Patent Publication Number: US-11380287-B2

Title: Display system, electronic device, and display method

Description:
This is a Continuation of U.S. application Ser. No. 16/228,847 filed Dec. 21, 2018, which in turn claims the benefit of: (a) JP 2018-172773 filed Sep. 14, 2018; and (b) JP 2017-246853 filed Dec. 22, 2017. The disclosure of the prior applications is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     1. Technical Field 
     The invention relates to a display system, an electronic device, and a display method. 
     2. Related Art 
     In the related art, a display device configured to receive and display a display image of an external device has been known (for example, see JP-A-2015-227919). JP-A-2015-227919 describes an example in which, to integrate display screens of a plurality of devices, a head mounted type display device (Head Mounted Display: HMD) receives a display image transmitted by an external device and causes a display unit to display the display image. 
     In a configuration disclosed in JP-A-2015-227919, assuming that all are displayed by the HMD, the display image of the external device can be integrated in display of the HMD. In contrast, in the related art, there is no example proposed for a technique for controlling display by a display device in correspondence to an external device different from the display device. 
     SUMMARY 
     An advantage of some aspects of the invention is to control display by a display device in correspondence to an external device. 
     To address the above-described issue, a display system according to an aspect of the invention includes an electronic device including a first display unit, and a display device having a head mounted type and connected to the electronic device, and in the display system, the electronic device includes an output unit configured to output an image, the display device includes an acquisition unit configured to acquire the image output by the electronic device, a second display unit configured to superimpose an image on an outside scene visually recognized in a state where the display device is worn, and to display the image, and a display controller configured to cause the second display unit to display the image acquired by the acquisition unit, and the display controller is configured to cause the second display unit to display the image in correspondence to a position of the electronic device visually recognized as an outside scene. 
     According to the aspect of the invention, when the image output by the electronic device is displayed by the display device having a head mounted type, the image is displayed to correspond to the position of the electronic device as the outside scene. For example, the image can be displayed by the display device in correspondence to a position of the first display unit visible as the outside scene. Accordingly, display in correspondence to the position of the electronic device visually recognized as the outside scene can be performed by the display device configured to superimpose the image on the outside scene and to display the image. 
     Additionally, according to an aspect of the invention, the electronic device includes an electronic device control unit configured to generate an image corresponding to a virtual display area wider than the first display unit, cause the first display unit to display a portion of the image generated, and cause the output unit to output at least a portion of the image generated, and the display controller provided in the display device is configured to cause the second display unit to display at least a portion of an image output by the electronic device, in correspondence to a position of the electronic device. 
     According to this configuration, the second display unit of the display device can be caused to perform display corresponding to the virtual display area wider than the first display unit of the electronic device. Thus, a display area larger than the first display unit can be displayed in correspondence to the position of the electronic device, and the first display unit can be expanded virtually by the display device. 
     Additionally, according to an aspect of the invention, the electronic device control unit is configured to cause the output unit to output the image obtained by removing a portion displayed by the first display unit from the image generated in correspondence to the virtual display area, and the display controller provided in the display device is configured to cause the second display unit to display an image output by the electronic device. 
     According to this configuration, when the display device performs display corresponding to the virtual display area wider than the first display unit of the electronic device, a portion of the image is displayed by the first display unit, and a portion obtained by removing the portion displayed by the first display unit is displayed by the second display unit. Thus, display including display of the electronic device combined with display of the display device can be achieved. For example, a display mode in which an image is displayed around the electronic device by the second display unit and the first display unit is virtually expanded can be achieved by the display device. 
     Additionally, according to an aspect of the invention, the display controller provided in the display device is configured to cause the image output by the electronic device to be displayed around the first display unit visually recognized as an outside scene. 
     According to this configuration, the image is displayed by the second display unit of the display device around the first display unit of the electronic device, and accordingly, the display mode in which the first display unit is virtually expanded can be achieved. 
     Additionally, according to an aspect of the invention, the electronic device control unit is configured to, based on a relative position of the first display unit with respect to the second display unit, cause the first display unit to display a portion of the image generated in correspondence to the virtual display area, and cause the output unit to output the image obtained by removing a portion displayed by the first display unit. 
     According to this configuration, the electronic device outputs the image displayed by the display device to correspond to the relative position of the first display unit with respect to the second display unit. Thus, an operation in which display corresponding to the position of the first display unit of the electronic device is performed by the display device can be achieved easily. 
     Additionally, according to an aspect of the invention, the electronic device control unit is configured to, based on a relative position of the first display unit with respect to the second display unit, cause the output unit to output an image obtained by masking a portion displayed by the first display unit, of the image generated in correspondence to the virtual display area. 
     According to this configuration, since the portion displayed by the first display unit of the electronic device is not displayed by the second display unit, the image displayed by the electronic device and the image displayed by the display device can be coordinated. 
     Additionally, according to an aspect of the invention, the electronic device control unit is configured to cause the output unit to output the image generated in correspondence to the virtual display area, and the display controller provided in the display device is configured to cause the second display unit to display an image obtained by cutting out a portion of the image output by the electronic device. 
     According to this configuration, in processing by the display device, a portion of the image displayed by the electronic device can be expanded and displayed by the second display unit. 
     Additionally, according to an aspect of the invention, the display controller is configured to, based on a relative position of the first display unit with respect to the second display unit, extract a portion of the image acquired by the acquisition unit, and cause the second display unit to display the portion. 
     According to this configuration, since the display device determines the relative position of the first display unit with respect to the display unit, and generates an image for display to correspond to this relative position, display corresponding to the position of the first display unit can be achieved without increasing a load on the electronic device. 
     Additionally, according to an aspect of the invention, the display controller is configured to, based on a relative position of the first display unit with respect to the second display unit, cause the second display unit to display an image obtained by masking a portion superimposed on the first display unit, of the image acquired by the acquisition unit. 
     According to this configuration, in processing by the display device, since the portion displayed by the first display unit is masked in the image displayed by the second display unit, the image displayed by the electronic device and the image displayed by the display device can be coordinated without increasing a load on the electronic device. 
     Additionally, according to an aspect of the invention, the electronic device control unit is configured to determine a position of the virtual display area, based on a position of the electronic device in a real space, and adjust a display mode of the second display unit, based on a relative position between the virtual display area and the second display unit. 
     According to this configuration, an image can be displayed by the display device in correspondence to the position of the electronic device in the real space. An effect such as using this image to supplement or expand the image displayed by the first display unit of the electronic device can be obtained. 
     Additionally, according to an aspect of the invention, the electronic device control unit is configured to initialize a display mode of the image by using a position of the first display unit as a reference, when the electronic device control unit detects the first display unit being present in the range where the first display unit is visually recognized through the second display unit. 
     According to this configuration, the display mode can be adjusted in correspondence to whether the first display unit of the electronic device can be recognized visually as the outside scene in the display device. 
     Additionally, according to an aspect of the invention, the second display unit includes a display unit for a left eye configured to emit imaging light toward a left eye of a user wearing the display device, and a display unit for a right eye configured to emit imaging light toward the right eye of the user, and in correspondence to a position of the first display unit visually recognized as an outside scene by the second display unit, a display position by the display unit for a left eye, and a display position by the display unit for a right eye are controlled, and a convergence angle of an image displayed by the second display unit is adjusted. 
     According to this configuration, the convergence angle of the image displayed by the display device is adjusted, and accordingly, a distance in which the display image of the display device is visually recognized can be made correspond to the position of the first display unit of the electronic device. Accordingly, the display by the display device and the display by the electronic device can be coordinated more appropriately. 
     Additionally, according to an aspect of the invention, the second display unit includes an optical system capable of adjusting a visual recognition distance that the user perceives to an image displayed by the second display unit, and the optical system is controlled in correspondence to a convergence angle of an image displayed by the second display unit. 
     According to this configuration, since a distance in which the display image of the display device is visually recognized is made correspond to the position of the first display unit of the electronic device, the display by the display device and the display by the electronic device can be coordinated more appropriately. 
     Additionally, to address the above-described issue, an electronic device according to an aspect of the invention is an electronic device connected with a display device having a head mounted type and configured to superimpose an image on an outside scene and to display the image, the electronic device including a first display unit, an output unit configured to output an image to the display device, and a control unit configured to, based on a relative position of the first display unit with respect to a second display unit provided in the display device, cause the output unit to output an image used when the second display unit displays an image corresponding to a position of the first display unit visually recognized as an outside scene by the display device. 
     According to this configuration, the electronic device connected with the display device outputs the image to the display device, and accordingly, the display device can perform display to correspond to the position of the first display unit of the electronic device as the outside scene. 
     Additionally, to address the above-described issue, a display method according to an aspect of the invention is a display method using an electronic device including a first display unit and a display device having a head mounted type and including a second display unit configured to superimpose an image on an outside scene and to display the image, the display method including outputting an image by the display device, and performing by the display device acquiring the image output by the electronic device, causing the second display unit to display the acquired image, and causing the second display unit to display the image in correspondence to a position of the electronic device visually recognized as an outside scene in the second display unit. 
     According to an aspect of the invention, when the image output by the electronic device is displayed by the display device, the image is displayed to correspond to the position of the electronic device as the outside scene. For example, since an image can be displayed by the display device in correspondence to the position of the electronic device visible as the outside scene, display corresponding to the display by the electronic device can be performed by the display device. 
     The aspects of the invention can also be achieved in various modes other than the display system, the electronic device, and the display method described above. For example, the aspects of the invention can be achieved in modes such as a program for executing the above-described display method by a computer, a recording medium storing the program, a server device configured to deliver the program, a transmission medium for transmitting the program, and a data signal in which the program is embodied on a carrier wave. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements. 
         FIG. 1  is an appearance view of an HMD and a PC constituting a display system. 
         FIG. 2  is a view illustrating a configuration of an optical system of the HMD. 
         FIG. 3  is a perspective view of a main portion of an image display unit as viewed from a head side of a user. 
         FIG. 4  is an explanatory view illustrating correspondence between a display unit of the HMD and the imaging range. 
         FIG. 5  is a block diagram of respective components constituting the display system. 
         FIG. 6  is an explanatory view illustrating processing for determining a relative position of the PC with respect to the image display unit. 
         FIG. 7  is a flowchart illustrating an operation of the display system. 
         FIG. 8  is a view illustrating an example of a display mode of the display system. 
         FIG. 9  is a view illustrating an example of a display mode of the display system. 
         FIG. 10  is a view illustrating an example of a display mode of the display system. 
         FIG. 11  is a flowchart illustrating an operation of the display system. 
         FIG. 12  is a view illustrating an example of a display mode of a display system in a second exemplary embodiment. 
         FIG. 13  is a flowchart illustrating an operation of a display system in a third exemplary embodiment. 
         FIG. 14  is a flowchart illustrating an operation of the display system in the third exemplary embodiment. 
         FIG. 15  is a block diagram of respective components constituting a display system in a fourth exemplary embodiment. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     1. First Exemplary Embodiment 
     1-1. Configuration of Display System 
       FIG. 1  is a view illustrating a configuration of a display system  1  according to a first exemplary embodiment to which the invention is applied. 
     The display system  1  includes a Head Mounted Display (HMD: head mounted type display device)  100 , and a Personal Computer (PC)  300  as an external device of the HMD  100 . 
     The HMD  100  is a display device including an image display unit  20  (second display unit) configured to cause a user to visually recognize a virtual image in a state where the display device is worn on a head of the user, and a connecting device  10  configured to control the image display unit  20 . The connecting device  10  includes a plurality of connectors  11  on a box-shaped case (may be referred to as a housing, or a body). The image display unit  20  and the connecting device  10  are connected via a connecting cable  40 . 
     In an example in  FIG. 1 , the connecting device  10  includes three connectors  11 A,  11 B, and  11 C. In the following description, when the connectors  11 A,  11 B, and  11 C are not distinguished from one another, the connectors  11 A,  11 B, and  11 C are collectively referred to as a connector  11 . The connector  11  is a wired interface to be connected with a communication cable, and via the communication cable, the connecting device  10  is connected with an external device. Each of the connectors  11 A,  11 B, and  11 C is, for example, a connector compliant with a known communication interface standard, and may be a connector having an identical shape, or may be a different type of connector. In the exemplary embodiment, as an example, the connector  11 A is a connector compliant with an HDMI (trade name) (High Definition Multimedia Interface) standard. Additionally, the connector  11 B is a Universal Serial Bus (USB) Type-C connector. Additionally, the connector  11 C is a MicroUSB connector. 
     In the example in  FIG. 1 , the connecting device  10  and the PC  300  are connected via a cable  2 . The cable  2  includes an HDMI cable  2 A connecting the PC  300  and the connector  11 A, and a USB cable  2 B connecting the PC  300  and the connector  11 B. In this example, the PC  300  is connected with the connecting device  10  via an HDMI interface for image transmission, and a USB interface for data communication. 
     The PC  300  is a computer including a display unit  330  configured to display an image, and corresponds to the electronic device of the invention. The PC  300  is preferably a portable computer, and examples of the PC  300  include a tablet type computer, a note type computer, and a smartphone. The PC  300  in  FIG. 1  includes the display unit  330  as the first display unit on a surface of a plate shaped body. The display unit  330  includes a display panel  331  ( FIG. 5 ) such as a liquid crystal display panel, and an organic Electro Luminescent (EL) display panel, and a touch sensor  332  ( FIG. 5 ) configured to detect a touch operation by a user is provided on a surface of the display panel  331 . 
     The PC  300  is configured to function as external equipment with respect to the HMD  100 . The external equipment may be any electronic device as long as the electronic device includes a display screen and has a function to display an image on the display screen, and the PC  300  is merely described as an example in the exemplary embodiment. 
     The image display unit  20  is a mounted body to be worn on a head of a user and is a so-called head mounted type display (HMD). That is, the HMD  100  includes a configuration where the connecting device  10  to be connected to an external device such as the PC  300  is connected with the image display unit  20  as an HMD body. The image display unit  20  has an eyeglasses-like shape in the exemplary embodiment. The image display unit  20  includes, in a body including a right holding part  21 , a left holding part  23 , and a front frame  27 , a right display unit  22  (display unit for a right eye), a left display unit  24  (display unit for a left eye), a right light-guiding plate  26 , and a left light-guiding plate  28 . 
     The right holding part  21  and the left holding part  23  extend rearward from both ends of the front frame  27 , respectively, and hold the image display unit  20  to a head of a user in a manner similar to temples of a pair of eyeglasses. Here, one of both the ends of the front frame  27  located on the right side of the user in a state where the user wears the image display unit  20  is referred to as an end ER, and the other end located on the left side of the user in a state where the user wears the image display unit  20  is referred to as an end EL. The right holding part  21  extends from the end ER of the front frame  27  to a position corresponding to the right side of the head of the user in a state where the user wears the image display unit  20 . The left holding part  23  extends from the end EL to a position corresponding to the left side of the head of the user in a state where the user wears the image display unit  20 . 
     The right light-guiding plate  26  and the left light-guiding plate  28  are provided on the front frame  27 . The right light-guiding plate  26  is located in front of the right eye of the user in a state where the user wears the image display unit  20 , and causes the user to visually recognize an image with the right eye. The left light-guiding plate  28  is located in front of the left eye of the user in a state where the user wears the image display unit  20 , and causes the user to visually recognize an image with the left eye. 
     The front frame  27  has a shape formed by coupling an end of the right light-guiding plate  26  and an end of the left light-guiding plate  28  to each other, and this coupling position corresponds to a position between eyebrows of the user in a state where the user wears the image display unit  20 . The front frame  27  may include a nose pad provided in the coupling position of the right light-guiding plate  26  and the left light-guiding plate  28 , and configured to abut on a nose of the user in a state where the user wears the image display unit  20 . In this case, the image display unit  20  can be held to the head of the user by the nose pad, the right holding part  21 , and the left holding part  23 . Additionally, a belt (not illustrated) configured to be in contact with to a back of the head of the user in a state where the user wears the image display unit  20  may be coupled to the right holding part  21  and the left holding part  23 , and in this case, the image display unit  20  can be held to the head of the user by the belt. 
     Each of the right display unit  22  and the left display unit  24  is a module obtained by unitizing an optical unit and a peripheral circuit. 
     The right display unit  22  is a unit related to image display by the right light-guiding plate  26 , and is provided on the right holding part  21 , and located near the right side of the head of the user in a state where the user wears the image display unit  20 . The left display unit  24  is a unit related to image display by the left light-guiding plate  28 , and is provided on the left holding part  23 , and located near the left side of the head of the user in a state where the user wears the image display unit  20 . Note that the right display unit  22  and the left display unit  24  are also collectively and simply referred to as a “display driving unit”. 
     The right light-guiding plate  26  and the left light-guiding plate  28  are optical parts formed with a light transmissive resin or the like, and are configured to guide imaging light output by the right display unit  22  and the left display unit  24  to the eyes of the user. The right light-guiding plate  26  and the left light-guiding plate  28  are, for example, prisms. 
     A dimmer plate (not illustrated) may be provided on each of surfaces of the right light-guiding plate  26  and the left light-guiding plate  28 . The dimmer plate is an optical element having a thin plate shape and a transmittance different according to a the wavelength range of light, and functions as a so-called wavelength filter. The dimmer plate is, for example, disposed to cover a front side of the front frame  27  being an opposite side to a side of the eyes of the user. An optical property of this dimmer plate can be selected appropriately to adjust a transmittance of light in any wavelength range such as visible light, infrared light, and ultraviolet light, and to adjust a light amount of outside light entering the right light-guiding plate  26  and the left light-guiding plate  28  from an outside and passing through the right light-guiding plate  26  and the left light-guiding plate  28 . 
     The image display unit  20  is configured to guide imaging light generated by the right display unit  22  and the left display unit  24  to the right light-guiding plate  26  and the left light-guiding plate  28 , respectively, and to use this imaging light to cause the user to visually recognize a virtual image to display an image. When outside light passes through the right light-guiding plate  26  and the left light-guiding plate  28  and enters the eyes of the user from in front of the user, imaging light constituting the virtual image and the outside light enter the eyes of the user, and visibility of the virtual image is affected by intensity of the outside light. Thus, for example, the dimmer plate can be mounted on the front frame  27 , and the optical property of the dimmer plate can be selected or adjusted appropriately to adjust easiness of visual recognition of the virtual image. In a typical example, the dimmer plate having a light transmittance to an extent that the user wearing the HMD  100  can visually recognize at least an external scene can be used. Additionally, when the dimmer plate is used, an effect such as protecting the right light-guiding plate  26  and the left light-guiding plate  28  to suppress a damage, adhesion of dust or the like on the right light-guiding plate  26  and the left light-guiding plate  28  can be expected. The dimmer plate may be provided detachably on the front frame  27  or each of the right light-guiding plate  26  and the left light-guiding plate  28 , or a plurality of types of dimmer plates may be replaceably mounted, or the dimmer plate may be omitted. 
     Each of the right display unit  22  and the left display unit  24  of the image display unit  20  is connected with the connecting device  10 . In the HMD  100 , the connecting cable  40  is connected with the left holding part  23 , and wiring connected with this connecting cable  40  is laid inside the image display unit  20  to connect each of the right display unit  22  and the left display unit  24  with the connecting device  10 . 
     A camera  61  is disposed on the front frame  27  of the image display unit  20 . The camera  61  desirably captures an image in an outside scene direction in which the user visually recognize an outside scene in a state where the user wears the image display unit  20 , and the camera  61  is provided at a position on a front face of the front frame  27  where the camera  61  does not block the outside light passing through the right light-guiding plate  26  and the left light-guiding plate  28 . In the example in  FIG. 1 , the camera  61  is disposed on the end ER side of the front frame  27 . The camera  61  may be disposed on the end EL side or may be disposed at the coupling of the right light-guiding plate  26  and the left light-guiding plate  28 . 
     The camera  61  is a digital camera including an imaging element such as a CCD and a CMOS, an imaging lens and the like, and the camera  61  according to the exemplary embodiment is a monocular camera, but may include a stereo camera. The camera  61  is configured to capture an image of at least a portion of an outside scene in a front side direction of the HMD  100 , in other words, in a direction of a field of view of the user in a state where the user wears the HMD  100 . The outside scene can be rephrased as a real space. 
     In other words, the camera  61  is configured to capture an image in the range or a direction superimposed on the field of view of the user, and is configured to capture an image in a direction in which the user fixates. A width of an angle of view of the camera  61  can be set appropriately, but in the exemplary embodiment, as described later, the width of an angle of view of the camera  61  includes an outside world the user visually recognizes through the right light-guiding plate  26  and the left light-guiding plate  28 . More preferably, the imaging range of the camera  61  is set to enable capturing all the field of view of the user that can be recognized visually through the right light-guiding plate  26  and the left light-guiding plate  28 . 
     The HMD  100  includes a distance sensor  64 . The distance sensor  64  is disposed on a border portion of the right light-guiding plate  26  and the left light-guiding plate  28 . In a state where the user wears the image display unit  20 , a position of the distance sensor  64  is nearly in the middle of both the eyes of the user in a horizontal direction, and is above both the eyes of the user in a vertical direction. 
     The distance sensor  64  is configured to detect a distance to an object to be measured and located in a preset measurement direction. The measurement direction of the distance sensor  64  in the exemplary embodiment is the front side direction of the HMD  100  and overlaps with an imaging direction of the camera  61 . 
       FIG. 2  is a plan view of a main portion illustrating a configuration of an optical system of the HMD  100 . In  FIG. 2 , a left eye LE and a right eye RE of a user are illustrated for explanation. 
     As illustrated in  FIG. 2 , the right display unit  22  and the left display unit  24  are disposed symmetrically on the right- and left-hand sides. As a configuration where the right eye RE of the user is caused to visually recognize an image, the right display unit  22  includes an Organic Light-Emitting Diode (OLED) unit  221  configured to emit imaging light. Additionally, the right display unit  22  includes a right optical system  251  including a lens group configured to guide imaging light L emitted by the OLED unit  221 , and the like. The imaging light L is guided by the right optical system  251  to the right light-guiding plate  26 . 
     The OLED unit  221  includes an OLED panel  223  and an OLED drive circuit  225  configured to drive the OLED panel  223 . The OLED panel  223  is a self-light emission type display panel including light-emitting elements disposed in a matrix and configured to emit light by organic electro-luminescence to emit red (R) color light, green (G) color light, and blue (B) color light respectively. The OLED panel  223  has, as one pixel, a unit including one R element, one G element, and one B element, and includes a plurality of the pixels, and the OLED panel  223  forms an image with the plurality of pixels disposed in a matrix. 
     The OLED drive circuit  225  is configured to, based on image data input from the connecting device  10 , select and power the light-emitting elements provided in the OLED panel  223  to cause the light-emitting elements of the OLED panel  223  to emit light. The OLED drive circuit  225  is fixed by bonding or the like to a rear face of the OLED panel  223 , namely, a back side of a light-emitting surface of the OLED panel  223 . The OLED drive circuit  225  may include, for example, a semiconductor device configured to drive the OLED panel  223 , and may be mounted on a substrate (not illustrated) fixed to the rear face of the OLED panel  223 . A temperature sensor  217  is mounted on this substrate. 
     Note that the OLED panel  223  may include a configuration in which light-emitting elements configured to emit white color light are disposed in a matrix, and color filters corresponding to the R color, the G color, and the B color respectively are disposed to be superimposed on the light-emitting elements. Additionally, the OLED panel  223  of a WRGB configuration including light-emitting elements configured to emit white (W) color light, in addition to the light-emitting elements configured to emit the R color light, the G color light, and the B color light respectively may be used. 
     The right optical system  251  includes a collimate lens configured to collimate the imaging light L emitted from the OLED panel  223 . The imaging light L collimated by the collimate lens enters the right light-guiding plate  26 . In an optical path configured to guide light inside the right light-guiding plate  26 , a plurality of reflective faces configured to reflect the imaging light L is formed. The imaging light L is reflected multiple times inside the right light-guiding plate  26  and then, is guided to the right eye RE side. In the right light-guiding plate  26 , a half mirror  261  (reflective face) located in front of the right eye RE is formed. The imaging light L is reflected by the half mirror  261  to be emitted from the right light-guiding plate  26  toward the right eye RE, and this imaging light L forms an image on a retina of the right eye RE, and causes the user to visually recognize the image. 
     Additionally, as a configuration in which the left eye LE of the user is caused to visually recognize an image, the left display unit  24  includes an OLED unit  241  configured to emit imaging light, and a left optical system  252  including a lens group configured to guide the imaging light L emitted by the OLED unit  241 , and the like. The imaging light L is guided by the left optical system  252  to the left light-guiding plate  28 . 
     The OLED unit  241  includes an OLED panel  243 , and an OLED drive circuit  245  configured to drive the OLED panel  243 . The OLED panel  243  is a self-light emission type display panel configured in a manner similar to the OLED panel  223 . The OLED drive circuit  245  is configured to, based on image data input from the connecting device  10 , select and power light-emitting elements provided in the OLED panel  243  to cause the light-emitting elements of the OLED panel  243  to emit light. The OLED drive circuit  245  is fixed by bonding or the like to a rear face of the OLED panel  243 , namely, a back side of a light-emitting surface of the OLED panel  243 . The OLED drive circuit  245  may include, for example, a semiconductor device configured to drive the OLED panel  243 , and may be mounted on a substrate (not illustrated) fixed to the rear face of the OLED panel  243 . A temperature sensor  239  is mounted on this substrate. 
     The left optical system  252  includes a collimate lens configured to collimate the imaging light L emitted from the OLED panel  243 . The imaging light L collimated by the collimate lens enters the left light-guiding plate  28 . The left light-guiding plate  28  is an optical element in which a plurality of reflective faces configured to reflect the imaging light L is formed, and the left light-guiding plate  28  is, for example, a prism. The imaging light L is reflected multiple times inside the left light-guiding plate  28  and then, is guided to the left eye LE side. In the left light-guiding plate  28 , a half mirror  281  (reflective face) located in front of the left eye LE is formed. The imaging light L is reflected by the half mirror  281  to be emitted from the left light-guiding plate  28  to the left eye LE, and this imaging light L forms an image on a retina of the left eye LE, and causes the user to visually recognize the image. 
     The HMD  100  functions as a see-through type display device. Namely, the imaging light L reflected by the half mirror  261  and outside light OL having passed through the right light-guiding plate  26  enter the right eye RE of the user. Additionally, the imaging light L reflected by the half mirror  281  and the outside light OL having passed through the half mirror  281  enter the left eye LE. Accordingly, the HMD  100  superimposes the imaging light L of an image processed internally and the outside light OL on each other, and causes the imaging light L and the outside light OL superimposed on each other to enter the eyes of the user, and the user views an outside scene through the right light-guiding plate  26  and the left light-guiding plate  28 , and visually recognizes the image formed by the imaging light L and superimposed on this outside scene. Each of the half mirrors  261  and  281  is an image extracting unit configured to reflect imaging light output by each of the right display unit  22  and the left display unit  24  and extract an image, and can be referred to as a display unit. 
     Note that the left optical system  252  and the left light-guiding plate  28  are collectively referred to as a “left light-guiding unit”, and the right optical system  251  and the right light-guiding plate  26  are collectively referred to as a “right light-guiding unit”. Configurations of the right light-guiding unit and the left light-guiding unit are not limited to the example described above, and can use any manner as long as imaging light is used to form a virtual image in front of the eyes of the user. For example, a diffraction grating may be used, or a semi-transmissive reflection film may be used. 
       FIG. 3  is a perspective view of a main portion of the image display unit  20  as viewed from the head side of the user, this is, a side being in contact with the head of the user of the image display unit  20 , in other words, a side visible with the right eye RE and the left eye LE of the user. In other words, back sides of the right light-guiding plate  26  and the left light-guiding plate  28  are visible. 
     In  FIG. 3 , the half mirror  261  configured to irradiate the right eye RE of the user with imaging light and the half mirror  281  configured to irradiate the left eye LE with imaging light are visible as approximately square-shaped regions. Additionally, all the right light-guiding plate  26  and the left light-guiding plate  28  including the half mirrors  261  and  281  transmit the outside light as described above. Thus, the user visually recognizes an outside scene through all the right light-guiding plate  26  and the left light-guiding plate  28 , and visually recognizes rectangular display images at positions of the half mirrors  261  and  281 . 
       FIG. 4  is an explanatory view illustrating correspondence between the image display unit  20  of the HMD  100  and the imaging range. 
     As described above, the camera  61  is disposed at the end on the right side in the image display unit  20 , and captures an image in a direction in which both the eyes of the user are directed, namely, in front of the user. 
       FIG. 4  is a view schematically illustrating a position of the camera  61  together with the right eye RE and the left eye LE of the user in a plan view. An angle of view (imaging range) C of the camera  61  is illustrated. Note that the angle of view C in a horizontal direction is illustrated in  FIG. 4 , but an actual angle of view of the camera  61  also extends in a top-bottom direction as in a manner similar to a general digital camera. 
     An optical axis of the camera  61  extends in a direction including a line of sight direction RD of the right eye RE and a line of sight direction LD of the left eye LE. The outside scene that can be recognized visually by the user in a state where the user wears the HMD  100  is not necessarily an infinitely distant scene. For example, as illustrated in  FIG. 4 , when the user fixates an object OB with both the eyes, the lines of sight RD and LD of the user are directed to the object OB. In this case, a distance from the user to the object OB often ranges from approximately 30 cm to 10 m, and more often ranges from approximately 1 m to 4 m. Thus, standards of an upper limit and a lower limit of the distance from the user to the object OB in normal use may be defined for the HMD  100 . These standards may be determined by research or an experiment, or may be set by the user. The optical axis and the angle of view of the camera  61  may preferably be set such that when the distance to the object OB in normal use corresponds to the set standard of the upper limit, and when the distance to the object OB in normal use corresponds to the set standard of the lower limit, this object OB is present within the angle of view. 
     Additionally, in general, a visual field angle of a human is approximately 200 degrees in the horizontal direction and approximately 125 degrees in the vertical direction, and an effective field of view excellent in information acceptance performance of the visual field angle of a human is approximately 30 degrees in the horizontal direction and approximately 20 degrees in the vertical direction. Further, a stable field of fixation in which a point of fixation at which a human fixates is promptly and stably visible ranges from approximately 60 degrees to 90 degrees in the horizontal direction, and ranges from approximately 45 degrees to 70 degrees in the vertical direction. In this case, when the point of fixation is located at the object OB in  FIG. 4 , the effective field of view is approximately 30 degrees in the horizontal direction and approximately 20 degrees in the vertical direction with the lines of sight RD and LD as the center. Additionally, the stable field of fixation ranges from approximately 60 degrees to 90 degrees in the horizontal direction and from approximately 45 degrees to 70 degrees in the vertical direction, and a visual field angle is approximately 200 degrees in the horizontal direction, and approximately 125 degrees in the vertical direction. Further, an actual visual field in which the user visually recognizes through the image display unit  20 , and through the right light-guiding plate  26 , and the left light-guiding plate  28  can be referred to as an actual Field Of View (FOV). In the configuration of the exemplary embodiment illustrated in each of  FIG. 1  and  FIG. 2 , the actual field of view corresponds to an actual visual field in which the user visually recognizes through the right light-guiding plate  26  and the left light-guiding plate  28 . The actual field of view is narrower than the visual field angle and the stable field of fixation, but wider than the effective field of view. 
     The angle of view C of the camera  61  can preferably capture an image in the range wider than the visual field of the user, and specifically, the angle of view C is preferably wider than at least the effective field of view of the user. Additionally, the angle of view C is more preferably wider than the actual field of view of the user. Further preferably, the angle of view C is wider than the stable field of fixation of the user, and most preferably, the angle of view C is wider than the visual field angles of both the eyes of the user. 
     The camera  61  may include a so-called wide angle lens as an imaging lens and may be configured to be capable of capturing an image at a wide angle of view. The wide angle lens may include lenses referred to as an ultrawide lens and a quasi wide lens, or may be a single focus lens or a zoom lens, or the camera  61  may be configured to include a lens group including a plurality of lenses. 
     Additionally, as described above, the camera  61  in the exemplary embodiment is disposed on the end ER side in the front frame  27  of the image display unit  20 , but may be disposed on the end EL side, or may be disposed at the coupling of the right light-guiding plate  26  and the left light-guiding plate  28 . In this case, a position in a right-left direction of the camera  61  is different from the position in  FIG. 4 , and the angle of view C is appropriately set according to the position of the camera  61 . Specifically, when the camera  61  is on the end EL side, the angle of view C is directed diagonally forward right in  FIG. 4 . Additionally, for example, when the camera  61  is disposed at the coupling of the right light-guiding plate  26  and the left light-guiding plate  28 , the angle of view C is directed toward a front side of the image display unit  20 . 
     When the user views an object with the right eye RE and the left eye LE, the user perceives and recognizes a distance to the object according to an angle formed by the line of sight direction of the right eye RE and the line of sight direction of the left eye LE. This angle is referred to as a convergence angle, and a convergence angle made when the object OB illustrated in  FIG. 4  is viewed is PA, for example. 
     A convergence angle made when the user views images displayed on the half mirrors  261  and  281  is an angle formed by a line of sight direction made when the image on the half mirror  261  is viewed with the right eye RE and a line of sight direction made when the image on the half mirror  281  is viewed with the left eye LE. A degree of the convergence angle in this case is determined by display positions of images on the half mirrors  261  and  281 . Therefore, a display position at which the right display unit  22  displays an image and a display position at which the left display unit  24  displays an image are adjusted, and accordingly, the convergence angle can be controlled to control a sense of distance visually recognized by the user. For example, with respect to the images displayed by the right display unit  22  and the left display unit  24 , the sense of distance visually recognized by the user (visual recognition distance) can be adjusted. 
     Additionally, the distance sensor  64  is disposed to be directed forward in the middle of the right light-guiding plate  26  and the left light-guiding plate  28 . 
     1-2. Control System of Display System 
       FIG. 5  is a block diagram illustrating configurations of the HMD  100  and the PC  300  constituting the display system  1 . 
     As described above, the HMD  100  includes the connecting device  10  and the image display unit  20  connected with each other via the connecting cable  40 . 
     As described above, the image display unit  20  includes the right display unit  22  and the left display unit  24 . The right display unit  22  includes a display unit substrate  210 . On the display unit substrate  210 , a connecting unit  211  configured to be connected with the connecting cable  40 , a reception unit (Rx)  213  configured to receive data input from the connecting device  10  via the connecting unit  211 , and an EEPROM  215  (storage unit) are mounted. 
     The connecting unit  211  connects the reception unit  213 , the EEPROM  215 , the temperature sensor  217 , the camera  61 , the distance sensor  64 , an illuminance sensor  65 , and an LED indicator  67  with the connecting device  10 . 
     The Electrically Erasable Programmable Read-Only Memory (EEPROM)  215  stores various kinds of data in a non-volatile manner. The EEPROM  215  stores, for example, data about light-emitting properties and display properties of the OLED units  221  and  241  provided in the image display unit  20 , and data about a property of a sensor provided in the right display unit  22  or the left display unit  24 . Specifically, the EEPROM  215  stores parameters regarding gamma correction of the OLED units  221  and  241 , data used to compensate for detection values of the temperature sensors  217  and  239 , and the like. These kinds of data are generated by inspection at the time of shipping of the HMD  100  from a factory, and are written into the EEPROM  215 . The data stored in the EEPROM  215  can be read by a control unit  120 . 
     The camera  61  captures an image in accordance with a signal input via the connecting unit  211  and outputs captured image data to the connecting unit  211 . 
     As illustrated in  FIG. 1 , the illuminance sensor  65  is provided at the end ER of the front frame  27  and is disposed to receive outside light coming from in front of the user wearing the image display unit  20 . The illuminance sensor  65  is configured to output a detection value corresponding to an amount of received light (intensity of received light). 
     As illustrated in  FIG. 1 , the LED indicator  67  is disposed near the camera  61  at the end ER of the front frame  27 . The LED indicator  67  is configured to be turned on during image capturing by the camera  61  to notify that the image capturing is in progress. 
     The temperature sensor  217  is configured to detect a temperature and output a voltage value or a resistance value corresponding to the detected temperature as a detection value. The temperature sensor  217  is mounted on the rear face side of the OLED panel  223  ( FIG. 3 ). The temperature sensor  217  may be mounted, for example, on the same substrate as the substrate on which the OLED drive circuit  225  is mounted. According to this configuration, the temperature sensor  217  mainly detects a temperature of the OLED panel  223 . 
     The distance sensor  64  is configured to execute distance detection, and output a signal indicating detection results to the connecting device  10  via the connecting unit  211 . As the distance sensor  64 , for example, an infrared ray type depth sensor, an ultrasonic type distance sensor, Time Of Flight (TOF) type distance sensor, and a distance detection unit configured to perform image detection and audio detection in combination can be used. Additionally, the distance sensor  64  may be configured to process an image obtained in stereo photographing by a stereo camera or a monocular camera to detect a distance. 
     In  FIG. 5 , the single distance sensor  64  is illustrated, but a pair of the distance sensors  64  and  64  illustrated in  FIG. 3  may operate simultaneously. Additionally, each of the pair of distance sensors  64  and  64  may be connected with the connecting unit  211  and operate independently of each other. 
     The reception unit  213  is configured to receive image data for displaying transmitted from the connecting device  10  via the connecting unit  211 , and output the image data to the OLED unit  221 . 
     The left display unit  24  includes the display unit substrate  210 . On the display unit substrate  210 , a connecting unit  231  configured to be connected with the connecting cable  40 , and a reception unit (Rx)  233  configured to receive data input from the connecting device  10  via the connecting unit  231  are mounted. Additionally, on the display unit substrate  210 , a six-axis sensor  235  and a magnetic sensor  237  are mounted. 
     The connecting unit  231  connects the reception unit  233 , the six-axis sensor  235 , the magnetic sensor  237 , and the temperature sensor  239  with the connecting device  10 . 
     The six-axis sensor  235  is a motion sensor (inertial sensor) including a three-axis acceleration sensor and a three-axis gyro (angular velocity) sensor. As the six-axis sensor  235 , an Inertial Measurement Unit (IMU) including the above-described sensors as modules may be adopted. The magnetic sensor  237  is a three-axis geomagnetic sensor, for example. 
     The temperature sensor  239  is configured to detect a temperature and output a voltage value or a resistance value corresponding to the detected temperature as a detection value. The temperature sensor  239  is mounted on the rear face side of the OLED panel  243  ( FIG. 3 ). The temperature sensor  239  may be mounted, for example, on the same substrate as the substrate on which the OLED drive circuit  245  is mounted. According to this configuration, the temperature sensor  239  mainly detects a temperature of the OLED panel  243 . 
     Additionally, the temperature sensor  239  may be built in the OLED panel  243  or the OLED drive circuit  245 . Additionally, the substrate may be a semiconductor substrate. Specifically, when the OLED panel  243  is mounted, as an Si-OLED, together with the OLED drive circuit  245  and the like to form an integrated circuit on an integrated semiconductor chip, the temperature sensor  239  may be mounted on this semiconductor chip. 
     Each component of the image display unit  20  operates with power supplied from the connecting device  10  via the connecting cable  40 . The image display unit  20  may include a power circuit (not illustrated) configured to perform voltage conversion or distribution of the power supplied via the connecting cable  40 . 
     The connecting device  10  includes an I/F (interface) unit  110 , the control unit  120 , a display controller  122 , a sensor control unit  124 , a power control unit  126 , a non-volatile storage  130 , an operating unit  140 , and a connecting unit  145 . The I/F unit  110  as an acquisition unit includes the connectors  11 A,  11 B, and  11 C. Additionally, the I/F unit  110  may include interface circuits (not illustrated) connected with the connectors  11 A,  11 B, and  11 C and configured to execute communication protocols compliant with respective communication standards. Additionally, the I/F unit  110  may be configured to receive power supply via the connectors  11 A,  11 B, and  11 C. 
     The I/F unit  110 , for example, may include an interface for a memory card capable of being connected with an external storage device or storage medium, or the like, or the I/F unit  110  may include a radio communication interface. The I/F unit  110  may be, for example, an interface substrate on which the connectors  11 A,  11 B, and  11 C, and an interface circuit are mounted. Additionally, a configuration in which the control unit  120 , the display controller  122 , the sensor control unit  124 , and the power control unit  126  of the connecting device  10  are mounted on a connecting device main substrate (not illustrated) may be adopted. In this case, on the connecting device main substrate, the connectors  11 A,  11 B, and  11 C of the I/F unit  110 , and an interface circuit may be mounted. 
     The control unit  120  is configured to control each component of the connecting device  10 . The control unit  120  includes a processor (not illustrated) such as a Central Processing Unit (CPU), and a microcomputer. The control unit  120  causes the processor to execute a program to control each component of the HMD  100  in cooperation of software and hardware. Additionally, the control unit  120  may include programmed hardware. The control unit  120  may include, together with the processor, a Random Access Memory (RAM) configured to form a work area and a Read Only Memory (ROM) configured to store a control program. Additionally, the control unit  120  may be a semiconductor device including a processor, a RAM, and a ROM integrated. 
     The control unit  120  is connected with the non-volatile storage  130 , the operating unit  140 , and the connecting unit  145 . 
     The display controller  122  is configured to execute various kinds of processing for the image display unit  20  to display an image based on image data input to the I/F unit  110 . For example, the display controller  122  is configured to execute various kinds of processing such as cutting out of a frame, resolution conversion (scaling), intermediate frame generation, and frame rate conversion. The display controller  122  is configured to output image data corresponding to each of the OLED unit  221  of the right display unit  22 , and the OLED unit  241  of the left display unit  24  to the connecting unit  145 . The image data input to the connecting unit  145  is transmitted to the connecting units  211  and  231  via the connecting cable  40 . 
     As a specific example of the “cutting out” of a frame, the display controller  122  lays out an entire image larger than a size of a display area in which the image display unit  20  displays an image, on an work area. The display area is, for example, an area in which an image is formed in each of the OLED units  221  and  241 . Additionally, a size of an image is indicated by the number of pixels, or resolution. The display controller  122  transfers only data of the cut out area of the laid out image to the right display unit  22  and the left display unit  24 . 
     Additionally, the display controller  122  may be configured to acquire image data larger than the display area of the image display unit  20 , generate image data including only image data extracted from the acquired image data and having a size to be displayed by the image display unit  20 , and transfer the generated image data to the right display unit  22  and the left display unit  24 . 
     For example, when the image data input to the I/F unit  110  is 3D (three dimensional) image data, the display controller  122  is configured to execute 3D image decode. In processing of the 3D image decode, the display controller  122  is configured to generate a frame for the right eye and a frame for the left eye from the 3D image data. Examples of a format of the 3D image data input to the I/F unit  110  include a side by side format, a top and bottom format, and a frame packing format, but 3D model data may be used. 
     The display controller  122  is connected with the connector  11 A and the connector  11 B provided in the I/F unit  110 . The display controller  122  is configured to execute processing on image data input to the connector  11 A and image data input to the connector  11 B, as an object to be processed. Additionally, the display controller  122  may have a function to transmit/receive various kinds of control data about transmission of image data to/from a device connected with the connector  11 A or the connector  11 B. 
     The sensor control unit  124  is configured to control the camera  61 , the distance sensor  64 , the illuminance sensor  65 , the temperature sensor  217 , the six-axis sensor  235 , the magnetic sensor  237 , and the temperature sensor  239 . Specifically, the sensor control unit  124  is configured to set and initialize a sampling period of each sensor according to control by the control unit  120 , and the sensor control unit  124  is configured to, in correspondence to the sampling period of each sensor, power each sensor, transmit control data, and acquire a detection value, for example. 
     Additionally, the sensor control unit  124  is connected with the connector  11 B of the I/F unit  110 , and is configured to output data about the detection value acquired from each sensor to the connector  11 B at preset timing. Accordingly, a device connected with the connector  11 B can acquire the detection value of each sensor of the HMD  100 , and captured image data of the camera  61 . The data output by the sensor control unit  124  may be digital data including the detection value. Additionally, the sensor control unit  124  may be configured to output data of results obtained by an arithmetic operation based on the detection value of each sensor. For example, the sensor control unit  124  is configured to integrally process detection values of a plurality of sensors, and function as a so-called sensor fusion processing unit. The sensor control unit  124  executes sensor fusion to output data determined from the detection values of the sensors, for example, track data of movement of the image display unit  20 , and relative coordinate data of the image display unit  20 . The sensor control unit  124  may have a function to transmit/receive various kinds of control data about transmission of data to/from a device connected with the connector  11 B. 
     A processor such as a CPU may execute a program to achieve the display controller  122  and/or the sensor control unit  124  in cooperation of software and hardware. Namely, each of the display controller  122  and the sensor control unit  124  includes a processor, and executes a program to execute the above-described operations. In this example, a processor constituting the control unit  120  may execute a program to achieve the display controller  122  and the sensor control unit  124 . In other words, the processor may be configured to execute the program to function as the control unit  120 , the display controller  122 , and the sensor control unit  124 . Here, the processor can be rephrased as a computer. 
     Additionally, each of the display controller  122  and the sensor control unit  124  may include programmed hardware such as a Digital Signal Processor (DSP) and a Field Programmable Gate Array (FPGA). Additionally, the display controller  122  and the sensor control unit  124  may be integrated to be constituted as a System-on-a-Chip (SoC)-FPGA. 
     The power control unit  126  is connected with the connector  11 B and the connector  11 C provided in the I/F unit  110 . The power control unit  126  is configured to, based on power supplied from the connectors  11 B and  11 C, supply power to each component of the connecting device  10  and the image display unit  20 . Additionally, the power control unit  126  may include a voltage conversion circuit (not illustrated) built in, and may be configured to be capable of supplying different voltage to each component of the connecting device  10  and the image display unit  20 . The power control unit  126  may include a programmed semiconductor device such as a logic circuit and the FPGA. Additionally, the power control unit  126  may include hardware (including a processor) common to the display controller  122  and/or the sensor control unit  124 . 
     Each of the display controller  122 , the sensor control unit  124  and the power control unit  126  may include a work memory for performing data processing, and may be configured to perform processing by using a work area of a RAM (not illustrated) provided in the control unit  120 . 
     The control unit  120  is configured to read data from the EEPROM  215  provided in the right display unit  22 , and the control unit  120  is configured to, based on the read data, set operations of the display controller  122  and the sensor control unit  124 . Additionally, the control unit  120  is configured to, according to an operation in the operating unit  140 , cause respective components including the display controller  122 , the sensor control unit  124 , and the power control unit  126  to operate. Additionally, the control unit  120  is configured to identify devices connected with the display controller  122 , the sensor control unit  124 , and the power control unit  126  via the I/F unit  110 , and control the display controller  122 , the sensor control unit  124 , and the power control unit  126  to execute operations appropriate for the respective devices. 
     Additionally, the control unit  120  is configured to control start and stop of powering the LED indicator  67 . For example, the control unit  120  turns on or blinks the LED indicator  67  in correspondence to timing at which the camera  61  starts and ends capturing an image. 
     The non-volatile storage  130  is a storage device configured to store data to be processed by the control unit  120 , and the like in a non-volatile manner. The non-volatile storage  130  is, for example, a magnetic recording device such as a Hard Disk Drive (HDD), or is a storage device using a semiconductor storage element such as a flash memory. 
     Additionally, the connecting device  10  may include a rechargeable battery (not illustrated), and may be configured to supply power to each component of the connecting device  10  and the image display unit  20  from this battery. 
     The PC  300  includes a control unit  310 , a non-volatile storage  320 , the display unit  330 , an I/F (interface) unit  341 , and a communication unit  345 . The control unit  310  (electronic device control unit) includes a processor (not illustrated) such as a CPU or a microcomputer, and this processor is configured to execute a program to control each component of the PC  300 . The control unit  310  may include a ROM configured to store, in a non-volatile manner, a control program to be executed by the processor (so-called computer), and a RAM constituting a work area of the processor. 
     The non-volatile storage  320  is configured to store, in a non-volatile manner, a program to be executed by the control unit  310  and data to be processed by the control unit  310 . The non-volatile storage  130  is, for example, a magnetic recording device such as an HDD, or is a storage device using a semiconductor storage element such as a flash memory. 
     The non-volatile storage  320  is configured to store, for example, content data  321  of contents including an image. The content data  321  is a file in a format that the control unit  310  can process, and includes image data, and may include audio data. 
     Additionally, the non-volatile storage  320  is configured to store an operating system (OS) as a basic control program executed by the control unit  310 , an application program operating by using the OS as a platform, and the like. Additionally, the non-volatile storage  320  is configured to store data processed during execution of the application program, data of processing results, and the like. 
     The display panel  331 , and the touch sensor  332  provided in the display unit  330  are connected with the control unit  310 . The display panel  331  is configured to display various images based on control of the control unit  310 . The touch sensor  332  is configured to detect a touch operation and output data indicating the detected operation to the control unit  310 . The data output by the touch sensor  332  is coordinate data indicating an operating position in the touch sensor  332 , or the like. 
     The I/F unit  341  is an interface connected with an external device, and corresponds to the output unit according to the invention. The I/F unit  341  is configured to execute communication compliant with, for example, a standard such as an HDMI interface and a USB interface. The I/F unit  341  includes a connector (not illustrated) to be connected with a cable (for example, the cable  2 ), and an interface circuit (not illustrated) configured to process a signal transmitted via the connector. The I/F unit  341  is an interface substrate including the connector and the interface circuit, and is connected with a main substrate on which a processor and the like of the control unit  310  are mounted. Alternatively, the connector and the interface circuit constituting the I/F unit  341  are mounted on a main substrate of the PC  300 . In the exemplary embodiment, the I/F unit  341  includes the HDMI interface, and the USB interface, and is connected with the connectors  11 A and  11 B via the HDMI cable  2 A and the USB cable  2 B, respectively. For example, the control unit  310  is configured to output image data via the HDMI cable  2 A, and receive data about an output value of a sensor and the like from the connecting device  10  via the USB cable  2 B. The I/F unit  341  can execute communication via the HDMI cable  2 A and communication via the USB cable  2 B, independently. Additionally, the I/F unit  341  may be a radio communication interface. In this case, the I/F unit  341  can be an interface substrate on which a communication circuit including an RF unit is mounted, or can be a circuit mounted on a main substrate. 
     The communication unit  345  is a communication interface configured to execute data communication with an external device. The communication unit  345  may be a wired communication interface capable of being connected with a cable, or may be a radio communication interface. For example, the communication unit  345  may be a wired LAN interface supporting Ethernet (trade name), or a wireless LAN interface supporting IEEE802.11 standards. 
     The control unit  310  is configured to execute the programs as described above to function as an input and output controller  311 , a detection value acquisition unit  312 , a position detection unit  313 , and an image adjustment unit  315 . 
     The input and output controller  311  is configured to, based on data input from the touch sensor  332 , detect input by the user. Additionally, the input and output controller  311  is configured to control input and output of data by the I/F unit  341  and the communication unit  345 . 
     The detection value acquisition unit  312  is configured to acquire data about a detection value of each sensor provided in the HMD  100 , from the connecting device  10  connected via the I/F unit  341 . The detection value acquisition unit  312  is configured to acquire captured image data of the camera  61 , and data about detection values of the distance sensor  64 , the illuminance sensor  65 , the EEPROM  215 , the six-axis sensor  235 , the magnetic sensor  237 , the temperature sensor  239 , and the like, from the connecting device  10 . The data acquired by the detection value acquisition unit  312  is data processed by the sensor control unit  124 , and may be data including the detection value of each sensor, or data statistically processed by the sensor control unit  124 . 
     The position detection unit  313  is configured to, based on the data acquired by the detection value acquisition unit  312 , detect a position of the HMD  100 . More specifically, the position detection unit  313  is configured to detect a relative position between the PC  300  and the image display unit  20 . Here, the relative position detected by the position detection unit  313  may be a position in a space in which the image display unit  20  and the PC  300  exist, or may include a relative direction between the image display unit  20  and the display unit  330 . For example, the relative position detected by the position detection unit  313  may be information indicating the position and/or the direction of the display unit  330  with respect to the image display unit  20 . Additionally, for example, the relative position detected by the position detection unit  313  may be information indicating the position and/or the direction of the image display unit  20  with respect to the PC  300 . Additionally, for example, the relative position detected by the position detection unit  313  may include coordinates in a three dimensional coordinate system set in the space in which the image display unit  20  and the PC  300  exist. 
     The position detection by the position detection unit  313  will be described later. 
     The image data PC  300  outputs to the connecting device  10  can include, in addition to image data obtained by playing the content data  321 , image data in a screen the PC  300  causes the display unit  330  to display. In this case, the connecting device  10  is configured to display an identical screen to a screen the display unit  330  display, and perform so-called mirroring display. 
     Additionally, the image adjustment unit  315  may be configured to cause the display unit  330  to display a larger image including an image the connecting device  10  is displaying and an image not displayed by the PC  300 . Additionally, for example, the connecting device  10  may be configured to expand and display a portion of the image the PC  300  displays. A display mode in the PC  300  will be described later. 
     1-3. Operation of Display System 
       FIG. 6  is an explanatory view illustrating processing for determining the relative position of the PC  300  with respect to the image display unit  20 , and particularly illustrates calibration processing.  FIG. 7  is a flowchart illustrating an operation of the display system  1 , and particularly illustrates an operation of the PC  300  in the calibration processing. 
     In  FIG. 6 , a visual field VR a user visually recognizes through the image display unit  20 , and an imaging range VC of the camera  61  are illustrated. In this example, the imaging range VC overlaps with the visual field VR but does not coincide with the visual field VR. The imaging range VC and the visual field VR may coincide with each other, or the imaging range VC may be present in the visual field VR. 
     The display system  1  is used to execute, as illustrated in  FIG. 6 , calibration in a state where the PC  300  exists in the imaging range VC of the camera  61 . 
     In the exemplary embodiment, a reference point P 1  is set on the display unit  330 , and a reference position P 2  is set on the image display unit  20 . The reference point P 1  is display a user can visually recognize, and is a so-called marker. The PC  300  can detect the reference point P 1  from the captured image data of the camera  61 , by image processing. The reference position P 2  is set as a reference of a position in the image display unit  20 , and may be a virtual position, or there may be no display nor object indicating the reference position P 2 . 
     The reference point P 1  may be any object or position explicitly and visually recognized, and it is not necessary to newly provide display or an object to be the reference point P 1 . A specific position of a pattern or a shape on the display unit  330  such as one of four corners of the display unit  330  may be used as the reference point P 1 . 
       FIG. 7  is a flowchart illustrating an operation of the display system  1 , and illustrates an operation of the PC  300  performing the calibration. 
     In the calibration, a user moves the head or the image display unit  20  to locate the reference point P 1  at a preset position in the visual field VR of the user (step S 11 ). When the position set in the visual field VR and the reference point P 1  are superimposed on each other, the user performs an operation for confirming the position on the image display unit  20  or the PC  300  (step S 12 ). For example, the user performs a knocking operation on the front frame  27  of the image display unit  20 . This operation can be detected as acceleration by the six-axis sensor  235 . Additionally, when the image display unit  20  is equipped with a knock sensor (not illustrated), such an operation can be detected based on a detection value of the knock sensor. The operation at step S 12  may be an operation including detection by the touch sensor  332 . Additionally, at step S 12 , the PC  300  may detect an operation by audio. Namely, in a configuration in which the PC  300  is equipped with a microphone, and the control unit  310  can process audio collected by the microphone, the control unit  310  can execute audio recognition processing for converting audio into a text, or audio command detection processing for detecting audio of a pattern registered in advance. In this configuration, the control unit  310  may detect audio produced by the user as an input operation at step S 12 . 
     The control unit  310  acquires captured image data of the camera  61  generated when the operation at step S 12  is detected, and determines a position of the reference point P 1  in the captured image data of the camera  61  (step S 13 ). Accordingly, the position in the captured image data of the camera  61  is associated with the position in the visual field VR of the user wearing the image display unit  20 . Therefore, when the PC  300  is imaged in the captured image data of the camera  61 , a relative position of the PC  300  with respect to the visual field VR can be specified from this captured image data. 
     The control unit  310  acquires data about output values of the six-axis sensor  235  and the magnetic sensor  237  (step S 14 ). The output values of the sensors acquired at step S 14  indicate a reference position of the image display unit  20  in a state where the reference point P 1  is superimposed on the set position in the visual field VR. For example, a direction and an amount of movement of the image display unit  20  from the reference position can be determined by integrating the output values of the six-axis sensor  235 . Additionally, based on the output values of the magnetic sensor  237 , a relative direction of the image display unit  20  with respect to the reference position of the image display unit  20  can be determined. Therefore, a relative position between the image display unit  20  and the PC  300  can be determined. 
     The control unit  310  generates calibration data including the output values acquired at step S 14 , stores the calibration data in the non-volatile storage  320  (step S 15 ) and ends this processing. 
     For example, steps S 13  and the S 15  are executed by the position detection unit  313 , and step S 14  is executed by the detection value acquisition unit  312 . 
     In the calibration processing illustrated in  FIG. 7 , the reference point P 1  of the PC  300  and the set position in the visual field VR are made correspond to each other, and relative position relation of the image display unit with respect to the reference position of the image display unit is associated. The calibration data generated in this processing is, for example, data indicating a reference of a relative position between the reference point P 1  and the visual field VR. In this calibration, in addition to superimposing the predetermined position in the visual field VR on the reference point P 1 , a technique in which the PC  300  is disposed in a preset distance from the image display unit  20  may be adopted at step S 11 . For example, at step S 11 , an image used for guiding placement of the PC  300  at a position separated by a predetermined distance from the image display unit  20  may be displayed by the image display unit  20 . This image can be used as a marker such as a straight line, a rectangle, and a point indicating a size of the PC  300  visually recognized when the PC  300  is located at the position separated by the predetermined distance. The user may adjust a relative position between the PC  300  and the user to cause the PC  300  superimposed on the marker of the image display unit  20  to be visible, and subsequently, may make the reference point P 1  correspond to the predetermined position to perform the operation at step S 12 . 
     Each of  FIG. 8 ,  FIG. 9 , and  FIG. 10  is a view illustrating an example of a display mode of the display system  1  in the exemplary embodiment. In each of  FIG. 8 ,  FIG. 9 , and  FIG. 10 , a visual field VR in which the user wearing the image display unit  20  can visually recognize through the image display unit  20  is illustrated. Additionally, in the example illustrated in each of these figures, a size and a position of a display area in which the image display unit  20  displays an image to enable the user to visually recognize are identical to a size and a position of the visual field VR, and the display area and the visual field VR overlap with each other. The invention is applicable to a configuration in which a display area of the image display unit  20  is smaller than the visual field VR. 
     In  FIG. 8 , a virtual image VD generated by the PC  300  is illustrated. The virtual image VD includes an area VD 1  including an image identical to an image the PC  300  causes the display unit  330  to display, and areas VD 2 , VD 3 , and VD 4  adjacent to the area VD 1 . That is, the virtual image VD is an image having a size larger than a size of the image displayed by the display unit  330 . 
     The PC  300  is configured to set a virtual display area larger than a display area of the display panel  331 , and generate the virtual image VD as an image to be displayed in this display area. The virtual display area and the virtual image VD may differ in resolution or size, but in the exemplary embodiment, the virtual display area and the virtual image VD are described to coincide with each other in resolution or size. 
     In the following description, a size of each of the image displayed by the display unit  330 , the virtual image VD, and the areas VD 1 , VD 2 , VD 3 , and VD 4  is indicated by display resolution. For example, when display resolution of the display unit  330  is 1920 dots horizontally×1080 dots vertically and resolution of the virtual image VD and the virtual display area is 3840 dots×2160 dots, a size of the virtual image VD is four times the display image of the display unit  330 . 
     Aspect ratios of the image displayed by the display unit  330  and the virtual image VD may differ from each other, but when the aspect ratios coincide with each other, there is an advantage that processing performed when the virtual image VD including the display image of the display unit  330  is generated can be executed rapidly. Additionally, there is an advantage that when the user visually recognizes both the display image of the display unit  330  and the virtual image VD, there is no uncomfortable feeling. Thus, the case where the aspect ratios coincide with each other is preferable. For a similar reason, the aspect ratios and the resolution of the respective areas VD 1  to VD 4  constituting the virtual image VD may not coincide with the aspect ratio and the resolution of the display unit  330 , but preferably coincide with the aspect ratio and the resolution of the display unit  330 . Additionally, the resolution of the virtual image VD may not be an integer multiple of the display resolution of the display unit  330 , but is preferably an integer multiple. 
     The size of the virtual image VD is preferably identical to or larger than a size of an image that the image display unit  20  can display. Namely, the resolution of the virtual image VD is preferably equal to or greater than the display resolution of the display area of the image display unit  20 . An example includes a configuration in which the display resolution of the display unit  330  is 1920 dots horizontally×1080 dots vertically, and the display resolution of the image display unit  20  is 3840 dots×1080 dots, and the resolution of the virtual image VD is 3840 dots×2160 dots. Additionally, the aspect ratios of the virtual image VD and the display area of the image display unit  20  may differ from each other, and the aspect ratios and the resolution of the respective areas VD 1  to VD 4  may not coincide with the aspect ratio and the resolution of the display area of the image display unit  20 . Additionally, the resolution of the virtual image VD may not be an integer multiple of the resolution of the display area of the image display unit  20 . 
     It can be said that the virtual image VD is an expanded display area obtained by expanding the image the PC  300  causes the display unit  330  to display. For example, when the display unit  330  displays a screen for operation as a user interface of an operating system or an application program executed by the PC  300 , the control unit  310  constitutes the screen for operation in correspondence to the display resolution of the display unit  330 . When the virtual image VD is used, the control unit  310  constitutes the screen as the user interface in correspondence to the resolution of the virtual image VD, and causes the display unit  330  to display a portion of the screen. The same applies to a case where the PC  300  plays the content data  321 , or a case where other images or the like are displayed. Accordingly, the virtual image VD includes the image displayed by the display unit  330 . In other words, the display unit  330  displays a portion of the virtual image VD. 
     Additionally, the size of each of the virtual image VD, the display image of the display unit  330 , and the image displayed by the image display unit  20  may be defined as a size in which the user wearing the image display unit  20  visually recognizes. 
     A size of an image is determined by a size of a pixel and resolution. It is appropriate that the size of the pixel of the display unit  330  be considered as a size of a pixel obtained when the user visually recognizes the display unit  330  through the image display unit  20 . Additionally, since the virtual image VD is not visually recognized unless the image display unit  20  displays the virtual image VD, it is appropriate that the size of the pixel of the virtual image VD be considered as a size obtained when the user visually recognizes a pixel of the image displayed by the image display unit  20 . Then, when a size in which the user wearing the image display unit  20  visually recognizes is a reference, the virtual image VD may be larger than the display unit  330 . In this case, the resolution of the virtual image VD may be equal to or less than the display resolution of the display unit  330 . Further, resolution of image data cut out of the virtual image VD and output to the image display unit  20  may be resolution equal to or less than the display resolution of the display unit  330 . The control unit  310  is configured to perform resolution conversion for converting the display image of the display unit  330  to an image having lower resolution, in processing for generating the virtual image VD including the display image of the display unit  330 , and add another image around the image obtained after the conversion to generate the virtual image VD. 
       FIG. 11  is a flowchart illustrating an operation related to display of the display system  1 , and particularly illustrates an operation of the PC  300 . In the exemplary embodiment, the HMD  100  is configured to display an image based on image data output by the PC  300  via the HDMI cable  2 A, and the PC  300  is configured to perform display control based on the relative position between the image display unit  20  and the PC  300 . 
     Hereinafter, with reference to  FIGS. 8 to 10  together with  FIG. 11 , the operation of the display system  1  will be described. 
     The operation illustrated in  FIG. 11  is an operation in which the control unit  310  performs display using the virtual image VD. In response to an operation detected by the touch sensor  332 , the control unit  310  instructs start of image output to the HMD  100 , and when a display mode using the virtual image VD is specified, the control unit  310  executes the operation in  FIG. 11 . 
     In the following description, a case where the display unit  330  is present in a visual field of the image display unit  20  refers to a case where the user wearing the HMD  100  can visually recognize through the image display unit  20  the display unit  330  of the PC  300  as an outside scene. Visual fields of the right eye RE and the left eye LE through the image display unit  20 , namely, the range of the outside scene visible to the user can be determined from a direction of the image display unit  20 . Additionally, as illustrated in  FIG. 4 , in a case where relation between the angle of view of the camera  61 , and the visual fields of the right eye RE and the left eye LE obtained when the outside scene is viewed through the image display unit  20  is known, the control unit  310  can determine from the captured image data of the camera  61  whether the display unit  330  is in the visual. 
     The control unit  310  acquires the captured image data of the camera  61  and the output value of each sensor from the connecting device  10  via the USB cable  2 B (step S 21 ). At step S 21 , the control unit  310  acquires at least the captured image data, and the output value of the distance sensor  64 . Step S 21  is executed by, for example, the detection value acquisition unit  312 . 
     The control unit  310  determines whether the display unit  330  is present in the captured image data of the camera  61  (step S 22 ). At step S 22 , the control unit  310  detects, for example, an image of the display unit  330  from the captured image data by pattern matching. 
     In a case where the display unit  330  is determined not to be present in the captured image data (step S 22 ; NO), the control unit  310  returns to step S 21 . 
     In a case where the display unit  330  is determined to be present in the captured image data (step S 22 ; YES), the control unit  310  detects, based on the output value of each sensor acquired at step S 21 , a position and an attitude of the display unit  330  (step S 23 ). At step S 23 , the control unit  310  determines, for example, based on execution of Simultaneous Localization and Mapping (SLAM) or the detection value of the distance sensor  64 , a relative position between the image display unit  20  and the display unit  330 . Additionally, the control unit  310  may be configured to detect the reference point P 1  of the display unit  330  by using the captured image data, and determine from the position of the reference point P 1  detected the relative position of the display unit  330  with respect to the image display unit  20 . 
     The control unit  310  maps, according to the position and the attitude determined at step S 23 , the position and the attitude of the display unit  330  in a three dimensional space (step S 24 ). The position and the attitude of the display unit  330  are expressed by three dimensional coordinates with the reference position P 2  being an origin or a reference point. 
     The control unit  310  disposes the virtual image VD in a three dimensional space, in correspondence to the position and the direction of the display unit  330  (step S 25 ). A size of the virtual image VD is preset. For example, as set data (not illustrated), data defining the resolution of the virtual image VD or the position of the virtual image VD to be set with respect to the display unit  330  is stored in the non-volatile storage  320 . 
     The control unit  310  disposes the virtual image VD to be parallel to the display unit  330 , and to be a face superimposed on the display unit  330 . In other words, the virtual image VD includes the display unit  330 , and is a virtual plane larger than the display unit  330 . The control unit  310  determines three dimensional coordinates with the reference position P 2  being an origin or a reference point, as for a reference position based on which a position of the virtual image VD such as positions of four corners or a position of the center of the virtual image VD can be specified. 
     The control unit  310  generates image data of the virtual image VD (step S 26 ). The virtual image VD is a screen obtained by virtually expanding the display unit  330  as described above, and, for example, is a screen constituting a user interface of an operating system. 
     The control unit  310  determines the range to be displayed in the virtual image VD by the image display unit  20  (step S 27 ). As illustrated in  FIG. 8 , the image display unit  20  displays a portion of the virtual image VD. The control unit  310  determines the range to be displayed in the virtual image VD by the image display unit  20  from a direction of the image display unit  20  and a relative position with respect to the virtual image VD. 
     The control unit  310  specifies a position of the display unit  330  in the range in which the image display unit  20  displays an image (step S 28 ). The image display unit  20  displays an image on the half mirrors  261  and  281 , and the range in which the image is visually recognized is superimposed on the visual field VR in the examples in  FIG. 8  to  FIG. 10 . When the display unit  330  is visually recognized through the image display unit  20  in the visual field VR of the user wearing the image display unit  20 , the control unit  310  specifies a position at which the display unit  330  is visible in the visual field VR. This position can be determined from the position and the attitude of the PC  300  specified at step S 23 . 
     The control unit  310  performs processing for cutting out or extracting the image present in the range to be displayed by the image display unit  20  from the virtual image VD (step S 29 ), and applies masking processing to the cut out image (step S 30 ). The range in which the masking processing is applied at step S 30  is the range in which the display unit  330  is superimposed on the image to be displayed by the image display unit  20 , or the range including a portion superimposed on the display unit  330 . 
     In the example illustrated in  FIG. 8 , the areas VD 1  and VD 2  of the virtual image VD are cut out as the range to be displayed by the image display unit  20 . The display unit  330  is visually recognized at a position at which the area VD 1  is displayed. In this case, the control unit  310  may apply the masking processing to all the area VD 1 , or may apply the masking processing only to the range in which the area VD 1  is superimposed on the display unit  330 . 
     The user can visually recognize an outside scene passing through the image display unit  20  in a state where the image display unit  20  displays the virtual image VD. Here, when the display unit  330  is present in the visual field VR that the image display unit  20  visually recognizes as the outside scene, an image displayed by the display unit  330  and an image displayed by the image display unit  20  superimposed on each other are visible for the user. To provide a better visual experience to the user in the above-described state, in the exemplary embodiment, processing for adjusting a display mode of the image display unit  20  to enhance visibility of the display unit  330  is performed. This processing is referred to as the masking processing. 
       FIG. 9  illustrates a state in which the control unit  310  applies the masking processing. In an example in  FIG. 9 , the masking processing is applied to all the area VD 1  being the range superimposed on the display unit  330 . The masking processing is, for example, processing for turning color data of a pixel (so-called pixel data, a pixel value) into a black color or a dark color. The image display unit  20  displays an image by causing light emitted by the OLED units  221  and  241  to enter the right eye RE and the left eye LE, and thus when the pixel value turns into the black color or the dark color, amounts of light entering the right eye RE and the left eye LE decrease. When an amount of light emitted by the image display unit  20  decreases, an amount of light of the outside light OL passing through the image display unit  20  relatively increases, and thus visibility of the outside scene is enhanced. Therefore, the user can visually recognize the outside scene favorably in the range in which the masking processing is applied, and the visibility of the display unit  330  as the outside scene is enhanced by the masking processing. 
     Accordingly, the masking processing performed by the control unit  310  is processing in which a pixel value of image data output to the connecting device  10  to cause the image display unit  20  to display is set to the black color (R, G, B=0, 0, 0) or a preset dark color to reduce an amount of light. 
     Since the pixel value in the range including the image displayed by the display unit  330  is changed by the masking processing to the black color or to the dark color in the image data that the PC  300  outputs to the connecting device  10 , the image displayed by the display unit  330  is substantially removed. Accordingly, when the range in which the image display unit  20  displays an image is superimposed on the display unit  330 , the control unit  310  outputs to the connecting device  10  the image data obtained by removing the image displayed by the display unit  330 . 
     In the image data subjected to the masking processing, the image in the area VD 1  being the area superimposed on the display unit  330  is removed by a mask, and an image in an area located around the removed image (the area VD 2  in  FIG. 10 ) is displayed by the image display unit  20 . 
     The control unit  310  sets a convergence angle of the image subjected to the masking processing (step S 31 ). At step S 31 , the control unit  310  sets the convergence angle of the image such that a portion of the virtual image VD to be displayed by the image display unit  20  is visually recognized as a plane including the display unit  330 . The PC  300  outputs image data including image data of an image to be displayed by the right display unit  22  of the image display unit  20 , and image data of an image to be displayed by the left display unit  24 . The control unit  310  adjusts a position of the virtual image VD in the image for the right display unit  22 , and a position of the virtual image VD in the image for the left display unit  24  to adjust a convergence angle between the left eye LE and the right eye RE of the user. 
     The control unit  310  starts outputting the image data to the connecting device  10  (step S 32 ). The connecting device  10  starts a processing in which the image data input to the I/F unit  110  is decoded by the display controller  122 , and is displayed by the right display unit  22  and the left display unit  24 . 
     Steps S 24  to S 32  are, for example, executed by the image adjustment unit  315 . 
     After the start of the display, the control unit  310  determines whether the visual field VR has moved (step S 33 ). Here, the movement of the visual field VR means movement of a relative position of the visual field VR with respect to the virtual image VD. At step S 33 , the image adjustment unit  315  performs the determination based on a detection value of the position detection unit  313 . Additionally, the following steps S 34  to S 39  are executed by the image adjustment unit  315 . 
       FIG. 10  illustrates an example in which the visual field VR has moved. In the example in  FIG. 10 , the visual field VR has moved upward as compared to the state in  FIG. 9 . Owing to this movement, the visual field VR is superimposed on the areas VD 1 , VD 2 , VD 3 , and VD 4  to cross the areas VD 1 , VD 2 , VD 3 , and VD 4 . 
     When the control unit  310  determines that the visual field VR has moved (step S 33 ; YES), the control unit  310  determines whether a position of the PC  300 , more specifically a position of the display unit  330  is out of the range in which the image display unit  20  displays an image (step S 34 ). At step S 34 , the control unit  310  performs the determination based on a relative position and a relative direction between the image display unit  20  and the display unit  330 . 
     When the control unit  310  determines that the position of the display unit  330  is out of the display range of the image display unit  20  (step S 34 ; YES), the control unit  310  cancels the masking processing applied at step S 30  (step S 35 ). The control unit  310  changes, in correspondence to the visual field VR having moved, the range to be cut out of the virtual image VD (step S 36 ), and returns to step S 33 . 
     In the example illustrated in  FIG. 10 , the control unit  310  cuts the range crossing the areas VD 1 , VD 2 , VD 3 , and VD 4  out of the virtual image VD, generates image data corresponding to the cut out image, and outputs the generated image data to the connecting device  10 . Accordingly, the image display unit  20  displays the range in which the virtual image VD is superimposed on the visual field VR. 
     Additionally, when the control unit  310  determines that the position of the display unit  330  is not out of the display range of the image display unit  20  (step S 34 ; NO), the display unit  330  is within the display range of the image display unit  20 . In this case, the control unit  310  determines whether the display unit  330  has moved from an outside of the display range of the image display unit  20  into the display range (step S 37 ). 
     In a case where, owing to the movement of the visual field VR, the display unit  330  enters the display range from the state where the display unit  330  has been out of the display range of the image display unit  20  (step S 37 ; YES), the control unit  310  initializes a state of image data to be output to the connecting device  10  (step S 38 ). During the initialization, the control unit  310  resets application/cancellation of the masking processing, the range to be cut out of the virtual image VD, or the like in the image data output to the connecting device  10  to an initial state. The control unit  310  returns to step S 23 , and executes again the processing for starting output of the image data. 
     Specific examples of the initialization processing at step S 38  includes the following examples. A first example includes processing in which when it is determined that all the display unit  330  has entered the visual field VR at step S 37 , the virtual image VD disposed and processed at step S 25  previously executed is used to generate a display image. Additionally, second processing includes processing for executing the processing at step S 23  and the subsequent steps in correspondence to the position of the display unit  330 , and newly resetting a position of the virtual image VD (including a depth). In addition to these kinds of processing, a specific example of the processing performed by the control unit  310  is arbitrary. 
     Additionally, in a case where the display unit  330  has not moved from the outside of the display range of the image display unit  20  into the display range (step S 37 ; NO), namely, in a case where the state in which the display unit  330  is in the display range of the image display unit  20  is continued, the control unit  310  shifts to step S 36 . 
     Additionally, when the control unit  310  determines that the visual field VR has not moved (step S 33 ; NO), the control unit  310  determines whether to end the display (step S 39 ). For example, when the display end is instructed by an operation on the display unit  330  or the like (step S 39 ; YES), the control unit  310  stops outputting the image data to the connecting device  10  and ends this processing. On the other hand, when the display is to be continued (step S 39 ; NO), the control unit  310  returns to step S 33 . 
     At step S 33 , in a case where the image display unit  20  has moved, for example, in a case where the user wearing the image display unit  20  has moved the head, the control unit  310  determines that the visual field VR has moved. Additionally, in a case where the PC  300  has moved in a state where the image display unit  20  has not moved, and accordingly, a relative position between the image display unit  20  and the PC  300  has changed, it may also be determined that the visual field VR has moved. That is, the movement of the visual field VR detected at step S 33  is a change in the relative position between the image display unit  20  and the PC  300 , and includes a case where the image display unit  20  moves, a case where the PC  300  moves, and a case where both the image display unit  20  and the PC  300  move. 
     Therefore, in any of a case where the user has moved the head, and a case where the user or another person has moved the PC  300 , the processing at step S 34  and the subsequent steps is executed depending on whether the position of the PC  300  is within the display range of the image display unit  20 . 
     In the processing illustrated in  FIG. 7  and  FIG. 11 , the display system  1  may use the captured image data of the camera  61 , instead of the distance sensor  64 , to detect a distance. For example, the display system  1  stores in advance as reference data in the non-volatile storage  130  or the non-volatile storage  320  data for associating a distance from the image display unit  20  to an object to be captured with a size of an image of an object to be captured and imaged in the captured image data of the camera  61 . In this case, the control unit  310  can calculate a distance from the image display unit  20  to the PC  300  or to the display unit  330 , based on a size of an image of the PC  300  or the display unit  330  in the captured image data of the camera  61 , and the reference data. 
     As described above, the display system  1  in the first exemplary embodiment includes the PC  300  including the display unit  330 , and the HMD  100  connected with the PC  300 . The PC  300  includes the I/F unit  341  configured to output an image. The HMD  100  includes the I/F unit  110  configured to acquire the image data output by the PC  300 . Additionally, the HMD  100  includes the image display unit  20  configured to enable an outside scene to be visually recognized, superimpose an image on the outside scene visually recognized in a state where the HMD  100  is worn, and display the image, and the display controller  122  configured to cause the image display unit  20  to display the image acquired by the acquisition unit. The display controller  122  is configured to cause the image display unit  20  to display the image in correspondence to the position of the PC  300  visually recognized as the outside scene. 
     Additionally, the PC  300  corresponds to the electronic device of the invention connected with the HMD  100 . The PC  300  includes the display unit  330 , and the I/F unit  341  configured to output an image data to the HMD  100 . Additionally, the PC  300  includes the control unit  310  configured to determine a relative position of the display unit  330  with respect to the image display unit  20  of the HMD  100 . The control unit  310  is configured to generate, based on the relative position of the display unit  330  with respect to the image display unit  20 , image data used for the image display unit  20  to display an image corresponding to the position of the display unit  330  visually recognized as the outside scene, and output the generated image data from the I/F unit  341 . 
     According to the display system  1  and the PC  300  to which the invention is applied, an image output by the PC  300  can be displayed by the HMD  100  in correspondence to the position of the display unit  330  of the PC  300  as the outside scene. For example, the image can be displayed by the HMD  100  in correspondence to the position of the display unit  330  of the PC  300  visible as the outside scene. Accordingly, the display corresponding to the display unit  330  of the PC  300  visually recognized as the outside scene can be performed by the HMD  100  configured to superimpose the image on the outside scene and display the image. 
     Additionally, the control unit  310  is configured to generate the virtual image VD corresponding to a virtual display area wider than the display unit  330 . The control unit  310  is configured to cause the display unit  330  to display a portion of the virtual image VD generated in correspondence to the virtual display area, and cause the I/F unit  341  to output an image for display including at least a portion of the virtual image VD. For example, the control unit  310  is configured to cause the display unit  330  to display a portion of the virtual image VD, and cause the I/F unit  341  to output an image obtained by removing a portion displayed by the display unit  330  from the virtual image VD. Additionally, the display system  1  is configured to cause the image display unit  20  provided in the HMD  100  to display an image based on image data output by control of the control unit  310 , in correspondence to the position of the display unit  330  visually recognized as the outside scene. Specifically, image data obtained by masking an area corresponding to a position superimposed on the display unit  330  in the image display unit  20  is output by the PC  300  to the connecting device  10 . Thus, display corresponding to the virtual image VD wider than the display unit  330  of the PC  300  can be performed on the image display unit  20  of the HMD  100 . Thus, the display unit  330  of the PC  300  can be expanded virtually by the HMD  100 . 
     Additionally, the control unit  310  is configured to generate image data obtained by removing an area displayed by the display unit  330  from the virtual image VD, and cause the I/F unit  341  to output the image data. The control unit  310  is configured to cause the image display unit  20  provided in the HMD  100  to display an image for display output by control of the control unit  310 , around the display unit  330  visually recognized as the outside scene. That is, when the virtual image VD corresponding to the virtual display area wider than the display unit  330  of the PC  300  is displayed by the HMD  100 , the virtual image VD obtained by removing an area displayed by the display unit  330  is displayed. Thus, display of the display unit  330  and display of the HMD  100  can be combined not to overlap with each other. For example, the image is displayed by the HMD  100  around the display unit  330  of the PC  300  and thus, the display mode in which the display unit  330  is virtually expanded can be achieved. 
     Additionally, the control unit  310  is configured to determine a relative position of the display unit  330  with respect to the image display unit  20  of the HMD  100 , and is configured to, based on the obtained relative position, perform the masking processing, generate image data, and cause the I/F unit  341  to output the image data. Accordingly, since the image data is generated in correspondence to the relative position of the display unit  330  with respect to the image display unit  20 , display corresponding to the position of the display unit  330  of the PC  300  can be achieved easily by the HMD  100 . 
     Additionally, the control unit  310  is configured to generate the virtual image VD and determine a position of the virtual image VD based on a position of the PC  300  in a real space. The control unit  310  is configured to adjust a display mode of the virtual image VD to be displayed by the image display unit  20  to correspond to a relative position between the virtual image VD and the image display unit  20 . Accordingly, the virtual image VD can be displayed by the HMD  100  in correspondence to the position of the display unit  330  of the PC  300  in the real space. An effect such as supplementing or expanding the display unit  330  can be obtained by this virtual image VD. 
     Additionally, the control unit  310  is configured to initialize a display mode of the virtual image VD by using a position of the display unit  330  detected as a reference when the control unit  310  detects that the display unit  330  is present in the range visually recognized as an outside scene in the image display unit  20 . Accordingly, the display mode can be adjusted in correspondence to whether the display unit  330  of the PC  300  can be recognized visually as the outside scene in the HMD  100 . Additionally, even when a visual recognition state of the display unit  330  of the PC  300  changes while the HMD  100  displays an image, an appropriate response to such a change can be made. 
     Additionally, the image display unit  20  includes the left display unit  24  configured to emit imaging light toward the left eye LE of the user, and the right display unit  22  configured to emit imaging light toward the right eye RE of the user in a state where the image display unit  20  is worn on the head of the user. Then, the control unit  310  is configured to control a display position by the left display unit  24  and a display position by the right display unit  22  in correspondence to a position of the display unit  330  visually recognized as an outside scene of the image display unit  20 , and adjust a convergence angle of an image to be displayed by the image display unit  20 . In this case, the convergence angle of the image to be displayed by the HMD  100  is adjusted, and accordingly, a distance in which the display image of the HMD  100  is visually recognized can be made correspond to the position of the display unit  330  of the PC  300 . Accordingly, the display by the HMD  100  and the display by the display unit  330  of the PC  300  can be coordinated more appropriately. 
     Note that, in the processing in  FIG. 11 , the display unit  330  may excessively approach to the image display unit  20  to an extent that the display unit  330  blocks a field of view passing through the image display unit  20 . An example of such a case includes a case where the position of the display unit  330  detected at step S 23  is closer to the image display unit  20  than the preset range. In this case, the control unit  310  may stop image output to the connecting device  10  and return to step S 21 . 
     In the above-described exemplary embodiment, the control unit  310  is configured to adjust image display positions in an image for the right eye RE and in an image for the left eye LE, and control a convergence angle to control a visual recognition distance that the user perceives to a display image of the image display unit  20 . 
     When the image display unit  20  can adjust the visual recognition distance that the user perceives to the display image of the image display unit  20 , by optical systems provided in the right display unit  22  and the left display unit  24 , this adjustment by control of the optical systems may be performed instead of the control of the convergence angle. That is, the optical system may be controlled such that the user perceives the display image of the image display unit  20  being a portion of the virtual image VD as an image located at an identical position to a position of the display unit  330 . In this case, a distance in which the display image of the image display unit  20  is visually recognized can be made correspond to the position of the display unit  330  of the PC  300 , and the display by the HMD  100  and the display by the PC  300  can be coordinated more appropriately. 
     An example of the above-described optical system includes a configuration in which a lens movable in a left-right direction connecting the right eye RE and the left eye LE is provided. In this configuration, the lens movable in the left-right direction is disposed in each of the right display unit  22  and the left display unit  24 . The lenses may be disposed, for example, between the right optical system  251  and the half mirror  261 , and between the left optical system  252  and the half mirror  281 , respectively. Additionally, the lens may be disposed inside each of the right optical system  251  and the left optical system  252 . Since a position of imaging light entering each of the right eye RE and the left eye LE moves in the left-right direction according to the position of the lens, the convergence angle can be changed. In this example, since the control unit  120  is configured to control the movement of the lens, and the control unit  310  is configured to output image data, and control data for specifying the lens position to the connecting device  10 , a convergence angle calculated by the control unit  310  can be achieved. 
     Additionally, as an optical system used by the image display unit  20  to output imaging light, a holography display device may be provided. In this case, the image display unit  20  includes, for example, a light source, and a Spatial Light Modulator (SLM) configured to modulate light from the light source. The SLM can use, for example, a reflection type spatial light phase modulator using liquid crystal (Liquid Crystal On Silicon (LCOS)-SLM). In this configuration, the connecting device  10  outputs display data to the SLM, and accordingly, reference light emitted from the light source is modulated by the SLM to form a stereoscopic image. In this case, image data output by the PC  300  to the connecting device  10 , or display data generated by the display controller  122  from the image data output by the PC  300  are adjusted and thus, a focal distance of the stereoscopic image formed by the image display unit  20  can be adjusted. Thus, instead of the control for adjusting the convergence angle in the exemplary embodiment, the focal distance of the stereoscopic image is controlled in the image display unit  20  configured as the holography display device and thus, a distance to which the user visually recognizes an image displayed by the image display unit  20  can be adjusted. 
     Additionally, a configuration in which a dimming shade is provided on an outer side of the image display unit  20  may be adopted. The dimming shade is a plate shaped electronic device including a liquid crystal panel or the like, and having light transmittance changing according to control of the control unit  310 . When the dimming shade is provided on the image display unit  20 , outside light OL passing through the dimming shade and further passing through the right light-guiding plate  26  and the left light-guiding plate  28  enters the right eye RE and the left eye LE of the user wearing the image display unit  20 . The user visually recognizes the outside scene by the outside light passing through the dimming shade and the image display unit  20 . Therefore, according to transmittance (light transmittance) of the dimming shade, visibility at which the user visually recognizes the outside scene changes. 
     When the control unit  310  executes the masking process, to enhance visibility of an area subjected to the masking process, the control unit  310  may perform control for enhancing the transmittance of the area in the dimming shade. 
     In the above-described first exemplary embodiment, the configuration in which a position of the display unit  330  in a display range of the image display unit  20  is specified, and an image is displayed by the image display unit  20  in correspondence to the position of the display unit  330  is described. That is, the image is displayed in correspondence to the relative position between the image display unit  20  and the display unit  330 . The invention is not limited to this configuration, and for example, a position of the PC  300  in a display range of the image display unit  20  may be detected or specified by using a portion or all of appearance of the PC  300  as a reference. 
     Namely, the control unit  310  determines, at step S 22 , whether at least a portion of the appearance of the PC  300  is present in the captured image data of the camera. At step S 22 , the control unit  310  detects, for example, an image of the PC  300  from the captured image data by pattern matching. Here, the control unit  310  may detect a shape of a corner of a housing of the PC  300 , a shape of a border portion between the display unit  330  and the housing in the PC  300 , a shape of a back surface side of the PC  300 , a painting color of a back surface of the PC  300 , or the like from the captured image of the camera  61  by the pattern matching. Additionally, the control unit  310  may detect a marker attached or fixed to the housing of the PC  300  from the captured image of the camera  61 . As the marker, for example, an image code such as a bar code and a two dimensional code, a character, or other images can be used. Additionally, a pattern or a shape of an outer packaging of the PC  300  may be a pattern or a shape functioning as a marker. For example, the PC  300  is not limited to a plane shape illustrated in  FIG. 1 , and may be a shape having a protrusion or a concave, or may include a configuration in which the control unit  310  detects the protrusion or the concave. In this case, the control unit  310  may specify a position or an attitude of the PC  300  from the captured image data, and may determine a relative position of the PC  300  with respect to the image display unit  20 . Additionally, the control unit  310  may perform processing for determining the relative position of the PC  300  with respect to the image display unit  20 , and based on the obtained relative position, determining a relative position between the image display unit  20  and the display unit  330 . 
     2. Second Exemplary Embodiment 
       FIG. 12  is a view illustrating an example of a display mode in a second exemplary embodiment to which the invention is applied. 
     The second exemplary embodiment is an example in which a virtual image VD different from the virtual image VD in the first exemplary embodiment is formed by a display system  1  including a common configuration to the configuration of the display system  1  in the first exemplary embodiment. 
     The virtual image VD illustrated in  FIG. 12  is, in a manner similar to the virtual image VD illustrated in  FIG. 8 , an image having a size larger than a size of an image displayed by a display unit  330 . In the second exemplary embodiment, a control unit  310  is configured to dispose all the image displayed by the display unit  330  in a virtual display area to generate the virtual image VD. 
     As illustrated in  FIG. 12 , the image displayed on all the virtual image VD includes identical contents to all the image displayed by the display unit  330 . The control unit  310  is configured to perform resolution conversion to generate the virtual image VD when resolution of a virtual display area does not coincide with resolution of the image displayed by the display unit  330  or display resolution of the display unit  330 . 
     The virtual image VD is divided into areas VD 1 , VD 2 , VD 3 , and VD 4 . A portion obtained by dividing a display image of the display unit  330  is assigned to each of the areas VD 1  to VD 4 . In the virtual image VD in  FIG. 12 , the display image of the display unit  330  is divided by four, and the divided areas are displayed in the areas VD 1 , VD 2 , VD 3 , and VD 4 , respectively. 
     In processing for cutting out (extracting) the range to be displayed by an image display unit  20  from the virtual image VD (step S 29  and step S 36  in  FIG. 11 ), the control unit  310  cuts out any of the areas VD 1  to VD 4  as a unit. That is, image data of any of the areas VD 1  to VD 4  is output to a connecting device  10 . 
     Then, in processing for determining whether a visual field VR has moved (step S 33 ), in a case where the visual field VR has crossed any of borders of the areas VD 1  to VD 4 , the control unit  310  determines that the visual field VR has moved. In this determination, in a case where the center of the visual field VR has moved across any of the borders of the areas VD 1  to VD 4 , namely, in a case where the center has moved from any of the areas VD 1  to VD 4  to the area adjacent, the control unit  310  determines positively. 
     In the second exemplary embodiment, a PC  300  is configured to cause the display unit  330  to display an image corresponding to the display unit  330 , generate the virtual image VD corresponding to the display image of the display unit  330 , and cause image data of an image including at least a portion of the virtual image VD to be output. The display system  1  is configured to cause the image display unit  20  provided in an HMD  100  to display an image based on image data output by control of the control unit  310 , in correspondence to a position of the display unit  330  visually recognized as an outside scene. Accordingly, at least a portion of the image displayed by the display unit  330  of the PC  300  can be displayed by the image display unit  20 , in correspondence to the position of the display unit  330  visually recognized as the outside scene in the image display unit  20 . Thus, a display image of the display unit  330  and an image displayed by the HMD  100  can be coordinated. 
     Additionally, the control unit  310  is configured to cause the I/F unit  341  to output an image obtained by cutting out a portion of the virtual image VD, and thus a portion of the display image of the display unit  330  can be expanded and displayed by the image display unit  20 . 
     Additionally, the control unit  310  is configured to determine a relative position of the display unit  330  with respect to the image display unit  20  of the HMD  100 , and based on the relative position determined, generate image data. Accordingly, display corresponding to the position of the display unit  330  of the PC  300  can be achieved easily by the HMD  100  including the image display unit  20 . 
     3. Third Exemplary Embodiment 
     Each of  FIG. 13  and  FIG. 14  is a flowchart illustrating an operation of a display system  1  in a third exemplary embodiment to which the invention is applied.  FIG. 13  illustrates an operation of a PC  300 , and  FIG. 14  illustrates an operation of an HMD  100 . 
     The third exemplary embodiment is an example in which an operation different from the operation in the first exemplary embodiment is executed by the display system  1  including a common configuration to the configuration of the display system  1  in the first exemplary embodiment. 
     In the third exemplary embodiment, while processing for detecting a relative position of the PC  300  with respect to an image display unit  20  is executed by the PC  300 , processing for cutting out a portion of a virtual image VD generated by the PC  300  is executed by the HMD  100 . 
     In the flowchart illustrated in  FIG. 13 , common processing to the processing in  FIG. 11  is denoted by an identical step number and description of the common processing will be omitted. 
     A control unit  310  is configured to execute processing at steps S 21  to S 28 . At step S 28 , the control unit  310  specifies a position of a display unit  330  in the range in which the image display unit  20  displays an image (step S 28 ). Here, the control unit  310  starts processing for outputting position data indicating the position of the display unit  330  specified at step S 28 , together with image data of the virtual image VD to the HMD  100  (step S 51 ). The position data output by the control unit  310  at step S 51  is data for cutting the image present in the range displayed by the image display unit  20  out of the virtual image VD. 
     The control unit  310  determines in a manner similar to step S 32  ( FIG. 11 ) whether a visual field VR has moved (step S 52 ). At step S 52 , an image adjustment unit  315  performs the determination based on a detection value of a position detection unit  313 . Additionally, steps S 53  to S 57  described below are executed by the image adjustment unit  315 . 
     When the control unit  310  determines that the visual field VR has moved (step S 52 ; YES), the control unit  310  determines whether a position of the PC  300  is out of the range in which the image display unit  20  displays an image (step S 53 ). At step S 53 , the control unit  310  may determine whether the position of the display unit  330  is out of the range in which the image display unit  20  displays an image. At step S 53 , the control unit  310  performs the determination based on a relative position and a relative direction between the image display unit  20  and the display unit  330 . 
     When it is determined that the position of the PC  300  is out of the display range of the image display unit  20  (step S 53 ; YES), position data to be output to the HMD  100  is changed in correspondence to the visual field VR having moved (step S 54 ), and the processing returns to step S 52 . 
     When the control unit  310  determines that the position of the PC  300  is not out of the display range of the image display unit  20  (step S 53 ; NO), the control unit  310  determines whether the PC  300  has moved from an outside of the display range of the image display unit  20  into the range of the image display unit  20  t (step S 55 ). 
     In a case where, owing to the movement of the visual field VR, the display unit  330  enters the display range from the state where the display unit  330  has been out of the display range of the image display unit  20  (step S 55 ; YES), the control unit  310  determines that display of the HMD  100  needs to be initialized (step S 56 ). The control unit  310  returns to step S 23 , and executes again the processing for starting output of the image data. This initialization processing is similar to the processing described at step S 38 , and in the operation example illustrated in each of  FIG. 13  and  FIG. 14 , the image display unit  20  performs the initialization. 
     When it is determined that the PC  300  has not moved from the outside of the display range of the image display unit  20  into the range of the image display unit  20  (step S 55 ; NO), the control unit  310  shifts to step S 54  and changes the position data. 
     At step S 52 , in a manner similar to step S 33 , in any of a case where the image display unit  20  has moved, and a case where the PC  300  has moved, as long as a relative position between the image display unit  20  and the PC  300  is changed, it is determined that the visual field VR has moved. 
     When the control unit  310  determines that the visual field VR has not moved (step S 52 ; NO), the control unit  310  determines whether to end the display (step S 57 ). For example, when display end is instructed by an operation on the display unit  330  or the like (step S 57 ; YES), the control unit  310  stops outputting the image data to a connecting device  10  and ends this processing. On the other hand, when the display is to be continued (step S 57 ; NO), the control unit  310  returns to step S 52 . 
     In the operation illustrated in  FIG. 14 , the control unit  120  of the HMD  100  starts processing for acquiring data of the virtual image VD output by the PC  300  and the position data (step S 61 ). The control unit  120  specifies, based on the acquired position data, a position of the display unit  330  in the range in which the image display unit  20  displays an image (step S 62 ). 
     The control unit  120  executes processing for cutting an image present in the range to be displayed by the image display unit  20  out of the virtual image VD (step S 63 ). The control unit  120  applies mask processing to the cut out image (step S 64 ). The range in which the masking processing is applied at step S 64  is identical to the range at step S 30  ( FIG. 11 ), and is the range in which the display unit  330  is superimposed on the image to be displayed by the image display unit  20 , or the range including a portion superimposed on the display unit  330 . 
     The control unit  120  sets a convergence angle of the image subjected to the masking processing (step S 65 ). At step S 65 , in a manner similar to the processing executed by the control unit  310  at step S 31  ( FIG. 11 ), the control unit  120  sets the convergence angle of the image such that a portion of the virtual image VD to be displayed by the image display unit  20  is visually recognized as a plane including the display unit  330 . The control unit  120  generates image data including image data of an image to be displayed by a right display unit  22  of the image display unit  20 , and image data of an image to be displayed by a left display unit  24 , and starts display (step S 66 ). Here, the control unit  120  adjusts a position of the virtual image VD in an image for the right display unit  22 , and a position of the virtual image VD in an image for the left display unit  24  and thus, the control unit  120  can adjust a convergence angle of a left eye LE and a right eye RE of a user. 
     The control unit  120  determines whether the position data output by the PC  300  has been changed (step S 67 ). When the control unit  120  determines that the position data has been changed (step S 67 ; YES), the control unit  120  determines whether a position of the PC  300  is out of the range in which the image display unit  20  displays an image (step S 68 ). The processing at step S 68  is, for example, similar to the processing executed by the control unit  310  at step S 34  ( FIG. 11 ). 
     When the control unit  120  determines that the position of the PC  300  is out of the display range of the image display unit  20  (step S 68 ; YES), the control unit  120  cancels the masking processing applied at step S 64  (step S 69 ). The control unit  120  changes, in correspondence to the position data changed, the range to be cut out of the virtual image VD (step S 70 ), and returns to step S 67 . 
     When the control unit  120  determines that the position of the PC  300  is not out of the display range of the image display unit  20  (step S 68 ; NO), the control unit  120  determines whether the PC  300  has moved from an outside of the display range of the image display unit  20  into the range of the image display unit  20  (step S 71 ). In a case where the PC  300  enters the display range from the state where the PC  300  has been out of the display range of the image display unit  20  (step S 71 ; YES), the control unit  120  initializes display of the image display unit  20  (step S 72 ). The initialization at step S 72  is, for example, similar to the initialization at step S 38  ( FIG. 11 ), and the control unit  120  resets application/canceling of the masking process, the range to be cut out of the virtual image VD, or the like to an initial state. The control unit  120  returns to step S 61 , and performs again the processing for starting the display. 
     In a case where the PC  300  has not moved from the outside of the display range of the image display unit  20  into the range of the image display unit  20  (step S 71 ; NO), the control unit  120  shifts to step S 70 . 
     Additionally, when the control unit  120  determines that the position data has not been changed (step S 67 ; NO), the control unit  120  determines whether to end the display (step S 73 ). For example, when display end is instructed by a command input from the PC  300  or an operation on the operating unit  140  or the like (step S 73 ; YES), the control unit  120  stops the display by the image display unit  20  and ends this processing. On the other hand, when the display is to be continued (step S 73 ; NO), the control unit  120  returns to step S 67 . 
     According to this third exemplary embodiment, the PC  300  is configured to specify the relative position of the PC  300  with respect to the image display unit  20 , and perform processing for determining the position of the PC  300  in the display range of the image display unit  20 , and the HMD  100  is configured to cut an image out of the virtual image VD to cause the image display unit  20  to display the cut out image. Accordingly, since the PC  300  and the HMD  100  are configured to mutually share and execute the processing, the configuration of the HMD  100  is simplified, and thus the HMD  100  can be reduced in a weight and a size. Additionally, since the image display unit  20  is configured to execute the processing for cutting the image out of the virtual image VD, for example, processing such as setting the convergence angle can be executed rapidly in the image display unit  20 . 
     In the operation described in the third exemplary embodiment, processing similar to steps S 33  to S 38  ( FIG. 11 ) may be executed. In this case, the processing at steps S 33 , S 34 , and S 37  is preferably executed by the control unit  310 . Additionally, preferably, the control unit  120  acquires processing results of steps S 33 , S 34 , and S 37  executed by the control unit  310 , and executes the processing at steps S 35 , S 36 , and S 38 . 
     4. Fourth Exemplary Embodiment 
       FIG. 15  is a block diagram of respective components constituting a display system  1 A according to a fourth exemplary embodiment. 
     The display system  1 A includes a configuration in which the HMD  100  in the display system  1  described in the first exemplary embodiment includes a control device  10 A instead of the connecting device  10 . The control device  10 A includes a control unit  121 , and the control unit  121  is configured to process image data input from a PC  300 . Except for the configurations of the control unit  121  and the related components, the display system  1 A includes components similar to the components of the display system  1 . The components common to the components of the display system  1  are denoted by identical reference signs and description of the common components will be omitted. 
     In a manner similar to the control unit  120  ( FIG. 5 ), the control unit  121  includes a processor (not illustrated) such as a CPU or a microcomputer, and is configured to cause the processor to execute a program to control each component of the HMD  100  in cooperation of software and hardware. Additionally, the control unit  121  may include programmed hardware. 
     The control unit  121  is connected with a non-volatile storage  130 , an operating unit  140 , and a connecting unit  145 . Additionally, the control unit  121  includes a position detection unit  123 , and an image adjustment unit  125 . In a manner similar to the position detection unit  313 , the position detection unit  123  is configured to detect a position of the HMD  100 . More specifically, the position detection unit  123  is configured to detect a relative position between the PC  300  and an image display unit  20 , based on an output value of a sensor provided in the image display unit  20 . Additionally, for example, the processing in which the control unit  310  determines the distance from the captured image data of the camera  61  to the object to be captured as described in the first exemplary embodiment can also be executed by the control unit  121 . 
     The relative position detected by the position detection unit  123  may be a position in a space in which the image display unit  20  and the PC  300  exist. Additionally, the relative position detected by the position detection unit  123  may include a relative direction between the image display unit  20  and a display unit  330 . For example, the relative position detected by the position detection unit  123  may be information indicating the position and/or the direction of the display unit  330  with respect to the image display unit  20 . Additionally, the relative position detected by the position detection unit  123  may be, for example, information indicating the position and/or the direction of the image display unit  20  with respect to the PC  300 . Additionally, the relative position detected by the position detection unit  123  may include, for example, coordinates in a three dimensional coordinate system set in a space in which the image display unit  20  and the PC  300  exist. 
     The image adjustment unit  125  is configured to perform image processing for image data input to an I/F unit  110 . The image processing executed by the image adjustment unit  125  is similar to the processing of the image adjustment unit  315  described in the first exemplary embodiment and the second exemplary embodiment. 
     For example, the image adjustment unit  125  is configured to perform processing such as resolution conversion (scaling), frame rate conversion, tone correction, and data format change on the image data input to the I/F unit  110 , in correspondence to specifications of the HMD  100 . 
     In a manner similar to the display system  1 , the display system  1 A is configured to execute the calibration processing illustrated in  FIG. 7 , and the operation illustrated in  FIG. 11 . 
     When the display system  1 A executes the operation in  FIG. 7 , steps S 13  to S 15  are executed by the position detection unit  123 . Additionally, when the display system  1 A executes the operation in  FIG. 11 , the position detection unit  123  executes steps S 21  and S 23 , and the image adjustment unit  125  executes steps S 22 , S 24  to S 39 . 
     In the fourth exemplary embodiment, the image adjustment unit  125  is configured to set a virtual display area corresponding to the virtual image VD, and dispose image data output by the PC  300  in the virtual display area to generate the virtual image VD. The image adjustment unit  125  is configured to cut the range to be displayed by the image display unit  20  out of the virtual image VD, apply the masking processing as necessary, and cause the image display unit  20  to display the image. 
     Namely, an HMD  100 A includes the control unit  121  configured to determine a relative position of the display unit  330  with respect to the image display unit  20 , process image data based on the relative position determined, and cause the image display unit  20  to display an image corresponding to a position of the display unit  330  of an outside scene. 
     Accordingly, since the HMD  100 A determines the relative position of the display unit  330  with respect to the image display unit  20 , and generates an image for display to correspond to this relative position, display corresponding to the position of the display unit  330  can be achieved without increasing a load on the PC  300 . 
     Additionally, in a configuration in which the PC  300  mirrors and outputs via the HDMI cable  2 A an image identical to the image displayed by the display unit  330 , the HMD  100 A adjusts a display image of the image display unit  20 . Namely, the HMD  100 A changes, in correspondence to a direction of the image display unit  20  and a relative position between the image display unit  20  and the PC  300 , a display mode of the image to be displayed by the image display unit  20 . 
     Therefore, the display system  1 A can achieve the effect of the display system  1  described in the first exemplary embodiment. Further, since the image data can be processed in the HMD  100 A, when general-purpose equipment configured to output image data is connected instead of the PC  300 , there is an advantage that a display mode can be changed in correspondence to the position or the direction of the image display unit  20 . 
     Note that the invention is not limited to the configurations in the above-described exemplary embodiments, and the invention can be implemented in various aspects without departing from the gist of the invention. 
     For example, in the above-described exemplary embodiments, the configuration in which the user visually recognizes the outside scene through the display unit is not limited to the configuration in which the right light-guiding plate  261  and the left light-guiding plate  281  transmit the outside light. For example, the invention is applicable to a display device configured to display an image in a state where an outside scene cannot be recognized visually. Specifically, the invention is applicable to a display device configured to display a captured image of the camera  61  for capturing an outside scene, an image or CG generated based on this captured image, an image based on image data stored in advance or based on image data input from an outside, or the like. This kind of display device can include a so-called closed type display device in which an outside scene cannot be recognized visually. Additionally, as described in the above-described exemplary embodiments, AR display in which an image is superimposed on a real space and is displayed in the real space, or Mixed Reality (MR) display in which a captured image in a real space and a virtual image are combined may be used. Alternatively, the invention is applicable to a display device configured to perform no processing of Virtual Reality (VR) display for displaying a virtual image. For example, a display device configured to display image data input from an outside or an analogue image signal is also, as a matter of course, encompassed as the application of the invention. 
     Additionally, instead of the image display unit  20 , for example, an image display unit of another type such as an image display unit worn as a hat may be adopted, as long as the image display unit includes a display unit configured to display an image in correspondence to a left eye of a user, and a display unit configured to display an image in correspondence to a right eye of the user. Additionally, the display device in the invention may be configured, for example, as a head mounted display mounted on a vehicle such as a car, and an airplane. Additionally, the display device in the invention may be configured, for example, as a head mounted display built in a body protector such as a helmet. In this case, a portion positioning a position with respect to a body of a user, and a portion positioned with respect to such a portion can be mounted parts. 
     Further, the HMD  100 A in the fourth exemplary embodiment may include a configuration in which the control device  10 A and the image display unit  20  are integrally constituted and are worn on a head of a user. Additionally, a note type computer, a tablet computer, a portable electronic device including a game machine, a portable telephone, a smartphone, and a portable media player, other dedicated equipment, or the like may be used as the control device  10 A. Additionally, in the above-described exemplary embodiments, a configuration in which the connecting device  10  and the image display unit  20  are connected via a radio communication line may be adopted. 
     Additionally, equipment connected with the HMD  100  or  100 A in the display system  1  is not limited to the PC  300 . The equipment may be, for example, a stationary television set, or a monitor for a stationary personal computer. Additionally, a projector configured to project an image on a display surface may be used instead of the PC  300 , and in this case, the projection surface on which the projector projects the image corresponds to the first display unit. Additionally, other than the above-described equipment, instead of the PC  300 , a portable or a stationary electronic device can be used. The PC  300  or various electronic devices used instead of the PC  300  may be connected wirelessly with the HMD  100  or  100 A. For example, instead of the connector  11 A, a radio image communication interface such as Miracast (trade name) or WirelessHD (trade name) may be used. Additionally, instead of the connector  11 B, a wireless LAN (including WiFi (trade name)) may be used, or Bluetooth (trade name) may be used. 
     Additionally, at least a portion of each function block illustrated in the block diagram may be configured to be achieved with hardware, or may be configured to be achieved in cooperation of hardware and software, and the invention is not limited to the configuration in which independent hardware resources are disposed as illustrated in the figure. 
     The entire disclosure of Japanese Patent Application No.:2017-246853, filed Dec. 22, 2017 and 2018-172773, filed Sep. 14, 2018 are expressly incorporated by reference herein.