Abstract:
An occupant sensing device that accurately detects the state of an occupant regardless of the influence of extraneous noise and outside light and the influence of a defect in detected data when lighting of auxiliary light is delayed. When a specific part detection possibility/impossibility determination unit determines that the detection of the position of a specific part, such as a head, in the latest image is impossible, on the basis of past data stored as data corresponding to images outputted from a camera earlier than the latest image in a storage unit, the position of the head is predicted and detected.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an occupant detecting device (occupant sensing device) for capturing the image of the behavior of an occupant seated on a seat in a vehicle with an image capturing unit such as a video camera or the like while also detecting the position of a particular region of the occupant. 
       BACKGROUND ART 
       [0002]    Heretofore, as disclosed in Japanese Laid-Open Patent Publication No. 2004-144512 (JP2004-144512A), there has been proposed an occupant detecting system for judging whether there is an occupant in a vehicle by capturing an image of the occupant with a camera disposed in the cabin of the vehicle and detecting the head of the imaged occupant. 
         [0003]    According to paragraph [0067] of JP2004-144512A, the disclosed occupant detecting system is capable of detecting the state of the occupant based on an image in an infrared range in which visible light is partially cut off, the image being stable in brightness at all times without being affected by changes in ambient brightness. 
         [0004]    Japanese Laid-Open Patent Publication No. 2005-284975 (JP2005-284975A) discloses a safety drive apparatus for detecting a line of sight of the driver of a vehicle with a camera, and judging the driver to be inattentive and reckless if the line of sight is directed toward an object such as a navigation device or the like continuously for a period of time that exceeds a threshold time. 
       SUMMARY OF INVENTION 
       [0005]    Sunlight contains more than a small amount of infrared radiation, and it is impossible to completely eliminate the effects of sunlight, which could have a significant influence on the captured images. Therefore, the captured images may possibly be saturated by sunlight. When the vehicle enters a tunnel, for example, the timing at which an auxiliary light is turned on may be delayed. Consequently, the occupant detecting system disclosed in JP2004-144512A suffers from a problem in that it is incapable of producing an image that enables appropriate detection of the head of an occupant. The safety drive apparatus disclosed in JP2005-284975A also suffers from the above problem, which occurs when the vehicle enters a tunnel, for example. 
         [0006]    The present invention has been made in view of the aforementioned problems. It is an object of the present invention to provide an occupant detecting device, which is capable of reliably detecting the behavior of an occupant of a vehicle without being affected by extraneous noise and ambient light, or by a loss of detection data due to a delay in turning on an auxiliary light. 
         [0007]    An occupant detecting device according to the present invention includes an image capturing unit disposed in a cabin of a vehicle for capturing images of a given area including a seat in the cabin continuously or intermittently at predetermined time intervals and successively outputting the captured images, a position detecting unit for detecting the position of a particular body region of an occupant seated on the seat in the images output from the image capturing unit, an occupant state detecting unit for detecting a state of the occupant based on the position of the particular body region, which is detected by the position detecting unit, a memory unit for successively storing data depending on the images that are successively output during a predetermined period from the image capturing unit, and a detectability determining unit for judging whether or not the position detecting unit is capable of detecting the position of the particular body region, wherein if the detectability determining unit judges that the position detecting unit is capable of detecting the position of the particular body region in a latest image that serves as a presently output image of the images successively output from the image capturing unit, then the position detecting unit detects the position of the particular body region based on the latest image, and if the detectability determining unit judges that the position detecting unit is incapable of detecting the position of the particular body region in the latest image, the position detecting unit detects the position of the particular body region based on past data that are stored in the memory unit as data depending on images output from the image capturing unit before the latest image. 
         [0008]    According to the present invention, in the event that it is impossible to detect the position of the particular body region, e.g., the position of the head of the occupant or the like, in the latest image, the position of the particular body region is detected based on past images. Therefore, the state of the occupant can reliably be detected and system reliability can be increased without being affected by loss of detection data due to a delay in turning on an auxiliary light. 
         [0009]    The past data may comprise first past data that serves as data depending on one of the images, which is output from the image capturing unit in the predetermined time interval before the latest image, among the data stored in the memory unit. Since the images are captured intermittently, the memory unit may have a reduced storage capacity, and even if it is impossible to detect the position of the particular body region in the latest image, the position of the particular body region can be detected using an image chronologically closest to the latest image, i.e., a penultimate image, so that the accuracy with which the position of the particular body region is detected can be prevented from being lowered. 
         [0010]    The past data may comprise the first past data, and second past data that serve as data depending on one of the images, which is output from the image capturing unit in the predetermined time interval before the first past data, and the position detecting unit may detect the position of the particular body region based on a change in position between the particular body region detected in the first past data and the particular body region detected in the second past data. Therefore, even if it is impossible to detect the position of the particular body region in the latest image, the position of the particular body region can be detected using an image chronologically closest, by one, with respect to the latest image, i.e., an antepenultimate image, as well as the image chronologically closest to the latest image, i.e., the penultimate image, so that the accuracy with which the position of the particular body region is detected can be increased. 
         [0011]    The occupant detecting device may further comprise a deceleration detecting unit for detecting a deceleration of the vehicle, wherein if the detectability determining unit judges that the position detecting unit is incapable of detecting the position of the particular body region in the latest image, then the position detecting unit detects the position of the particular body region based on the past data, which are stored in the memory unit, and the deceleration detected by the deceleration detecting unit. Consequently, the accuracy with which the position of the particular body region is detected using past images can be increased. 
         [0012]    The past data that are stored in the memory unit may comprise coordinate data representing the position of the particular body region detected by the position detecting unit or numerical data representing distance data between the position of the particular body region and a position of a particular region in the cabin of the vehicle, and the occupant state detecting unit may detect the state of the occupant based on the numerical data stored in the memory unit. Since the memory unit stores only numerical data representing the position of the particular region, rather than image data per se, the storage capacity of the memory unit, as well as the operational load, can be reduced. 
         [0013]    According to the present invention, if it is impossible to detect the position of the occupant in a captured image, the position of the occupant is detected using a past image or past images. Therefore, the behavior of the occupant can reliably be detected without being affected by extraneous noise and ambient light, or by a loss of detection data due to a delay in turning on an auxiliary light. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0014]      FIG. 1  is a block diagram of an airbag system incorporating an occupant detecting device according to a first embodiment of the present invention; 
           [0015]      FIG. 2  is a flowchart of an operation sequence of the airbag system and the occupant detecting device shown in  FIG. 1 ; 
           [0016]      FIG. 3  is a timing chart illustrating energization of an auxiliary light at a time that a vehicle enters a tunnel; 
           [0017]      FIGS. 4A through 4D  are diagrams illustrating a process of predicting the position of a head at a time that latest image data is lost; 
           [0018]      FIG. 5  is a diagram illustrating a process of linearly predicting the position of a head at a time that latest image data is lost; 
           [0019]      FIG. 6  is a diagram illustrating a process of predicting the position of a head at a time that latest image data is lost, while taking into account a G value detected by a fore-and-aft G sensor; 
           [0020]      FIG. 7  is a diagram illustrating a process of linearly predicting the position of a head at a time that latest image data is lost, and a process of predicting the position of the head while taking into account a G value detected by a fore-and-aft G sensor; and 
           [0021]      FIG. 8  is a block diagram of an airbag system incorporating an occupant detecting device according to a second embodiment of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0022]    Embodiments of the present invention will be described below with reference to the drawings. 
       First Embodiment 
       [0023]      FIG. 1  is a block diagram of an airbag system  12  incorporating an occupant detecting device  10  according to a first embodiment of the present invention. 
         [0024]    The occupant detecting device  10  basically includes a camera  14  such as a video camera or the like, and an occupant detection ECU (Electronic Control Unit)  16  (occupant detection control device). 
         [0025]    The airbag system  12  comprises the occupant detecting device  10 , an airbag ECU  18 , inflator and airbag assemblies  20 , and a G sensor  30  (fore-and-aft acceleration sensor). 
         [0026]    The inflator and airbag assemblies  20  are mounted respectively on the steering wheel, which is positioned in front of the driver seated in the vehicle, and the instrument panel, which is positioned in front of the front passenger seat of the vehicle. If the vehicle has side curtain airbags, then additional inflator and airbag assemblies  20  also are mounted in both C pillars of the vehicle. 
         [0027]    The camera  14  is disposed in the cabin of the vehicle, and is mounted on the roof of the vehicle in the vicinity of an upper central region of the front windshield of the vehicle. Alternatively, the camera  14  may be disposed on the instrument panel or the dashboard of the vehicle. 
         [0028]    According to the present embodiment, the camera  14  has an image capturing area that covers an object to be imaged, which is the head (particular region) of the driver seated on the driver seat, and includes the face of the driver. The camera  14  is capable of capturing an image in a visible range or an infrared range, and successively outputs image data D representing the head of the driver. 
         [0029]    The camera  14  preferably comprises two stereo cameras, which are capable of directly measuring the distance up to the head of the driver in order to detect the position of the head, i.e., the distance from the position of the mounted inflator and airbag assembly  20  to the head of the driver. However, even if the camera  14  is a monocular camera, the position of the head, i.e., the distance from the position of the mounted inflator and airbag assembly  20  to the head, can be detected on the basis of a fixed object in the cabin, e.g., a known position (fixed position, reference position) of a room mirror or the like, for example. 
         [0030]    The camera  14  successively outputs image data D at given time intervals on the order of milliseconds, for example. The image data D are stored in a memory  22  of the occupant detection ECU  16 . The time intervals at which the image data D are output from the camera  14  may be of any appropriate value, which is selected by a camera control ECU, not shown, depending on the application of the occupant detecting device  10 . 
         [0031]    The memory  22  stores latest image data Dn, penultimate image data D 1 , which are output before the latest image data Dn, and antepenultimate image data D 2 , which are output before the penultimate image data D 1 . When the occupant detection ECU  16  receives new image data A from the camera  14 , the occupant detection ECU  16  deletes the antepenultimate image data D 2  from the memory  22  without updating thereof, and the penultimate image data D 1  prior to updating thereof becomes the antepenultimate image data D 2 . The occupant detection ECU  16  converts the latest image data Dn prior to updating thereof into the penultimate image data D 1 , and the new image data A received from the camera  14  becomes the latest image data Dn. The memory  22  may comprise a FIFO (First In First Out) memory. 
         [0032]    The occupant detection ECU  16  and the airbag ECU  18  are in the form of a computer including a microcomputer, which includes a CPU (Central Processing Unit), memories such as a ROM (including an EEPROM) and a RAM (Random Access Memory), and other components including input/output devices such as an A/D converter and a D/A converter, and a timer that serves as a time measuring unit, etc. The computer functions as various function performers (function performing means) when the CPU reads and executes programs stored in the ROM. If necessary, the RAM includes a video RAM for temporarily storing image data D. The memory  22  also includes a video RAM. 
         [0033]    The occupant detection ECU  16  includes, in addition to the memory  22 , a particular region detectability determiner  24 , a position detector  26 , and an occupant state detector  28 . 
         [0034]    The position detector  26  and the airbag ECU  18  are supplied with a fore-and-aft acceleration G value from the G sensor  30 , which serves as a fore-and-aft acceleration sensor. 
         [0035]    The particular region detectability determiner  24  judges whether or not the latest image data Dn includes a head therein as a particular region according to a pattern matching process or the like. If the latest image data Dn includes a head, then the particular region detectability determiner  24  outputs a result “POSSIBLE (PARTICULAR REGION IS DETECTABLE)” to the position detector  26 . If the latest image data Dn does not include a head, then the particular region detectability determiner  24  outputs a result “IMPOSSIBLE (PARTICULAR REGION IS UNDETECTABLE)” to the position detector  26 . 
         [0036]    If supplied with the result “POSSIBLE”, the position detector  26  detects the position of a particular region of the body of the occupant who is seated on the seat, e.g., the position of the head, from the latest image data Dn stored in the memory  22 . On the other hand, if supplied with the result “IMPOSSIBLE”, the position detector  26  detects the position of the head of the occupant who is seated on the seat by predicting the position when the latest image data Dn are not acquired, based on the penultimate image data D 1  and the antepenultimate image data D 2 , which are stored in the memory  22 . 
         [0037]    If supplied with the result “IMPOSSIBLE”, the position detector  26  also can detect the position of the head of the occupant who is seated on the seat by predicting the position when the latest image data Dn are not acquired, based on the penultimate image data D 1  and the antepenultimate image data D 2 , which are stored in the memory  22 , and also on the fore-and-aft acceleration G value (actually the deceleration G value in the event that the vehicle is involved in a collision) from the G sensor  30 . 
         [0038]    The occupant state detector  28  detects the state of the occupant based on the position of the head, which is detected by the position detector  26 . The state of the occupant represents whether or not the head of the occupant is within a given area, i.e., whether the occupant is present, whether the size of the head indicates an adult or a child, i.e., whether the occupant is an adult or a child, and whether or not the position of the head is spaced by a given distance from the position of the inflator and airbag assembly  20 . The detected state of the occupant is supplied to the airbag ECU  18  in the form of a corresponding code from the occupant state detector  28 . According to the background art, whether the occupant is an adult or a child is determined in accordance with a measured value from a weight sensor disposed below the seat. In contrast thereto, according to the present embodiment, however, the camera  14  is used to judge whether the occupant is an adult or a child. Therefore, it is possible to judge whether the occupant is an adult or a child more accurately and inexpensively than is possible with the background art. 
         [0039]    The airbag ECU  18  decides whether or not the airbags of the inflator and airbag assemblies  20  should be inflated, i.e., inflated or kept folded, based on the content of the supplied code. 
         [0040]    The airbag system  12 , which incorporates the occupant detecting device  10 , basically is constructed as described above. Operations of the airbag system  12  according to the first embodiment of the present invention will be described below with reference to the flowchart shown in  FIG. 2 . 
         [0041]    In step S 1 , the occupant detection ECU  16  acquires image data D from the camera  14 , and stores the acquired image data D as latest image data Dn in the memory  22 . 
         [0042]    In step S 2 , the particular region detectability determiner  24  judges whether or not the latest image data Dn stored in the memory  22  includes a head as a particular region, according to a pattern matching process or the like. 
         [0043]    If the latest image data Dn includes a head as a particular region (step S 2 : YES), then the particular region detectability determiner  24  outputs information indicating that positional detection is “POSSIBLE” to the position detector  26 . If the latest image data Dn does not include a head as a particular region (step S 2 : NO), then the particular region detectability determiner  24  outputs information indicating that positional detection is “IMPOSSIBLE” to the position detector  26 . 
         [0044]    According to an example in which the latest image data Dn does not include a head as a particular region and thus positional detection is “IMPOSSIBLE”, the vehicle carrying the occupant detecting device  10  enters a tunnel, for example, at time ta. At time tb, upon elapse of a period td from time ta, an auxiliary light is automatically turned on. Therefore, image data D captured at time t−1 immediately after time tb includes an image of the head (step S 2 : YES). However, it can be seen that latest image data Dn, which are captured at time t 0  immediately after the time ta at which the vehicle enters the tunnel, do not represent an image of a head due to underexposure (step S 2 : NO). It can also be understood that the penultimate image data D 1  and the antepenultimate image data D 2 , which precede the latest image data Dn at time t 0  prior to the time to at which the vehicle enters the tunnel, both represent data in which the head can be detected. In step S 1 , the times t 2 , t 1 , t 0 , and t−1 (at equal time intervals) correspond to respective image acquisition timings. 
         [0045]    If the particular region detectability determiner  24  judges that a head can be detected as a particular region from the latest image data Dn (step S 2 : YES), then in step S 3 , the position detector  26  calculates a distance Dis (occupant state) from the inflator and airbag assembly  20 , for example, to the head based on the latest image data Dn, and based on the size of the head, the occupant state detector  28  detects whether the occupant state represents an adult or a child. The occupant state detected by the occupant state detector  28  is stored in the memory  22  in association with the latest image data Dn. 
         [0046]    In step S 5 , the occupant state, which represents information concerning the distance Dis and identifying information concerning whether the occupant is an adult or a child, is supplied from the occupant state detector  28  to the airbag ECU  18 . The airbag ECU  18  decides whether or not the airbag should be inflated, based on the supplied occupant state, which represents information concerning the distance Dis and identifying information concerning whether the occupant is an adult or a child, and based on the fore-and-aft acceleration G value from the G sensor  30 . 
         [0047]    If the particular region detectability determiner  24  judges that a head cannot be detected as a particular region from the latest image data Dn, for example as at time t 0  in  FIG. 3  (step S 2 : NO), then in step S 4  (around time t 0 ), the position detector  26  predicts the present position of the head. 
         [0048]    In order to predict the present position of the head, as shown in  FIG. 4A , it is assumed that when an occupant  52  is seated on a seat (front seat)  50  in the vehicle (the occupant is shown as being seated on a front passenger seat for illustrative purposes), and that the camera  14  is disposed near an upper central region of a front windshield  54 , the occupant  52  is detected as an adult from the antepenultimate image data D 2 . Further, as shown in  FIG. 4B , the head  56  of the occupant  52  is spaced from the inflator and airbag assembly  20  (indicated as “A/B” in  FIGS. 4B ,  4 C,  4 D for illustrative purposes) by a distance Dis of 900 [mm] at time t 2 . In addition, as shown in  FIG. 4C , the occupant  52  is detected as an adult from the penultimate image data D 1 , and the head of the occupant  52  is spaced from the inflator and airbag assembly  20  by a distance Dis of 600 [mm] at time t 1 . 
         [0049]    As shown in  FIG. 5 , latest image data Dn that are not acquired at time t 0  can be predicted linearly from the antepenultimate image data D 2  and the penultimate image data D 1 , based on the fact that the occupant  52  is an adult, the distance Dis is 900 [mm] at time t 2 , and the distance Dis is 600 [mm] at time t 1 . The head  56  is predicted as moving 300 [mm] in the direction (forward direction) indicated by the two-dot-and-dash line, and as being spaced from the inflator and airbag assembly  20  by a distance Dis of 300 [mm]. 
         [0050]    When the occupant state, which indicates that the occupant  52  is an adult and that the head  56  of the occupant  52  is spaced 300 [mm] from the inflator and airbag assembly  20  is delivered to the airbag ECU  18 , the airbag ECU  18  executes a predetermined program to inflate the airbag or to keep the airbag in a folded state. 
         [0051]    The program, which is executed by the airbag ECU  18  to inflate the airbag or to keep the airbag in a folded state, is dependent on the type of vehicle. In view of the fore-and-aft acceleration G value from the G sensor  30 , the airbag should not be inflated if the occupant  52  is a child. Even if the occupant  52  is an adult and it is determined that the airbag should be inflated, when the distance Dis from the inflator and airbag assembly  20  to the head  56  is smaller than a certain threshold value, the inflator ejects a smaller amount of gas into the airbag than when the distance Dis from the inflator and airbag assembly  20  to the head  56  is greater than the certain threshold value. Furthermore, if an occupant  52  who is detected as an adult is leaning on a side windshield, the side curtain airbag is not inflated. 
         [0052]    Regardless of whether the airbag ECU  18  should inflate the airbag or keep the airbag in a folded state, in step S 6 , the memory  22  stores the latest image data Dn (including information concerning the distance Dis and identifying information concerning whether the occupant is an adult or a child), which is captured directly by the camera  14 , or the predicted image data D updated as latest image data Dn, stores the previous latest image data Dn, which is updated as penultimate image data D 1 , and further stores the prior penultimate image data D 1 , which is updated as antepenultimate image data D 2 . 
         [0053]    If latest image data Dn are not captured (step S 2 : NO), then in addition to linearly predicting the latest image data Dn as shown in  FIG. 5 , an occupant state, i.e., the distance Dis from the inflator and airbag assembly  20  to the occupant, preferably is corrected using the fore-and-aft acceleration G value from the G sensor  30 . 
         [0054]    A process of correcting the distance Dis from the inflator and airbag assembly  20  using the fore-and-aft acceleration G value from the G sensor  30  will be described below with reference to  FIG. 6 . 
         [0055]    It is assumed, in the event that a loss of latest image data Dn occurs at the latest time t 0  due to noise or the like, then as shown in  FIG. 6 , the occupant  52  is detected as being an adult from the antepenultimate image data D 2 , and the head  56  of the occupant  52  is spaced from the inflator and airbag assembly  20  by a distance Dis of 900 [mm] at time t 2 . In addition, the occupant  52  is detected as being an adult from the penultimate image data D 1 , and the head of the occupant  52  is spaced from the inflator and airbag assembly  20  by a distance Dis of 700 [mm] at time t 1 . The respective occupant states are stored in the memory  22 . 
         [0056]    As shown in  FIG. 7 , if the fore-and-aft acceleration G value from the G sensor  30  is not taken into account (simple prediction), then latest image data Dn are predicted linearly based on the fact that the occupant is an adult and the head  56  of the occupant  52  is spaced from the inflator and airbag assembly  20  by a distance Dis of 500 [mm] (“NO G CORRECTION” in  FIG. 7 ). However, if the deceleration G value is G=a×G (see  FIG. 6 ) at time t 0 , then latest image data Dn, which takes into account the fore-and-aft acceleration G value, are predicted based on the fact that the occupant is an adult and the head  56  of the occupant  52  is spaced from the inflator and airbag assembly  20  by a distance Dis of 300 [mm], rather than 500 [mm]. Consequently, the distance that the head  56  is moved is corrected by a greater amount as a result of the deceleration G value. 
         [0057]    According to the first embodiment, as described above, the occupant detecting device  10  essentially includes the camera  14 , which serves as an image capturing unit and is disposed in the cabin of the vehicle for capturing images of a given area including the seat  50  in the cabin continuously or intermittently at predetermined time intervals, the camera  14  successively outputting the captured images, the position detector  26 , which serves as a position detecting unit for detecting within the images the position of the head  56  as a particular body region of the occupant  52  who is seated on the seat  50 , and the occupant state detector  28 , which serves as an occupant state detecting unit for detecting the state of the occupant  52  based on the position of the head  56  detected by the position detector  26 . 
         [0058]    The occupant detecting device  10  also includes the memory  22 , which serves as a memory unit for successively storing data depending on images that are successively output from the camera  14  during a predetermined period ranging from time t 2  to time t 0 . The occupant detecting device  10  further includes the particular region detectability determiner  24 , which functions as a particular region detectability determining unit for judging whether or not the position detector  26  is capable of detecting the position of the head  56 . If the particular region detectability determiner  24  judges that the position detector  26  is capable of detecting the position of the head  56  in the latest image (latest image data Dn), as a presently output image from among the images that are successively output from the camera  14 , then the position detector  26  detects the position of the head  56  (the distance Dis from the inflator and airbag assembly  20  in the first embodiment) based on the latest image (latest image data Dn). On the other hand, if the particular region detectability determiner  24  judges that the position detector  26  is incapable of detecting the position of the head  56  in the latest image (latest image data Dn), then the position detector  26  detects the position of the head  56  by predicting the position based on past data (the penultimate image data D 1  and the antepenultimate image data D 2  according to the first embodiment), which are stored in the memory  22  as data depending on images output from the camera  14  before the latest image (the latest image data Dn). 
         [0059]    As described above, while the camera  14  is capturing images in periodic cycles, if the position of the head  56  cannot be detected from the latest image (latest image data Dn), then the position of the head  56  is detected from past images (the penultimate image data D 1  and the antepenultimate image data D 2 ). Consequently, the state of the occupant  52  can reliably be detected, thereby increasing system reliability without being affected by a loss of detection data caused by a delay in turning on the auxiliary light. 
         [0060]    The past data, based on which the latest position (present position) of the head  56  is detected as a particular region, preferably is the penultimate image data D 1  (first past data) and the antepenultimate image data D 2  (second past data). Except upon detecting a collision, however, only the penultimate image data D 1  may be used as the latest image data Dn, for thereby reducing the storage capacity of the memory  22  as images are captured intermittently. More specifically, even if it is impossible to detect the position of a particular region such as the head  56  or the like in the latest image, the position of a particular region such as the head  56  or the like can be detected using the image that is closest to the latest image, i.e., the penultimate image data D 1  preceding the latest image data, so that the accuracy with which the position of the particular region is detected can be prevented from being lowered due to loss of data. 
         [0061]    The occupant detecting device  10  further includes the G sensor  30 , which serves as a deceleration detecting unit for detecting deceleration of the vehicle. As described above with reference to  FIG. 7 , if the particular region detectability determiner  24  judges that the position detector  26  cannot detect the position of the head  56  in the latest image (latest image data Dn), then the position detector  26  detects the position of the head  56  based on the past data (the penultimate image data D 1  and the antepenultimate image data D 2 ), which are stored in the memory  22 , together with the deceleration value detected by the G sensor  30 . Therefore, the accuracy with which the position of the head  56  is detected using past images can be increased. 
         [0062]    The past data stored in the memory  22  comprise coordinate data of the position of the head detected by the position detector  26 , e.g., xyz three-dimensional data, based on the fixed position of the room mirror or based on the distance Dis, as numerical data representing the distance data between the position of the head  56  and the inflator and airbag assembly  20  as a particular region in the vehicle cabin. The occupant state detector  28  detects the state of the occupant  52  based on the numerical data stored in the memory  22 . Since the memory  22  stores only numerical data that represents the position of the particular region, rather than the image data per se output from the camera  14 , the storage capacity of the memory  22  can be reduced, and the operational load imposed by the processing sequence can also be reduced. 
       Second Embodiment 
       [0063]      FIG. 8  is a block diagram of an inattentive driving warning apparatus  60  that incorporates an occupant detecting device  10 A according to a second embodiment of the present invention. 
         [0064]    The occupant detecting device  10 A includes a camera  14  and an inattentive driving determination ECU  70 . The inattentive driving warning apparatus  60  includes the occupant detecting device  10 A and a warning device  66 . 
         [0065]    The camera  14 , the memory  22 , and the particular region detectability determiner  24  may be the same as those of the occupant detecting device  10  shown in  FIG. 1 . 
         [0066]    The camera  14  successively outputs facial images as image data D at predetermined times. The memory  22  successively stores latest image data Dn, penultimate image data D 1 , and antepenultimate image data D 2 , and updates the stored image data at predetermined times. The image data stored in the memory  22  may be image data captured by the camera  14 , or may be data detected by a line-of-sight and face-direction detector  62 . 
         [0067]    The particular region detectability determiner  24  judges whether the latest image data Dn includes a facial image according to a pattern matching process. 
         [0068]    The line-of-sight and face-direction detector  62 , which serves as a line-of-sight and face-direction detecting unit, carries out a recognition process such as a feature quantity calculating process and a shape determining process with respect to eyeballs of the driver of the vehicle as an object to be detected, on the facial image output from the camera  14 , and detects the positions of the left and right eyes, e.g., the central positions of the irises, the central positions of Purkinje images as infrared reflected images on the surface of the corneas, or the central positions of the eyeballs. The line-of-sight and face-direction detector  62  then detects the line-of-sight direction of the driver by processing the detected positions, and calculates the angle (gazing angle) of the line-of-sight direction with respect to a frontal direction of the driver seated on the driver seat. 
         [0069]    The line-of-sight and face-direction detector  62  also detects the central position of the face and the left and right end positions of the face based on the facial image output from the camera  14 , and detects the direction of the driver&#39;s face according to a cylinder process, which calculates the direction of the face by approximating the face of a person rendered in a cylindrical shape, based on the detected positions. 
         [0070]    The inattentive driving determination ECU  70  includes an inattentive driving determiner  64 , which judges that the driver is inattentive, and outputs a judgment signal to the warning device  66  if the line-of-sight direction or the face direction detected by the line-of-sight and face-direction detector  62  resides continuously within a predetermined inattentive direction region stored in a memory  68  for a predetermined period of time (inattentive driving judgment time), which is set in a timer  72  (time measuring means). 
         [0071]    When the warning device  66  receives the judgment signal, which is indicative of inattentive driving, the warning device  66  outputs a warning to the driver in the form of a sound (speech sound) from a non-illustrated speaker, vibrations from a non-illustrated vibrator that is incorporated in the steering wheel of the vehicle, or light emitted from a light source disposed at the position of the camera  14 . 
         [0072]    Owing to the inattentive driving warning apparatus  60  shown in  FIG. 8 , if the particular region detectability determiner  24  judges that it is impossible to detect a line-of-sight direction and a face direction based on latest image data Dn, then the line-of-sight and face-direction detector  62  detects the latest (present) line-of-sight direction and the face direction by predicting the line-of-sight direction and face direction based on past images, preferably penultimate image data D 1  and antepenultimate image data D 2 . Accordingly, the inattentive driving determiner  64  can determine if the driver is inattentive, thereby increasing system reliability without being affected by extraneous noise and ambient light, or by a loss of detection data due to a delay in turning on the auxiliary light. 
         [0073]    The present invention is not limited to the above embodiments, but may employ various arrangements based on the disclosure of the present description. For example, the present invention also may be applied to a drowsy driving detecting and warning technology for detecting when an occupant, i.e., the driver, of a vehicle becomes drowsy if the eyes of the driver are closed for a threshold period of time or longer, and issuing a warning.