JP7053341B2 - Processing equipment and programs - Google Patents

Description

The present invention relates to a processing device and a program, and more particularly to a processing device and a program that perform detection processing based on a captured image.

Conventionally, there is a technique of capturing an image reflected by a vehicle occupant and processing the captured image to identify a detection target. In this type of technology, it is required to detect the driver's head for the purpose of estimating the driver's physical condition and arousal level. In order to detect the driver's head, a technique has been proposed in which a pre-learned classifier is collated with an image taken (see, for example, Patent Document 1).

The processing device of Patent Document 1 includes an image pickup unit that captures an image to be detected by an operator who operates an operation unit of an in-vehicle device that can be operated by a driver and a passenger, and image data output from the image pickup unit. A differential processing unit that performs differential processing based on this to create a horizontal differential image and a vertical differential image, and a first polar coordinate system having the operation unit as a coordinate origin are set, and the horizontal differential image and the vertical direction are set. A calculation unit that calculates the first angular and radial differentials based on the differential image, the calculated first angular differential, the first radial differential, and the first. The binary image creating unit that creates the first binary image based on the conditions, and the first and second straight lines that have a first interval and are substantially parallel based on the first binary image. An operator discrimination device is configured to include an extraction unit for extracting a straight line and a discrimination unit for discriminating the operator based on the extracted first and second straight lines.

Japanese Unexamined Patent Publication No. 2009-294843

However, the technique of Patent Document 1 has a problem that although information on the surface of the head can be obtained, information on the position of the head, for example, the position of the center of the head cannot be obtained.

Therefore, an object of the present invention is to provide a technique for acquiring information on the position of the center of the occupant's head in the technique for detecting the occupant's head.

[1] In order to achieve the above object, an acquisition unit for acquiring a distance image in which an imaging region including a vehicle occupant is an imaging target and in which distance information to the imaging target is assigned to each pixel is used. A pixel group constituting the distance image, which is extracted according to the correspondence between the coordinate system in the vehicle interior space of the vehicle and the coordinate system in the distance image, and has a high possibility that the head of the occupant exists. Provided is a processing device including a control unit that identifies the head of the occupant and executes a position detection process for finding the center position of the head in the identified occupant's head with respect to the high likelihood region. do.
[2] The control unit executes a search process for searching for a specific coordinate having the smallest variation in distance from each pixel detected as the head of the occupant, and the specific specific specified as a result of the search process. The processing device according to the above [1] may be used, in which the coordinates are the center position of the head.
[3] Further, the control unit determines the variation in the distance between each pixel detected as the head of the occupant, the coordinates corresponding to the center of the head, and a plurality of coordinates set around the center of the head. The processing apparatus according to the above [1] or [2] may be used to search for the coordinates having the minimum evaluation value as the specific coordinates as the search process.
[4] Further, the control unit changes the coordinates corresponding to the center of the head by a specified distance, and searches for the coordinates having the minimum evaluation value as specific coordinates, as the search process. The processing apparatus according to the above [3] may be executed.
[5] Further, the control unit is the processing device according to the above [4], wherein the specified distance is set to a distance shorter than a predetermined distance when the specific coordinates are not changed. May be good.
[6] Further, the control unit continues the position detection process depending on whether or not the difference between the evaluation value for the head center position after the update and the evaluation value for the head center position before the update is equal to or greater than a predetermined threshold value. The processing apparatus according to any one of the above [3] to [5], which determines whether or not to do so, may be used.
[7] In order to achieve the above object, an acquisition step of acquiring a distance image in which an imaging region including a vehicle occupant is an imaging target and a distance information to the imaging target is assigned to each pixel, and an acquisition step. A pixel group constituting the distance image, which is extracted according to the correspondence between the coordinate system in the vehicle interior space of the vehicle and the coordinate system in the distance image, and has a high possibility that the head of the occupant exists. In order to cause the computer to execute a control step of identifying the head of the occupant and performing a position detection process for determining the center position of the head in the identified occupant's head in the high likelihood region. Provide the program of.
[8] The control step executes a search process for searching for a specific coordinate having the smallest variation in distance from each pixel detected as the head of the occupant, and the specific specific specified as a result of the search process. The program according to the above [7] may be used, in which the coordinates are the center position of the head.
[9] Further, in the control step, the variation in the distance between each pixel detected as the head of the occupant and the coordinates corresponding to the center of the head and a plurality of coordinates set around the center of the head is obtained. The program according to the above [7] or [8] may be used to search for the coordinates having the minimum evaluation value as the specific coordinates as the search process.
[10] Further, in the control step, the search process is to change the coordinates corresponding to the center of the head by a specified distance and search for the coordinates having the minimum evaluation value as specific coordinates. The program to be executed may be the program described in the above [9].
[11] Further, even in the program according to the above [10], the control step sets the specified distance to a distance shorter than a predetermined distance when the specific coordinates are not changed. good.
[12] Further, the control step continues the position detection process depending on whether or not the difference between the evaluation value for the head center position after the update and the evaluation value for the head center position before the update is equal to or greater than a predetermined threshold value. The program according to any one of [9] to [11] above may be used to determine whether or not to perform the program.

According to the processing apparatus and the program of the present invention, it is possible to acquire information on the position of the center of the head of the occupant in the technique of detecting the head of the occupant.

FIG. 1 is a coordinate diagram showing three-dimensionally the relationship of the coordinate system in a state where the processing device according to the embodiment of the present invention is mounted on a vehicle. FIG. 2 is a flowchart showing an operation of acquiring the position of the center of gravity of the head in the processing apparatus according to the embodiment of the present invention. FIG. 3A is a pixel group diagram showing a three-dimensional pixel group in the vehicle coordinate system (w, l, h) in the detection area, and FIG. 3B is a region from the pixel group in the detection area. It is the extraction pixel group diagram which narrowed down. FIG. 4A is a pixel group diagram extracted by Step 2, FIG. 4B is a pixel group diagram when the pixel group is divided in the direction of the l-axis, and FIG. 4C is a high pixel group diagram. It is a pixel group diagram extracted as a likelihood region. FIG. 5 is a chart showing a head model definition example of the head width and the head height. FIG. 6A is a pixel group diagram extracted by Step 3, FIG. 6B is a pixel group diagram when the pixel group is divided in the direction of the w-axis, and FIG. 6C is a high pixel group diagram. It is a pixel group diagram extracted as a likelihood region. FIG. 7 is a diagram showing the crown extracted as the maximum value in the h direction. FIG. 8A is a pixel group diagram in the vehicle coordinate system (w, l, h) showing the extracted head top, and FIG. 8B is wh from which the head is extracted according to the head model definition example. It is a pixel group diagram in a plane, FIG. 8C is a pixel group diagram in a lh plane from which a head is extracted according to a head model definition example, and FIG. 8D is a pixel showing an extracted head region. It is a group map. FIG. 9 is a pixel group diagram showing the extracted head position (center of gravity position of the head region). FIG. 10 is a flowchart showing an operation of acquiring the head center position in the processing apparatus according to the embodiment of the present invention. FIG. 11A is a diagram showing the position of the center of gravity of the pixel group in the head region, and FIG. 11B is a diagram showing the corrected head center position as a result of executing the search process for searching the head position. It is a figure which shows.

(Embodiment of the present invention)
The processing device 1 according to the embodiment of the present invention acquires a distance image in which the image pickup region including the occupant 5 of the vehicle 8 is the image pickup target, and the distance information to the image pickup target is assigned to each pixel. The TOF camera 10 as an acquisition unit and the pixel group constituting the distance image are extracted according to the correspondence between the coordinate system in the vehicle interior space of the vehicle 8 and the coordinate system in the distance image, and the head of the occupant 5 exists. Control to execute a position detection process for specifying the head 50 of the occupant 5 and obtaining the head center position C in the specified occupant's head for a high likelihood region which is a pixel group having a high possibility of It is composed of a part and a part.

The pixel group is a set of points corresponding to the pixels imaged by the TOF camera 10, and the position is displayed by the coordinate system in the vehicle interior space of the vehicle 8, the coordinate system in the TOF camera 10, and the like. It is a set of points in space. The high-likelihood region is a region in which a detection target is likely to exist. Specifically, for example, it is a region in which the number of pixel groups in the region is large or the pixel group density is high.

(TOF camera 10)
The acquisition unit can be used as long as it can recognize the image pickup target in three dimensions, but in the present embodiment, the TOF (Time Of Flight) camera 10 is used as the acquisition unit. The TOF camera 10 can detect the time until the light of the light source hits the object to be measured and returns for each pixel, and can take a three-dimensional image including the position information corresponding to the distance in the depth direction. After emitting infrared light or the like, the TOF camera 10 receives the reflected light that is reflected by the object and returns, measures the time from the light emission to the light reception, and measures the time from the light emission to the light reception, and the distance to the object to be imaged for each pixel. Is detected.

As shown in FIG. 1, for example, the TOF camera 10 is attached near the rear-view mirror, and the imaging region including the occupant 5 of the vehicle 8 is targeted for imaging. The image captured by the TOF camera 10 includes coordinates (u, v) and pixel values d (u, v) as depth information at these coordinates (u, v). The acquired pixel value d (u, v) (u = 0, 1, ... U-1, v = 0, 1, ... V-1) is an object to be imaged (the object referred to here is the driver). And in-vehicle devices). The reference numeral U in the embodiment means the horizontal width [pixel] in the captured image, and the reference numeral V means the vertical width [pixel] in the captured image. That is, a distance image is generated by assigning the distance information in the three-dimensional space to each pixel in the image captured by the TOF camera 10.

なお、（ｃ_ｘ、ｃ_ｙ）は、画像中心座標、ｆは、レンズ焦点距離である。 (Camera coordinate system obtained from distance image)
The coordinate values u, v in the range image and the pixel value d (u, v) in the coordinates (u, v) are converted into points (x, y, z) in the three-dimensional space using the following equation. Then, a three-dimensional pixel group in the camera coordinate system (x, y, z) shown in FIG. 1 can be created.

Note that (c _x , _cy ) is the image center coordinates, and f is the lens focal length.

(Vehicle coordinate system)
The camera coordinate system (x, y, z) can be converted into a vehicle coordinate system (w, l, h) whose origin is the driver (for example, the position of the hip bone) to be detected. The conversion method is a combination of general coordinate rotation conversion, translation conversion, and scale conversion. The coordinate axes after conversion are w-axis in the right direction of the driver, l-axis (el-axis) in the anterior direction, h-axis in the upper direction, and the origin is the position of the hipbone of the driver.

(Control unit 20)
The control unit 20 includes, for example, a microcomputer for performing coordinate conversion, head identification processing, head identification processing, and the like. As shown in FIG. 1, the control unit 20 is connected to the TOF camera 10. The control unit 20 includes a CPU (Central Processing Unit) 21 that performs calculations and processing on the acquired data according to a stored program, a RAM (Random Access Memory) 22 that is a semiconductor memory, and a ROM (Read Only Memory) 23. ing.

(Operation of processing device 1)
2 and 10 will be described with reference to a flowchart showing the operation of the processing apparatus 1 according to the embodiment of the present invention. The control unit 20 executes the following calculations and processes according to each flowchart.

(Step 1)
The TOF camera 10 as an acquisition unit acquires a distance image in which the image pickup region including the occupant 5 of the vehicle 8 is the image pickup target, and the distance information to the image pickup target is assigned to each pixel. This distance image can be acquired as one frame of the frames captured at predetermined time intervals. The acquired distance image functions as an input (three-dimensional pixel group) in the following processing. The distance image is converted into the camera coordinate system and the vehicle coordinate system described above. As a result, as shown in FIG. 3A, the three-dimensional pixel group 201 included in the detection area can be extracted. In the following processing, operations, processing, and the like are executed in the three-dimensional pixel group of the vehicle coordinate system (w, l, h).

(Step2)
The control unit 20 first extracts the pixel group 202 in the detection area as shown in FIG. 3B as the extraction of the crown portion. The area is narrowed down by defining the detection area and extracting the pixel group included in the space. The detection area is a space above the vehicle interior where the head 50 is considered to be present when seated. For example, the origin is the driver hipbone position 203, and the range is −510 <w <360, 280 <l <700, 430 <h <750. The unit is mm (hereinafter the same).

When the pixel group extracted by Step 1 is viewed from the w-axis direction in order to extract the region including the head 50, as shown in FIG. 4A, the region having the highest pixel group density has high likelihood. It is considered that the head 50 and the body portion 70 are included as the region (the body portion 70 is considered to exist below the head 50). Here, based on the width D of the head model definition (FIG. 5), the region is divided in the direction of the l-axis (FIG. 4 (b)), and the region 204 having the largest number of pixel groups on the lh plane is extracted (FIG. 4). (C)).

(Step 3)
When the area 204 (FIG. 6A) of the pixel group extracted by Step 2 is viewed from the l-axis direction in order to extract the area including the crown, the area with the highest pixel group density is the high likelihood area. It is considered that the crown is included as. Here, it is divided in the direction of the w-axis based on the width D defined by the head model (FIG. 6 (b)), and the region 205 having the largest number of pixel groups on the wh plane is extracted (FIG. 6 (c)). ..

(Step 4)
The control unit 20 executes a parietal region specifying process for calculating the parietal region position. As shown in FIG. 7, among the pixel groups extracted by Step 3, the highest portion on the h-axis is considered to be the crown 60. The crown 60 may be extracted by averaging some of the large values of the pixel group 205 (FIG. 6 (c)) extracted in the h direction. Let the coordinates of the extracted crown 60 be (wt, lt, ht).

(Step 5)
The control unit 20 extracts the head region. The head 50 is extracted from the head 60 and the head model definition (FIG. 5) extracted by the extraction process of the head. The head region 206 is obtained by extracting a pixel group as shown in FIGS. 8A to 8D with reference to the coordinates (wt, lt, ht) of the crown 60. The head region 206 is in the range of wt-w ₁ <w <wt + w ₁ , lt-l ₁ <l <lt + l ₁ , ht-h ₁ <h <ht. When the head model definition example (FIG. 5) is adapted, w ₁ = 176/2, l ₁ = 176/2, and h ₁ = 146. It should be noted that h ₁ is set to h ₁ = 206-60 = 146 by subtracting 60 from the height H defined in the head model, assuming the lack of information on the hair portion due to the characteristics of the TOF camera.

(Step 6)
The control unit 20 executes a head identification process for calculating the head position. In the region 206 extracted in Step 5, as shown in FIG. 9, the center of gravity of the pixel group of the head region 206 included in the region defined by the above w, l, and h ranges is obtained as the head position. The center of gravity position G (wg, lg, hg) can be output.

(Step 7)
The control unit 20 performs initialization. The control unit 20 sets the initial value of the head center position C as the center of gravity position G output in Step 6. That is, the coordinates of the head center position C in space are (wg, lg, hg). Also, let s be the coordinate update step width. The initial value of s is, for example, 1 [mm].

ここで、ｎは、頭部領域に含まれる点の数、ｐｋは頭部領域に含まれる点（ｐ＝０，１，…，ｎ－１）、ｄ（ａ，ｂ）は、点ａ，ｂ間のユークリッド距離とする。 (Step 8)
The control unit 20 has (wc, lc, hc) and 26 surrounding points ((wc ± s, lc, hc), (wc, lc ±) adjacent to this point (wc, lc, hc) in the three-dimensional direction. s, hc), (wc, lc, hc ± s), (wc ± s, lc ± s, hc), (wc ± s, lc, hc ± s), (wc, lc ± s, hc ± s) , (Wc ± s, lc ± s, hc ± s)), the value (variance) of the following evaluation function is calculated.

Here, n is the number of points included in the head region, pk is the points included in the head region (p = 0,1, ..., n-1), and d (a, b) is the point a, Let it be the Euclidean distance between b.

(Step 9)
The control unit 20 updates the coordinates having the smallest evaluation value among the 27 points calculated in Step 8 as the head center position C. This evaluation value is a value indicating the variation in the distance between the coordinates corresponding to the center of the head and the plurality of coordinates set around the center of the head.

(Step 10)
The control unit 20 determines whether or not the head center position C has changed (updated). If the head center position C changes, the process proceeds to Step 11 (Step 10: Yes), and if the head center position C does not change, the process proceeds to Step 12 (Step 10: No).

(Step 11)
The control unit 20 determines whether or not the distance difference between the initial position of the head center position C and the updated position is less than the threshold value. If it is less than the threshold value, the process proceeds to Step 13 (Step 11: Yes), and if it is not less than the threshold value, the process proceeds to Step 14 (Step 11: No).

(Step 12)
The control unit 20 updates the step width s of the coordinates to a smaller value (for example, 1/10), returns to Step 8, and repeats the search process.

(Step 13)
The control unit 20 compares the evaluation value for the head center position after the update with the evaluation value for the head center position before the update, and determines whether the difference is less than the threshold value. If it is less than the threshold value, the process proceeds to Step 15 (Step 13: Yes), and if it is not less than the threshold value, the process returns to Step 8 and the search process is repeated.

(Step 14)
The control unit 20 returns the head center position C before updating. That is, when the specific coordinates are not changed, the specified distance is set to be shorter than the predetermined distance.

(Step15)
The control unit 20 outputs the head center position C as the head position and ends the process. By the series of operations shown above, the initial position (center of gravity position G) of the pixel group in the head region shown in FIG. 11A is corrected to the head center position C shown in FIG. 11B. The region 207 shows the region around the center of gravity position G in the region 206 in FIG.

The above processing execution can be repeatedly executed as a series of operations shown above.

(Embodiment as a program)
An acquisition step of acquiring a distance image, which is a distance image of the image pickup area including the occupant 5 of the vehicle 8 as an image pickup target, and the distance information to the image pickup target is assigned to each pixel, which is shown by the processing device 1 on the computer. A pixel group constituting a distance image, which is extracted according to the correspondence between the coordinate system in the vehicle interior space of the vehicle 8 and the coordinate system in the distance image, and has a high possibility that the head 50 of the occupant 5 exists. A computer performs a control step of specifying the head 50 of the occupant 5 with respect to the high likelihood region, and executing a position detection process for obtaining the head center position C in the specified occupant's head 50. A computer for executing a computer is also one of the embodiments of the present invention.

Step 1 described in the operation of the processing device 1 is an example of an acquisition step for acquiring a distance image, Steps 7 to 15 are an example of a control step for executing a position detection process, and the flowcharts shown in FIGS. 2 and 10 are executed. The processing control to be performed can be an embodiment of a program for causing a computer to execute.

A computer-readable recording medium on which the above program is recorded is also one of the embodiments of the present invention.

(Effect of embodiment)
According to the embodiment of the present invention, it has the following effects.
(1) The processing apparatus according to the embodiment of the present invention is a distance image in which an imaging region including an occupant 5 of a vehicle 8 is an imaging target, and a distance image in which distance information to an imaging target is assigned to each pixel. The TOF camera 10 as the acquisition unit to be acquired and the pixel group constituting the distance image are extracted according to the correspondence between the coordinate system in the vehicle interior space of the vehicle 8 and the coordinate system in the distance image, and the head of the occupant 5. A position detection process is executed in which the head 50 of the occupant 5 is specified for the high-probability region, which is a pixel group in which is likely to exist, and the head center position C in the specified occupant's head is obtained. It is configured to have a control unit and a control unit. The head position detected based on the pixel group (three-dimensional pixel group) obtained by converting each pixel of the distance image obtained from the TOF camera into the three-dimensional space is biased toward the face surface, but the head is approximated by a sphere. This makes it possible to correct the detection position to the center of the head.
(2) It is possible to detect the position of the center of the object from the information on the surface of the object. That is, regardless of the direction in which the face is photographed, the position near the center of the head can always be detected as the head position.
(3) From the above, in the technique of detecting the head of the occupant of the vehicle, it becomes possible to provide a processing device and a program for acquiring information on the position of the center of the occupant's head.

Although some embodiments of the present invention have been described above, these embodiments are merely examples and do not limit the invention according to the claims. In addition, these novel embodiments can be implemented in various other embodiments, and various omissions, replacements, changes, etc. can be made without departing from the gist of the present invention. Moreover, not all combinations of features described in these embodiments are essential as means for solving the problems of the invention. Further, these embodiments are included in the scope and gist of the invention, and are also included in the scope of the invention described in the claims and the equivalent scope thereof.

1 ... Processing device, 5 ... Crew, 8 ... Vehicle, 10 ... TOF camera, 20 ... Control unit, 50 ... Head, 60 ... Head top, 70 ... Body part, 201, 202, 204, 205, 206, 207 ... Area, 203 ... Driver hipbone position, C ... Head center position, G ... Center of gravity position

Claims (10)

An acquisition unit that acquires a distance image in which an imaging region including a vehicle occupant is an imaging target and distance information to the imaging target is assigned to each pixel corresponding to the coordinates of a given two-dimensional coordinate system .
The coordinates of the pixels in the two-dimensional coordinate system of the distance image acquired by the acquisition unit and the distance information of the coordinates are converted into points on the three-dimensional space to create a three-dimensional pixel group, and the three-dimensional The first coordinate system of the pixel group is converted into the second coordinate system with the occupant as the origin, and the head of the occupant is extracted from the three-dimensional pixel group in the converted second coordinate system. A control for executing a position detection process for identifying the head of the occupant in a high-probability region, which is a group of pixels having a high possibility of existence, and determining the center position of the head in the identified head of the occupant. Department and
Have,
The control unit specifies the coordinates of the center of gravity of the occupant's head, and sets the specified coordinates of the center of gravity as the initial value of the head center position.
A search process is executed in which the coordinates that minimize the evaluation value indicating the variation in the distance between the coordinates of the center of gravity and the plurality of coordinates set around the coordinates of the center of gravity are updated as the coordinates of the head center position. ,
Processing equipment. In the second coordinate system, the control unit has a first axis in which the right direction of the vehicle is positive and negative in the left direction from the origin, a second axis in which the front direction of the vehicle is positive, and the control unit. When the third axis is positive in the upward direction of the vehicle,
Based on the predetermined width according to the predetermined head model, the extracted high-likelihood region is divided in the direction of the second axis, and the first region having the largest number of pixel groups is extracted. ,
The first region is divided in the direction of the first axis based on the width, and the second region having the largest number of pixel groups is extracted.
Further, in the extracted second region, the highest portion along the positive direction of the third axis is defined as the crown of the occupant.
By adapting the head model to the crown of the occupant, the occupant's head area is identified.
The coordinates of the center of gravity of the head region are specified as the coordinates of the center of gravity of the occupant's head.
The processing apparatus according to claim 1. As the search process, the control unit changes the coordinates of the head center position by a specified distance and newly searches for the coordinates that minimize the evaluation value as the coordinates of the head center position. The processing apparatus according to claim 1 or 2 , which is executed. The processing device according to claim 3 , wherein the control unit sets the specified distance to a distance shorter than a predetermined distance when the coordinates of the head center position are not changed. The control unit determines whether to continue the position detection process depending on whether or not the difference between the evaluation value for the head center position after the update and the evaluation value for the head center position before the update is equal to or greater than a predetermined threshold value. The processing apparatus according to any one of claims 1 to 4 . An acquisition step of acquiring an image pickup area including a vehicle occupant and assigning distance information to the image pickup target for each pixel corresponding to the coordinates of a given two-dimensional coordinate system, and an acquisition step.
The coordinates of the pixels in the two-dimensional coordinate system of the distance image acquired in the acquisition step and the distance information of the coordinates are converted into points on the three-dimensional space to create a three-dimensional pixel group, and the three-dimensional The first coordinate system of the pixel group is converted into the second coordinate system with the occupant as the origin, and the head of the occupant is extracted from the three-dimensional pixel group in the converted second coordinate system. A control for executing a position detection process for identifying the head of the occupant in a high-probability region, which is a group of pixels having a high possibility of existence, and determining the center position of the head in the identified head of the occupant. Steps and
Have,
In the control step, the coordinates of the center of gravity of the occupant's head are specified, and the coordinates of the specified center of gravity are set as the initial value of the head center position.
A search process is executed in which the coordinates that minimize the evaluation value indicating the variation in the distance between the coordinates of the center of gravity and the plurality of coordinates set around the coordinates of the center of gravity are updated as the coordinates of the head center position. , A program that lets your computer do that. The control step is a first axis in which the right direction of the vehicle is positive and negative in the left direction from the origin in the second coordinate system, a second axis in which the front direction of the vehicle is positive, and the control step. When the third axis is positive in the upward direction of the vehicle,
Based on the predetermined width according to the predetermined head model, the extracted high-likelihood region is divided in the direction of the second axis, and the first region having the largest number of pixel groups is extracted. ,
The first region is divided in the direction of the first axis based on the width, and the second region having the largest number of pixel groups is extracted.
Further, in the extracted second region, the highest portion along the positive direction of the third axis is defined as the crown of the occupant.
By adapting the head model to the crown of the occupant, the occupant's head area is identified.
The program according to claim 6 , wherein the coordinates of the center of gravity of the head region are specified as the coordinates of the center of gravity of the occupant's head . The control step changes the coordinates of the head center position by a specified distance, and newly searches for the coordinates that minimize the evaluation value as the coordinates of the head center position , as the search process. The program of claim 7 to be executed. The program according to claim 8 , wherein the control step sets the defined distance to a distance shorter than a predetermined distance when the coordinates of the head center position are not changed. The control step determines whether to continue the position detection process depending on whether or not the difference between the evaluation value for the head center position after the update and the evaluation value for the head center position before the update is equal to or greater than a predetermined threshold value. The program according to any one of claims 6 to 9 .

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