Patent Publication Number: US-7590263-B2

Title: Vehicle vicinity monitoring apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a vehicle vicinity monitoring apparatus for monitoring a vicinity of a vehicle with an imaging unit mounted on the vehicle. 
     2. Description of the Related Art 
     There has been developed a vehicle vicinity monitoring apparatus for obtaining images of one object with two imaging units mounted on a vehicle, either measuring the distance up to the object based on the parallax between the obtained images, or measuring the position in an actual space of the object with respect to the vehicle, and informing the driver of whether there is an obstacle ahead of the vehicle or not (see Japanese Laid-Open Patent Publication No. 2003-216937). 
     In order to accurately measure the position of or the distance up to the object, the angles at which the imaging units are mounted need to be determined with accuracy. Particularly, if the object exists in a distant position, then any slight difference between the mounted angles of the imaging units tends to cause a large error in the measurement of the position of or the distance up to the object. One solution is to perform an aiming process in which a target placed in a known position is imaged by the imaging units, and the mounted angles of the imaging units are determined based on the target images in the obtained images. 
     Templates representative of images of provisional targets may be stored in a given memory, and the position of the target in the obtained image may be determined by performing matching (template matching) on images actually obtained by the imaging units. 
     The aiming process is primarily carried out on vehicles in a manufacturing plant when the vehicles are shipped out of the manufacturing plant. However, the aiming process is also carried out on vehicles in various inspection facilities after the vehicles are shipped out of the manufacturing plant. Therefore, the positions of targets with respect to vehicles cannot uniformly be established, and hence it is difficult to set appropriate templates for those various inspection facilities. 
     Images obtained by an imaging unit may not necessarily be produced stably for various reasons, so that the positions of targets with respect to vehicles may not accurately be determined even by the template matching process. 
     The position of the object is determined from the images thereof in the obtained images by determining the distance up to the object based on the parallax and thereafter applying the distance to an optical perspective transformation model of the imaging unit. 
     The distance up to an object to be detected while the vehicle is being driven is set within a relatively long-distance range, i.e., a range from 30 m to 100 m. The distance up to the object can actually be regarded as being infinite. It is known that if the distance up to the object is infinite, a simplified perspective transformation model may be applicable for a simplified procedure for detecting the position of the object and high-speed calculations. 
     Generally, the aiming process is performed in indoor inspection facilities. Therefore, inspection targets are often located at a relatively short distance from the vehicle due to space limitations. With the inspection targets located at a relatively short distance from the vehicle, however, the position determined by the simplified perspective transformation model tends to suffer a large error. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a vehicle vicinity monitoring apparatus which is capable of determining accurate information about an object with respect to a vehicle depending on the distance of the object from the vehicle. 
     Another object of the present invention is to provide a vehicle vicinity monitoring apparatus which is capable of determining an accurate mounted angle of an imaging unit mounted on a vehicle. 
     Still another object of the present invention is to provide a vehicle vicinity monitoring apparatus which is capable of highly accurately calculating the position of an object with respect to a vehicle regardless of the distance up to the object, and of calculating the position of the object according to a simple process particularly if the distance up to the object is long. 
     According to the present invention, there is provided a vehicle vicinity monitoring apparatus for use on a vehicle, comprising an imaging unit for obtaining an image of a vicinity of the vehicle, an object distance detecting unit for detecting a distance up to an object, and an object information calculating unit for calculating information as to the object with a calculation method corresponding to the distance up to the object which is detected by the object distance detecting unit. With this arrangement, information as to the object can accurately be determined depending on the distance up to the object. 
     The vehicle vicinity monitoring apparatus may further comprise a coordinate reference value memory unit for storing reference coordinates of an object whose image is obtained by the imaging unit for adjustment, and a template memory unit for storing a plurality of templates representing obtained images of objects depending on the distance from the imaging unit, wherein the object information calculating unit comprises a template selecting unit for selecting one of the templates stored in the template memory unit depending on the distance from the imaging unit to the object, and an object coordinate calculating unit for performing template matching on the image obtained by the imaging unit by using the template selected by the template selecting unit, and calculating coordinates of the object. 
     The object information calculating unit may further comprise a mounted angle calculating unit for comparing the reference coordinates read from the coordinate reference value memory unit and the coordinates calculated by the object coordinate calculating unit with each other to determine a mounted angle of the imaging unit on the vehicle. 
     Since there are a plurality of templates selectively available depending on the distance up to the object, an appropriate template can be selected, and coordinates of the object in the image can accurately and simply be determined using the template. 
     The object coordinate calculating unit may perform template matching on each of a plurality of images obtained by the imaging unit, and the mounted angle calculating unit may compare the reference coordinates read from the coordinate reference value memory unit and average values of the coordinates calculated by the object coordinate calculating unit with each other to determine a mounted angle of the imaging unit on the vehicle. 
     With the above arrangement, even if the imaging unit or the imaging environment is somewhat unstable, the average value of the coordinates of the object that is determined from the plural images cancels an error, making it possible to determine a more accurate mounted angle of the imaging unit. 
     The template memory unit may store templates corresponding to a plurality of prescribed distances, respectively, and the template selecting unit may select a template based on the prescribed distances and the distance from the imaging unit to the object. Since the templates corresponding to the respective prescribed distances are provided, even if there does not exist a template corresponding to a distance that fully coincides with the distance up to the object, an appropriate template can be selected by referring to the prescribed distances. Therefore, the number of templates used is suppressed, and the storage capacity of the temperature memory unit can be reduced. 
     The template selecting unit may select a template corresponding to a prescribed distance which is equal to or smaller than, and closest to the distance from the imaging unit to the object. Thus, it is possible to select a template having an image which is essentially of the same shape as the image of the object in the obtained image, for thereby accurately performing the pattern matching. Furthermore, since the image on the template is greater in size than the image of the object in the obtained image, the effect of other images in the background is reduced. 
     The object information calculating unit may calculate the position in an actual space of the object with a perspective transformation model which corresponds to the distance up to the object which is detected by the object distance detecting unit. 
     By thus selecting a perspective transformation model depending on the distance up to the object, the position of the object can be calculated highly accurately regardless of the distance up to the object. 
     The vehicle vicinity monitoring apparatus may further comprise a model memory unit for storing a first expression based on a short-distance pin-hole model as an optical perspective transformation model of the imaging unit and a second expression based on a long-distance pin-hole model as an optical perspective transformation model of the imaging unit, and the object information calculating unit may calculate the position of the object according to the first expression if the distance up to the object which is detected by the object distance detecting unit is equal to or smaller than a predetermined threshold, and may calculate the position of the object according to the second expression if the distance up to the object which is detected by the object distance detecting unit exceeds the predetermined threshold. 
     The position of the object can be calculated highly accurately regardless of the distance up to the object by selectively using either the first expression based on the short-distance pin-hole model or the second expression based on the long-distance pin-hole model depending on the distance up to the object. Inasmuch as the second expression can be expressed in a simpler form than the first expression by regarding the distance up to the object as being infinite, the position of the object can be calculated simply. 
     The vehicle vicinity monitoring apparatus may further comprise a model memory unit for storing a first expression based on a short-distance pin-hole model as an optical perspective transformation model of the imaging unit and a second expression based on a long-distance pin-hole model as an optical perspective transformation model of the imaging unit, and a mode selecting unit for selecting, as an execution mode, an inspection mode for obtaining an image of an inspection target at a known distance to detect a mounted angle of the imaging unit, or a normal mode for obtaining an image of an actual object at an unknown distance, and the object information calculating unit may detect the position of the inspection target according to the first expression when the mode selecting unit selects the inspection mode, and may detect the position of the actual object according to the second expression when the mode selecting unit selects the normal mode. 
     By thus selectively using the first expression or the second expression depending on whether the mode is the aiming mode or the normal mode, the position of the object can be calculated highly accurately regardless of the mode. In particular, the first expression based on the short-distance pin-hole model is used in the aiming mode, the inspection target may be placed at a short distance, making it possible to perform the aiming process in an indoor environment. In the normal mode, the second expression can be expressed in a simple form by regarding the distance up to the object as being infinite, and hence the position of the object can be calculated simply. Each of the first and second expressions may comprise a plurality of expressions. 
     The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which preferred embodiments of the present invention are shown by way of illustrative example. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic perspective view of a night vision system installed on a vehicle which incorporates a vehicle vicinity monitoring apparatus according to an embodiment of the present invention; 
         FIG. 2  is a functional block diagram of an ECU of the night vision system shown in  FIG. 1 ; 
         FIG. 3  is a block diagram showing stored data of an image memory in the ECU shown in  FIG. 2 ; 
         FIG. 4  is a perspective view of an aiming target control apparatus and the vehicle; 
         FIG. 5  is a perspective view of a modified target plate; 
         FIG. 6  is a perspective view of a service aiming setting apparatus and the vehicle; 
         FIG. 7  is a diagram showing a general perspective transformation model; 
         FIG. 8  is a diagram showing the manner in which an image is transformed onto a focusing plane by the perspective transformation model; 
         FIG. 9  is a flowchart of an aiming process; 
         FIG. 10  is a diagram showing data stored in a template memory; 
         FIGS. 11 through 14  are flowcharts of the aiming process; 
         FIG. 15  is a diagram showing a template matching process in an aiming mode; 
         FIG. 16  is a flowchart of a mounting angle calculating process and a process of calculating clipping areas in left and right camera images; 
         FIG. 17  is a diagram showing a process of setting a clipping area in a reference area; 
         FIG. 18  is a diagram showing a pitch alignment adjusting process performed on left and right clipping areas; 
         FIG. 19  is a diagram showing the positional relationship between the left and right clipping areas after the pitch alignment adjusting process has been performed thereon; 
         FIG. 20  is a diagram showing a template matching process in a normal mode; and 
         FIG. 21  is a flowchart of a processing sequence of the normal mode. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A vehicle vicinity monitoring apparatus according to an embodiment of the present invention will be described below with reference to  FIGS. 1 through 21 . 
     As shown in  FIG. 1 , a night vision system (vehicle vicinity monitoring apparatus)  10  according to an embodiment of the present invention is installed on a vehicle  12 . The night vision system  10  has an ECU (Electronic Control Unit)  14  serving as a main controller, a left infrared camera  16 L (a first imaging unit, hereinafter also referred to as slave camera  16 L), a right infrared camera  16 R (a second imaging unit, hereinafter also referred to as master camera  16 R), an HUD (Head-Up Display)  18  for displaying a detected image, a speaker  20  for outputting an alarm sound, a speed sensor  22  for detecting a running speed, a yaw rate sensor  24  for detecting a yaw rate of the vehicle  12  when the vehicle  12  is driven, a solar radiation sensor  26 , a headlight switch  28 , a main switch  30  for selectively activating and inactivating the night vision system  10 , and a connector  32  for connecting the night vision system  10  to an external computer system. These components of the night vision system  10  may be connected to each other by intravehicular communication lines that are used by other systems on the vehicle  12 . 
     The infrared cameras  16 R,  16 L are mounted respectively in the right and left ends of a horizontal grill hole defined in a lower bumper region. The infrared cameras  16 R,  16 L are oriented forwardly at respective symmetrical positions and horizontally spaced from each other by an inter-camera distance (also referred to as “base length”) B. Each of the infrared cameras  16 R,  16 L detects far-infrared radiation to obtain an infrared image in which higher-temperature areas represent higher luminance, and supplies the obtained image to the ECU  14 . 
     The HUD  18  is disposed on an upper surface of an instrumental panel at a position directly in front of the driver seated on a driver&#39;s seat of the vehicle  12 , while trying not to obstruct the front vision of the driver. When the night vision system  10  is turned off, the HUD  18  is retracted down in the instrumental panel. If it is judged that the present time is nighttime based on information from the solar radiation sensor  26  and also that the headlights (or fog lamps) are turned on based on information from the headlight switch  28 , then the HUD  18  pops up from the instrumental panel when the main switch  30  is turned on. The HUD  18  has an image display panel comprising a concave mirror for reflecting and projecting an image sent from within the instrumental panel. The night vision system  10  may be automatically activated by an automatic lighting function regardless of whether the main switch  30  is operated or not. The luminance of the image display panel of the HUD  18  may be made adjustable by a suitable switch. 
     The ECU  14  processes stereographic infrared images obtained by the infrared cameras  16 R,  16 L to detect heat-source objects based on the parallax between the infrared images, and displays the detected heat-source objects as white silhouettes on the HUD  18 . When the ECU  14  identifies a pedestrian among the heat-source objects, the ECU  14  controls the speaker  20  to output an alarm sound and also controls the HUD  18  to highlight the identified pedestrian with a surrounding frame having a striking color for thereby drawing the driver&#39;s attention. The ECU  14  performs such an attention drawing function (or an informing function) at such good timing to allow the driver to take a sufficient danger avoiding action, by predicting a period of time until the vehicle  12  reaches the position of the pedestrian in a predetermined speed range. 
     In order for the infrared cameras  16 R,  16 L to be able to accurately determine the positions, distances, and shapes of far heat-source objects, the infrared cameras  16 R,  16 L are subject to an adjustment process called an aiming process (which will be described later) when they are manufactured in the manufacturing plant or when they are inspected at regular intervals. 
     As shown in  FIG. 2 , the ECU  14  comprises an image input unit  40  for converting analog infrared images obtained by the respective infrared cameras  16 R,  16 L into digital gray-scale images, a binarizer  42  for generating binary images from the gray-scale images based on a threshold value, an image memory  44  for storing the binary images and the gray-scale images, an aiming mode execution unit  48  for storing camera parameters produced as a result of the aiming process into a camera parameter memory  46 , a normal mode execution unit  50  for performing a normal image processing process while referring to sensors including the speed sensor  22 , etc. and the camera parameter memory  46 , and controlling the HUD  18  and the speaker  20 , and a mode selector  52  for selecting either an aiming mode or a normal mode at a time based on an instruction transmitted from an external computer system through the connector  32 . 
     As shown in  FIG. 3 , the image memory  44  stores a right gray-scale image  54  and a right binary image  56  based on an infrared image obtained by the right infrared camera  16 R, and a left gray-scale image  58  based on an infrared image obtained by the left infrared camera  16 L. These images are horizontally elongate digital images of scenes in front of the vehicle  12 . The right gray-scale image  54  and the left gray-scale image  58  are made up of pixels whose luminance levels are represented by a number of gradations, e.g., 256 gradations. The right binary image  56  is made up of pixels whose luminance levels are represented by 0 and 1. Actually, the image memory  44  can store a plurality of these images. 
     As shown in  FIG. 2 , the aiming mode execution unit  48  has a manufacturing plant mode unit  70  for performing the aiming process with an aiming target control apparatus  100  (see  FIG. 4 ) as the external computer system in the manufacturing plant in which the vehicle  12  is manufactured, and a service mode unit  72  for performing the aiming process with a service aiming setting apparatus  120  (see  FIG. 5 ) as the external computer system in a service factory or the like. Either the manufacturing plant mode unit  70  or the service mode unit  72  is selected at a time based on an instruction from a corresponding one of the external computer systems. 
     The aiming mode execution unit  48  has a parameter input unit  74  for inputting certain parameters from the external computer system when the aiming process is initiated, an initializing unit  76  for making initial settings required by the aiming process, a template matching unit  78  for performing template matching on the gray-scale images  54 ,  58  stored in the image memory  44 , a luminance adjustment LUT setting unit  80  for setting a luminance adjustment LUT for adjusting the luminance of image signals produced by the infrared cameras  16 R,  16 L, a camera image distortion correcting unit  82  for correcting image distortions caused due to individual differences as to focal lengths, pixel pitches, etc. between the infrared cameras  16 R,  16 L, a camera mounting angle calculating unit (a mounted angle calculating unit, an object information calculating unit)  84  for calculating respective mounting angles (a pan angle and a pitch angle) of the infrared cameras  16 R,  16 L, a camera image clipping coordinate calculating unit  86  for calculating clipping coordinates used as a reference for clipping processed ranges from images, and a parallax offset value calculating unit  88  for calculating a parallax offset value as an error which is contained in the parallax between object images because the optical axes of the infrared cameras  16 R,  16 L are not parallel to each other. 
     The parallax offset value calculating unit  88  functions as an actual parallax calculating unit for calculating an actual parallax between images of an object which are obtained by the infrared cameras  16 R,  16 L, and a parallax corrective value calculating unit for clipping image areas from the images obtained by the infrared cameras  16 R,  16 L according to respective pan angles thereof and calculating a parallax offset value for increasing range-finding accuracy. 
     The initializing unit  76  has a template setting unit (a template selecting unit, an object information calculating unit)  94  for selecting one of six templates TP 1 , TP 2 , TP 3 , TP 4 , TP 5 , TP 6  (collectively also referred to as “template TP”) that have been prepared depending on the distance up to objects. The ECU  14  has a model memory  96  for storing, as a formula, a perspective transformation model for determining the position of an object. The aiming mode execution unit  48  and the normal mode execution unit  50  calculate the position of an imaged object using the perspective transformation model stored in the model memory  96 . The model memory  96  stores a short-distance model for objects at short distances and a long-distance model for objects at long distances. 
     The ECU  14  has a CPU (Central Processing Unit) as a main controller, a RAM (Random Access Memory) and a ROM (Read Only Memory) as a memory device, and other components. The above functions of the ECU  14  are implemented in software when the CPU reads a program and executes the program in cooperation with the memory device. 
     As shown in  FIG. 4 , the aiming target control apparatus  100  has positioning devices  102  for positioning the vehicle  12 , a gate  104  disposed at a known distance Zf in front of the infrared cameras  16 R,  16 L on the vehicle  12  that is positioned by the positioning devices  102 , and a main control device  106  for communicating with the ECU  14  through the connector  32  and controlling the gate  104 . The gate  104  has two vertical posts  108  horizontally spaced from each other by a distance which is slightly greater than the width of the vehicle  12 , and a horizontally elongate target plate  110  having left and right ends movably supported respectively by the posts  108 . The target plate  110  is vertically movable along the posts  108  by the main control device  106 . The target plate  110  supports thereon an array of eight aiming targets  112   a ,  112   b ,  112   c ,  112   d ,  112   e ,  112   f ,  112   g ,  112   h  (collectively also referred to as “aiming target(s)  112 ”) as heat sources that are successively arranged horizontally from the left in the order named. 
     The four left aiming targets  112   a  through  112   d  are spaced at relatively small intervals d (d&lt;B) and belong to a left target group  114 . The four right aiming targets  112   e  through  112   h  are also spaced at the intervals d and belong to a right target group  116 . The aiming target  112   d  on the right end of the left target group  114  and the aiming target  112   e  on the left end of the right target group  116  are spaced from each other by a distance which is equal to the base length B. These aiming targets  112   d ,  112   e  are positioned just in front of the infrared cameras  16 L,  16 R, respectively. 
     The aiming targets  112   a  through  112   h  are not limited to heat sources such as heating bodies, but may be in the form of small metal plates (aluminum plates or the like)  118   a  through  118   h  as heat reflecting plates, as shown in  FIG. 5 . Since the aiming targets  112   a  through  112   h  in the form of metal plates reflect heat (infrared radiation) generated and radiated by the vehicle  12 , the aiming targets  112   a  through  112   h  can be imaged by the infrared cameras  16 R,  16 L. According to the modification shown in  FIG. 5 , the aiming targets  112   a  through  112   h  do not need to be selectively turned on and off, and do not consume electric power. If the target plate  110  is made of a material having a low heat reflectance, then a clear contrast is obtained between the metal plates  118   a  through  118   h  and the target plate  110  in the obtained images. 
     As shown in  FIG. 6 , the service aiming setting apparatus  120  has positioning markers  122  indicative of the positions of the wheels of the vehicle  12  in an aiming setting process, a headlight tester  124  disposed at a certain distance (hereinafter referred to as object distance) Z in front of the infrared cameras  16 R,  16 L on the vehicle  12  that is positioned based on the positioning markers  122 , and a main control device  126  for communicating with the ECU  14  through the connector  32 . The headlight tester  124  is movable along a rail  128  in directions parallel to the transverse direction of the vehicle  12  and has a lifter table  130  which is vertically movable. The lifter table  130  supports thereon a target plate  132  having three aiming targets  134   a ,  134   b ,  134   c  (collectively also referred to as “aiming target(s)  134 ”) as heat sources that are successively arranged horizontally. The aiming targets  134  are spaced at the intervals d (d&lt;B). The aiming target  134  may be identical to or substantially the same as the aiming target  112  of the gate  104  shown in  FIG. 4 . 
     A general perspective transformation model M, and a short-distance model and a long-distance model that are stored in the model memory  96  will be described below. 
     As shown in  FIG. 7 , the perspective transformation model M is a model representative of a process for obtaining an image w having a height y from an object w having a height Y through a lens  138  having a focal length f. Specifically, a light ray from a point Pa on an end of the object W to the center O of the lens  138  travels straight through the lens  138 , and a light ray traveling from the point Pa parallel to the optical axis C is refracted at a point O′ in the lens  138 . These light rays are converged at a point Pb. A light ray from a point Pa′ on the other end of the object W to the center O of the lens  138  travels straight along the optical axis C and reaches a point Pb′. The light rays from the object W which is spaced from the lens  138  by a distance Z are focused by the lens  138  to form the object w having the height y, whose one end is on the point Pb and the other end on the point Pb′, at a focusing distance F from the lens  138  remotely from the object W. The image w is inverted from the object W. 
     Since a triangle defined by three points Pa, Pa′, O and a triangle defined by three points Pb, Pb′, O are similar to each other, and a triangle defined by three points O, O′, Pc and a triangle defined by three points Pb, Pb′, Pc where Pc represents the position on the optical axis C at the focal length f of the lens  138  toward the image w, are similar to each other, the following equations (1), (2) are satisfied:
 
 y/Y=F/Z   (1)
 
 y/Y =( F−f )/ f   (2)
 
     By deleting y, Y from the equations (1), (2), the following equation (3) is obtained:
 
 F=fZ /( Z−f )  (3)
 
     Since the object distance Z is known in the aiming mode, the focusing distance F is established according to the equation (3) in steps S 8 , S 33  to be described later. Actually, the equation (3) may be included in expressions (7-1) through (7-4) to be described later. 
     If the object W is sufficiently far away from the lens  138  (Z&gt;&gt;f), then the equation (3) can be approximated by the following approximate expression (4):
 
 F≈f (= fZ/Z )  (4)
 
     The width X of the object W can also be expressed by a perspective transformation model M similar to the perspective transformation model M used with respect to the height Y, and the width of the object w is represented by x. The actual image w is focused on the side of the lens  138  which is opposite to the object W. For simplifying the model, however, a hypothetical focusing plane S may be provided on the same side of the lens  138  as the object W at the position of the focusing distance F from the lens  138 . Therefore, as shown in  FIG. 8 , the object W and the image w are represented by similar erected images with respect to the lens center O, and the object W is transformed onto the focusing plane S. 
     As shown in  FIG. 8 , the width x and the height y of the image w on the focusing plane S are expressed by the following equations (5), (6):
 
 x=F/Z·X/p   (5)
 
 y=F/Z·Y/p   (6)
 
     where p is a parameter representing the pixel pitch of an actual digital image to which the focusing plane S is applied. If the object W is positioned at a relatively short distance, then since an error caused when the expression (4) is applied is not negligible, the equation (3) is substituted for F in the equations (5), (6). As a result, a perspective transformation model at the time the object W is positioned at a relatively short distance is expressed by the following first expression group of expressions (7-1) through (7-4): 
     
       
         
           
             
               
                 
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     The first expression group is included in the short-distance model stored in the model memory  96 . When the mode selector  52  selects the aiming mode in step S 3  to be described later, the first expression group is selected by the aiming mode execution unit  48 , and used to calculate the positions of the aiming targets  112  or  134 . Specifically, in a manufacturing plant aiming mode, a value that is automatically set as the known distance Zf is used as the object distance Z, and in a service aiming mode, the object distance Z input from the main control device  126  is used. Since the aiming targets  112  or  134  have known coordinates X in the transverse direction of the vehicle and known coordinates Y in the direction of the height, theoretical coordinates Pb (x, y) of the image w on the focusing plane S are determined according to the expressions (7-1), (7-2). In the service aiming mode, the height coordinates Y are corrected based on the camera height H (see  FIG. 1 ). 
     Thereafter, the theoretical coordinates Pb (x, y) and the actually obtained coordinates in the actual image of the aiming targets  112  are compared with each other to determine mounting angles of the infrared cameras  16 R,  16 L. Alternatively, theoretical coordinates of the aiming targets  112  may be determined from the coordinates in the actual image according to the expressions (7-3), (7-4), and compared with the known coordinates X, Y to determine mounting angles of the infrared cameras  16 R,  16 L. 
     Because the first expression group is established based on the equation (3) representative of the focusing distance F, theoretical coordinates Pb (x, y) can accurately be determined, with the result that mounting angles of the infrared cameras  16 R,  16 L can be determined highly accurately. 
     If the object W is distant, then the expression (4) may be used as an approximate expression, and the equations (5), (6) are represented by the following second expression group of expressions (8-1) through (8-4): 
     
       
         
           
             
               
                 
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     The second expression group is included in the long-distance model stored in the model memory  96 . When the mode selector  52  selects the normal mode in step S 3  to be described later, the second expression group is selected by the normal mode execution unit  50 , and used to calculate the position of the object. Specifically, after the object distance Z up to the object is calculated from the parallax between the two images obtained by the infrared cameras  16 R,  16 L, coordinates X, Y in the space of the object are determined from the coordinates in the images according to the expressions (8-3), (8-4). Generally, in the normal mode, the object distance Z is sufficiently greater than the focal distance f, and hence the error of the expression (4) is of a negligible level, so that the coordinates X, Y of the object can be determined sufficiently accurately according to the expressions (8-3), (8-4). Since the expressions (8-3), (8-4) are simpler than the above expressions (7-3), (7-4), the expressions (8-3), (8-4) make it possible to perform faster calculations. 
     In the normal mode, if the determined object distance Z is equal to or smaller than a predetermined threshold, then the expressions (7-3), (7-4) may be used. 
     The aiming process to be performed on the night vision system  10  using the aiming target control apparatus  100  or the service aiming setting apparatus  120  will be described below. 
     The aiming process includes a manufacturing plant aiming mode to be performed in a manufacturing plant using the aiming target control apparatus  100  and a service aiming mode to be performed in a service factory using the service aiming setting apparatus  120 . 
     In the manufacturing plant aiming mode, the vehicle  12  is positioned by the positioning devices  102 , and the main control device  106  is connected to the connector  32  of the vehicle  12 . The main control device  106  sends an instruction for performing the manufacturing plant aiming mode using the aiming target control apparatus  100  to the ECU  14 . The aiming targets  112   a  through  112   h  are positionally adjusted to a prescribed height depending on the type of the vehicle  12 . 
     In the service aiming mode, the vehicle  12  is positioned with the wheels aligned with the respective positioning markers  122 , and the main control device  126  is connected to the connector  32  of the vehicle  12 . The main control device  126  sends an instruction for performing the service aiming mode using the service aiming setting apparatus  120  to the ECU  14 . The aiming targets  134   a  through  134   c  are positionally adjusted to a prescribed height. 
       FIGS. 9 ,  11  through  14  show the aiming process that is mainly performed by the aiming mode execution unit  48  of the ECU  14 . The aiming process will be described in detail below with reference to  FIGS. 9 ,  11  through  14 . 
     In step S 1  shown in  FIG. 9 , analog stereographic infrared images are input from the infrared cameras  16 R,  16 L to the image input unit  40 . The image input unit  40  converts the analog stereographic infrared images into digital gray-scale images  54 ,  58  in step S 2 . The gray-scale images  54 ,  58  are stored in the image memory  44  until predetermined instructions for clearing or overwriting are input. A plurality of these gray-scale images  54 ,  58  can be stored in the image memory  44 . The gray-scale images  54 ,  58  are converted by the binarizer  42  into binary images, and the right binary image  56  is stored in the image memory  44 . 
     In step S 3 , the mode selector  52  determines whether the aiming mode or the normal mode is to be executed according to an instruction from the main control device  106  or  126 . If the normal mode is to be executed, then control goes to step S 5 . If the aiming mode is to be executed, then control goes to step S 4 . 
     In the normal mode in step S 5 , the normal mode execution unit  50  operates to refer to the camera parameters stored in the camera parameter memory  46 , and controls the HUD  18  and the speaker  20  to search for an object and draw the driver&#39;s attention if necessary. 
     In the aiming mode in step S 4 , the mode selector  52  determines which of the aiming target control apparatus  100  and the service aiming setting apparatus  120  is to be used. If it is judged that the aiming target control apparatus  100  is to be used, then control goes to step S 6  in order for the manufacturing plant mode unit  70  to perform the manufacturing plant aiming mode. If it is judged that the service aiming setting apparatus  120  is to be used, then control goes to step S 30  (see  FIG. 12 ) in order for the service mode unit  72  to perform the service aiming mode. The manufacturing plant aiming mode and the service aiming mode will successively be described below. 
     In the manufacturing plant aiming mode, a distance from the infrared cameras  16 R,  16 L to the target plate  110  is set in step S 6 . In this case, the object distance Z is automatically set as the known distance Zf 
     In step S 7 , the template setting unit  94  selects a reference template depending on the object distance Z. As shown in  FIG. 10 , the templates TP 1 , TP 2 , TP 3 , TP 4 , TP 5 , TP 6  represent respective small image data produced by imaging respective provisional targets arranged at prescribed distances. The prescribed distances are set as distances Z 1 , Z 2 , Z 3 , Z 4 , Z 5 , Z 6  which are defined at equal intervals (or equal ratio intervals) and which are successively far from the infrared cameras  16 R,  16 L (Z 1 &lt;Z 2 &lt; . . . &lt;Z 6 ). The templates TP 1 , TP 2 , TP 3 , TP 4 , TP 5 , TP 6  are stored in the template memory  95  in the ECU  14 . The provisional targets are identical to the aiming targets  112 . In the manufacturing plant aiming mode, if the known distance Zf is Zf=Z 3 , then the template TP 3  is selected as a reference template. 
     In step S 8 , the focusing distance F is established based on the perspective transformation model M (see  FIG. 7 ). 
     Steps S 6  through S 8  are carried out by the initializing unit  76  only once for the first time when the aiming process is performed, while referring to a parameter representative of the number of times that they are executed. 
     In step S 9  (an object extracting unit), a template matching process is performed based on the reference template selected in step S 7 . Specifically, correlative calculations are performed on the gray-scale images  54 ,  58  of the aiming target  112  obtained by the infrared cameras  16 R,  16 L and the template TP, and coordinates of a gray-scale image for which the results of the correlative calculations are minimum are calculated and stored in step S 10  (an object coordinate calculating unit, an object information calculating unit). For correlative calculations, SAD (the sum of absolute differences) per pixel is used, for example. 
     In step S 11 , it is confirmed whether the number of each of acquired gray-scale images  54 ,  58  has reached a predetermined number N or not. If the number of acquired gray-scale images  54 ,  58  has reached the predetermined number N, then control goes to step S 12 . If the number of acquired gray-scale images  54 ,  58  is smaller than the predetermined number N, then control goes back to step S 1  to continuously acquire gray-scale images  54 ,  58  and calculate and store target coordinates. 
     In step S 12 , an average value Pave of the calculated N sets of target coordinates is calculated. If it is judged that target coordinates are properly calculated in step S 13 , then control goes to step S 14  (see  FIG. 11 ). If it is judged that target coordinates are not properly calculated in step S 13 , then control goes back to step S 3 . 
     In step S 14  shown in  FIG. 11 , a luminance adjustment LUT is set. Specifically, in order to reliably perform the template matching process based on correlative calculations, the levels of luminance signals of the aiming target  112  which are detected by the infrared cameras  16 R,  16 L are compared with each other, and a luminance adjustment LUT is set such that the luminance signal from the infrared camera  16 R, which is used as a reference for the correlative calculations, will be greater at all times than the luminance signal from the infrared camera  16 L at each of the luminance levels. If it is judged that the process of setting a luminance adjustment LUT is properly performed in step S 15 , then control goes to step S 16 . 
     In step S 16 , an image distortion corrective value for correcting image distortions caused due to individual differences as to focal lengths, pixel pitches, etc. between the infrared cameras  16 R,  16 L is calculated. If it is judged that an image distortion corrective value is properly calculated in step S 17 , then control goes to step S 18 . 
     In step S 18 , a pan angle and a pitch angle (also referred to as a tilt angle), which serve as mounting angles of the left and right cameras, i.e., the infrared cameras  16 R,  16 L, are calculated. If it is judged that mounting angles of the left and right cameras are properly calculated in step S 19 , then control goes to step S 20 . 
     The pan angle refers to an angle by which the infrared cameras  16 R,  16 L are turned in a hypothetical camera array plane including the optical axes of the infrared cameras  16 R,  16 L which are at the same height. The pan angle extends in a direction of parallax, i.e., the x direction (see  FIG. 8 ) in obtained images. The pitch angle refers to an angle of depression/elevation in a vertical plane normal to the hypothetical camera array plane. The pitch angle extends in the y direction in obtained images. 
     In step S 20 , clipping coordinates for clipping image areas to be processed from the images obtained by the infrared cameras  16 R,  16 L are calculated. If it is judged that clipping coordinates are properly calculated in step S 21 , then control goes to step S 22 . 
     In step S 22 , a parallax offset value, which represents an error contained in the parallax between object images because the optical axes of the infrared cameras  16 R,  16 L are not parallel to each other, is calculated. If it is judged that a parallax offset value is properly calculated in step S 23 , then control goes to step S 24 . 
     In step S 24 , the luminance adjustment LUT, the image distortion corrective value, the pan angle and the pitch angle, the clipping coordinates, and the parallax offset value which are determined respectively in steps S 14 , S 16 , S 18 , S 20 , and S 22  are stored in the camera parameter memory  46 . If these parameters are properly stored, then the manufacturing plant aiming mode (or the service aiming mode) is finished. At this time, the ECU  14  sends a signal indicating that the aiming mode is finished to the main control device  106  or  126 . If the normal mode is to be subsequently executed, then a predetermined restarting process may be performed. If the answers to the branching processes in steps S 17 , S 19 , S 21 , S 23 , and S 25  are negative, then control goes back to step S 3  as when the answer to the branching process in step S 13  is negative. 
     The service aiming mode will be described below. In the service aiming mode, steps S 1  through S 3  (see  FIG. 9 ) are executed in the same manner as with the manufacturing plant aiming mode. Control then branches from step S 4  to step S 30  for the service mode unit  72  to perform a processing sequence shown in  FIGS. 12 through 14 . 
     In step S 30  shown in  FIG. 12 , a distance from the infrared cameras  16 R,  16 L to the target plate  132 , i.e., the object distance Z, is input and set. Specifically, the object distance Z is input as a numerical value in a range from Z 1  to Z 7  (&gt;Z 6 ) from the main control device  126 , and supplied to the ECU  14 . The object distance Z may be determined by inputting a distance from a location that can easily be measured, e.g., a positioning marker  122 , and subtracting a predetermined offset from the input distance. Alternatively, a laser beam distance detector may be used as an object distance detecting unit to automatically detect and input the object distance Z. 
     In step S 31 , the height H (see  FIG. 1 ) of the infrared cameras  16 R,  16 L is confirmed and input. 
     In step S 32 , the template setting unit  94  selects one of the templates TP 1  through TP 6  depending on the object distance Z as a reference template. As described above, the templates TP 1  through TP 6  are set as prescribed distances Z 1  through Z 6  when the image of the provisional target is obtained. In step S 32 , the corresponding prescribed distance is equal to or smaller than the object distance Z, and a template closest to the object distance Z is selected. Specifically, if the object distance Z is in the range from Z 1  to Z 2 ′, from Z 2  to Z 3 ′, from Z 3  to Z 4 ′, from Z 4  to Z 5 ′, from Z 5  to Z 6 ′, and from Z 6  to Z 7 , then the templates TP 1  through TP 6  are successively selected correspondingly. Z 2 ′, Z 3 ′, Z 4 ′, Z 5 ′, Z 6 ′ represent values that are smaller than Z 2 , Z 3 , Z 4 , Z 5 , Z 6 , respectively, by a minimum input unit. More specifically, if the object distance Z is in the range from Z 4  to Z 5 ′, the template Z 4  is selected. 
     In step S 33 , the focusing distance F is set in the same manner as with step S 8 . Steps S 30  through S 33  are carried out by the initializing unit  76  only once for the first time when the aiming process is performed, while referring to a parameter representative of the number of times that they are executed. 
     In step S 34 , the position of the target plate  132  is confirmed. Specifically, in the service aiming mode, the target plate  132  is placed successively in a central position PC, a left position PL, and a right position PR (see  FIG. 6 ). When step S 34  is executed for the first time, a signal for positional confirmation is sent to the main control device  126  to place the target plate  132  in the central position PC. In response to the signal, the main control device  126  displays a message “PLACE TARGET IN CENTRAL POSITION PC AND PRESS “Y” KEY” on the monitor screen, for example. According to the message, the operator moves the headlight tester  124  along the rail  128  either manually or with a given actuator until the target plate  132  is placed in the central position PC, and then presses the “Y” key. 
     Step S 34  is executed repeatedly. At every N executions, the main control device  126  displays a message such as “PLACE TARGET IN LEFT POSITION PL AND PRESS “Y” KEY” or “PLACE TARGET IN RIGHT POSITION PR AND PRESS “Y” KEY” on the monitor screen, for drawing attention of the operator so that the operator may move the target plate  132  to be placed in the left position PL or the right position PR, and press the “Y” key. If it is confirmed that: the target plate  132  is positioned in the central position PC for the first time and the “Y” key is pressed; or the target plate  132  is positioned in the left position PL for the first time and the “Y” key is pressed; or the target plate  132  is positioned in the right position PR for the first time and the “Y” key is pressed, then control goes to step S 35 . Substantive process is not performed except for the above timing. 
     In step S 35 , control is branched depending on the position of the target plate  132  at the time. If the target plate  132  is placed in the central position PC (in first through Nth cycles), then control goes to step S 36 . If the target plate  132  is placed in the left position PL, then control goes to step S 41  (see  FIG. 13 ). If the target plate  132  is placed in the right position PR, then control goes to step S 46  (see  FIG. 14 ). 
     In step S 36 , a template matching process is performed in the same manner as with step S 9 . 
     In step S 37 , target coordinates of the aiming target  134  are calculated and stored in the same manner as with step S 10 . 
     In step S 38 , the number of acquired gray-scale images  54 ,  58  is confirmed in the same manner as with step S 11 . If the number of each of acquired gray-scale images  54 ,  58  is N or more, then control goes to step S 39 . If the number of acquired gray-scale images is smaller than N, then control goes back to step S 1 . In the second and subsequent cycles, steps S 3  through S 8  and steps S 30  through S 35  are skipped. 
     In step S 39 , an average value Pave of the target coordinates at the central position PC is calculated in the same manner as with step S 12 . If it is judged that target coordinates are normally calculated in step S 40 , then control goes back to step S 1 . If it is judged that target coordinates are not normally calculated in step S 40 , then control goes back to step S 3 . 
     The target plate  132  is placed in the left position PL, and steps S 41  through S 45  shown in  FIG. 13  are similarly executed. 
     Then, the target plate  132  is placed in the right position PR, and steps S 46  through S 50  shown in  FIG. 14  are similarly executed. 
     If it is judged that target coordinates are normally calculated in final step S 50 , then control goes back to step S 14  (see  FIG. 11 ). Subsequently, the same process as the manufacturing plant aiming mode is performed, and camera parameters are stored in the camera parameter memory  46 . 
     Details of step S 36  for performing the template matching process using the selected reference template (hereinafter referred to as template TPs) will be described below with reference to  FIG. 15 . 
     As shown in  FIG. 15 , the selected template TPs is moved vertically and horizontally by small distances in a given sequence in the right gray-scale image  54 , and the pattern matching process is performed in each of the positions of the selected template TPs to check a pattern match against the background image based on the SAD referred to above. 
     The size of a provisional target image  140  on the template TPs is greater than the size of the image of each of the aiming targets  134   a  through  134   c  in the right gray-scale image  54 . This is because the prescribed distance is equal to or smaller than the object distance Z and the template closest to the object distance Z is selected in step S 32 . 
     When the template TPs is moved to the position of the aiming target  134   c  as indicated by the two-dot-and-dash lines TP′ in  FIG. 15 , the image  140  and the aiming target  134   c  are essentially aligned with each other, with their higher and lower luminance areas overlapping each other, and the SAD is of a sufficiently small value. It is now judged that a pattern match is achieved, and the target coordinates of the aiming target  134   c  are identified from the central point of the template TPs at the time. Specifically, the coordinates Pb (x, y) (see  FIG. 8 ) of the central point of the area indicated by the two-dot-and-dash lines TP′ are stored as Pt[i] in the memory (step S 10 ). The parameter i is a counter representing the number of processing cycles, and is incremented from i=1 to i=N depending on the number of right gray-scale images  54 . Though target coordinates are actually determined with respect to each of the aiming targets  134   a  through  134   c , representative target coordinates Pt[i] are illustrated for the sake of brevity. 
     In step S 12 , the average value Pave is calculated according to the following expression (9): 
     
       
         
           
             
               
                 
                   
                     P 
                     ave 
                   
                   ← 
                   
                     
                       ( 
                       
                         
                           ∑ 
                           
                             i 
                             = 
                             1 
                           
                           N 
                         
                         ⁢ 
                         
                           Pt 
                           ⁡ 
                           
                             [ 
                             i 
                             ] 
                           
                         
                       
                       ) 
                     
                     / 
                     N 
                   
                 
               
               
                 
                   ( 
                   9 
                   ) 
                 
               
             
           
         
       
     
     Because of the averaging process, even if the infrared cameras  16 R,  16 L or the environments (e.g., the temperature) in which to obtain images are somewhat unstable, errors caused by the instability are canceled out by the average value Pave, allowing accurate target coordinates to be determined. 
     It is assumed that the service aiming mode is performed in an inspection area of a general service factory or the like. Therefore, it is difficult to fully remove unwanted heat sources for radiating or reflecting infrared radiation other than the aiming targets  134   a  through  134   c . and these unwanted heat sources may possibly be detected as relatively weak radiation levels or small images. For example, another heat source  142 , e.g., a distant light, is present near the aiming target  134   c  in the right gray-scale image  54 , and is obtained as an image smaller than the aiming target  134   c  in the right gray-scale image  54 . Since the size of the image  140  of the template TPs is greater than the image of the aiming target  134   c , when the templates TPs is moved to the position of the heat source  142 , the SAD is of a considerably large value, and is clearly distinguished from the aiming target  134   c.    
     With respect to the aiming targets  134   a ,  134   b , target coordinates Pt[i] are also identified and an average value Pave is determined in the same manner as described above. The aiming targets  134   a  through  134   c  can be identified from their relative positional relationship. 
     The right gray-scale image  54  shown in  FIG. 15  is obtained when the headlight tester  124  is placed in the central position PC. The same process as described above is performed when the headlight tester  124  is placed in the right position PR or the left position PL, or when the left gray-scale image  58  is obtained. The same process as described above is also performed in step S 9  for the template matching process in the manufacturing plant aiming mode. 
     Details of the processing sequence from step S 18  for calculating mounting angles of the infrared cameras  16 R,  16 L to step S 20  for calculating clipping coordinates for clipping image areas to be processed from the images obtained by the infrared cameras  16 R,  16 L, will be described below with respect to the processing of data from the infrared camera  16 R with reference to  FIG. 16 . In  FIG. 16 , steps S 18 , S 19 , S 20  shown in  FIG. 11  are not distinguished from each other. 
     In step S 101  shown in  FIG. 16 , reference coordinates P 0  representative of spatial coordinates of the target are read from the memory (a coordinate reference value memory unit). 
     In step S 102 , the reference coordinates P 0  are converted into reference coordinates P 0 ′ (x0, y0) in the image according to the expressions (7-1), (7-2) representing the short-distance model. In the aiming mode, the short-distance model is selected in advance, and the coordinates of the target at a relatively short distance can accurately be transformed onto the image. 
     If the reference coordinates P 0  are stored as values in the actual space, for example, then when the position of the target is changed, the actually measured coordinates can directly be input from the main control device  106  or  126 . The actually measured coordinates that are input are accurately transformed based on the short-distance model. 
     In step S 103  (a mounting angle calculating unit, an object information calculating unit), the reference coordinates P 0 ′ in the image and the average value Pave determined in step S 12  are compared with each other to determine a difference Δx between the pan angles and a difference Δy between the pitch angles. 
     The differences Δx, Δy represent mounting angles as errors of the pan and pitch angles of the infrared cameras  16 R,  16 L with respect to design reference values depending on the reference coordinates P 0 ′. Specifically, if the design reference values are set to 0°, then when the difference Δx is of a value corresponding to 2° and the difference Δy is of a value corresponding to 1°, the pan angle is determined as 2° and the pitch angle as 1°. 
     In step S 104 , as shown in  FIG. 17 , a clipping area  162 R is determined by moving a reference area  160 R in the right gray-scale image  54  by the difference Δx in the x direction and the difference Δy in the y direction. The reference area  160 R is established based on the reference coordinates P 0 , and is an area serving as a reference for use in image processing when the infrared camera  16 R is oriented accurately forwardly. Using the clipping area  162 R in image processing is as effective as using the infrared camera  16 R, which is mechanically adjusted so that it is oriented accurately forwardly. 
     The clipping area  162 R has an end point Q 1  that is produced by moving an end point Q 0  of the reference area  160 R horizontally by the difference Δx and vertically by the difference Δy. The coordinates of the end point Q 1  may be recorded on behalf of the clipping area  162 R. Though not described in detail, the left gray-scale image  58  obtained by the left infrared camera  16 L is similarly processed. 
     Then, steps S 105  through S 108  are carried out to perform pitch alignment adjustment for the clipping area  162 R and a clipping area  162 L which are established independently of each other. The pitch alignment adjustment refers to a process for relating the clipping areas  162 R,  162 L to achieve alignment in the pitch direction with each other based on the image of the object that is actually obtained. In the description which follows, the right gray-scale image  54  is an image obtained when the target plate  132  is placed in the right position PR, and the left gray-scale image  58  is an image obtained when the target plate  132  is placed in the left position PL. As described above, the target plate  132  is set to a constant height regardless of whether it is placed in the right position PR or the left position PL. 
     In step S 105 , as shown in  FIG. 18 , y coordinates yr 1 , yr 2 , yr 3  of the aiming targets  134   a ,  134   b ,  134   c  in the clipping area  162 R extracted from the right gray-scale image  54  are determined, and an average value yra (=(yr 1 +yr 2 +yr 3 )/3) of the y coordinates yr 1 , yr 2 , yr 3  is determined. 
     In step S 106 , y coordinates yl 1 , yl 2 , yl 3  of the aiming targets  134   a ,  134   b ,  134   c  in the clipping area  162 L extracted from the left gray-scale image  58  are determined, and an average value yla (=(yl 1 +yl 2 +yl 3 )/3) of the y coordinates yl 1 , yl 2 , yl 3  is determined. 
     In step S 107 , the difference Δya between the average value yra in the right clipping area  162 R and the average value yla in the left clipping area  162 L is determined as Δya yra−yla. 
     In step S 108 , a corrected image area is established by moving the left clipping area  162 L by the difference Δya in the y direction, i.e., the pitch direction. In the example shown in  FIG. 18 , since yra&lt;yla, the difference Δya is negative, the left clipping area  162 L is moved downwardly, shifting an end point Q 2  to an end point Q 2 ′. The coordinates of the end point Q 2 ′ are stored on behalf of the left clipping area  162 L. 
     According to the pitch alignment adjustment, since the left clipping area  162 L is moved with respect to the right clipping area  162 R for equalizing the pitch angles based on the aiming targets  134   a  through  134   c  that are actually imaged, a distortion of the vehicle body and manufacturing errors of camera supports or stays can be compensated for. Therefore, when the clipping areas  162 R,  162 L are horizontally juxtaposed as shown in  FIG. 19 , relatively coordinates (yra in  FIG. 19 ) in the clipping areas  162 R,  162 L of the obtained images of the same object are in conformity with each other. 
     As a result, a quick and reliable pattern matching process can be performed in the normal mode. Specifically, as shown in  FIG. 20 , a small image including an image  170  of an object which is extracted from the right clipping area  162 R as a reference image is clipped as a template TPr, and placed at the same position in the left clipping area  164 L as a comparison image. Then, the template TPr is moved to the right, i.e., in the positive x direction, in the left clipping area  164 L, while a template matching process is being performed based on correlative calculations such as the SAD. Because the image  170  in the left clipping area  162 L and a corresponding image  172  of the same object in the left clipping area  162 L have the same y coordinates, the template TPr is moved a suitable distance depending on the parallax, and matches the image  172  when it reaches the broken-line position in  FIG. 20 . Therefore, a template match is achieved without essentially moving the template TPr in the y direction. The pattern matching process can thus be performed simply and quickly without the need for excessively widening the search area in the y direction. At this time, the SAD is very small for reliably determining whether a pattern match is achieved or not. The pattern matching process is reliable also because the template TPr does not match another image  174  which has a different y coordinate, but is similar to the image  172 . 
     The processing sequence shown in  FIG. 16  may be performed based on an image that is obtained when the target plate  132  is placed in the central position PC. For the pitch alignment adjustment, either one of the clipping areas  162 R,  162 L may be used as a reference, or both of the clipping areas  162 R,  162 L may be moved according to predetermined standards. Furthermore, inasmuch as the aiming targets  112   a  through  112   h  of the aiming target control apparatus  100  are set to the same height, the pitch alignment adjustment may be performed in the manufacturing plant aiming mode. For the pitch alignment adjustment in the manufacturing plant aiming mode, the average value yra may be determined from the right target group  116  in the right grays-scale image  54 , and the average value yla may be determined from the left target group  114  in the left grays-scale image  58 . 
     The pitch alignment adjustment may also be performed by obtaining an image of a general heat source, rather than the aiming targets  112 ,  134  that are to be imaged for inspection purposes. Even if the distance to and the height of the heat source are unknown, the pitch alignment adjustment can be performed by obtaining the image of the same heat source with the infrared cameras  16 R,  16 L. 
     A process of detecting an actual object in the normal mode after the aiming process is finished will be described below with reference to  FIG. 21 . The normal mode is repeatedly performed at small time intervals by the normal mode execution unit  50 . 
     First, in step S 201  shown in  FIG. 21 , analog stereographic infrared images are input from the infrared cameras  16 R,  16 L to the image input unit  40 . The image input unit  40  generates the right gray-scale image  54  and the left gray-scale image  58 , and the binarizer  42  generates the right binary image  56 . The right gray-scale image  54 , the left gray-scale image  58 , and the right binary image  56  are stored in the image memory  44 . 
     Thereafter, an object is extracted based on the right binary image  56  in step S 202 . The parallax between the right gray-scale image  54  and the left gray-scale image  58  is determined, and the distance up to the object is calculated from the parallax in step S 203  (an object distance detecting unit). The pattern matching can quickly and reliably be performed because it is carried out on the clipping area  162 R in the right gray-scale image  54  and the clipping area  162 L in the left gray-scale image  58 . 
     Then, the relative position of the object with respect to the vehicle  12  is calculated in step S 204 . After the calculated position is corrected based on behaviors of the vehicle  12 , a moving vector of the object is calculated in step S 205 . At this time, the position of the actual object can accurately and quickly be detected by the ECU  14  based on the expressions (8-1) through (8-4) representing the long-distance model stored in the model memory  96 . 
     Referring to the moving vector etc., road structures and vehicles are identified and excluded in step S 206 . Then, it is determined whether there is a pedestrian or not from the shape or the like of the object in step S 207 . 
     Thereafter, the right gray-scale image  54  is displayed on the HUD  18 . If it is judged that there is a pedestrian within a certain range in step S 207 , then the image of the pedestrian is enclosed by a highlighting frame, and the speaker  20  is energized to radiate a sound to draw the driver&#39;s attention in step S 209 . 
     In the night vision system  10  according to the present embodiment, as described above, since the templates TP 1  through TP 6  corresponding to the six prescribed distances are stored in the template memory  95 , an appropriate template can be selected based on the object distance Z. Therefore, the template matching process is accurately performed, and accurate pan angles and pitch angles of the infrared cameras  16 R,  16 L can be determined from the determined target coordinates. 
     Even if there does not exist a template TP corresponding to a distance that fully coincides with the object distance Z, since an appropriate template based on the object distance Z is selected, the number of templates is suppressed, and the storage capacity of the template memory  95  is reduced. 
     In the night vision system  10  according to the present embodiment, the position of an object can be calculated highly accurately regardless of the mode by selectively using either the expressions (7-1) through (7-4) of the first expression group or the expressions (8-1) through (8-4) of the second expression group depending on whether the mode is the aiming mode or the normal mode. Particularly, since the aiming mode is performed based on a short-distance pin-hole model, the aiming targets  112  (or  134 ) may be placed at a short distance, making it possible to perform the aiming process in an indoor environment. In the normal mode, the second expression group can be expressed in a simple form by regarding the object distance as being infinite, and hence the calculating procedure can be simplified. 
     The pin-hole models are not limited to two models for long and short distances, but may be three or more models depending on the distance up to the object. 
     Although a certain preferred embodiment of the present invention has been shown and described in detail, it should be understood that various changes and modifications may be made therein without departing from the scope of the appended claims.