first embodiment, when the current object width WC is smaller than the past object width WO, the driving support ECU  20  corrects the right end point Xr and the left end point Xl of the current lateral position XC based on the smaller deviation amount DV of the right and left deviation amounts DV of the target object Ob. Accordingly, the right end point Xr and the left end point Xl of the object width WO are corrected by the same deviation amount DV to suppress significant displacements of the right and left positions of the object width WO as compared to the true value, and acquire the proper object width. 
     The true value of the object width is unlikely to exceed the maximum value of the past lateral width, and the driving support ECU  20  uses the maximum value as the estimated lateral width WE. According to the foregoing configuration, it is possible to prevent the object width WO from being excessively extended. 
     The driving support ECU  20  sets the position of the past object width WO shifted in the lateral direction D 2  by the volume based on the smaller deviation amount DV as the corrected lateral position AX. According to the foregoing configuration, setting the lateral position X of the past object width WO shifted by the same deviation amount DV as the corrected lateral position X makes it possible to prevent significant displacement of the center of the object width WO as compared to the true value. 
     When the right and left sides of the object width WO of the target object Ob are displaced in the same lateral direction, the driving support ECU  20  corrects the lateral position X of the object width W in the same direction of displacement based on the smaller deviation amount DV. When the relative positions of the target object Ob and the subject vehicle CS change in the lateral direction D 2 , the lateral position X of the target object Ob changes in the same direction. In such a case, the driving support ECU  20  corrects the right and left sides of the lateral position X in the same lateral direction based on the smaller deviation amount DV. According to the foregoing configuration, the object width WO can be correctly acquired even when the relative positions of the target object Ob and the subject vehicle CS change in the lateral direction D 2 . 
     Second Embodiment 
     In a second embodiment, instead of using the maximum value of the object width WO recorded in the acquisition history as the estimated lateral position XE, the driving support ECU  20  uses the previous object width WO recorded in the acquisition history as the estimated lateral position XE. 
       FIG. 8  illustrates changes in object width WO at times t 11  to t 13  when the target object Ob moves to the right in the lateral direction D 2  (indicated by an arrow in the drawing). An object width WO(t 13 ) at time t 13  is set as the current object width WO, and an object width WO(t 12 ) at time t 12  is set as the previous object width WO. 
     In the example illustrated in  FIG. 8 , in step S 11  of  FIG. 6 , the driving support ECU  20  acquires the current object width WC (WO(t 13 )) based on the lateral position X at time t 13 . Then, in step S 12 , the driving support ECU  20  acquires an estimated lateral width WE (object width WO(t 12 )) based on the estimated lateral position XE at time t 12 . 
     In step S 15 , the driving support ECU  20  calculates the correction value ADV according to the smaller deviation amount DV of the estimated lateral width WE calculated according to a previous lateral position XO and the current lateral position XC. Then, in step S 17  or S 18 , the driving support ECU  20  corrects the current lateral position XC according to the calculated correction value ADV. Referring to  FIG. 8 , the left end point Xl is changed leftward to extend the corrected object width WO(t 13 ) in the lateral direction. 
     As described above, when the target object Ob moves laterally, the deviation amount of the object width WO includes a displacement resulting from the incorrect acquisition of the object width WO and a displacement resulting from the lateral movement of the object. Accordingly, the driving support ECU  20  corrects the deviation amount using the previous value of the object width WO. According to the foregoing configuration, even when the target object Ob moves in the lateral direction, the deviation amount resulting from the lateral movement of the target object Ob is diminished by the difference between the previous value and the current value to allow the lateral width of the target object Ob to be correctly acquired. 
     OTHER EMBODIMENTS 
     The camera sensor  31  may not calculate the lateral position X and the azimuth angle θ of the target object Ob but the driving support ECU  20  may calculate the lateral position X and the azimuth angle θ of the target object Ob. In this case, the camera sensor  31  includes the imaging unit  32  and the ECU I/F  36  illustrated in  FIG. 1 , and the driving support ECU  20  includes functionally the object recognition unit  34  and the positional information calculation unit  35 . Then, the driving support ECU  20  calculates the lateral position X and the azimuth angle θ of the target object Ob based on the captured image output from the camera sensor  31 . 
     The camera sensor  31  and the driving support ECU  20  may be configured as an integral device. In this case, the camera sensor  31  includes the functions of the lateral width acquisition unit  21 , the history calculation unit  22 , the determination unit  23 , the correction unit  24 , and the collision determination unit  25 . 
     A driving support device  10  may be configured to recognize the target object Ob based on the result of detection of the target object Ob by the camera sensor  31  and the result of detection of the target object Ob by the radar sensor  37 . 
     When it is determined in step S 13  of  FIG. 6  that the current object width WC is larger, the lateral position X with the maximum object width WO recorded in the acquisition history may be updated as the lateral position X of the target object Ob. 
     The deviation amounts DV may be calculated by a comparison between the current lateral position XC and the average value of a plurality of past lateral positions X recorded in the acquired history. For example, the driving support ECU  20  calculates the respective average values of the right end point Xr and the left end point Xl of the plurality of past lateral positions X. Then, the driving support ECU  20  calculates the deviation amounts DV by comparing the right end point Xr and the left end point Xl of the current lateral position XC with the calculated average values of the right end point Xr and the left end point Xl. 
     Instead of determining the probability of a collision between the subject vehicle CS and the target object Ob using the object width WO, the collision determination unit  25  may determine the probability of a collision between the subject vehicle CS and the target object Ob using the position of a central point as seen in the lateral direction D 2  determined from the right and left end positions Xr and Xl. In this case, the driving support ECU  20  calculates the position of the target object Ob in the lateral direction D 2  with the risk of a collision between the target object Ob and the subject vehicle CS based on the movement path of the position of the central point. Then, the driving support ECU  20  determines the probability of a collision according to the calculated position of the target object Ob in the lateral direction D 2 . 
     The present disclosure has been described so far according to the embodiment, but it is noted that the present disclosure is not limited to the foregoing embodiment or structure. The present disclosure includes various modifications and changes in a range of equivalency. In addition, various combinations and modes, and other combinations and modes including only one element of the foregoing combinations and modes, less or more than the one element fall within the scope and conceptual range of the present disclosure.