Patent Publication Number: US-11043194-B2

Title: Image display system, storage medium having stored therein image display program, image display method, and display device

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The disclosure of Japanese Patent Application No. 2019-033866, filed on Feb. 27, 2019 and the disclosure of Japanese Patent Application No. 2019-33867, filed on Feb. 27, 2019, are incorporated herein by reference. 
     FIELD 
     The technology shown here relates to an image display system, a storage medium having stored therein an image display program, an image display method, and a display device that are capable of displaying a stereoscopic image. 
     BACKGROUND AND SUMMARY 
     Conventionally, there is a three-dimensional image display device that causes a user to visually confirm two images having parallax with each other with their left and right eyes, thereby displaying a three-dimensional image. For example, in the three-dimensional image display device, a smartphone is accommodated in a goggle apparatus that the user can wear, and the user looks into a stereoscopic image displayed on a display screen of the smartphone through the goggle apparatus and thereby can view the stereoscopically displayed image. 
     The three-dimensional image display device, however, does not at all take into account the presentation of a user interface image for receiving a touch operation of the user when the stereoscopic image is displayed on the display screen. Thus, there is room for improvement in convenience regarding a method for presenting a user interface image. 
     Therefore, it is an object of an exemplary embodiment to provide an image display system, a storage medium having stored therein an image display program, an image display method, and a display device that are capable of improving convenience regarding the presentation of a user interface image. 
     To achieve the above object, the exemplary embodiment can employ, for example, the following configurations. It should be noted that it is understood that, to interpret the descriptions of the claims, the scope of the claims should be interpreted only by the descriptions of the claims. If there is a conflict between the descriptions of the claims and the descriptions of the specification, the descriptions of the claims take precedence. 
     In an exemplary configuration of an image display system according to the exemplary embodiment, an image display system includes a display device having a display screen configured to display an image, and a goggle apparatus to which the display device is attachable. The image display system includes a computer configured to: set the display device to a first display mode or a second display mode different from the first display mode; in the first display mode, display on the display screen a first image including a content image that is a non-stereoscopic image, and a first user interface image; and in the second display mode, display on the display screen a second image including a content image composed of a left-eye image and a right-eye image having parallax with each other, and a second user interface image corresponding to the first user interface image. In the second display mode, the second user interface image is displayed at a position different from a position on the display screen where the first user interface image is displayed in the first display mode. 
     Based on the above, when a display mode is switched, a user interface image is displayed at different positions. Thus, it is possible to improve convenience regarding the presentation of a user interface image. 
     Further, the computer is further configured to detect whether or not the display device is in an attached state where the display device is attached to the goggle apparatus, or detect whether or not the display device is in a halfway attached state where the display device is being attached to the goggle apparatus. In this case, when the display device is set to the first display mode, the display device may be switched to the second display mode based on the detection result. 
     Based on the above, based on an attached state where a display device is attached to a goggle apparatus or a halfway attached state where the display device is being attached to the goggle apparatus, the display mode is switched. Thus, it is possible to seamlessly switch the display mode. 
     Further, the display device may include an illuminance sensor. In this case, the goggle apparatus may include a light-shielding member. The light-shielding member is configured to, when the display device is in the attached state where the display device is attached to the goggle apparatus, or is in the halfway attached state where the display device is being attached to the goggle apparatus, block light from the display device to the illuminance sensor. Based on a detection result of the illuminance sensor, it may be detected whether or not the display device is in the attached state where the display device is attached to the goggle apparatus, or it may be detected whether or not the display device is in the halfway attached state where the display device is being attached to the goggle apparatus. 
     Based on the above, based on a light blocking state of the display device, it is possible to easily detect whether or not the display device is in the attached state, or whether or not the display device is in the halfway attached state. 
     Further, the display device may include a touch panel on the display screen. In this case, the first user interface image displayed on the display screen may enable an operation instruction corresponding to a touch operation on the touch panel. The second user interface image displayed on the display screen may enable an operation instruction corresponding to a touch operation on the touch panel in a state where the display device is attached to the goggle apparatus. 
     Based on the above, it is possible to improve convenience regarding the presentation of a user interface image for receiving a touch operation. 
     Further, as the content image composed of the left-eye image and the right-eye image, an image corresponding to the content image displayed as the non-stereoscopic image may be displayed on the display screen. 
     Based on the above, it is possible to seamlessly switch a stereoscopic image and a non-stereoscopic image for the same content image. 
     Further, in the second display mode, the content image displayed in the first display mode immediately before being set in the second display mode may be displayed as a stereoscopic image composed of a left-eye image and a right-eye image on the display screen. 
     Based on the above, it is possible to seamlessly switch a stereoscopic image and a non-stereoscopic image for the same content image. 
     Further, in the second display mode, the left-eye image may be displayed in a first area of the display screen, the right-eye image may be displayed in a second area of the display screen that is different from the first area, and the second user interface image may be displayed in a third area of the display screen that is different from the first area and the second area. 
     Based on the above, it is possible to prevent a first area and a second area for displaying a stereoscopic image from being defaced by being subjected to a touch operation, and also prevent a finger for performing a touch operation on a second user interface image from entering the field of view in the state where the stereoscopic image is viewed. 
     Further, a user interface image that has substantially the same function as and has a different shape from the first user interface image may be displayed as the second user interface image. 
     Based on the above, it is possible to display a user interface image having a shape suitable for an operation and the display of a stereoscopic image. 
     Further, in the second display mode, by adjusting a shape of the second user interface image to match a shape of a third area of the display screen that is different from the first area of the display screen for displaying the left-eye image and the second area of the display screen for displaying the right-eye image, the second user interface image may be displayed in the third area. 
     Based on the above, it is possible to display a user interface image having an appropriate shape. 
     Further, the third area may be set in an upper portion or a lower portion of the display screen that is sandwiched between the first area and the second area of the display screen. 
     Based on the above, it is possible to display a user interface image that does not hinder the display of a stereoscopic image. 
     Further, the third area may be set in a lower portion of the display screen that is sandwiched between the first area and the second area of the display screen. 
     Based on the above, it is possible to display a user interface image that does not hinder the display of a stereoscopic image and facilitates an operation. 
     Further, the goggle apparatus may include an opening portion configured to, when the display device is attached to the goggle apparatus, expose the third area that is a part of the display screen at least to outside. 
     Based on the above, it is possible to perform a touch operation for touching a user interface image in the state where a display device is attached to a goggle apparatus. 
     Further, the opening portion may be formed at a position corresponding to a nose of a user when the user wears the goggle apparatus. 
     Based on the above, it is possible to form an opening portion without impairing a light blocking effect. 
     Further, in the first display mode, the first user interface image may be displayed in a superimposed manner on a content image displayed on the display screen. 
     Based on the above, it is possible to display a relatively large content image without being influenced by the display of a user interface image. 
     Further, in the second display mode, the second user interface image may be displayed as a non-stereoscopic image on the display screen. 
     Based on the above, the operation of touching a user interface image is facilitated. 
     Further, the display device may further include a display device side connection end configured to electrically connect to another apparatus. In this case, the goggle apparatus may include a goggle apparatus side connection end configured to electrically connect to the display device side connection end. In accordance with a connection between the display device side connection end and the goggle apparatus side connection end, it may be detected whether or not the display device is in an attached state where the display device is attached to the goggle apparatus, or it may be detected whether or not the display device is in a halfway attached state where the display device is being attached to the goggle apparatus. 
     Based on the above, it is possible to certainly detect that a display device is attached to a goggle apparatus, or certainly detect that the display device is in a halfway attached state where the display device is being attached to the goggle apparatus. 
     Further, the exemplary embodiment may be carried out in the forms of a storage medium having stored therein an image display program, an image display method, and a display device. 
     According to the exemplary embodiment, when a display mode is switched, a user interface image is displayed at different positions. Thus, it is possible to improve convenience regarding the presentation of a user interface image. 
     These and other objects, features, aspects and advantages of the exemplary embodiments will become more apparent from the following detailed description of the exemplary embodiments when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing a non-limiting example of the state where a left controller  3  and a right controller  4  are attached to a main body apparatus  2 ; 
         FIG. 2  is a diagram showing a non-limiting example of the state where each of the left controller  3  and the right controller  4  is detached from the main body apparatus  2 ; 
         FIG. 3  is six orthogonal views showing a non-limiting example of the main body apparatus  2 ; 
         FIG. 4  is six orthogonal views showing a non-limiting example of the left controller  3 ; 
         FIG. 5  is six orthogonal views showing a non-limiting example of the right controller  4 ; 
         FIG. 6  is a block diagram showing a non-limiting example of the internal configuration of the main body apparatus  2 ; 
         FIG. 7  is a block diagram showing non-limiting examples of the internal configurations of the main body apparatus  2  and the left controller  3  and the right controller  4 ; 
         FIG. 8  is a perspective view showing a non-limiting example of the external appearance of a goggle apparatus  150 ; 
         FIG. 9  is a front view showing a non-limiting example of the state where the main body apparatus  2  is attached to the goggle apparatus  150 ; 
         FIG. 10  is a front view showing a non-limiting example of the state of the main body apparatus  2  attached to the goggle apparatus  150 ; 
         FIG. 11  is a diagram showing a non-limiting example of the shape of a front surface abutment portion  151   b  that is in surface contact with a part of a front surface of the main body apparatus  2 ; 
         FIG. 12  is a diagram showing a non-limiting example of the internal structure of the goggle apparatus  150 ; 
         FIG. 13  is a side view showing a non-limiting example of the state of the main body apparatus  2  attached to the goggle apparatus  150 ; 
         FIG. 14  is a diagram showing a non-limiting example of the state of a user viewing an image displayed by an image display system; 
         FIG. 15  is a diagram showing a non-limiting example of the state of the user holding the image display system; 
         FIG. 16  is a diagram showing non-limiting examples of images displayed on the main body apparatus  2  in a stereoscopic display mode and a non-stereoscopic display mode; 
         FIG. 17  is a diagram showing a non-limiting example of a data area of a DRAM  85  of the main body apparatus  2 ; and 
         FIG. 18  is a flow chart showing a non-limiting example of game processing executed by the game system  1 . 
     
    
    
     DETAILED DESCRIPTION OF NON-LIMITING EXAMPLE EMBODIMENTS 
     An image display system according to an exemplary embodiment is described below. An example of the image display system according to the exemplary embodiment includes a game system  1  (as a minimum configuration, a main body apparatus  2  included in the game system  1 ) and a goggle apparatus  150 . An example of the game system  1  includes a main body apparatus (an information processing apparatus; which functions as a game apparatus main body in the exemplary embodiment)  2 , a left controller  3 , and a right controller  4 . Each of the left controller  3  and the right controller  4  is attachable to and detachable from the main body apparatus  2 . That is, the game system  1  can be used as a unified apparatus obtained by attaching each of the left controller  3  and the right controller  4  to the main body apparatus  2 . Further, in the game system  1 , the main body apparatus  2 , the left controller  3 , and the right controller  4  can also be used as separate bodies (see  FIG. 2 ). Hereinafter, first, the hardware configuration of the game system  1  according to the exemplary embodiment is described, and then, the control of the game system  1  according to the exemplary embodiment is described. 
       FIG. 1  is a diagram showing an example of the state where the left controller  3  and the right controller  4  are attached to the main body apparatus  2 . As shown in  FIG. 1 , each of the left controller  3  and the right controller  4  is attached to and unified with the main body apparatus  2 . The main body apparatus  2  is an apparatus for performing various processes (e.g., game processing) in the game system  1 . The main body apparatus  2  includes a display  12 . Each of the left controller  3  and the right controller  4  is an apparatus including operation sections with which a user provides inputs. 
       FIG. 2  is a diagram showing an example of the state where each of the left controller  3  and the right controller  4  is detached from the main body apparatus  2 . As shown in  FIGS. 1 and 2 , the left controller  3  and the right controller  4  are attachable to and detachable from the main body apparatus  2 . It should be noted that hereinafter, the left controller  3  and the right controller  4  will occasionally be referred to collectively as a “controller”. 
       FIG. 3  is six orthogonal views showing an example of the main body apparatus  2 . As shown in  FIG. 3 , the main body apparatus  2  includes an approximately plate-shaped housing  11 . In the exemplary embodiment, a main surface (in other words, a surface on a front side, i.e., a surface on which the display  12  is provided) of the housing  11  has a generally rectangular shape. 
     It should be noted that the shape and the size of the housing  11  are optional. As an example, the housing  11  may be of a portable size. Further, the main body apparatus  2  alone or the unified apparatus obtained by attaching the left controller  3  and the right controller  4  to the main body apparatus  2  may function as a mobile apparatus. The main body apparatus  2  or the unified apparatus may function as a handheld apparatus or a portable apparatus. 
     As shown in  FIG. 3 , the main body apparatus  2  includes the display  12 , which is provided on the main surface of the housing  11 . The display  12  displays an image generated by the main body apparatus  2 . In the exemplary embodiment, the display  12  is a liquid crystal display device (LCD). The display  12 , however, may be a display device of any type. 
     Further, the main body apparatus  2  includes a touch panel  13  on a screen of the display  12 . In the exemplary embodiment, the touch panel  13  is of a type that allows a multi-touch input (e.g., a capacitive type). The touch panel  13 , however, may be of any type. For example, the touch panel  13  may be of a type that allows a single-touch input (e.g., a resistive type). 
     The main body apparatus  2  includes speakers (i.e., speakers  88  shown in  FIG. 6 ) within the housing  11 . As shown in  FIG. 3 , speaker holes  11   a  and  11   b  are formed on the main surface of the housing  11 . Then, sounds output from the speakers  88  are output through the speaker holes  11   a  and  11   b.    
     Further, the main body apparatus  2  includes a left terminal  17 , which is a terminal for the main body apparatus  2  to perform wired communication with the left controller  3 , and a right terminal  21 , which is a terminal for the main body apparatus  2  to perform wired communication with the right controller  4 . 
     As shown in  FIG. 3 , the main body apparatus  2  includes a slot  23 . The slot  23  is provided on an upper side surface of the housing  11 . The slot  23  is so shaped as to allow a predetermined type of storage medium to be attached to the slot  23 . The predetermined type of storage medium is, for example, a dedicated storage medium (e.g., a dedicated memory card) for the game system  1  and an information processing apparatus of the same type as the game system  1 . The predetermined type of storage medium is used to store, for example, data (e.g., saved data of an application or the like) used by the main body apparatus  2  and/or a program (e.g., a program for an application or the like) executed by the main body apparatus  2 . Further, the main body apparatus  2  includes a power button  28 . 
     The main body apparatus  2  includes a lower terminal  27 . The lower terminal  27  is a terminal for the main body apparatus  2  to communicate with a cradle. In the exemplary embodiment, the lower terminal  27  is a USB connector (more specifically, a female connector). Further, when the unified apparatus or the main body apparatus  2  alone is mounted on the cradle, the game system  1  can display on a stationary monitor an image generated by and output from the main body apparatus  2 . Further, in the exemplary embodiment, the cradle has the function of charging the unified apparatus or the main body apparatus  2  alone mounted on the cradle. Further, the cradle has the function of a hub device (specifically, a USB hub). 
     The main body apparatus  2  includes an illuminance sensor  29 . In the exemplary embodiment, the illuminance sensor  29  is provided in a lower portion of the main surface of the housing  11  and detects the illuminance (brightness) of light incident on the main surface side of the housing  11 . It should be noted that an image can be displayed by setting the display  12  to an appropriate brightness in accordance with the illuminance of the light detected by the illuminance sensor  29 . In the exemplary embodiment, based on the detected illuminance, it is determined whether or not the main body apparatus  2  is attached to the goggle apparatus  150  described below. 
       FIG. 4  is six orthogonal views showing an example of the left controller  3 . As shown in  FIG. 4 , the left controller  3  includes a housing  31 . In the exemplary embodiment, the housing  31  has a vertically long shape, i.e., is shaped to be long in an up-down direction (i.e., a y-axis direction shown in  FIGS. 1 and 4 ). In the state where the left controller  3  is detached from the main body apparatus  2 , the left controller  3  can also be held in the orientation in which the left controller  3  is vertically long. The housing  31  has such a shape and a size that when held in the orientation in which the housing  31  is vertically long, the housing  31  can be held with one hand, particularly the left hand. Further, the left controller  3  can also be held in the orientation in which the left controller  3  is horizontally long. When held in the orientation in which the left controller  3  is horizontally long, the left controller  3  may be held with both hands. 
     The left controller  3  includes an analog stick  32 . As shown in  FIG. 4 , the analog stick  32  is provided on a main surface of the housing  31 . The analog stick  32  can be used as a direction input section with which a direction can be input. The user tilts the analog stick  32  and thereby can input a direction corresponding to the direction of the tilt (and input a magnitude corresponding to the angle of the tilt). It should be noted that the left controller  3  may include a directional pad, a slide stick that allows a slide input, or the like as the direction input section, instead of the analog stick. Further, in the exemplary embodiment, it is possible to provide an input by pressing the analog stick  32 . 
     The left controller  3  includes various operation buttons. The left controller  3  includes four operation buttons  33  to  36  (specifically, a right direction button  33 , a down direction button  34 , an up direction button  35 , and a left direction button  36 ) on the main surface of the housing  31 . Further, the left controller  3  includes a record button  37  and a “−” (minus) button  47 . The left controller  3  includes a first L-button  38  and a ZL-button  39  in an upper left portion of a side surface of the housing  31 . Further, the left controller  3  includes a second L-button  43  and a second R-button  44 , on the side surface of the housing  31  on which the left controller  3  is attached to the main body apparatus  2 . These operation buttons are used to give instructions depending on various programs (e.g., an OS program and an application program) executed by the main body apparatus  2 . 
     Further, the left controller  3  includes a terminal  42  for the left controller  3  to perform wired communication with the main body apparatus  2 . 
       FIG. 5  is six orthogonal views showing an example of the right controller  4 . As shown in  FIG. 5 , the right controller  4  includes a housing  51 . In the exemplary embodiment, the housing  51  has a vertically long shape, i.e., is shaped to be long in the up-down direction. In the state where the right controller  4  is detached from the main body apparatus  2 , the right controller  4  can also be held in the orientation in which the right controller  4  is vertically long. The housing  51  has such a shape and a size that when held in the orientation in which the housing  51  is vertically long, the housing  51  can be held with one hand, particularly the right hand. Further, the right controller  4  can also be held in the orientation in which the right controller  4  is horizontally long. When held in the orientation in which the right controller  4  is horizontally long, the right controller  4  may be held with both hands. 
     Similarly to the left controller  3 , the right controller  4  includes an analog stick  52  as a direction input section. In the exemplary embodiment, the analog stick  52  has the same configuration as that of the analog stick  32  of the left controller  3 . Further, the right controller  4  may include a directional pad, a slide stick that allows a slide input, or the like, instead of the analog stick. Further, similarly to the left controller  3 , the right controller  4  includes four operation buttons  53  to  56  (specifically, an A-button  53 , a B-button  54 , an X-button  55 , and a Y-button  56 ) on a main surface of the housing  51 . Further, the right controller  4  includes a “+” (plus) button  57  and a home button  58 . Further, the right controller  4  includes a first R-button  60  and a ZR-button  61  in an upper right portion of a side surface of the housing  51 . Further, similarly to the left controller  3 , the right controller  4  includes a second L-button  65  and a second R-button  66 . 
     Further, the right controller  4  includes a terminal  64  for the right controller  4  to perform wired communication with the main body apparatus  2 . 
       FIG. 6  is a block diagram showing an example of the internal configuration of the main body apparatus  2 . The main body apparatus  2  includes components  81  to  91 ,  97 , and  98  shown in  FIG. 6  in addition to the components shown in  FIG. 3 . Some of the components  81  to  91 ,  97 , and  98  may be mounted as electronic components on an electronic circuit board and accommodated in the housing  11 . 
     The main body apparatus  2  includes a processor  81 . The processor  81  is an information processing section for executing various types of information processing to be executed by the main body apparatus  2 . For example, the processor  81  may be composed only of a CPU (Central Processing Unit), or may be composed of a SoC (System-on-a-chip) having a plurality of functions such as a CPU function and a GPU (Graphics Processing Unit) function. The processor  81  executes an information processing program (e.g., a game program) stored in a storage section (specifically, an internal storage medium such as a flash memory  84 , an external storage medium attached to the slot  23 , or the like), thereby performing the various types of information processing. 
     The main body apparatus  2  includes a flash memory  84  and a DRAM (Dynamic Random Access Memory)  85  as examples of internal storage media built into the main body apparatus  2 . The flash memory  84  and the DRAM  85  are connected to the processor  81 . The flash memory  84  is a memory mainly used to store various data (or programs) to be saved in the main body apparatus  2 . The DRAM  85  is a memory used to temporarily store various data used for information processing. 
     The main body apparatus  2  includes a slot interface (hereinafter abbreviated as “I/F”)  91 . The slot I/F  91  is connected to the processor  81 . The slot I/F  91  is connected to the slot  23 , and in accordance with an instruction from the processor  81 , reads and writes data from and to the predetermined type of storage medium (e.g., a dedicated memory card) attached to the slot  23 . 
     The processor  81  appropriately reads and writes data from and to the flash memory  84 , the DRAM  85 , and each of the above storage media, thereby performing the above information processing. 
     The main body apparatus  2  includes a network communication section  82 . The network communication section  82  is connected to the processor  81 . The network communication section  82  communicates (specifically, through wireless communication) with an external apparatus via a network. In the exemplary embodiment, as a first communication form, the network communication section  82  connects to a wireless LAN and communicates with an external apparatus, using a method compliant with the Wi-Fi standard. Further, as a second communication form, the network communication section  82  wirelessly communicates with another main body apparatus  2  of the same type, using a predetermined communication method (e.g., communication based on a unique protocol or infrared light communication). It should be noted that the wireless communication in the above second communication form achieves the function of enabling so-called “local communication” in which the main body apparatus  2  can wirelessly communicate with another main body apparatus  2  placed in a closed local network area, and the plurality of main body apparatuses  2  directly communicate with each other to transmit and receive data. 
     The main body apparatus  2  includes a controller communication section  83 . The controller communication section  83  is connected to the processor  81 . The controller communication section  83  wirelessly communicates with the left controller  3  and/or the right controller  4 . The communication method between the main body apparatus  2  and the left controller  3  and the right controller  4  is optional. In the exemplary embodiment, the controller communication section  83  performs communication compliant with the Bluetooth (registered trademark) standard with the left controller  3  and with the right controller  4 . 
     The processor  81  is connected to the left terminal  17 , the right terminal  21 , and the lower terminal  27 . When performing wired communication with the left controller  3 , the processor  81  transmits data to the left controller  3  via the left terminal  17  and also receives operation data from the left controller  3  via the left terminal  17 . Further, when performing wired communication with the right controller  4 , the processor  81  transmits data to the right controller  4  via the right terminal  21  and also receives operation data from the right controller  4  via the right terminal  21 . Further, when communicating with the cradle, the processor  81  transmits data to the cradle via the lower terminal  27 . As described above, in the exemplary embodiment, the main body apparatus  2  can perform both wired communication and wireless communication with each of the left controller  3  and the right controller  4 . Further, when the unified apparatus obtained by attaching the left controller  3  and the right controller  4  to the main body apparatus  2  or the main body apparatus  2  alone is attached to the cradle, the main body apparatus  2  can output data (e.g., image data or sound data) to the stationary monitor or the like via the cradle. 
     Here, the main body apparatus  2  can communicate with a plurality of left controllers  3  simultaneously (in other words, in parallel). Further, the main body apparatus  2  can communicate with a plurality of right controllers  4  simultaneously (in other words, in parallel). Thus, a plurality of users can simultaneously provide inputs to the main body apparatus  2 , each using a set of the left controller  3  and the right controller  4 . As an example, a first user can provide an input to the main body apparatus  2  using a first set of the left controller  3  and the right controller  4 , and simultaneously, a second user can provide an input to the main body apparatus  2  using a second set of the left controller  3  and the right controller  4 . 
     The main body apparatus  2  includes a touch panel controller  86 , which is a circuit for controlling the touch panel  13 . The touch panel controller  86  is connected between the touch panel  13  and the processor  81 . Based on a signal from the touch panel  13 , the touch panel controller  86  generates, for example, data indicating the position where a touch input is provided. Then, the touch panel controller  86  outputs the data to the processor  81 . 
     Further, the display  12  is connected to the processor  81 . The processor  81  displays a generated image (e.g., an image generated by executing the above information processing) and/or an externally acquired image on the display  12 . 
     The main body apparatus  2  includes a codec circuit  87  and speakers (specifically, a left speaker and a right speaker)  88 . The codec circuit  87  is connected to the speakers  88  and a sound input/output terminal  25  and also connected to the processor  81 . The codec circuit  87  is a circuit for controlling the input and output of sound data to and from the speakers  88  and the sound input/output terminal  25 . 
     Further, the main body apparatus  2  includes an acceleration sensor  89 . In the exemplary embodiment, the acceleration sensor  89  detects the magnitudes of accelerations along predetermined three axial (e.g., xyz axes shown in  FIG. 1 ) directions. It should be noted that the acceleration sensor  89  may detect an acceleration along one axial direction or accelerations along two axial directions. 
     Further, the main body apparatus  2  includes an angular velocity sensor  90 . In the exemplary embodiment, the angular velocity sensor  90  detects angular velocities about predetermined three axes (e.g., the xyz axes shown in  FIG. 1 ). It should be noted that the angular velocity sensor  90  may detect an angular velocity about one axis or angular velocities about two axes. 
     The acceleration sensor  89  and the angular velocity sensor  90  are connected to the processor  81 , and the detection results of the acceleration sensor  89  and the angular velocity sensor  90  are output to the processor  81 . Based on the detection results of the acceleration sensor  89  and the angular velocity sensor  90 , the processor  81  can calculate information regarding the motion and/or the orientation of the main body apparatus  2 . 
     The illuminance sensor  29  is connected to the processor  81 , and the detection result of the illuminance sensor  29  is output to the processor  81 . Based on the detection result of the illuminance sensor  29 , the processor  81  can calculate information regarding the brightness of the periphery of the main body apparatus  2 . 
     The main body apparatus  2  includes a power control section  97  and a battery  98 . The power control section  97  is connected to the battery  98  and the processor  81 . Further, although not shown in  FIG. 6 , the power control section  97  is connected to components of the main body apparatus  2  (specifically, components that receive power supplied from the battery  98 , the left terminal  17 , and the right terminal  21 ). Based on a command from the processor  81 , the power control section  97  controls the supply of power from the battery  98  to the above components. 
     Further, the battery  98  is connected to the lower terminal  27 . When an external charging device (e.g., the cradle) is connected to the lower terminal  27 , and power is supplied to the main body apparatus  2  via the lower terminal  27 , the battery  98  is charged with the supplied power. 
       FIG. 7  is a block diagram showing examples of the internal configurations of the main body apparatus  2 , the left controller  3 , and the right controller  4 . It should be noted that the details of the internal configuration of the main body apparatus  2  are shown in  FIG. 6  and therefore are omitted in  FIG. 7 . 
     The left controller  3  includes a communication control section  101 , which communicates with the main body apparatus  2 . As shown in  FIG. 7 , the communication control section  101  is connected to components including the terminal  42 . In the exemplary embodiment, the communication control section  101  can communicate with the main body apparatus  2  through both wired communication via the terminal  42  and wireless communication not via the terminal  42 . The communication control section  101  controls the method for communication performed by the left controller  3  with the main body apparatus  2 . That is, when the left controller  3  is attached to the main body apparatus  2 , the communication control section  101  communicates with the main body apparatus  2  via the terminal  42 . Further, when the left controller  3  is detached from the main body apparatus  2 , the communication control section  101  wirelessly communicates with the main body apparatus  2  (specifically, the controller communication section  83 ). The wireless communication between the communication control section  101  and the controller communication section  83  is performed in accordance with the Bluetooth (registered trademark) standard, for example. 
     Further, the left controller  3  includes a memory  102  such as a flash memory. The communication control section  101  includes, for example, a microcomputer (or a microprocessor) and executes firmware stored in the memory  102 , thereby performing various processes. 
     The left controller  3  includes buttons  103  (specifically, the buttons  33  to  39 ,  43 ,  44 , and  47 ). Further, the left controller  3  includes the analog stick (“stick” in  FIG. 7 )  32 . Each of the buttons  103  and the analog stick  32  outputs information regarding an operation performed on itself to the communication control section  101  repeatedly at appropriate timing. 
     The communication control section  101  acquires information regarding an input (specifically, information regarding an operation or the detection result of the sensor) from each of input sections (specifically, the buttons  103 , the analog stick  32 , and the sensors  104  and  105 ). The communication control section  101  transmits operation data including the acquired information (or information obtained by performing predetermined processing on the acquired information) to the main body apparatus  2 . It should be noted that the operation data is transmitted repeatedly, once every predetermined time. It should be noted that the interval at which the information regarding an input is transmitted from each of the input sections to the main body apparatus  2  may or may not be the same. 
     The above operation data is transmitted to the main body apparatus  2 , whereby the main body apparatus  2  can obtain inputs provided to the left controller  3 . That is, the main body apparatus  2  can determine operations on the buttons  103  and the analog stick  32  based on the operation data. Further, the main body apparatus  2  can calculate information regarding the motion and/or the orientation of the left controller  3  based on the operation data (specifically, the detection results of the acceleration sensor  104  and the angular velocity sensor  105 ). 
     The left controller  3  includes a power supply section  108 . In the exemplary embodiment, the power supply section  108  includes a battery and a power control circuit. Although not shown in  FIG. 7 , the power control circuit is connected to the battery and also connected to components of the left controller  3  (specifically, components that receive power supplied from the battery). 
     As shown in  FIG. 7 , the right controller  4  includes a communication control section  111 , which communicates with the main body apparatus  2 . Further, the right controller  4  includes a memory  112 , which is connected to the communication control section  111 . The communication control section  111  is connected to components including the terminal  64 . The communication control section  111  and the memory  112  have functions similar to those of the communication control section  101  and the memory  102 , respectively, of the left controller  3 . Thus, the communication control section  111  can communicate with the main body apparatus  2  through both wired communication via the terminal  64  and wireless communication not via the terminal  64  (specifically, communication compliant with the Bluetooth (registered trademark) standard). The communication control section  111  controls the method for communication performed by the right controller  4  with the main body apparatus  2 . 
     The right controller  4  includes input sections similar to the input sections of the left controller  3 . Specifically, the right controller  4  includes buttons  113  and the analog stick  52 . These input sections have functions similar to those of the input sections of the left controller  3  and operate similarly to the input sections of the left controller  3 . 
     The right controller  4  includes a power supply section  118 . The power supply section  118  has a function similar to that of the power supply section  108  of the left controller  3  and operates similarly to the power supply section  108 . 
     Next, with reference to  FIGS. 8 to 15 , a description is given of the goggle apparatus  150 , which is an example of an apparatus forming the image display system by attaching the game system  1  (specifically, the main body apparatus  2 ) to the apparatus. It should be noted that  FIG. 8  is a perspective view showing an example of the external appearance of the goggle apparatus  150 .  FIG. 9  is a front view showing an example of the state where the main body apparatus  2  is attached to the goggle apparatus  150 .  FIG. 10  is a front view showing an example of the state of the main body apparatus  2  attached to the goggle apparatus  150 .  FIG. 11  is a diagram showing an example of the shape of a front surface abutment portion  151   b  that is in surface contact with a part of a front surface of the main body apparatus  2 .  FIG. 12  is a diagram showing an example of the internal structure of the goggle apparatus  150 .  FIG. 13  is a side view showing an example of the state of the main body apparatus  2  attached to the goggle apparatus  150 .  FIG. 14  is a diagram showing an example of the state of a user viewing an image displayed by the image display system.  FIG. 15  is a diagram showing an example of the state of the user holding the image display system. It should be noted that  FIG. 11  is a diagram viewed from the same direction as in  FIG. 10  in the state (a transparent state) where a part of the goggle apparatus  150  (a part of a main body  151 , a lens frame member  152 , a lens  153 , and a plate-like member  154 ) is removed to show the front surface abutment portion  151   b  in an easily understandable manner. 
     In  FIGS. 8 to 13 , the goggle apparatus  150  includes a main body  151 , a lens frame member  152 , a lens  153 , and a plate-like member  154 . Here, the goggle apparatus, which is an example of the apparatus included in the image display system, is not limited to a configuration described below so long as the goggle apparatus is worn fitted to the face of the user by covering the left and right eyes of the user, and has the function of blocking at least a part of external light and the function of supporting a stereoscopic view for the user with a pair of lenses. For example, the types of the goggle apparatus may include those used in various states, such as a goggle apparatus that is fitted to the face of the user by the user holding the goggle apparatus, a goggle apparatus that is fitted to the face of the user by fixing the goggle apparatus to the head of the user, and a goggle apparatus into which the user looks in the state where the goggle apparatus is placed. Further, the goggle apparatus may function as a so-called head-mounted display by being worn on the head of the user in the state where the main body apparatus  2  is attached to the goggle apparatus, or may have a helmet-like shape as well as the goggle-like shape. In the following description of the goggle apparatus  150 , a goggle-type goggle apparatus that is worn by the user while fitted to the face of the user by the user holding the goggle apparatus is used. 
     The main body  151  includes an attachment portion to which the main body apparatus  2  is detachably fixed by the attachment portion being in contact with a front surface, a back surface, an upper surface, and a lower surface of the main body apparatus  2 . The attachment portion includes a front surface abutment portion that is in surface contact with a part of the front surface (the surface on which the display  12  is provided) of the main body apparatus  2 , a back surface abutment portion that is in surface contact with the back surface of the main body apparatus  2 , an upper surface abutment portion that is in surface contact with the upper surface of the main body apparatus  2 , and a lower surface abutment portion that is in surface contact with the lower surface of the main body apparatus  2 . The attachment portion is formed into an angular tube which includes a gap formed by being surrounded by the front surface abutment portion, the back surface abutment portion, the upper surface abutment portion, and the lower surface abutment portion, and of which both left and right side surfaces are opened. Both side surfaces of the attachment portion (a side surface further in a positive x-axis direction shown in  FIG. 8 , and a side surface further in a negative x-axis direction shown in  FIG. 8 ) open so that the attachment portion is attachable from the left side surface side or the right side surface side of the main body apparatus  2 . Then, as shown in  FIG. 9 , when the main body apparatus  2  is attached to the goggle apparatus  150  from the opening on the right side surface side of the main body apparatus  2 , the front surface abutment portion is in contact with the front surface of the main body apparatus  2 , the back surface abutment portion is in contact with the back surface of the main body apparatus  2 , the upper surface abutment portion is in contact with the upper surface of the main body apparatus  2 , and the lower surface abutment portion is in contact with the lower surface of the main body apparatus  2 . It should be noted that as shown in  FIG. 11 , in a front surface abutment portion  151   b  of the main body  151 , an opening portion is formed so as not to hinder at least the field of view for display images (a left-eye image and a right-eye image) on the display  12  when the main body apparatus  2  is attached. 
     As shown in  FIGS. 9 and 13 , the main body apparatus  2  is attached to the goggle apparatus  150  by inserting the main body apparatus  2  in a sliding manner into the gap of the attachment portion of the main body  151  from the left side surface side or the right side surface side of the main body apparatus  2  along the front surface abutment portion, the back surface abutment portion, the upper surface abutment portion, and the lower surface abutment portion of the attachment portion. Further, the main body apparatus  2  can be detached from the goggle apparatus  150  by sliding the main body apparatus  2  to the left or the right along the front surface abutment portion, the back surface abutment portion, the upper surface abutment portion, and the lower surface abutment portion of the attachment portion from the state where the main body apparatus  2  is attached to the goggle apparatus  150 . As described above, the main body apparatus  2  can be detachably attached to the goggle apparatus  150 . 
     The lens frame member  152  is fixedly provided on the opening portion side formed in a front surface portion of the main body  151 . The lens frame member  152  includes a pair of lens frames opened so as not to hinder the field of view for display images (a left-eye image IML and a right-eye image IMR) displayed on the display  12  of the main body apparatus  2  attached to the main body  151 . Further, on outer edges formed in upper, lower, left, and right portions of the lens frame member  152 , joint surfaces to be joined to the main body apparatus  2  are formed, and in a central portion of the outer edge formed in the lower portion, a V-shaped recessed portion for coming into contact with the nose of the user wearing the goggle apparatus  150  is formed. 
     The lens  153  includes a pair of a left-eye lens  153 L and a right-eye lens  153 R, and for example, is a pair of Fresnel lenses. The left-eye lens  153 L and the right-eye lens  153 R are fitted into the lens frames of the lens frame member  152 . Specifically, the left-eye lens  153 L is fitted into one of the lens frames opened so as not to hinder the field of view for the left-eye image IML displayed on the display  12  of the main body apparatus  2  attached to the main body  151 . When the user looks into the left-eye lens  153 L with their left eye, the user can view the left-eye image IML. Further, the right-eye lens  153 R is fitted into the other lens frame opened so as not to hinder the field of view for the right-eye image IMR displayed on the display  12  of the main body apparatus  2  attached to the main body  151 . When the user looks into the right-eye lens  153 R with their right eye, the user can view the right-eye image IMR. It should be noted that typically, the left-eye lens  153 L and the right-eye lens  153 R may be circular or elliptical magnifying lenses, and may be lenses that distort images and cause the user to visually confirm the images. For example, the left-eye lens  153 L may distort the left-eye image IML (described below) displayed distorted into a circular or elliptical shape, in a direction opposite to the distortion of the image and cause the user to visually confirm the image, and the right-eye lens  153 R may distort the right-eye image IMR (described below) displayed distorted into a circular or elliptical shape, in a direction opposite to the distortion of the image and cause the user to visually confirm the image, whereby the user may stereoscopically view the images. Further, a configuration may be employed in which the left-eye lens  153 L and the right-eye lens  153 R are integrally formed. 
     The main body  151  includes the abutment portion provided protruding from the front surface side of the main body  151  to outside by surrounding the outer edges of the lens frame member  152  in an angular tube shape. In the abutment portion, an end surface protruding from the front surface side to outside is disposed on the near side of the lens  153  when the lens  153  is viewed from outside the goggle apparatus  150 . The end surface is placed furthest on the near side (furthest in a negative z-axis direction) of the goggle apparatus  150  in the state where the main body apparatus  2  is attached. Then, the end surface of the abutment portion of the main body  151  has a shape that fits the face of the user (typically, the periphery of both eyes of the user) when the user looks into the goggle apparatus  150  to which the main body apparatus  2  is attached. The end surface has the function of fixing the positional relationships between the eyes of the user and the lens  153  by abutting the face of the user. 
     Further, when the user views a three-dimensional image displayed on the display  12  using the image display system, the abutment portion can block external light on the left-eye lens  153 L and the right-eye lens  153 R. This can improve a sense of immersion for the user viewing the three-dimensional image displayed on the display  12 . It should be noted that when blocking light, the abutment portion does not need to completely block external light. For example, as shown in  FIG. 15 , in a part of the abutment portion formed into a tubular shape, a recess may be formed. It should be noted that the recess of the abutment portion exemplified in  FIG. 15  is formed at the position of a lower portion of the midpoint between the left-eye lens  153 L and the right-eye lens  153 R. This is a position that the nose of the user viewing the three-dimensional image displayed on the display  12  abuts. That is, the recess of the abutment portion can avoid the strong abutment between the abutment portion and the nose of the user. Even if the light blocking effect somewhat deteriorates, a feeling of discomfort regarding the abutment between the abutment portion and the nose can be reduced. 
     As shown in  FIG. 10 , the plate-like member  154  is fixedly provided within the main body  151 , which is a portion between the lens frame member  152  and the display  12  when the main body apparatus  2  is attached to the attachment portion of the main body  151 . For example, a part of the plate-like member  154  has a shape along the V-shaped recessed portion of the lens frame member  152  and is placed as a wall (hereinafter referred to as a “first wall portion”) connecting between the recessed portion and the display  12  of the main body apparatus  2  attached to the main body  151 . Then, a space surrounded by the first wall portion is an opening portion  154   h  that exposes a part of the display  12  of the main body apparatus  2  attached to the main body  151  to outside and functions as an operation window that enables the user to perform a touch operation on the part through the space. It should be noted that a part of the first wall portion of the plate-like member  154  may open as shown in  FIG. 12 . 
     Further, as shown in  FIG. 12 , as an example, the plate-like member  154  is provided standing in a vertical direction between the left-eye lens  153 L and the right-eye lens  153 R and placed as a wall (hereinafter referred to as a “second wall portion”) connecting between the recessed portion and the display  12  of the main body apparatus  2  attached to the main body  151 . Then, the second wall portion is disposed between the left-eye image IML and the right-eye image IMR displayed on the display  12 , so as to divide the images in the state where the main body apparatus  2  is attached to the main body  151 . The second wall portion functions as a division wall provided between the left-eye image IML and the right-eye image IMR. Then, the plate-like member  154  is provided by extending the first wall portion to the second wall portion, and the first wall portion and the second wall portion are formed of integrated members. 
     In  FIGS. 10, 13, 14, and 15 , the image display system is formed by attaching the main body apparatus  2  to the goggle apparatus  150 . Here, in the exemplary embodiment, the main body apparatus  2  is attached such that the entirety of the main body apparatus  2  is covered by the goggle apparatus  150 . Then, when the main body apparatus  2  is attached to the goggle apparatus  150 , the user can view only the left-eye image IML displayed in a left area of the display  12  through the left-eye lens  153 L and can view only the right-eye image IMR displayed in a right area of the display  12  through the right-eye lens  153 R. Thus, by viewing the left-eye lens  153 L with their left eye and viewing the right-eye lens  153 R with their right eye, the user of the image display system can visually confirm the left-eye image IML and the right-eye image IMR. Thus, by displaying the left-eye image IML and the right-eye image IMR having parallax with each other on the display  12 , it is possible to display a three-dimensional image having a stereoscopic effect to the user. 
     As shown in  FIGS. 14 and 15 , when the user views the three-dimensional image displayed on the display  12  while holding the image display system obtained by attaching the main body apparatus  2  to the goggle apparatus  150 , the user can hold with their left hand a left side portion of the goggle apparatus  150  to which the main body apparatus  2  is attached, and can hold a right side portion of the goggle apparatus  150  with their right hand. The user thus holds the left and right side portions of the goggle apparatus  150 , whereby it is possible to maintain the state where the main body apparatus  2  is stably attached. 
     Further, in the image display system, even in the state where the main body apparatus  2  is attached to the goggle apparatus  150 , a touch operation can be performed on a part of the touch panel  13  provided on the screen of the display  12 , through the opening portion  154   h  formed surrounded by the first wall portion of the plate-like member  154  (a third area of the display  12  described below). Further, based on the detection results of the acceleration sensor  89  and/or the angular velocity sensor  90  provided in the main body apparatus  2 , the image display system can calculate information regarding the motion and/or the orientation of the main body apparatus  2 , i.e., the motion and/or the orientation of the image display system including the goggle apparatus  150 . Thus, the image display system can calculate the orientation based on the direction of gravity of the head of the user looking into the goggle apparatus  150  to which the main body apparatus  2  is attached. Further, when the orientation or the direction of the head of the user looking into the goggle apparatus  150  to which the main body apparatus  2  is attached changes, the image display system can calculate the direction or the angle of the change. Further, when the user looking into the goggle apparatus  150  to which the main body apparatus  2  is attached vibrates the image display system by hitting the image display system, the image display system can detect the vibration. Thus, when the user views the three-dimensional image displayed on the display  12  through the left-eye lens  153 L and the right-eye lens  153 R in the state the main body apparatus  2  is attached to the goggle apparatus  150 , a play style is achieved in which a touch operation through the opening portion  154   h , an operation based on the orientation based on the direction of gravity of the image display system, the operation of changing the orientation of the image display system, and the operation of vibrating the image display system can be performed. 
     It should be noted that when the image display system according to the exemplary embodiment is used, an operation may be performed using at least one of the left controller  3  and the right controller  4  detached from the main body apparatus  2 . For example, when the image display system is operated using the left controller  3 , the user views the three-dimensional image displayed on the display  12 , while holding the goggle apparatus  150  to which the main body apparatus  2  is attached with their right hand, and also performs the operation while holding the detached left controller  3  alone with their left hand. In this case, operation information regarding the operations performed on the left controller  3  and/or the right controller  4  detached from the main body apparatus  2  is transmitted to the main body apparatus  2  through wireless communication with the main body apparatus  2 . Specifically, the operation information regarding the operation performed on the left controller  3  is wirelessly transmitted from the communication control section  101  of the left controller  3  and received by the controller communication section  83  of the main body apparatus  2 . Further, the operation information regarding the operation performed on the right controller  4  is wirelessly transmitted from the communication control section  111  of the right controller  4  and received by the controller communication section  83  of the main body apparatus  2 . 
     As described above, in the exemplary embodiment, a portable image display system where the user views a three-dimensional image while holding the portable image display system can be formed by attaching the main body apparatus  2  to the goggle apparatus  150 . Further, in the image display system according to the exemplary embodiment, the user views the three-dimensional image displayed on the display  12  of the main body apparatus  2 , while causing the face of the user to abut the goggle apparatus  150 . Thus, the positional relationships between stereo speakers (the left speaker  88 L and the right speaker  88 R) provided in the main body apparatus  2  and the ears of the user are also fixed, and the left and right speakers are placed near the ears of the users. Thus, the main body apparatus  2  can output sounds based on the positional relationships between a sound output apparatus and the ears of a viewer without forcing the viewer to use earphones or speakers. For example, the main body apparatus  2  can control a sound source using so-called 3D audio effect technology based on the positional relationships between the sound output apparatus and the ears of the viewer. 
     Next, with reference to  FIGS. 9, 10, and 16 , a description is given of images displayed on the main body apparatus  2 . It should be noted that  FIG. 16  is a diagram showing examples of images displayed on the main body apparatus  2  in a stereoscopic display mode and a non-stereoscopic display mode. 
     The image display system according to the exemplary embodiment is set to either of a stereoscopic display mode used to stereoscopically view an image displayed on the display  12  by attaching the main body apparatus  2  to the goggle apparatus  150 , and a non-stereoscopic display mode used to directly view an image displayed on the display  12  by detaching the main body apparatus  2  from the goggle apparatus  150 , thereby non-stereoscopically viewing the image. Then, the image display system displays the image corresponding to the set mode on the display  12  of the main body apparatus  2 . Here, the stereoscopic image to be stereoscopically viewed may be stereoscopically viewed by the user viewing a right-eye image and a left-eye image having parallax with each other with their right eye and left eye. In this case, the non-stereoscopic image to be non-stereoscopically viewed is an image other than that of the above two-image display (stereoscopic display), and typically, may be viewed by the user viewing a single image with their right eye and left eye. It should be noted that in the exemplary embodiment, the non-stereoscopic display mode is used as an example of a first display mode. Further, in the exemplary embodiment, the stereoscopic display mode is used as an example of a second display mode. 
     In the stereoscopic display mode, the image display system forms a content image as a display target (e.g., an image for displaying a part of a virtual space or real space) using the left-eye image IML and the right-eye image IMR having parallax with each other, displays the left-eye image IML in the left area of the display  12 , and displays the right-eye image IML in the right area of the display  12 . Specifically, as shown in  FIG. 9 , in the stereoscopic display mode, the left-eye image IML is displayed in a first area, which is an approximately elliptical area that can be viewed through the left-eye lens  153 L when the main body apparatus  2  is attached to the goggle apparatus  150 , and is also a part of the left area of the display  12 . Further, in the stereoscopic display mode, the right-eye image IMR is displayed in a second area, which is an approximately elliptical area that can be viewed through the right-eye lens  153 R when the main body apparatus  2  is attached to the goggle apparatus  150 , and is also a part of the right area of the display  12 . 
     Here, as described above, in the state where the main body apparatus  2  is attached to the goggle apparatus  150 , the second wall portion of the plate-like member  154  is placed between the left-eye image IML displayed in the first area of the display  12  and the right-eye image IMR displayed in the second area of the display  12 . Thus, the left-eye image IML and the right-eye image IMR are divided by the second wall portion of the plate-like member  154  as a division wall. Thus, it is possible to prevent the right-eye image IMR from being visually confirmed through the left-eye lens  153 L, or the left-eye image IML from being visually confirmed through the right-eye lens  153 R. 
     As an example, images of the virtual space viewed from a pair of virtual cameras (a left virtual camera and a right virtual camera) having parallax with each other and placed in the virtual space are generated as the left-eye image IML and the right-eye image IMR. The pair of virtual cameras is placed in the virtual space, corresponding to the orientation of the main body apparatus  2  based on the direction of gravity in real space. Then, the pair of virtual cameras changes its orientation in the virtual space, corresponding to a change in the orientation of the main body apparatus  2  in real space and controls the direction of the line of sight of the virtual cameras in accordance with the orientation of the main body apparatus  2 . Consequently, by the operation of changing the orientation of the main body apparatus  2  (the image display system) to look around, the user wearing the image display system can change the display range of the virtual space to be stereoscopically viewed, can look over the virtual space that is stereoscopically viewed, and therefore can have an experience as if actually being at the location of the virtual cameras. It should be noted that in the exemplary embodiment, the main body apparatus  2  matches the direction of a gravitational acceleration acting on the main body apparatus  2  and the direction of gravity in the virtual space acting on the virtual cameras and also matches the amount of change in the orientation of the main body apparatus  2  and the amount of change in the direction of the line of sight of the virtual cameras. This increases the reality of the operation of looking over the virtual space to be stereoscopically viewed based on the orientation of the main body apparatus  2 . 
     Further, the image display system displays on the display  12   a  user interface image IMU for receiving a touch operation on the touch panel  13  of the main body apparatus  2 . For example, a user interface image IMUa displayed in the stereoscopic display mode is displayed in the display area of the display  12  where a touch operation can be performed through the opening portion  154   h  of the goggle apparatus  150 . For example, as described above, the opening portion  154   h  is formed surrounded by the first wall portion of the plate-like member  154  and enables a touch operation on a part of the display  12  of the main body apparatus  2  attached to the goggle apparatus  150  (specifically, an area near the center of the lower portion of the display  12 ) through the V-shaped recessed portion of the lens frame member  152  that abuts the nose of the user. As an example, as shown in  FIG. 9 , even in the state where the main body apparatus  2  is attached to the goggle apparatus  150 , the opening portion  154   h  enables a touch operation on a third area set in the lower portion of the display  12  sandwiched between the first area and the second area of the display  12 . 
     For example, in the stereoscopic display mode, two user interface images IMUa 1  and IMUa 2  are displayed in the third area of the display  12 . As an example, the user interface image IMUa 1  is an operation icon for, when its display position is subjected to a touch operation through the touch panel  13 , giving an operation instruction to retry a game from the beginning. Further, the user interface image IMUa 2  is an operation icon for, when its display position is subjected to a touch operation through the touch panel  13 , giving an operation instruction to end the game. Then, the two user interface images IMUa 1  and IMUa 2  are displayed next to each other in the third area of the display  12 , in sizes matching the shape of the third area. Consequently, the user can give a plurality of operation instructions based on touch operations by performing a touch operation on either of the two user interface images IMUa 1  and IMUa 2  through the opening portion  154   h  even in the state where the main body apparatus  2  is attached to the goggle apparatus  150 . It should be noted that the two user interface images IMUa 1  and IMUa 2  may be displayed near the third area that enables a touch operation by exposing a part of the display  12  to outside. That is, parts of the two user interface images IMUa 1  and/or IMUa 2  may be displayed outside the third area. It should be noted that in the exemplary embodiment, the user interface image IMUa is used as an example of a second user interface image. 
     The two user interface images IMUa 1  and IMUa 2  are images displayed in the stereoscopic display mode and are displayed in the third area outside the first area that can be viewed with the left eye of the user and the second area that can be viewed with the right eye of the user in the display  12  of the main body apparatus  2  attached to the goggle apparatus  150 . That is, the user interface images IMUa 1  and IMUa 2  displayed in the third area are displayed outside the field of view of the user visually confirming the user interface images IMUa 1  and IMUa 2  through the goggle apparatus  150 , do not include two images having parallax with each other, and therefore are displayed as non-stereoscopic images that cannot be stereoscopically viewed. Further, the user interface images IMUa 1  and IMUa 2  as targets of touch operations are displayed outside the first area and the second area for displaying a stereoscopic image, and therefore, the first area and the second area are less likely to be subjected to a touch operation. Thus, it is possible to prevent the first area and the second area for displaying a stereoscopic image from being defaced by the display  12  being subjected to a touch operation, and also prevent a finger for performing a touch operation from entering the field of view in the state where the stereoscopic image is viewed. 
     It should be noted that in another exemplary embodiment, the user interface images IMUa 1  and IMUa 2  may be displayed on the display  12  as a stereoscopic image that can be stereoscopically viewed in the stereoscopic display mode. In this case, the user interface images IMUa 1  and IMUa 2  are displayed on the display  12  as a stereoscopic image by including two images having parallax with each other. Typically, one of images to be stereoscopically viewed is displayed in a part of the first area, and the other image to be stereoscopically viewed is displayed in a part of the second area. 
     As shown in  FIG. 16 , in the non-stereoscopic display mode, the image display system forms the above content image as the display target using a single image IMS as a non-stereoscopic image, and as an example, displays the single image IMS in the entirety of the display area of the display  12 . 
     As an example, an image of the virtual space viewed from a single virtual camera placed in the virtual space is generated as the single image IMS. The single virtual camera is placed in the virtual space, corresponding to the orientation of the main body apparatus  2  based on the direction of gravity in real space. Then, the single virtual camera changes its orientation in the virtual space, corresponding to a change in the orientation of the main body apparatus  2  in real space and controls the direction of the line of sight of the virtual camera in accordance with the orientation of the main body apparatus  2 . Consequently, by the operation of changing the orientation of the main body apparatus  2  to look around, the user holding the main body apparatus  2  detached from the goggle apparatus  150  can look over the virtual space by changing the display range of the virtual space displayed on the display  12 , and therefore can have an experience as if actually being at the location of the virtual camera. It should be noted that in the exemplary embodiment, also in the non-stereoscopic display mode, the main body apparatus  2  matches the direction of a gravitational acceleration acting on the main body apparatus  2  and the direction of gravity in the virtual space acting on the virtual camera and also matches the amount of change in the orientation of the main body apparatus  2  and the amount of change in the direction of the line of sight of the virtual camera. This also increases the reality of the operation of looking over the virtual space to be non-stereoscopic viewed based on the orientation of the main body apparatus  2 . It should be noted that in the exemplary embodiment, the single image IMS is used as an example of a non-stereoscopic image. 
     Further, a user interface image IMUb displayed in the non-stereoscopic display mode is displayed on the display  12  in a superimposed manner on, for example, the content image (the single image IMS) displayed on the display  12 . For example, as shown in  FIG. 16 , also in the non-stereoscopic display mode, two user interface images IMUb 1  and IMUb 2  are displayed on the display  12 . As an example, the user interface image IMUb 1  is an image corresponding to the user interface image IMUa 1  and is an operation icon for, when its display position is subjected to a touch operation through the touch panel  13 , giving an operation instruction to retry a game from the beginning. Further, the user interface image IMUb 2  is an image corresponding to the user interface image IMUa 2  and is an operation icon for, when its display position is subjected to a touch operation through the touch panel  13 , giving an operation instruction to end the game. Here, the image corresponding to the user interface image IMUa indicates that the design and/or the size of the image are different from those of the user interface image IMUa, but the function of the image is substantially the same (e.g., the content of an operation instruction given by performing a touch operation on the image is the same) as that of the user interface image IMUa. It should be noted that the image corresponding to the user interface image IMUa may not only have substantially the same function as that of the user interface image IMUa displayed in the non-stereoscopic display mode, but also have the same design and size as those of the user interface image IMUa, i.e., the image may be completely the same as the user interface image IMUa. It should be noted that in the exemplary embodiment, the user interface image IMUb is used as an example of a first user interface image. 
     The two user interface images IMUb 1  and IMUb 2  are displayed in corner areas (e.g., an upper left corner area and an upper right corner area) of the display  12  that are different from the third area. It should be noted that areas where touch operations can be performed on the two user interface images IMUb 1  and IMUb 2  are not limited, and therefore, the two user interface images IMUb 1  and IMUb 2  can be displayed larger than the user interface image IMUa displayed in the stereoscopic display mode and can be displayed in sizes and shapes that facilitate a touch operation of the user and at positions where the visibility of the content image (the single image IMS) is unlikely to be impaired by a touch operation. 
     Based on the result of detecting whether or not the main body apparatus  2  is in an attached state where the main body apparatus  2  is attached to the goggle apparatus  150 , or whether or not the main body apparatus  2  is in a halfway attached state where the main body apparatus  2  is being attached to the goggle apparatus  150 , the image display system according to the exemplary embodiment can automatically switch the stereoscopic display mode and the non-stereoscopic display mode. For example, in the main body apparatus  2 , the illuminance sensor  29  is provided that detects the illuminance (brightness) of light incident on the main surface side of the housing  11 . Based on the detection result of the illuminance by the illuminance sensor  29 , the main body apparatus  2  can detect whether or not the main body apparatus  2  is in the attached state where the main body apparatus  2  is attached to the goggle apparatus  150 , or whether or not the main body apparatus  2  is in the halfway attached state where the main body apparatus  2  is being attached to the goggle apparatus  150 . Specifically, when the main body apparatus  2  is attached to the goggle apparatus  150 , or when the main body apparatus  2  is in the halfway attached state, the illuminance detected by the illuminance sensor  29  decreases. Thus, a threshold allowing the detection of the decreased illuminance is provided, and it is detected whether or not the illuminance is greater than or equal to the threshold. Thus, it is possible to detect whether or not the main body apparatus  2  is in the attached state, or whether or not the main body apparatus  2  is in the halfway attached state. Here, “the fact that the main body apparatus  2  is in the attached state” detected by the main body apparatus  2  based on the detection result of the illuminance by the illuminance sensor  29  is the fact that the main body apparatus  2  is in the state where the main body apparatus  2  is completely attached to the goggle apparatus  150 . Further, “the fact that the main body apparatus  2  is in the halfway attached state” detected by the main body apparatus  2  based on the detection result of the illuminance by the illuminance sensor  29  is the fact that the main body apparatus  2  is in the state where the main body apparatus  2  is at a stage prior to the state where the main body apparatus  2  is completely attached to the goggle apparatus  150 . 
     When the illuminance sensor  29  detects whether or not the main body apparatus  2  is in the attached state, or whether or not the main body apparatus  2  is in the halfway attached state, a plurality of forms are possible. As a first example, as shown in  FIG. 11 , in the attachment portion of the goggle apparatus  150  for detachably fixing the main body apparatus  2 , when the front surface abutment portion  151   b  of the main body  151  in surface contact with a part of the front surface (the surface on which the display  12  is provided) of the main body apparatus  2  in the attached state is formed by covering a light-receiving surface or a light-receiving hole of the illuminance sensor  29 , the front surface abutment portion  151   b  enters the state where the front surface abutment portion  151   b  covers the light-receiving surface or the light-receiving hole of the illuminance sensor  29 , whereby it is detected whether or not the main body apparatus  2  is in the attached state where the main body apparatus  2  is attached to the goggle apparatus  150 , or whether or not the main body apparatus  2  is in the halfway attached state where the main body apparatus  2  is being attached to the goggle apparatus  150 . As an example, when the light-receiving surface or the light-receiving hole of the illuminance sensor  29  is provided in a corner portion of the main body apparatus  2 , and if the main body apparatus  2  is inserted into the attachment portion of the goggle apparatus  150  from the corner portion side, the light-receiving surface or the light-receiving hole enters the state where the light-receiving surface or the light-receiving hole is covered by the front surface abutment portion  151   b  in an early period of this attachment operation. Thus, based on the detection result of the illuminance by the illuminance sensor  29 , it is possible to detect that the main body apparatus  2  “is in the halfway attached state”. Further, if the main body apparatus  2  is inserted into the attachment portion of the goggle apparatus  150  from the side surface side opposite to the corner portion where the light-receiving surface or the light-receiving hole of the illuminance sensor  29  is provided, the light-receiving surface or the light-receiving hole enters the state where the light-receiving surface or the light-receiving hole is covered by the front surface abutment portion  151   b  in a terminal period of this attachment operation. Thus, based on the detection result of the illuminance by the illuminance sensor  29 , it is possible to detect that the main body apparatus  2  “is in the attached state”. As another example, when the light-receiving surface or the light-receiving hole of the illuminance sensor  29  is provided on the center side of the lower portion of the main body apparatus  2 , and if the main body apparatus  2  is inserted into the attachment portion of the goggle apparatus  150 , the light-receiving surface or the light-receiving hole enters the state where the light-receiving surface or the light-receiving hole is covered by the front surface abutment portion  151   b  from an early period to an intermediate period of this attachment operation, no matter which direction the main body apparatus  2  is inserted from. Thus, based on the detection result of the illuminance by the illuminance sensor  29 , it is possible to detect that the main body apparatus  2  “is in the halfway attached state”. It should be noted that in the first example, the front surface abutment portion  151   b  of the main body  151  is used as an example of a light-shielding portion. 
     As a second example, even when the front surface abutment portion  151   b  is not formed by covering the light-receiving surface or the light-receiving hole of the illuminance sensor  29 , using the fact that the inside of the main body  151  is relatively dark, it is detected whether or not the main body apparatus  2  is in the attached state where the main body apparatus  2  is attached to the goggle apparatus  150 , or whether or not the main body apparatus  2  is in the halfway attached state where the main body apparatus  2  is being attached to the goggle apparatus  150 . For example, the state where external light is incident on the inside of the main body  151  of the goggle apparatus  150  through the left-eye lens  153 L and the right-eye lens  153 R is possible. Even in this state, the attached state of the main body apparatus  2  is detected by detecting that the illuminance is greater than that outside the main body  151 . As an example, when the light-receiving surface or the light-receiving hole of the illuminance sensor  29  is provided in a corner portion of the main body apparatus  2 , and if the main body apparatus  2  is inserted into the attachment portion of the goggle apparatus  150  from the corner portion side, the light-receiving surface or the light-receiving hole is inserted into the main body  151  in an early period of this attachment operation. Thus, based on the detection result of the illuminance by the illuminance sensor  29 , it is possible to detect that the main body apparatus  2  “is in the halfway attached state”. Further, if the main body apparatus  2  is inserted into the attachment portion of the goggle apparatus  150  from the side surface side opposite to the corner portion where the light-receiving surface or the light-receiving hole of the illuminance sensor  29  is provided, the light-receiving surface or the light-receiving hole is inserted into the main body  150  in a terminal period of this attachment operation. Thus, based on the detection result of the illuminance by the illuminance sensor  29 , it is possible to detect that the main body apparatus  2  “is in the attached state”. As another example, when the light-receiving surface or the light-receiving hole of the illuminance sensor  29  is provided on the center side of the lower portion of the main body apparatus  2 , and if the main body apparatus  2  is inserted into the attachment portion of the goggle apparatus  150 , the light-receiving surface or the light-receiving hole is inserted into the main body  151  from an early period to an intermediate period of this attachment operation, no matter which direction the main body apparatus  2  is inserted from. Thus, based on the detection result of the illuminance by the illuminance sensor  29 , it is possible to detect that the main body apparatus  2  “is in the halfway attached state”. It should be noted that in the second example, the main body  151  is used as another example of the light-shielding portion. 
     As a third example, even when the front surface abutment portion  151   b  is not formed by covering the light-receiving surface or the light-receiving hole of the illuminance sensor  29 , using the fact that the inside of the main body  151  darkens by the user wearing the goggle apparatus  150  to which the main body apparatus  2  is attached, it is detected that the main body apparatus  2  is in the attached state where the main body apparatus  2  is attached to the goggle apparatus  150 . For example, in the state where the user does not wear the goggle apparatus  150 , it is possible that external light is incident on the main body  151  of the goggle apparatus  150  through the left-eye lens  153 L and the right-eye lens  153 R. In this case, the external light incident through the left-eye lens  153 L and the right-eye lens  153 R is blocked by the user wearing the goggle apparatus  150 . Thus, the attached state of the main body apparatus  2  can be detected by detecting that the illuminance of the inside of the main body  151  decreases. As an example, when light incident on the light-receiving surface or the light-receiving hole of the illuminance sensor  29  placed in the main body  151  of the goggle apparatus  150  is blocked by the main body  151  and the face of the user, based on the detection result of the illuminance by the illuminance sensor  29 , it is possible to detect that the main body apparatus  2  “is in the attached state”. Further, in this example, it is possible to detect not only whether or not the main body apparatus  2  is in the attached state where the main body apparatus  2  is attached to the goggle apparatus  150 , but also whether or not the user wears the goggle apparatus  150  to which the main body apparatus  2  is attached. It should be noted that in the third example, the main body  151  is used as another example of the light-shielding portion. 
     When it is determined that the main body apparatus  2  is not in the state where the main body apparatus  2  is attached to the goggle apparatus  150 , the image display system according to the exemplary embodiment sets the display mode of the main body apparatus  2  to the non-stereoscopic display mode. On the other hand, in the main body apparatus  2  set to the non-stereoscopic display mode, when it is determined that the main body apparatus  2  changes from a non-attached state where the main body apparatus  2  is not attached to the goggle apparatus  150  to the attached state where the main body apparatus  2  is attached to the goggle apparatus  150 , the main body apparatus  2  changes the content image of a displayed non-stereoscopic image to a stereoscopic image, thereby displaying the same content image on the display  12 . As an example, when the single virtual camera is set in the virtual space to display the single image IMS in the non-stereoscopic display mode, and a virtual space image is generated, the main body apparatus  2  sets virtual cameras for displaying the left-eye image IML and the right-eye image IMR by changing the single virtual camera to the pair of virtual cameras (the left virtual camera and the right virtual camera) having parallax with each other, without changing the position and the direction of the line of sight of the single virtual camera, thereby switching to the generation of a virtual space image in the stereoscopic display mode. Further, in the main body apparatus  2  set to the stereoscopic display mode, when it is determined that the main body apparatus  2  changes from the attached state where the main body apparatus  2  is attached to the goggle apparatus  150  to the non-attached state where the main body apparatus  2  is not attached to the goggle apparatus  150 , the main body apparatus  2  changes the content image of a displayed stereoscopic image to a non-stereoscopic image, thereby displaying the same content image corresponding to the content image of the stereoscopic image, as a non-stereoscopic image on the display  12 . As an example, when the pair of virtual cameras is set in the virtual space to display the left-eye image IML and the right-eye image IMR in the stereoscopic display mode, and a virtual space image is generated, the main body apparatus  2  sets a virtual camera for displaying the single image IMS by changing the pair of virtual cameras to the single virtual camera without changing the position and the direction of the line of sight of the pair of virtual cameras, thereby switching to the generation of a virtual space image in the non-stereoscopic display mode. As described above, the content image of a non-stereoscopic image (e.g., a virtual space image) corresponding to the content image of a stereoscopic image (e.g., a virtual space image) or the content image of a stereoscopic image (e.g., a virtual space image) corresponding to the content image of a non-stereoscopic image (e.g., a virtual space image) indicates that there is only a difference between a stereoscopic image and a non-stereoscopic image in either case. However, the content image of a non-stereoscopic image corresponding to the content image of a stereoscopic image and the content image of a stereoscopic image corresponding to the content image of a non-stereoscopic image may be different in display range. Typically, the content image of a stereoscopic image may have a display range smaller than that of the content image of a non-stereoscopic image. 
     Further, when the display mode is switched, the image display system according to the exemplary embodiment changes the size, the shape, and the position of the user interface image IMU and displays the user interface image IMU on the display  12 . For example, in the main body apparatus  2  set to the non-stereoscopic display mode, when it is determined that the main body apparatus  2  changes from the non-attached state where the main body apparatus  2  is not attached to the goggle apparatus  150  to the attached state where the main body apparatus  2  is attached to the goggle apparatus  150 , the main body apparatus  2  changes the shapes of the user interface images IMUb 1  and IMUb 2  displayed in a superimposed manner on the content image in the corner areas of the display  12  to the user interface images IMUa 1  and IMUa 2  and also moves the display positions of the user interface images IMUa 1  and IMUa 2  to the third area of the display  12 , thereby displaying the user interface image IMU having the same function. Further, in the main body apparatus  2  set to the stereoscopic display mode, when it is determined that the main body apparatus  2  changes from the attached state where the main body apparatus  2  is attached to the goggle apparatus  150  to the non-attached state where the main body apparatus  2  is not attached to the goggle apparatus  150 , the main body apparatus  2  changes the shapes of the user interface images IMUa 1  and IMUa 2  displayed in the third area of the display  12  to the user interface images IMUb 1  and IMUb 2  and also moves the display positions of the user interface images IMUb 1  and IMUb 2  so that the user interface images IMUb 1  and IMUb 2  are displayed in a superimposed manner on the content image in the corner areas of the display  12 , thereby displaying the user interface image IMU having the same function. 
     It should be noted that in the above exemplary embodiment, an example has been used where based on the detection result of the illuminance by the illuminance sensor  29 , it is detected whether or not the main body apparatus  2  is in the attached state where the main body apparatus  2  is attached to the goggle apparatus  150 , or whether or not the main body apparatus  2  is in the halfway attached state where the main body apparatus  2  is being attached to the goggle apparatus  150 . Alternatively, based on another detection result, it may be detected whether or not the main body apparatus  2  is in the attached state where the main body apparatus  2  is attached to the goggle apparatus  150 , or whether or not the main body apparatus  2  is in the halfway attached state where the main body apparatus  2  is being attached to the goggle apparatus  150 . As an example, based on a detection result obtained by a connection terminal provided in the main body apparatus  2  and a connection terminal provided in the goggle apparatus  150  being electrically connected together by the main body apparatus  2  entering the attached state or the halfway attached state, or a detection result obtained by a predetermined switch mechanism provided in the main body apparatus  2  being turned on or off by the main body apparatus  2  entering the attached state or the halfway attached state, it may be detected whether or not the main body apparatus  2  is in the attached state where the main body apparatus  2  is attached to the goggle apparatus  150 , or whether or not the main body apparatus  2  is in the halfway attached state where the main body apparatus  2  is being attached to the goggle apparatus  150 . As another example, based on the image capturing result of image capturing means (an image sensor) provided in the main body apparatus  2 , it may be determined whether or not a predetermined image is captured, or it may be determined whether or not captured luminance is greater than or equal to a threshold, thereby detecting whether or not the main body apparatus  2  is in the attached state where the main body apparatus  2  is attached to the goggle apparatus  150 , or detecting whether or not the main body apparatus  2  is in the halfway attached state where the main body apparatus  2  is being attached to the goggle apparatus  150 . Further, as another example, when the main body apparatus  2  enters the attached state where the main body apparatus  2  is attached to the goggle apparatus  150 , or the halfway attached state where the main body apparatus  2  is being attached to the goggle apparatus  150 , the user may be urged to perform a predetermined operation. Then, based on the fact that the predetermined operation is performed, it may be detected whether or not the main body apparatus  2  is in the attached state where the main body apparatus  2  is attached to the goggle apparatus  150 , or whether or not the main body apparatus  2  is in the halfway attached state where the main body apparatus  2  is being attached to the goggle apparatus  150 . 
     Further, in the above exemplary embodiment, the third area is set in a lower portion of the display  12  on the lower side of the center of the display  12  sandwiched between the first area and the second area of the display  12 , thereby enabling a touch operation on the third area. Alternatively, the third area may be set in another area of the display  12 . As a first example, the third area may be set in an upper portion of the display  12  on the upper side of the center of the display  12  sandwiched between the first area and the second area of the display  12 . As a second example, the third area may be set in an upper portion (i.e., the upper left corner area of the display  12 ) or a lower portion (i.e., a lower left corner area of the display  12 ) sandwiched between the first area of the display  12  and the left end of the display  12 . As a third example, the third area may be set in an upper portion (i.e., the upper right corner area of the display  12 ) or a lower portion (i.e., a lower right corner area of the display  12 ) sandwiched by the second area of the display  12  and the right end of the display  12 . No matter which area the third area is set in, the user interface image IMUa matching the shape of the third area is displayed in the third area, and the opening portion  154   h  that enables a touch operation on the third area is formed in the goggle apparatus  150 , thereby enabling an operation similar to that in the above description. It should be noted that when the third area is set between the first area and the second area sandwiched between the first area and the second area, the third area may be shifted to the left or the right from an intermediate position between the first area and the second area. 
     Further, in the above exemplary embodiment, as the function of a user interface image, the function of a user interface image displayed on the display  12  to receive a touch operation on the touch panel  13  is used as an example. Alternatively, the user interface image that does not receive a touch operation may be used. For example, the user interface image may be character information, an icon, or the like that does not enable a touch operation, but presents some information to the user. As an example, the user interface image may be an image representing the content of an instruction corresponding to a button operation or a stick operation on the left controller  3  or the right controller  4 , the operation of moving the controller main body, or the like. 
     Further, the left-eye image IML and the right-eye image IMR may also be displayed outside the display area of the display  12  that can be viewed through the left-eye lens  153 L and the right-eye lens  153 R (typically, outside the first area and/or outside the second area), and parts of the left-eye image IML and the right-eye image IMR may also be displayed in the third area where a touch operation can be performed. Further, the left-eye image IML and the right-eye image IMR may be displayed in a range smaller than that of the display area of the display  12  that can be viewed through the left-eye lens  153 L and the right-eye lens  153 R (typically, the first area and/or the second area). 
     Next, with reference to  FIGS. 17 and 18 , a description is given of an example of a specific process executed by the game system  1  in the exemplary embodiment.  FIG. 17  is a diagram showing an example of a data area set in the DRAM  85  of the main body apparatus  2  in the exemplary embodiment. It should be noted that in the DRAM  85 , in addition to the data shown in  FIG. 17 , data used in another process is also stored, but is not described in detail here. 
     In a program storage area of the DRAM  85 , various programs Pa, which are executed by the game system  1 , are stored. In the exemplary embodiment, as the various programs Pa, a communication program for wirelessly communicating with the left controller  3  and the right controller  4 , an application program for performing information processing (e.g., game processing) based on data acquired from the operation sections (the left controller  3 , the right controller  4 , the touch panel  13 , the acceleration sensor  89 , and the angular velocity sensor  90 ), the illuminance sensor  29 , and the like are stored. It should be noted that the various programs Pa may be stored in advance in the flash memory  84 , or may be acquired from a storage medium attachable to and detachable from the game system  1  (e.g., a predetermined type of a storage medium attached to the slot  23 ) and stored in the DRAM  85 , or may be acquired from another apparatus via a network such as the Internet and stored in the DRAM  85 . The processor  81  executes the various programs Pa stored in the DRAM  85 . 
     Further, in a data storage area of the DRAM  85 , various data used for processes such as a communication process and information processing executed by the game system  1  is stored. In the exemplary embodiment, in the DRAM  85 , operation data Da, angular velocity data Db, acceleration data Dc, illuminance data Dd, orientation data De, operation object data Df, virtual camera data Dg, left-eye virtual space image data Dh, right-eye virtual space image data Di, stereoscopic view UI (user interface) image data Dj, non-stereoscopic view virtual space image data Dk, non-stereoscopic view UI (user interface) image data Dm, image data Dn, and the like are stored. 
     The operation data Da is operation data appropriately acquired from each of the left controller  3  and/or the right controller  4  and the touch panel  13 . As described above, operation data transmitted from each of the left controller  3  and/or the right controller  4  and the touch panel  13  includes information regarding an input (specifically, information regarding an operation or the detection result of each sensor) from each of the input sections (specifically, buttons, analog sticks, and sensors). In the exemplary embodiment, operation data is transmitted in a predetermined cycle from each of the left controller  3  and/or the right controller  4  through wireless communication, and the operation data Da is appropriately updated using the received operation data. It should be noted that the update cycle of the operation data Da may be such that the operation data Da is updated every frame, which is the cycle of the processing described later executed by the main body apparatus  2 , or is updated every cycle in which the above operation data is transmitted through the wireless communication. Further, operation data indicating that the touch panel  13  is operated is acquired in each cycle of the above processing, stored in the operation data Da in accordance with the acquisition, and updated. 
     The angular velocity data Db is data indicating angular velocities generated in the main body apparatus  2  and detected by the angular velocity sensor  90 . For example, the angular velocity data Db includes data indicating angular velocities about the xyz axes generated in the main body apparatus  2 , and the like. 
     The acceleration data Dc is data indicating accelerations generated in the main body apparatus  2  and detected by the acceleration sensor  89 . For example, the acceleration data Dc includes data indicating accelerations in the xyz axis directions generated in the main body apparatus  2 , and the like. 
     The illuminance data Dd is data indicating the illuminance of the periphery of the main body apparatus  2  detected by the illuminance sensor  29 . 
     The orientation data De is data indicating the orientation of the main body apparatus  2  in real space. As an example, the orientation data De includes data indicating the orientation based on a gravity vector indicating a gravitational acceleration generated in the main body apparatus  2 , and data indicating a change in the orientation of the main body apparatus  2 . 
     The operation object data Df is data indicating the position, the direction, the orientation, the action, and the like in the virtual space of an object operated by the user. 
     The virtual camera data Dg is data indicating the position, the direction, the viewing angle, the magnification, and the like of a virtual camera (the pair of left and right virtual cameras in the stereoscopic display mode and the single virtual camera in the non-stereoscopic display mode) set in the virtual space. 
     The left-eye virtual space image data Dh is data for generating the left-eye image IML in the stereoscopic display mode. The right-eye virtual space image data Di is data for generating the right-eye image IMR in the stereoscopic display mode. The stereoscopic view UI image data Dj is data indicating the position, the shape, the size, and the like of the user interface image IMUa in the stereoscopic display mode. 
     The non-stereoscopic view virtual space image data Dk is data for generating the single image IMS in the non-stereoscopic display mode. The non-stereoscopic view UI image data Dm is data indicating the position, the shape, the size, and the like of the user interface image IMUb in the non-stereoscopic display mode. 
     The image data Dn is data for displaying images (e.g., an image of a virtual object, a user interface image, an information image, a field image, a background image, and the like) on the display screen when a game is performed. 
     Next, with reference to  FIG. 18 , a detailed example of information processing (game processing) according to the exemplary embodiment is described.  FIG. 18  is a flow chart showing an example of game processing executed by the game system  1 . In the exemplary embodiment, a series of processes shown in  FIG. 18  is performed by the processor  81  executing a communication program or a predetermined application program (a game program) included in the various programs Pa. Further, the information processing shown in  FIG. 18  is started at any timing. 
     It should be noted that the processes of all of the steps in the flow chart shown in  FIG. 18  are merely illustrative. Thus, the processing order of the steps may be changed, or another process may be performed in addition to (or instead of) the processes of all of the steps, so long as similar results are obtained. Further, in the exemplary embodiment, descriptions are given on the assumption that the processor  81  performs the processes of all of the steps in the flow chart. Alternatively, a processor or a dedicated circuit other than the processor  81  may perform the processes of some of the steps in the flow chart. Yet alternatively, part of the processing performed by the main body apparatus  2  may be executed by another information processing apparatus capable of communicating with the main body apparatus  2  (e.g., a server capable of communicating with the main body apparatus  2  via a network). That is, all the processes shown in  FIG. 18  may be executed by the cooperation of a plurality of information processing apparatuses including the main body apparatus  2 . 
     In  FIG. 18 , the processor  81  performs initialization in the game processing (step S 200 ), and the processing proceeds to the next step. For example, in the initialization, the processor  81  initializes parameters for performing the processing described below. As an example, using acceleration data stored in the acceleration data Dc, the processor  81  calculates the direction of a gravity vector of a gravitational acceleration acting on the main body apparatus  2  and sets the initial orientation of the main body apparatus  2  based on the direction of the gravity vector, thereby updating the orientation data De. Further, the processor  81  sets the initial orientation of the virtual camera in the virtual space so that the direction of the initial orientation of the virtual camera is similar to a direction in the relationships between the direction of the gravity vector of the gravitational acceleration acting on the main body apparatus  2  and the xyz axis directions of the main body apparatus  2 , thereby updating the virtual camera data Dg. Here, being similar to a direction in the relationships of the xyz axes of the main body apparatus  2  means having such a placement relationship that a positive z-axis direction (the depth direction of the screen) based on the direction of the gravitational acceleration in real space is the same as the direction of the line of sight of the virtual camera based on the direction of gravity in the virtual space, and a positive x-axis direction (the left direction of the screen) based on the direction of the gravitational acceleration in real space is the same as the left direction of the virtual camera based on the direction of gravity in the virtual space. 
     Next, the processor  81  acquires various pieces of data and updates the operation data Da, the angular velocity data Db, the acceleration data Dc, and the illuminance data Dd (step S 201 ), and the processing proceeds to the next step. For example, the processor  81  acquires operation data from the left controller  3  and/or the right controller  4  and updates the operation data Da. Further, the processor  81  acquires touch operation data from the touch panel  13  and updates the operation data Da. Further, the processor  81  acquires inertia data (acceleration data and angular velocity data) from the inertial sensors (the acceleration sensor  89  and the angular velocity sensor  90 ) provided in the main body apparatus  2  and updates the acceleration data Dc and the angular velocity data Db. Further, the processor  81  acquires illuminance data from the illuminance sensor  29  and updates the illuminance data Dd. 
     Next, the processor  81  calculates the orientation of the main body apparatus  2  (step S 202 ), and the processing proceeds to the next step. For example, using the acceleration data and the angular velocity data stored in the angular velocity data Db and the acceleration data Dc, the processor  81  calculates the direction of the gravity vector of the gravitational acceleration acting on the main body apparatus  2 , thereby updating the orientation data De. Further, the processor  81  calculates the direction of rotation and the amount of rotation from the initial orientation of the main body apparatus  2 , thereby updating the orientation data De. For example, the processor  81  calculates the direction of rotation and the amount of rotation about the xyz axis directions of the main body apparatus  2  in the initial orientation, thereby updating the orientation data De. It should be noted that the direction of rotation can be represented by the positivity and negativity of the amount of rotation. Thus, only data indicating the amount of rotation may be stored in the orientation data De. For example, the processor  81  may add the amount of rotation based on the angular velocity data acquired in step S 202  in the current processing to the amount of rotation calculated in step S 202  in the previous processing, thereby calculating a new amount of rotation. 
     Next, the processor  81  performs the process of determining whether or not the main body apparatus  2  is attached to the goggle apparatus  150  (step S 203 ), and the processing proceeds to the next step. For example, based on a threshold for detecting the illuminance when the main body apparatus  2  is attached to the goggle apparatus  150 , when the illuminance indicated by the illuminance data Dd indicates low illuminance less than the threshold, the processor  81  determines in the above step S 203  that the main body apparatus  2  is attached to the goggle apparatus  150 . 
     Next, the processor  81  determines whether or not the display mode is the stereoscopic display mode (step S 204 ). For example, when it is determined in the attachment determination process in the above step S 203  that the main body apparatus  2  is attached to the goggle apparatus  150 , the determination is affirmative in the above step S 204 , and the processor  81  performs the processing in the stereoscopic display mode. On the other hand, when it is determined in the attachment determination process in the above step S 203  that the main body apparatus  2  is not attached to the goggle apparatus  150 , the determination is negative in the above step S 204 , and the processor  81  performs the processing in the non-stereoscopic display mode. Then, when the processor  81  performs the processing in the stereoscopic display mode, the processing proceeds to step S 205 . On the other hand, when the processor  81  performs the processing in the non-stereoscopic display mode, the processing proceeds to step S 213 . 
     In step S 205 , the processor  81  performs an object action process, and the processing proceeds to the next step. For example, with reference to the operation data Da, when the operation of causing an operation object in the virtual space to perform an action is performed, the processor  81  sets the motion of the operation object corresponding to the operation. Then, based on the set motion of the operation object, the processor  81  sets the position, the direction, the orientation, the action, and the like in the virtual space of the operation object, thereby updating the operation object data Df. 
     In the object action process in the above step S 205 , the following object action control is possible. As a first example, using as an operation target an operation object determined in advance, the operation object is caused to perform an action. In this case, based on inputs to the input sections of the left controller  3  and/or the right controller  4 , the operation object determined in advance is moved, caused to perform an action, or deformed. As a second example, an operation object is selected as an operation target based on an operation, and the operation object is caused to perform an action. In this case, using as an operation target an operation object placed at a predetermined display position (e.g., an operation object displayed in a superimposed manner on an indicator displayed at the center of the display screen), based on inputs to the input sections of the left controller  3  and/or the right controller  4 , the operation object selected as the operation target is moved, caused to perform an action, or deformed. As a third example, the operation object as the operation target is caused to perform an action based on a vibration to the goggle apparatus  150  to which the main body apparatus  2  is attached. For example, a gravitational acceleration component is removed from the accelerations in the xyz axis directions in the main body apparatus  2  indicated by the acceleration data Dc, and when the accelerations after the removal indicate that a vibration having a magnitude greater than or equal to a predetermined magnitude is applied to the main body apparatus  2 , the operation object as the operation target is caused to perform an action in accordance with the vibration. It should be noted that as the method for extracting the gravitational acceleration, any method may be used. For example, an acceleration component averagely generated in the main body apparatus  2  may be calculated, and the acceleration component may be extracted as the gravitational acceleration. 
     Next, the processor  81  performs the process of causing the pair of left and right virtual cameras to operate (step S 206 ), and the processing proceeds to the next step. For example, the processor  81  rotates the orientation of the pair of left and right virtual cameras in the virtual space by the amount of rotation calculated in step S 202  from the initial orientation and sets the orientation, thereby updating the virtual camera data Dg. For example, in the state where the positional relationship between the pair of left and right virtual cameras is fixed, the processor  81  rotates from the initial orientation the virtual cameras about the left-right direction of the virtual cameras by the same amount as the amount of rotation about the left-right axial direction (the x-axis direction) of the main body apparatus  2  calculated in step S 202 , rotates from the initial orientation the virtual cameras about the up-down direction of the virtual cameras by the same amount as the amount of rotation about the up-down axial direction (the y-axis direction) of the main body apparatus  2  calculated in step S 202 , and rotates from the initial orientation the virtual cameras about the direction of the line of sight of the virtual cameras by the same amount as the amount of rotation about the screen depth axial direction (the z-axis direction) of the main body apparatus  2  calculated in step S 202 , thereby setting the orientation of the pair of left and right virtual cameras in the virtual space. 
     Next, the processor  81  performs the process of generating a left-eye virtual space image (step S 207 ), and the processing proceeds to the next step. For example, based on the operation object data Df, the processor  81  places the operation object in the virtual space. Then, the processor  81  generates a virtual space image viewed from, between the pair of left and right virtual cameras set in the virtual camera data Dg, the left virtual camera as a left-eye virtual space image, thereby updating the left-eye virtual space image data Dh. 
     Next, the processor  81  performs the process of generating a right-eye virtual space image (step S 208 ), and the processing proceeds to the next step. For example, the processor  81  generates a virtual space image viewed from, between the pair of left and right virtual cameras set in the virtual camera data Dg, the right virtual camera as a right-eye virtual space image, thereby updating the right-eye virtual space image data Di. 
     Next, the processor  81  performs the process of generating a stereoscopic view user interface image (step S 209 ), and the processing proceeds to the next step. For example, the processor  81  generates a stereoscopic view user interface image matching the shape of the third area of the display  12  (see  FIG. 9 ), thereby updating the stereoscopic view UI image data Dj. 
     Next, the processor  81  performs a display control process for displaying the left-eye virtual space image in the first area of the display  12  (step S 210 ), and the processing proceeds to the next step. For example, the processor  81  displays the left-eye virtual space image set in the left-eye virtual space image data Dh as the left-eye image IML in the entirety of the first area of the display  12  (see  FIG. 9 ). 
     Next, the processor  81  performs a display control process for displaying the right-eye virtual space image in the second area of the display  12  (step S 211 ), and the processing proceeds to the next step. For example, the processor  81  displays the right-eye virtual space image set in the right-eye virtual space image data Di as the right-eye image IMR in the entirety of the second area of the display  12  (see  FIG. 9 ). 
     Next, the processor  81  performs a display control process for displaying the stereoscopic view UI image in the third area of the display  12  (step S 212 ), and the processing proceeds to step S 219 . For example, the processor  81  displays the user interface image set in the stereoscopic view UI image data Dj as the user interface image IMUa (e.g., the two user interface images IMUa 1  and IMUa 2 ) at a predetermined position in the third area of the display  12  (see  FIG. 9 ). 
     On the other hand, when it is determined in the above step S 204  that the display mode is the non-stereoscopic display mode, then in step S 213 , the processor  81  performs an object action process, and the processing proceeds to the next step. For example, with reference to the operation data Da, when the operation of causing an operation object in the virtual space to perform an action is performed, the processor  81  sets the motion of the operation object corresponding to the operation. Then, based on the set motion of the operation object, the processor  81  sets the position, the direction, the orientation, the action, and the like in the virtual space of the operation object, thereby updating the operation object data Df. It should be noted that the object action process in the above step S 213  is similar to the object action process in step S 205  described above, and therefore is not described in detail. 
     Next, the processor  81  performs the process of causing the single virtual camera to operate (step S 214 ), and the processing proceeds to the next step. For example, the processor  81  rotates the orientation of the single virtual camera in the virtual space by the amount of rotation calculated in step S 202  from the initial orientation and sets the orientation, thereby updating the virtual camera data Dg. For example, the processor  81  rotates from the initial orientation the single virtual camera about the left-right direction of the virtual camera by the same amount as the amount of rotation about the left-right axial direction (the x-axis direction) of the main body apparatus  2  calculated in step S 202 , rotates from the initial orientation the single virtual camera about the up-down direction of the virtual camera by the same amount as the amount of rotation about the up-down axial direction (the y-axis direction) of the main body apparatus  2  calculated in step S 202 , and rotates from the initial orientation the single virtual camera about the direction of the line of sight of the virtual camera by the same amount as the amount of rotation about the screen depth axial direction (the z-axis direction) of the main body apparatus  2  calculated in step S 202 , thereby setting the orientation of the single virtual camera in the virtual space. 
     Next, the processor  81  performs the process of generating a virtual space image (step S 215 ), and the processing proceeds to the next step. For example, the processor  81  generates a virtual space image viewed from the virtual camera set in the virtual camera data Dg, thereby updating the non-stereoscopic view virtual space image data Dk. 
     Next, the processor  81  performs the process of generating a non-stereoscopic view user interface image (step S 216 ), and the processing proceeds to the next step. For example, the processor  81  generates a non-stereoscopic view user interface image to be displayed in a superimposed manner on the single image IMS on the display  12  (see  FIG. 16 ), thereby updating the non-stereoscopic view UI image data Dm. 
     Next, the processor  81  performs a display control process for displaying the virtual space image in the entirety area of the display  12  (step S 217 ), and the processing proceeds to the next step. For example, the processor  81  displays the virtual space image set in the non-stereoscopic view virtual space image data Dk as the single image IMS in the entirety area of the display  12  (see  FIG. 16 ). 
     Next, the processor  81  performs a display control process for displaying the non-stereoscopic view UI image in a superimposed manner on the single image IMS (step S 218 ), and the processing proceeds to step S 219 . For example, the processor  81  displays the user interface image set in the non-stereoscopic view UI image data Dm as the user interface image IMUb (e.g., the two user interface images IMUb 1  and IMUb 2 ) in a superimposed manner on the single image IMS in the upper left corner area and the upper right corner area of the display  12  (see  FIG. 16 ). 
     In step S 219 , the processor  81  performs a user interface operation process, and the processing proceeds to the next step. For example, with reference to the operation data Da, when a touch operation is performed on the touch panel  13 , the processor  81  sets a user operation instruction corresponding to the touch operation in accordance with the user interface image displayed on the display  12  overlapping the position where the touch operation is performed. Then, the processor  81  performs a process corresponding to the set user operation instruction. 
     Next, the processor  81  determines whether or not the game is to be ended (step S 220 ). Examples of a condition for ending the game in the above step S 220  include the fact that the result of the game is finalized, the fact that a user performs the operation of ending the game, and the like. When the game is not to be ended, the processing returns to the above step S 201 , and the process of step S 201  is repeated. When the main game is to be ended, the processing of the flow chart ends. Hereinafter, the series of processes of steps S 201  to S 220  is repeatedly executed until it is determined in step S 220  that the game is to be ended. 
     As described above, in the exemplary embodiment, when the normal display mode (the non-stereoscopic display mode) and the stereoscopic display mode are switched, a user interface image is displayed at positions different corresponding to the set display mode. Thus, it is possible to improve convenience regarding the presentation of a user interface image. Further, based on the state of the attachment of the main body apparatus  2  to the goggle apparatus  150 , the display mode is automatically switched. Thus, it is possible to seamlessly switch the display mode. Further, in the exemplary embodiment, in the stereoscopic display mode, a user interface image is displayed in the third area different from the first area and the second area of the display  12  where the right-eye image and the left-eye image are displayed. Thus, it is possible to display a user interface image that does not hinder the display of a stereoscopic image. 
     It should be noted that in the above exemplary embodiment, the image display system is formed by attaching the main body apparatus  2  having an information processing function to the goggle apparatus  150 . Alternatively, the image display system may be formed in another form. As a first example, an image display system that displays a stereoscopic image may be formed by providing in the goggle apparatus  150  a control section that generates an image by performing the above information processing (game processing), and attaching to the goggle apparatus  150  a display device having the function of displaying the image. In this case, the control section provided in the goggle apparatus  150  outputs image data for displaying a stereoscopic image and a user interface image on the display device to the display device, whereby the stereoscopic image and the user interface image are displayed on the display device. It should be noted that in the form of the first example, it does not matter which of the display device and the goggle apparatus  150  a mechanism for detecting the attachment situation of the display device, a mechanism for detecting the orientation of the image display system, a mechanism for receiving a user operation, and the like are provided in. As a second example, separately from the goggle apparatus  150  to which a display device is attached, a control apparatus connected in a wireless or wired manner to the display device may be provided, and an image display system may be formed of the display device, the goggle apparatus  150 , and the control apparatus. In this case, operation data, acceleration data, angular velocity data, illuminance data, and the like are output from the display device to the control apparatus, and a content image and a user interface image in a display mode based on the illuminance data are output from the control apparatus to the display device. It should be noted that also in the form of the second example, it does not matter which of the display device and the goggle apparatus  150  a mechanism for detecting the attachment situation of the display device, a mechanism for detecting the orientation of the image display system, a mechanism for receiving a user operation, and the like are provided in. Then, in accordance with the operation data, the acceleration data, and the angular velocity data acquired from the display device and/or the goggle apparatus  150 , the control apparatus controls the display range of the content image to be displayed and outputs the content image to the display device. It should be noted that in the exemplary embodiment, the main body apparatus  2  is used as an example of a display device. 
     It should be noted that in the above exemplary embodiment, the method for detecting the orientation of the main body apparatus  2  is merely an example. Alternatively, the orientation of the main body apparatus  2  may be detected using another method or another piece of data. As an example, the main body apparatus  2  and/or the goggle apparatus  150  to which the main body apparatus  2  is attached may be captured from outside, and the orientations of the main body apparatus  2  and/or the goggle apparatus  150  may be detected using the captured image. Further, a controller for controlling the action of an operation object may be not only the left controller  3  or the right controller  4 , but also another controller. 
     Further, the game system  1  and/or the main body apparatus  2  may be any apparatus, and may be a mobile game apparatus, any mobile electronic device (a PDA (Personal Digital Assistant), a mobile phone, a smart device (a smartphone or the like), a personal computer, a camera, a tablet, or the like. If these pieces of hardware can execute a game application, any of these pieces of hardware can function as a game apparatus. 
     Further, in the above exemplary embodiment, an example has been used where a left-eye image and a right-eye image having parallax with each other are displayed on the left side and the right side of the screen of the display  12 , whereby a stereoscopic image is displayed. Alternatively, the left-eye image and the right-eye image may be displayed on different screens from each other. For example, when the display  12  provided in the main body apparatus  2  is formed of a plurality of display screens, a left-eye image is displayed on one of the plurality of display screens, and a right-eye image is displayed on the other one of the plurality of display screens. In this case, the user views the left-eye image displayed on the one of the plurality of display screens through the left-eye lens  153 L with their left eye and also views the right-eye image displayed on the other one of the plurality of display screens through the right-eye lens  153 R with their right eye and thereby can view a stereoscopic image through the goggle apparatus  150 . 
     Further, a stereoscopic image and a non-stereoscopic image to be displayed on the main body apparatus  2  are displayed as a game image by the processor  81  executing information processing (game processing) in accordance with a user operation, or displayed as a moving image or a still image by the processor  81  reproducing the moving image or reproducing the still image in accordance with a user operation. That is, a stereoscopic image and a non-stereoscopic image to be displayed on the main body apparatus  2  are generated by the processor  81  of the main body apparatus  2  performing information processing (e.g., game processing, a moving image reproduction process, or a still image reproduction process). Alternatively, at least a part of the process of generating the stereoscopic image and the non-stereoscopic image may be performed by another apparatus. For example, if the main body apparatus  2  is further configured to communicate with another apparatus (e.g., a server, another image display device, another game apparatus, another mobile terminal, or another information processing apparatus), the other apparatus may operate in conjunction with to perform the steps. Another apparatus may thus perform at least some of the steps, thereby enabling processing similar to that described above. Further, the above information processing can be performed by a processor or the cooperation of a plurality of processors, the processor or the plurality of processors included in an information processing system including at least one information processing apparatus. Further, in the above exemplary embodiment, information processing can be performed by the processor  81  of the main body apparatus  2  executing a predetermined program. Alternatively, part or all of the processing of the flow charts may be performed by a dedicated circuit included in the main body apparatus  2 . 
     Here, according to the above variations, it is possible to achieve the exemplary embodiment also by a system form such as cloud computing, or a system form such as a distributed wide area network or a local area network. For example, in a system form such as a distributed local area network, it is possible to execute the processing between a stationary information processing apparatus (a stationary game apparatus) and a mobile information processing apparatus (a mobile game apparatus) by the cooperation of the apparatuses. It should be noted that, in these system forms, there is no particular limitation on which apparatus performs the above processing. Thus, it goes without saying that it is possible to achieve the exemplary embodiment by sharing the processing in any manner. 
     Further, the processing orders, the setting values, the conditions used in the determinations, and the like that are used in the information above processing are merely illustrative. Thus, it goes without saying that the exemplary embodiment can be achieved also with other orders, other values, and other conditions. 
     Further, the above program may be supplied to the game system  1  not only through an external storage medium such as an external memory, but also through a wired or wireless communication link. Further, the program may be stored in advance in a non-volatile storage device included in the apparatus. It should be noted that examples of an information storage medium having stored therein the program may include CD-ROMs, DVDs, optical disk storage media similar to these, flexible disks, hard disks, magneto-optical disks, and magnetic tapes, as well as non-volatile memories. Alternatively, an information storage medium having stored therein the program may be a volatile memory for storing the program. It can be said that such a storage medium is a storage medium readable by a computer or the like. For example, it is possible to provide the various functions described above by causing a computer or the like to load a program from the storage medium and execute it. 
     While some exemplary systems, exemplary methods, exemplary devices, and exemplary apparatuses have been described in detail above, the above descriptions are merely illustrative in all respects, and do not limit the scope of the systems, the methods, the devices, and the apparatuses. It goes without saying that the systems, the methods, the devices, and the apparatuses can be improved and modified in various manners without departing the spirit and scope of the appended claims. It is understood that the scope of the systems, the methods, the devices, and the apparatuses should be interpreted only by the scope of the appended claims. Further, it is understood that the specific descriptions of the exemplary embodiment enable a person skilled in the art to carry out an equivalent scope on the basis of the descriptions of the exemplary embodiment and general technical knowledge. When used in the specification, the components and the like described in the singular with the word “a” or “an” preceding them do not exclude the plurals of the components. Furthermore, it should be understood that, unless otherwise stated, the terms used in the specification are used in their common meanings in the field. Thus, unless otherwise defined, all the jargons and the technical terms used in the specification have the same meanings as those generally understood by a person skilled in the art in the field of the exemplary embodiment. If there is a conflict, the specification (including definitions) takes precedence. 
     As described above, the exemplary embodiment can be used as an image display system, an image display program, an image display method, a display device, and the like that are capable of improving convenience regarding the presentation of a user interface image.