JP2006277618A - Image generation device and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably provide an image, wherein a CG object is brought close to a viewpoint position, while maintaining a natural operation feeling and/or to provide an image, wherein the CG object is distanced away from the viewpoint position for allowing observation of the whole of the large CG object. <P>SOLUTION: A first detection means detects a position and an attitude of a video camera photographing a real image. A second detection means detects a position and an attitude for generating a computer graphics (CG) image. Based on the detection results about the position and attitude by the first and second detection means, the real image and the CG are synthesized together. In this process, it is determined whether a distance between the positions detected by the first and second detection means is within a predetermined range or not. If it is determined that the distance is outside the predetermined range, the position for generating the CG is changed from the position detected by the second detection means (S205). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image generation technique, and more specifically, a mixed reality image that can superimpose a real-world image and a computer-generated image and can display both images in alignment. It is about presentation.

  Conventionally, a real-world image and a three-dimensionally modeled computer image (CG) image are superimposed and displayed, and it is as if an object (virtual object) drawn in CG exists in the real world. There is an apparatus that presents mixed reality (MR) that can be seen as such (Patent Document 1). This type of apparatus includes a real video shooting unit (for example, a video camera) for shooting a real video, a CG video generation unit that creates a CG video as viewed from the position where the real video is shot, A video display unit (for example, an HMD (head mounted display) or a monitor) can be provided. In addition, in order to correctly display the positional relationship between the CG and the real image even if the position and orientation of the line of sight of the real image capturing unit change, it is possible to detect the line of sight position and line of sight of the real image capturing unit (video camera). And a line-of-sight position and orientation detection unit (for example, a position and orientation sensor).

  The CG video generation unit places the CG modeled three-dimensionally in a virtual space having the same scale as the real space, and renders the CG as observed from the gaze position and gaze direction detected by the gaze position / posture detection unit. When the CG video generated in this way and the real video are superimposed, as a result, even if the real video shooting unit observes from any gaze position and gaze direction, the video correctly generated in CG in the real space Can be displayed. The type of CG, change of arrangement, animation, etc. can be freely performed as in the case of general CG. It is also possible to provide another position / orientation sensor for designating the position of the CG and draw the CG at a location according to the value of the position / orientation sensor. Further, in such a configuration, it has been conventionally performed to hold a position / orientation sensor for determining the position of the CG and to observe the CG while the observer freely changes the position and orientation of the CG. .

  Note that the real image capturing unit that captures an image of the real space is, for example, a video camera, and captures an image in the direction of the line of sight of the camera and captures it in the memory. For example, an HMD (Head Mount Display) is used as a video display device that synthesizes and displays a real space video and CG. When an HMD is used instead of a normal monitor, and the video camera is mounted in the direction of the line of sight of the HMD, an image in the direction in which the observer is facing can be displayed on the HMD, and the direction is turned Since CG can be drawn, it is possible to enhance the immersive feeling of the observer.

  Note that the video display device may be an HMD called an optical see-through type that does not include a video camera and allows the state of the front surface of the HMD to be observed as-is through. In this case, the above-described real image shooting unit does not use video shooting but optically displays the real space in front of the HMD on the display device as it is. With this type of HMD, the scenery in front of the observer can be observed as-is without any digital processing, and CG can be superimposed on the screen.

  Further, as the position / orientation detection unit, a magnetic position / orientation sensor or the like is used, and by attaching this to the video camera (or HMD to which the video camera is attached), the position / orientation of the line of sight of the video camera. Is detected. A magnetic position and orientation sensor detects the relative position and orientation between a magnetism generator (transmitter) and a magnetic sensor (receiver), and is a product FASTRAK (trademark) manufactured by Polhemus, USA. Etc. This is a device that detects the three-dimensional position (X, Y, Z) and posture (Roll, Pitch, Yaw) of a sensor in real time in a specific region.

With the above configuration, the observer can observe the world in which the real image and the CG image are superimposed through the HMD. For example, when an observer wearing an HMD looks around, a real image capturing device (video camera) provided in the HMD captures a real image, and a line-of-sight position and orientation detection unit (position and orientation sensor) provided in the HMD Detects the direction of the line of sight of the video camera, and in response to this, the CG video generation unit generates (renders) a CG video viewed from the line of sight position and orientation, and superimposes it on the real video for display.
JP 2000-350859 A

In the conventional system, when drawing a CG object at the position of the position and orientation sensor held by hand, the following problems exist. That is,
(1) When the sensor was brought close to the eyes to observe the inside of the CG, the sensor malfunctioned due to the influence of electricity or metal of the HMD, and the display position of the CG was unstable.
(2) When a large CG object is displayed, even if the hand holding the receiver is fully extended, the hand cannot be kept far enough, and the entire CG object cannot be observed.

  The present invention has been made in view of the above problems, and can stably provide an image in which a CG object is brought close to a viewpoint position while maintaining a natural feeling of operation, and / or a large image. An object of the present invention is to provide an image in a state where the CG object is moved away from the viewpoint position so that the entire CG object can be observed.

In order to achieve the above object, an image generation apparatus according to the present invention comprises the following arrangement. That is,
An image generation device that generates an image in which a computer image is superimposed on a real image captured by an imaging unit,
First detection means for detecting the position and orientation of the photographing means;
Second detection means for detecting a position and orientation at which the computer image is to be generated;
Synthesizing means for synthesizing the computer image with a real image obtained by the imaging means based on the position and orientation detected by the first and second detecting means;
Determination means for determining whether or not the distance between the positions detected by the first and second detection means is within a predetermined range;
And changing means for changing a position where the computer image is to be generated when the determining means determines that the relationship is outside a predetermined range.

Further, an image generation method according to the present invention for achieving the above object is as follows:
An image generation method for generating an image in which a computer image is superimposed on a real image shot by a shooting means,
A first detection step of detecting the position and orientation of the photographing means;
A second detection step of detecting a position and orientation at which the computer image is to be generated;
A synthesizing step of synthesizing the computer image with a real image obtained by the imaging means based on the position and orientation detected by the first and second detecting steps;
A determination step of determining whether or not a distance between the positions detected in the first and second detection steps is within a predetermined range;
A change step of changing a position where the computer image should be generated when the determination step determines that the relationship is outside a predetermined range.

  According to the present invention, it is possible to stably provide an image in which the CG object is brought close to the viewpoint position while maintaining a natural feeling of operation, and / or the entire large CG object can be observed. Therefore, it is possible to provide an image in a state where the CG object is moved away from the viewpoint position.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the accompanying drawings.

<First Embodiment>
FIG. 1 is a block diagram showing the configuration of the mixed reality presentation system according to the first embodiment. As shown in FIG. 1, a position / orientation sensor controller 103, an HMD controller 130, and memories 106 and 107 are connected to the CPU 101 via a bus 102. The HMD controller 130 is connected to the HMD 104 and the video camera 105, and controls input of video from the video camera 105 and output of video to be displayed on the HMD. Position and orientation sensors 108 and 109 are connected to the position and orientation sensor controller 103. The position / orientation sensor 108 is attached to the HMD 104 and is used to detect the line-of-sight position and orientation of the video camera 106 attached to the HMD 104. On the other hand, the position / orientation sensor 109 is for designating the position / orientation of the CG displayed in the MR space. In addition, the number of sensors is two here, but the number of sensors is not limited to this, and it is possible to provide as many sensors as necessary in the system. In this case, a plurality of CGs can be assigned to each position and orientation sensor. Further, two or more HMDs may be prepared to have two or more observers.

  Note that the position (line of sight position) of the video camera 105 represented by the line of sight position and orientation of the video camera 105 is the position of the observer, that is, the viewpoint position. In the following embodiments, such a viewpoint position is referred to as a line-of-sight position.

  Each unit indicated by reference numerals 110 to 116 included in the memory 106 is a control program for realizing the function of the corresponding processing unit by the CPU 101. The data and parameters indicated by reference numerals 120 to 129 stored in the memory 107 are held for use when executing the mixed reality presentation process of the present embodiment. Note that the memories 106 and 107 may be the same. The functions and areas of each part of the memories 106 and 107 will become clear by the mixed reality presentation operation described in detail below.

  The movement setting unit 116 in the memory 106 determines how the CG object is closer to the line-of-sight position than a predetermined distance or when the CG object is further than the predetermined distance from the line-of-sight position, and how to move the object position. Is set. Specifically, the values of the near limit distance 125, the far limit distance 126, the near magnification 127, and the far magnification 128 of the memory 107 are set.

  The near limit distance 125 is a value that designates how far the CG object approaches the line-of-sight position when the object is moved. Similarly, the far limit distance 126 is a value that specifies how far the CG object moves from the line-of-sight position before the movement process is performed. The near magnification 127 is a coefficient that designates how close to the viewpoint to display when the CG object is closer to the line-of-sight position than the near limit distance 125. Details of the calculation of the CG object position using the near magnification 127 will be described in the description of the processing of the CG object moving unit 115. The far magnification 128 specifies how far the CG object is displayed from the viewpoint rather than the actual distance when the CG object is further away from the line-of-sight position than the far limit distance 126. Details of the calculation of the CG object position using the far magnification 128 will also be described in the description of the processing of the CG object moving unit 125. The above values are set in the system prior to the presentation of the mixed reality image by the movement setting unit 116 providing a user interface (not shown). In this case, the user interface may have any form.

  Next, the overall flow of the image presentation process according to the present embodiment will be described. FIG. 2 is a flowchart for explaining the overall processing flow.

  First, in step S <b> 201, the real video shooting unit 110 captures a video shot using the video camera 105 and writes the captured video as a real image 120 in the memory 107. In step S <b> 202, the position / orientation detection unit 112 detects the position / orientation of the video camera 105 using the position / orientation sensor 108, and records this in the memory 107 as the line-of-sight position / orientation 121. Subsequently, in step S <b> 203, the position / orientation detection unit 112 further detects the position / orientation of the position / orientation sensor 109, and records this in the memory 107 as the CG position / orientation 122.

Next, in step S204, the CG object distance calculation unit 114 obtains the distance between the line-of-sight position of the video camera 105 and the CG position (recorded as the line-of-sight position / posture 121 and CG position / posture 122, respectively). The distance L between two points p1 (x1, y1, z1) and p2 (x2, y2, z2) in space is
L = √ {(x ² −x 1) ² + (y ² −y 1) ² + (z ² −z 1) ² }
It is obtained by. The CG object distance calculation unit 114 records the value calculated by the above formula in the memory 107 as the object distance 129.

  Next, in step S205, the CG object moving unit 115 determines whether or not the positional relationship between the position of the CG object and the line-of-sight position of the video camera satisfies a predetermined condition, and if so, moves the CG object. Then, the CG position / posture 122 is updated. The processing of the CG object moving unit 115 will be described later with reference to FIGS.

  Next, in step S <b> 206, the CG video generation unit 111 writes the CG video as a CG image 124 in the memory 107. Note that the CG looks at the CG model existing at the position and orientation determined by the CG position and orientation 122 from the position and orientation of the video camera determined by the line-of-sight position and orientation 121, as in the conventional mixed reality presentation device. Thus, the CG model data 123 is rendered.

  In step S207, the video display unit 113 combines the real image 120 and the CG image 124 recorded in the memory 107 to generate a mixed reality image (MR image), which is displayed on a display device (in this example, the HMD 106). To display.

  The MR image for one screen can be displayed as described above, but it is possible to present the MR image as a moving image by repeating this entire process one after another.

  Next, details of the CG object moving unit 115 will be described. FIG. 3 is a flowchart for explaining processing by the CG object moving unit 115. In the following, Pe (Xe, Ye, Ze) is a position vector indicating the line-of-sight position, Ps (Xs, Ys, Zs) is a position vector indicating the position indicated by the position and orientation sensor 109, and Po (Xo, Yo, Zo) is It is a position vector indicating the position of the CG object to which the CG object moving unit 115 moves. The distance between each position is described as L (Pn, Pm), thereby indicating the distance between the two points Pn and Pm. For example, L (Pe, Ps) is the distance between the sensor position Ps and the line-of-sight position Pe. Further, the near limit distance 125 of the memory 107 in FIG. 1 is described as Ln, the far limit distance 126 as Lf, the near magnification 127 as Mn, and the far magnification 128 as Mf.

  First, in step S301, the CG object moving unit 115 determines whether or not the object distance 129 is closer to the line-of-sight position than the near limit distance 125. If it is determined that they are close, the object position is calculated by a method described later in FIG. 4A in step S303, and the CG object display position is changed. If not, the process proceeds to step S302.

  In step S302, it is determined whether the object distance 129 is longer than the far limit distance 126. If it is determined that the object is far, in step S304, the object position is calculated by the method described later with reference to FIG. 4B, and the CG object display position is changed. If it is not far away, the process ends.

First, the object position calculation method in step S303 will be described with reference to FIG. FIG. 4A shows a case where the position Ps of the position / orientation sensor 109 is closer to the line-of-sight position Pe than the near limit distance 125 (Ln). Note that Pi (Xi, Yi, Zi) in FIG. 4A is on the straight line connected from Pe to Ps, and the distance from Pe is Ln (a preset near limit distance 126). It is a position vector indicating a certain position. Therefore, Pi is
Pi = Pe + U (Pe, Ps) × Ln
It can be expressed as In the above equation, U (Pe, Ps) represents a unit vector from Pe to Ps.

At this time, the position vector Po indicating the position of the object to be moved is expressed by the following equation:
Po = Ps + (Ps-Pi) * Mn
It is obtained by. Note that (Ps−Pi) in the above equation represents a vector from the point Pi to the point Ps. That is, when the position / orientation sensor 109 exists at a position closer to the line-of-sight position than the near limit distance 125, the position of the CG object is changed to a position Po closer to the line-of-sight position. The amount of movement can be adjusted by the value of the near magnification 127 (Mn).

  By adjusting the position of the object as described above, it is possible to bring the CG object closer to the viewpoint without having the position / orientation sensor 109 extremely close to the eyes (line-of-sight position). Therefore, the CG object can be observed at a short distance without causing the sensor to malfunction due to the influence of electricity or metal of the HMD 104 and causing the display position of the CG to become unstable.

Next, the object position calculation method in step S304 will be described with reference to FIG. FIG. 4B shows a case where the position and orientation sensor 109 is farther from the line-of-sight position detected by the position and orientation sensor 108 than the far limit distance 126. Pi (Xi, Yi, Zi) in FIG. 4 (B) is on a line segment connecting Pe and Ps, and the distance from Pe is Lf (a preset far limit distance 126). Is a position vector indicating. In this case, Pi is Pi = Pe + U (Pe, Ps) × Lf
It can be expressed as U (Pe, Ps) in the above equation represents a unit vector from Pe to Ps.

At this time, the position vector Po indicating the position of the object to be moved is expressed by the following equation:
Po = Ps + (Ps−Pi) × Mf
It is obtained by. In the above equation, (Pi-Ps) represents a vector from the point Pi to the point Ps. Thus, when the position and orientation sensor 109 exists at a position farther from the line-of-sight position than the far limit distance 126, the position of the CG object is changed to a position Po farther from the line-of-sight position. The amount of movement can be adjusted by the value of the far magnification 128 (Mf).

  By adjusting the position of the object as described above, the entire image of a large CG object that cannot be confirmed even if the hand holding the position / orientation sensor 109 is moved far away is simply stretched and the sensor 109 is moved away. It becomes possible to observe.

  As described above, according to the first embodiment, it is possible to bring the CG object closer to the viewpoint without bringing the position / orientation sensor 109 closer to the eyes (HMD). Therefore, it is possible to observe a CG object in a close state without causing the position / orientation sensor 109 to malfunction due to the influence of electricity or metal of the HMD 104 and causing the display position of the CG to become unstable. In addition, it is possible to observe the entire large CG object that cannot be confirmed even if the hand holding the position / orientation detection vessel 109 is moved far away by simply reaching out the hand. Furthermore, if the CG object is at a normal distance from the viewpoint, it can be displayed at the position of the hand holding the position / orientation sensor 109, and also when the CG object moves from the range to a state close to or far from the viewpoint. It is possible to present a mixed reality that moves the position without causing such a sense of incongruity.

<Second Embodiment>
Regarding the far magnification 128, in the first embodiment, some value is set in advance. In the second embodiment, the far magnification can be set according to the size of the object to be observed. For example, a far magnification is calculated such that the entire position of the CG object is moved to a position where it can be displayed on the screen of the video display device (eg, HMD) at the position where the arm is extended to the maximum by holding the position and orientation sensor 109. It can be determined as a magnification of 128. In the second embodiment, this process will be described.

  5 and 6 are diagrams for explaining a method of determining the far magnification 128 according to the second embodiment. In FIG. 5, it is assumed that the angle of view θ of the video display device is known, and the size of the boundary box 501 that wraps the entire CG object to be displayed is also known. If the angle of view of the video display device and the size of the CG object are known, it is possible to calculate how far the CG object is from the viewpoint and whether the entire CG can be displayed on the screen. The distance between the CG object and the viewpoint at which the entire CG object can be displayed on the screen is Pf as shown in FIG.

  Now, as shown in FIG. 6, the observer of the position / orientation sensor 109 in a state where the observer who has the attitude / position sensor 109 for specifying the position of the CG object has fully extended the arm having the position / orientation sensor 109. Let Sf be the distance between the position and the line-of-sight position (the position detected by the position and orientation sensor 108). As in the first embodiment, the far limit distance 126 is Lf. In order to be able to observe the entire CG object with the hand extended, the CG object may be displayed at a distance Pf from the viewpoint in this state (distance is Sf).

In the case of FIG. 6, the distance Pf between the CG object and the line-of-sight position is Mf.
Pf = Sf + (Sf−Lf) × Mf
Therefore, the far magnification Mf is
Mf = (Pf−Sf) / (Sf−Lf)
It becomes.

  If the distance between the viewing angle of the display device, the size of the CG object to be displayed, and the position of the line of sight with the arm extended to the maximum and the sensor position obtained from the position and orientation sensor 109 is known, the far magnification 128 is set as described above. It is possible to set automatically as follows. Thus, it is possible to automatically set a far magnification so that the entire CG can be observed with the arm holding the position sensor extended.

  In this case, the user obtains a distance Pf at which the entire CG object fits on the screen, for example, from the size of the CG object and the angle of view θ of the image display device, and records it in the memory 107 (the CPU 101 automatically calculates it). It may be) For example, by giving a predetermined instruction input in a state where the hand holding the position / orientation sensor 109 is fully extended, the distance between the line-of-sight position and the object position detected in that state is determined as Sf. Mf is calculated by using the above equation based on the above-described Pf and Sf and a preset far limit distance Lf, and is recorded in the memory 107 as a far magnification 128. Since the subsequent processing is the same as that of the first embodiment, description thereof is omitted.

  As described above, according to the above embodiments, the position / orientation detection sensor 109 is a CG object that is at a normal distance from the line-of-sight position (between the position of the near limit distance 125 and the position of the far limit distance 126). When the CG object is displayed at a position determined by the position / orientation detection sensor 109 and the CG object moves from the range to a state close to or far from the line-of-sight position, the CG is displayed according to the near magnification 127 and the far magnification 128, respectively. The position of the object is changed. In the above embodiment, when the position / orientation detection sensor 109 exists closer to the line-of-sight position than the position of the near-limit distance 125, the position of the CG object is drawn closer to the line-of-sight position. When the position / orientation detection sensor 109 exists at a position farther than that, the position of the CG object is changed to be drawn further away.

  As described above, according to the second embodiment, since the appropriate far magnification 128 is automatically set according to the size of the CG object, the operability is improved.

  In the present invention, a software program (in the embodiment, a program corresponding to the flowchart shown in the figure) that realizes the functions of the above-described embodiment is directly or remotely supplied to the system or apparatus, and the computer of the system or apparatus Is also achieved by reading and executing the supplied program code.

  Accordingly, since the functions of the present invention are implemented by computer, the program code installed in the computer also implements the present invention. In other words, the present invention includes a computer program itself for realizing the functional processing of the present invention.

  In that case, as long as it has the function of a program, it may be in the form of object code, a program executed by an interpreter, script data supplied to the OS, or the like.

  As a recording medium for supplying the program, for example, floppy (registered trademark) disk, hard disk, optical disk, magneto-optical disk, MO, CD-ROM, CD-R, CD-RW, magnetic tape, nonvolatile memory card ROM, DVD (DVD-ROM, DVD-R) and the like.

  As another program supply method, a client computer browser is used to connect to an Internet homepage, and the computer program of the present invention itself or a compressed file including an automatic installation function is downloaded from the homepage to a recording medium such as a hard disk. Can also be supplied. It can also be realized by dividing the program code constituting the program of the present invention into a plurality of files and downloading each file from a different homepage. That is, a WWW server that allows a plurality of users to download a program file for realizing the functional processing of the present invention on a computer is also included in the present invention.

  In addition, the program of the present invention is encrypted, stored in a storage medium such as a CD-ROM, distributed to users, and key information for decryption is downloaded from a homepage via the Internet to users who have cleared predetermined conditions. It is also possible to execute the encrypted program by using the key information and install the program on a computer.

  In addition to the functions of the above-described embodiments being realized by the computer executing the read program, the OS running on the computer based on an instruction of the program is a part of the actual processing. Alternatively, the functions of the above-described embodiment can be realized by performing all of them and performing the processing.

  Furthermore, after the program read from the recording medium is written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, the function expansion board or The CPU or the like provided in the function expansion unit performs part or all of the actual processing, and the functions of the above-described embodiments are realized by the processing.

It is a block diagram which shows the structure of the mixed reality presentation system by embodiment. It is a flowchart explaining the mixed reality presentation process by embodiment. It is a flowchart explaining the change process of the CG object position by embodiment. It is a figure explaining the movement process of a CG object. It is a figure explaining the relationship between the CG object which can display the whole CG object, and a gaze position by 2nd Embodiment. It is a figure explaining the calculation method of the far magnification by 2nd Embodiment.

Claims (12)

An image generation device that generates an image in which a computer image is superimposed on a real image captured by an imaging unit,
First detection means for detecting the position and orientation of the photographing means;
Second detection means for detecting a position and orientation at which the computer image is to be generated;
Synthesizing means for synthesizing the computer image with a real image obtained by the imaging means based on the position and orientation detected by the first and second detecting means;
Determination means for determining whether or not the distance between the positions detected by the first and second detection means is within a predetermined range;
An image generating apparatus comprising: a changing unit that changes a position where the computer image is to be generated when the determining unit determines that the relationship is outside a predetermined range.   The changing means moves the position where the computer image is to be generated further away from the position of the photographing means when the distance between the positions detected by the first and second detecting means is longer than a first predetermined distance. The image generation apparatus according to claim 1, wherein the image generation apparatus is changed as follows.   The changing means changes the position where the computer image should be generated closer to the position of the photographing means when the distance between the positions detected by the first and second detecting means is shorter than a second predetermined distance. The image generation apparatus according to claim 1, wherein the image generation apparatus is an image generation apparatus.   The changing means calculates a distance difference between the distance between the positions detected by the first and second detecting means and the first predetermined distance, and calculates a moving distance based on the distance difference and a predetermined first coefficient. The position where the computer image is to be generated is a position obtained by adding the moving distance in a direction away from the position detected by the first detection means to the position detected by the second detection means The image generation apparatus according to claim 2, wherein:   The changing means calculates a distance difference between the distance between the positions detected by the first and second detecting means and the second predetermined distance, and calculates a moving distance based on the distance difference and a predetermined second coefficient. The position where the computer image is to be generated is a position obtained by adding the moving distance so as to approach the position detected by the first detection means with respect to the position detected by the second detection means The image generation apparatus according to claim 3, wherein:   The first coefficient is based on the size of the generated computer image and the angle of view of the image display device, and the distance between the positions detected by the first and second detection means is a distance designated by the user. 5. The image generation apparatus according to claim 4, wherein the image generation apparatus is set so as to be converted into a distance having a size that fits within a screen of the image display apparatus. An image generation method for generating an image in which a computer image is superimposed on a real image shot by a shooting means,
A first detection step of detecting the position and orientation of the photographing means;
A second detection step of detecting a position and orientation at which the computer image is to be generated;
A synthesizing step of synthesizing the computer image with a real image obtained by the imaging means based on the position and orientation detected by the first and second detecting steps;
A determination step of determining whether or not a distance between the positions detected in the first and second detection steps is within a predetermined range;
An image generation method comprising: a change step of changing a position where the computer image is to be generated when it is determined by the determination step that the relationship is outside a predetermined range.   In the changing step, when the distance between the positions detected in the first and second detection steps is longer than a first predetermined distance, the position where the computer image is to be generated is further away from the position of the photographing unit. The image generation method according to claim 7, wherein the image generation method is changed as follows.   In the changing step, when the distance between the positions detected in the first and second detecting steps is shorter than a second predetermined distance, the position where the computer image is to be generated is changed so as to be closer to the position of the photographing unit. The image generation method according to claim 7 or 8, characterized in that:   The changing step calculates a distance difference between the distance between the positions detected by the first and second detection steps and the first predetermined distance, and calculates a moving distance based on the distance difference and a predetermined first coefficient. A position where the computer image is to be generated by calculating and adding the movement distance in a direction away from the position detected in the first detection step to the position detected in the second detection step The image generation method according to claim 8, wherein:   The changing step calculates a distance difference between the distance between the positions detected by the first and second detection steps and the second predetermined distance, and calculates a moving distance based on the distance difference and a predetermined second coefficient. The position where the computer image is to be generated is a position obtained by adding the moving distance so as to approach the position detected in the first detection step with respect to the position detected in the second detection step. The image generation method according to claim 9, wherein:   The first coefficient is based on the size of the generated computer image and the angle of view of the image display device, and the distance between the positions detected in the first and second detection steps is a distance designated by the user. The image generation method according to claim 10, wherein the entire computer image is set to be converted into a distance having a size that can be accommodated in a screen of the image display device.

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