Patent Publication Number: US-2018039470-A1

Title: Image output control method and display device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of International Application PCT/JP2015/063281 filed on May 8, 2015 and designated the U.S., the entire contents of which are incorporated herein by reference. 
    
    
     FIELD 
     The embodiments discussed herein relate to an image output control method, and a display device. 
     BACKGROUND 
     In the related art technology, an external display having a large screen or a projector is coupled to a table terminal having a small screen of a size of approximately six to eight inches to use the small screen and the large screen. For example, a technology disclosed in the relate art provides a configuration to switch between a mirror display mode for displaying the same data on respective screens of the mobile terminal and the external display device, and an extended display mode for displaying different data; and the extended display mode is selected based on activation of a predetermined application (see, e.g., Patent Document 1). 
     RELATED-ART DOCUMENTS 
     Patent Documents 
     Patent Document 1: Japanese Laid-open Patent Publication No. 2011-217236 
     Patent Document 2: Japanese Laid-open Patent Publication No. 2014-53014 
     An aspect of embodiments may provide an image output control method executed by a computer to perform an image output process using respective screens of a plurality of display devices having different screen functions. The image output control method includes implementing a screen function in a first display device of the display devices to act as an image output destination, in response to failing to implement the screen function in a second display device of the display devices due to the different screen functions, and switching, after having the screen function implemented in the first display device, the image output destination to the second display device. 
     The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating an example of an overall configuration of a display device according to an embodiment; 
         FIG. 2  is a table illustrating examples of a display pattern according to an embodiment; 
         FIG. 3A to 3D  are diagrams illustrating cases where a layout of a large screen is disordered; 
         FIG. 4  is a diagram illustrating an example of a functional configuration of a tablet terminal according to an embodiment; 
         FIG. 5  is a diagram illustrating an operation example upon activation of an application for every display pattern according to an embodiment; 
         FIGS. 6A and 6B  are diagrams illustrating examples of a rendering area according to an embodiment; 
         FIG. 7  is a diagram illustrating an example of a hardware configuration of a table terminal according to an embodiment; 
         FIG. 8  is a diagram illustrating an example of a software configuration of a tablet terminal according to an embodiment; 
         FIG. 9  is a flowchart illustrating an example of an application activation process according to an embodiment; 
         FIGS. 10A and 10B  are diagrams illustrating examples of screens resulting from an application activation process according to an embodiment; 
         FIGS. 11A and 11B  are diagrams illustrating examples of screens resulting from an application activation process according to an embodiment; 
         FIG. 12  is a flowchart illustrating an example of an application termination process according to an embodiment; 
         FIG. 13  is a diagram illustrating an example of a launcher display screen and a display attribute information table according to an embodiment; and 
         FIG. 14  is a flowchart illustrating an example of an application activation process according to a modification of the embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     In the above-described related art technology, when an application designed to be optimum according to a small screen size of the tablet terminal  10  is displayed on an external display with a large screen or a projector, an image is displayed with a large size, which not expected by the application, or an image is displayed with a disordered layout. 
     For example, an application for a tablet terminal is created with an optimum design for a small screen mounted on a tablet terminal. To display such an application on an external display, an application designed for a small screen results in being displayed on a large screen. As a result, sizes of characters and buttons are displayed larger than expected on the external display, the layout may be disordered according to the resolution, or images may not fit in a rendering area of the screen of the external display. 
     The following illustrates embodiments of the present invention with reference to the accompanying renderings. In the present specification and the rendering, the same reference numerals are assigned to constituent elements having substantially the same functional configurations, and duplicated explanation will be omitted. 
     Overall Configuration 
     First, an example of an overall configuration of a display device according to an embodiment of the present invention will be described with reference to  FIG. 1 . A display device according to an embodiment includes a tablet terminal  10  and an external display  20 . The tablet terminal  10  is coupled to the external display  20 . In the present embodiment, two screens of the table terminal  10  and the external display  20  are integrally managed. The table terminal  10  and the external display  20  are examples of a display device. 
     The screen mounted on the tablet terminal  10  has a size of approximately six to eight inches, which is smaller than the size of the screen of the external display  20 . Hence, in recent years, as depicted in  FIG. 1 , a large-screen external display  20  or a projector is coupled to a tablet terminal  10  having a small screen, such that the display devices are used to function as an alternative to a PC. 
     The tablet terminal  10  and the external display  20  are examples of two or more display devices having different screen functions. A screen of the table terminal  10  (hereinafter also referred to as a “main body screen”) and a screen of the external display  20  (hereinafter also referred to as an “external screen”) are examples of respective screens of two or more display devices. The differences in the functions of the screens of the display devices include at least one of a difference in screen resolution and presences or absence of a touch function of the screen. 
     In the present embodiment, there is a tablet terminal  10  as a main body, and a screen output control process according to the embodiment described later is executed when an application operates on an OS (Operating System) of the tablet terminal  10 . 
     The external display  20  may be a television, a projector, a signage, or other display device insofar as the external display  20  has a larger screen than the main body screen of the tablet terminal  10 . An HDMI (registered trademark) (High-Definition Multimedia Interface) cable or a DisplayPort cable may be used as a cable for connecting with the external display  20 . A DVI (Digital Visual Interface) cable or analog RGB cable may alternatively be used for connecting with the external display  20 . The table terminal  10  and the external display  20  may be wirelessly coupled (Wireless Display). 
     According to the present embodiment, in the configuration of the display device depicted in  FIG. 1 , an output destination of an image may optionally be switched between the main body screen built in the main body of the tablet terminal  10  and an external screen of the external display  20 .  FIG. 2  illustrates patterns (hereinafter also referred to as “display patterns”) that may be considered as combinations of the image output destinations on the main body screen of the tablet terminal  10  and on the external screen of the external display  20 . Depending on the specification of the OS, for example, in a case of Windows (registered trademark), any one of the display patterns depicted in  FIG. 2  may be selected and output to the screens. Display patterns  1  to  5  will be described below. 
     Display Pattern  1   
     The display pattern  1  indicates that a screen is displayed only on the main body screen. In this case, a screen managed by an OS is displayed on the main body screen (of the table terminal  10 ), and even when the external display  20  is coupled to the tablet terminal  10 , the external screen is in a non-operating status to not display anything. 
     Display Pattern  2   
     The display pattern  2  indicates that a screen is extended to be displayed on two screens; the main body screen of the tablet terminal  10  acts as a main (first) display, and an external screen of the external display  20  acts as a second display. In this case, the OS manages respective display areas of the main body screen and the external screen to be a continuous rendering area, and different contents are displayed on the main body screen and the external screen, respectively. Specifically in this status, a coordinate origin is set on the main body screen, and the upper left corner of the main body screen acts as the coordinate origin (0,0) (see  FIGS. 6A and 6B ). In this case, desktop icons, a task tray, etc. are displayed on the main body screen, for example. As described above, the extended display in which the coordinate origin is set on the main body screen is referred to as “extended display ( 1 )”. 
     Display Pattern  3   
     The display pattern  3  indicates that a screen is extended to be displayed on two screens; the external screen display acts as a main-display and the main body screen acts as the second display. In this case, the OS manages respective display areas of the main body screen and the external screen to be a continuous rendering area, and different contents are displayed on the main body screen and the external screen, respectively. Specifically in this status, the coordinate origin is set on the external screen, and the upper left of the external screen acts as the coordinate origin (0,0). In this case, desktop icons, a task tray, etc. are displayed on the external screen, for example. As described above, the extended display in which the coordinate origin is set on the external screen is referred to as “extended display ( 2 )”. 
     Display Pattern  4   
     The display pattern  4  indicates a screen is duplicated to be displayed on two screens of the main body screen and the external screen. In this case, the main body screen and the external screen are considered as rendering areas having the same resolution, and the same contents are displayed on the two screens. 
     Display Pattern  5   
     The display pattern  5  indicates that a screen display is performed only on the external screen. In this case, a screen managed by the OS is displayed on the external screen, and even when the external display  20  is coupled to the tablet terminal  10 , the main body screen is in a non-operating status to not displaying anything. 
     Disordered Layout 
     Some of applications for the tablet terminal  10  may have a function of creating an image with an optimum design to be displayed on a small main body screen mounted on the table terminal  10  in improved viewability. Some other applications may be made with a user interface that is easy to operate with a touch panel on the main body screen. 
     In a case where such an application is displayed on the external screen, the applications designed for the small screen result in being displayed on the large screen. This may display the size of the character or the button to be larger than expected. Further, due to the resolution, the layout may become disordered or an image may exceed beyond the rendering area of the screen. 
     Further, even when the application for the tablet terminal  10  is made to be easy to touch for operating with the touch panel or digitizer, a user is not able to perform an input operation by touching the external display  20  not having a touch panel, which may lose user operability. For example, display statuses that may occur due to the difference between the resolution of the main body screen and the resolution of the external screen will be described with reference to  FIGS. 3A to 3C . 
     Resolution of Main Body Screen=Resolution of External Screen Resolution 
     In a case where the resolution of the main body screen and the resolution of the external screen are the same, and the display pattern  5  (displayed only on the external display  20 ) is set, as depicted in  FIG. 3A , an image displayed on the main body screen is displayed directly on the external screen without disordering the layout. The image is not displayed on the main body screen. 
     However, in a case where an application designed for the tablet terminal  10  generates a screen for a user to easily perform a touch operation on the screen of a small size of approximately 6 inches, an image may be displayed unnecessarily larger on the external screen. For example, as depicted in  FIG. 3B , in a case where a screen that is maximized is displayed on a full screen of the main body screen, and four or more buttons (user interface) are arranged on the main body screen, only four buttons may be displayed on the external screen of the external display  20 . In addition, in a case where an application is activated while presentation is being performed with a projector, such a display will be rendered on an entire screen. Further, buttons etc. displayed on the external screen will not be directly touched unless the function of the touch panel is installed in the external display  20 . Hence, a mouse or the like may need to be used for performing operations, leading to deficiencies in user operability and convenience. 
     Resolution of Main Body Screen&gt;Resolution of External Screen Resolution 
     In a case where the resolution of the main body screen is higher than the resolution of the external screen, and the display pattern  5  (displayed only on the external display  20 ) is similarly set, an image displayed on the main body screen with high resolution is displayed on the external screen with low resolution. In such a case, reproducing the layout displayed on the main body screen directly on the external screen when the application is executed by the OS may be unachieved. 
     The layout to be displayed, as actually appears, depends on the mechanism and application of the OS. For example, in a case where the size of each component (each image) on the screen is automatically adjusted such that the components such as buttons constituting the application fit within the main body screen, the layout may appear incorrectly despite the UI components fitting within the external screen. Further, in a case where such automatic adjustment is not performed, as depicted in  FIG. 3C , the layout may be exceed beyond the rendering area of the external screen. Further, a user is unable to directly touch the buttons or the like displayed on the external screen unless the function of the touch panel is installed in the external display  20 . Even when the function of the touch panel is installed in the external display  20 , a user is unable to touch the buttons disposed on the out-of-screen portion of the layout. 
     Resolution of Main Body Screen&lt;Resolution of External Screen Resolution 
     In a case where the resolution of the main body screen is lower than the resolution of the external screen, and the display pattern  5  (displayed only on the external display  20 ) is similarly set, an image displayed on the main body screen with low resolution is displayed on the external screen with high resolution. Hence, as depicted in  FIG. 3D , there is a possibility that an extremely small image, though being sufficiently disposed within the rendering area of the external screen, may be displayed. In such a case, a user is also unable to directly touch the buttons or the like displayed on the external screen unless the function of the touch panel is installed in the external display  20 . Even when the function of the touch panel is installed in the external display  20 , a display status of images that are extremely small may result in substantial impracticality for a user to touch, leading to erroneous operations. 
     In this embodiment, since the size and resolution of the main body screen of the tablet terminal  10  differ from those of the external screen of the external display  20 , some defects such as disordering the layout may occur when the application for the tablet terminal  10  is displayed on the external display. The present embodiment may be enabled to eliminate such defects. In addition, with respect to a user being unable to touch operations with respect to the buttons or the like displayed on the external display  20  because the external display  20  is not provided with a touch panel, the present embodiment may also be enabled to eliminate such defects. 
     Functional Configuration 
     An application configured to execute an image output control method according to the present embodiment is activated on an OS  2  of the tablet terminal  10  as depicted in  FIG. 4 , for example. The application  1  executed in the present embodiment includes an activation processor  11  and a main processor  12 . The activation processor  11  executed image output control upon activation of the application  1 . The main processor  12  performs necessary processes via the application  1 . 
     The activation processor  11  includes a screen display status determination unit  13 , a rendering area specifying unit  14 , and a screen switching processor  15 . The screen display status determination unit  13  checks a display status of a screen when the application  1  is activated. The rendering area specifying unit  14  specifies an area on the screen for displaying an image created by execution of the application  1 . The screen switching processor  15  requests the OS  2  to switch an output destination (display destination) of the screen as required. 
     The OS  2  has a screen manager  16 . The screen manager  16  manages a connection status of a display device such as the tablet terminal  10  having the main body screen and the external display  20  having the external screen and the display status of which display devices are being displayed. 
     A Graphics driver  17  is installed in the OS  2 . The graphics driver  17  has a screen switching controller  18 . In response to a screen switching request from the OS  2 , the screen switching controller  18  performs switching control of the screen output destination with respect to a graphics controller (sees  FIGS. 6A and 6B ). When the activation of the application  1  is started, the screen display status determination unit  13  acquires, from the screen manager  16  of the OS  2 , a connection status of another display device such as the external display  20  and information on the screen output destination. In the present embodiment, the connection status of the display may be acquired by detecting that a connection line such as the HDMI cable has coupled to the tablet terminal  10  and the external display  20 . 
     The screen display status determination unit  13  obtains screen output destination information by acquiring a screen mode from the screen manager  16 . The screen mode is set in a screen mode setting table  4 .  FIG. 5  illustrates an example of a screen mode setting table  4 . The screen mode setting table  4  includes settings of a screen mode  41  and a display patterns  42  before the activation of the application, and respective definitions of screen operations  43  upon activation of the application  1  with respect to the display patterns  42 . On this point, the screen mode  41  of the display pattern  42  includes a setting “ON”. Note that respective display patterns of  FIG. 5  correspond to the display patterns of  FIG. 2 . The screen mode setting table  4  is stored in the storage  3  of the tablet terminal  10 . The registration table  5  stored in the storage  3  will be described in a modification of the present embodiment. 
     In the example of  FIG. 5 , in a case of the display pattern  42  set before activation of the application in the screen mode setting table  4  being “1”, to “activate the application directly on the main body screen” is defined as the operation  43  upon activation of the application  1 . In this case, switching of the screen output destination does not occur. 
     In a case of the display patter  42  before activation of the application  1  being “2”, to “activate the application  1  in the rendering area of the main body screen, from among a combination of the rendering areas of the main body screen and the external screen” is defined as the operation  43  upon activation of the application  1 . In this case, switching of the screen output destination does not occur. 
     In a case of the display patter  42  before activation of the application  1  being “3”, to “activate the application  1  in the rendering area of the main body screen, from among a combination of the rendering areas of the main body screen and the external screen” is defined as the operation  43  upon activation of the application  1 . In this case, switching of the screen output destination does not occur. 
     In a case of the display patter  42  before activation of the application  1  being “4”, to “switch destination of output to ‘extended display ( 2 )’ and subsequently activate the application  1  in the rendering areas of the main body screen” is defined as the operation  43  upon activation of the application  1 . 
     In a case of the display pattern  42  before activation of the application  1  being “5”, to “switch destination of output to ‘extended display ( 2 )’ and subsequently activate the application  1  in the rendering area of the main body screen” is defined as the operation  43  upon activation of the application  1 . 
     In the example of  FIG. 5 , the screen mode  41  of the display pattern  5  is “ON”. In this case, a user only uses the external display  20  coupled to the tablet terminal  10  for outputting a screen on the external display  20  and the main body screen is disabled. Accordingly, the screen switching processor  15  that has acquired the screen mode  41  requests the screen manager  16  of the OS  2  to switch the screen output destination. The OS receives such a request, and requests the graphics driver  17  to switch the screen. As a result, the main body screen is enabled for display. 
     In a case where switching is not required or in a case where switching of the screen has been completed, the rendering area specifying unit  14  of the application  1  performs control to display a window of the application  1  in the rendering area corresponding to the main body screen, based on the information on the rendering area acquired from the screen manager  16  of the OS  2 . 
       FIGS. 6A and 6B  illustrates examples of a rendering area set by the rendering area specifying unit  14  according to the present embodiment.  FIGS. 6A and 6B  illustrate the rendering area managed by the OS  2  when the two screens are displayed in an extended manner. For example, in an OS such as Windows, rendering areas of two screens are managed as one continuous area. 
     For example, as depicted in  FIG. 6A , in a case of the main body screen of the tablet terminal  10  and the external screen of the external display  20  having the same resolution, an area obtained by connecting two rendering areas of the same size is managed as a rendering area. 
     By contrast, in a case of the main body screen and the external screen having different resolutions being coupled, as depicted in  FIG. 6B , rendering areas of different sizes that are coupled is managed as one rendering area. The window W 1  to W 3  of the application  1  may be arranged in this rendering area without any restriction. 
     An example of a display pattern combining the main body screen and the external screen is as illustrated in  FIG. 2 . In the present embodiment, when the application  1  is activated in each of the conditions with the display patterns depicted in  FIG. 2 , the activated application  1 , which is activated by performing a corresponding one of the operations  43  upon activation of the application  1  depicted in  FIG. 5 , is displayed on the main body screen. 
     Hardware Configuration 
     Next, a description is given, with reference to  FIG. 7 , of an example of the hardware configuration of the tablet terminal  10 . The tablet terminal  10  includes a CPU  100 , a main memory  201 , an eMMC (embedded Multi Media Card)  202 , a touch panel  203 , and a built-in display  204 . The CPU  100  includes a graphics controller  101 , a memory controller  102 , a storage controller  103 , and a USB controller  104 . 
     The memory controller  102  manages the main memory (main storage)  201  of the tablet terminal  10 . The graphics controller  101  manages display contents of screens and manages the display devices such as the external display  20 . The graphics controller  101  manages a part of the area in the main memory  201  as a VRAM (Video RAM) area and manages the status of the rendering area using the main memory  201 . The graphics controller  101  is coupled to the built-in display  204 . In addition, the graphics controller  101  may be coupled to the external display  20  using an HDMI cable or the like. 
     A nonvolatile storage (auxiliary storage) such as the eMMC  202  or the like is coupled to the storage controller  103 . The eMMC  202  and the like stores the OS  2  and the application  1 . For example, the touch panel  203  enables an input operation by touch on the screen of the built-in display  204 . As a result, the tablet terminal  10  functions as an input device and provides a user with an operation tool. In the example of  FIG. 7 , the touch panel  203  is coupled by the USB controller  104 ; alternatively, the touch panel  203  may be coupled by other interfaces. In addition, the tablet terminal  10  may be provided with a digitizer in place of a touch panel, or provided with both the digitizer and the touch panel. 
     In this example, the memory controller  102  and the graphics controller  101  are included in the CPU  100 ; however, these controllers may be constituted by chips differing from the CPU  100 . 
     As described above, the main body of the tablet terminal  10  is provided with the built-in display  204  and is not generally provided with a keyboard. Hence, a user may perform input operations on a screen by directly touching the main body screen of the tablet terminal  10  via a touch panel  203  or with a digitizer. In this description, the tablet terminal  10  is used as an example of display devices; however, a PC (personal computer) having a keyboard may be used in place of the tablet terminal  10 . Further, the tablet terminal may be a mobile device such as a smartphone, a portable information terminal (Personal Digital Assistant: PDA), a mobile phone, a mobile music device, a game machine, or the like. 
     Software Configuration 
     Next, a description is given, with reference to  FIG. 8 , of an example of the software configuration of the tablet terminal  10 . In the present embodiment, it is assumed that in the tablet terminal  10 , the application  1  is operating on the OS  2  under the control of the CPU  100 . 
     In the OS  2 , device drivers for the respective devices are installed in order to operate various devices. In this embodiment, in particular, in order to use the graphics function, the graphics driver  17  is installed as depicted in  FIG. 8 . Further, an application  1 , which is a main entity of the present embodiment, is installed in the OS  2 . A process performed by the application  1  on the device driver is executed by access from an API (application programming interface) whose specifications are disclosed by the OS  2  and the device driver. Therefore, when the application  1  switches between the main body screen of the tablet terminal  10  and the external screen of the external display  20  as the screen output destination, the application  1  requests the OS  2  to switch using the API. The OS  2  requests switching to the graphics driver  17 . Finally, the graphics driver  17  controls the hardware graphics controller  101  based on software processes to implement necessary processes. The above has illustrated the overall configuration, functional configuration, hardware configuration, software configuration, and basic operation policy of the display device when implementing the image output control method according to the present embodiment. The functions of the respective components in  FIGS. 6A and 6B  are implemented by causing the CPU  100  to execute the image output control program installed in the OS  2  to perform an image output process using the main body screen and the external screen. 
     The following illustrates an implementation method of the image output control process in the application  1 . In the present embodiment, two methods, i.e., the first method and the second method, may be given as a method of implementing the image output control process in the application  1 . The first method is to implement the image output control process in a specific application  1  designed for the tablet terminal  10 . The second method is to implement the image output control process in a launcher for activating a group of applications. The first method will be described as a present embodiment, and the second method will be described as a modification of the present embodiment. 
     Implementation in Specific Application  1 : First Method 
     In this case, the function of the present embodiment is implemented in the application  1  itself that is designed for a small screen. Specifically, among the processes of the application  1 , a function of the image output control process of the present embodiment is implemented in an initially retrieved process such as activation, initialization, or the like. The following illustrates a flow of an image output control process, which is executed upon activation of the application  1 , as will be described with reference to  FIG. 9 . 
     First, the activation processor  11  determines whether the external display  20  is coupled (step S 10 ). In a case where the activation processor  11  determines that the external display  20  is not coupled, the main body screen alone will act as an output destination. Accordingly, the activation processor  11  causes the application  1  to operate without performing any additional processes (step S 14 ), and ends this process. 
     By contrast, in a case where the activation processor  11  determines that the external display  20  is coupled, the screen display status determination unit  13  determines an output destination of the screen, based on the screen mode setting table  4  (step S 12 ). The screen display status determination unit  13  determines screen destination of the output based on the screen mode  41  set in the screen mode setting table  4  depicted in  FIG. 5 . 
     For example, in a case where the screen mode  41  is set (ON) to the display pattern  1 , the screen destination of the output will be the main body screen alone. In this case, there is no need to switch the screen destination of the output to the main body screen. Thus, the activation processor  11  activates the application  1  on the main body screen without performing any additional processes (step S 14 ), and ends this process. 
     In a case where the screen mode  41  is set (ON) to the display pattern  2  or the display pattern  3 , the screen destination of the output will be a rendering area combining rendering areas of both the main body screen and the external screen, such that an image or the like is extendedly displayed across the two screens (i.e., an image or the like is displayed on both screens). In this case, irrespective of the main body screen acting as the main (first) display or the second display, the screen switching processor  15  switches a coordinate origin to specify the rendering area of the main body screen, thereby making the main body screen to act as the screen output destination. After switching the coordinate origin, the activation processor  11  activates the application  1  on the main body screen (step S 16 ), and ends this process. 
     The main body screen may be specified by any method, and not specifically limited to specifying coordinates of the rendering area corresponding to the main body screen in a case where the main body screen and the external screen from continuous rendering areas. For example, in a case where the OS  2  manages an ID for uniquely identifying each of the screens, enabling specification of a display destination of the application  1 , the ID for identifying the corresponding screen may be used for specifying the main body screen as the display destination of the application  1 . 
     In a case where the screen mode  41  is set (ON) to the display pattern  4 , the screen output destination will be a rendering area combining the rendering areas of the main body screen and the external screen, and a duplicated image will be displayed on each of the screens. Further, as depicted in  FIG. 5 , in a case where the screen mode  41  is set (ON) to the display pattern  5 , the screen output destination will be the external display alone. In these cases, the main body screen needs to be enabled, and the screen output destination needs to be switched to the main body screen. Accordingly, in a case where the main body screen is disabled, the rendering area specifying unit  14  specifies the main body screen as the rendering area, and records information on the screen output destination before being switched in the main memory  201  or the like (step S 18 ). Thereafter, the screen switching processor  15  switches the screen output destination to the extended display ( 2 ). After switching the screen output destination, the activation processor  11  activated the application  1  in the rendering area of the main body screen (step S 20 ), and ends this process. 
     According to the image output control process described above, the application  1  will be displayed on the main body screen every time the application  1  is activated. According to the present embodiment, upon the activation of the specific application  1  with a design optimized for the small screen of the tablet terminal  10 , the external display  20  or the projector may be coupled to output the screen without any deterioration in display of the external display  20  or the projector. That is, according to the present embodiment, display deterioration may be prevented by displaying the application  1  invariably within the rendering area of the main body screen of the tablet terminal  10 . 
     For example, in a case where a user attempts to activate the application  1  with the display pattern  5 , in which the main body screen is disabled and only the external display  20  is selected as the screen output destination, an image will not normally be displayed on the main body screen because the main body screen is disabled. 
     Hence, according to the present embodiment, in such a case, when a user attempts to activate the application  1 , the screen output destination is switched to enable the disabled main body screen, and the application  1  is subsequently activated, thereby enabling the main body screen to perform display by the application  1 . In this case, “to enable the main body screen” specifically indicates to “switch to the extended display ( 2 ) of the display pattern  3 ”. As a result, it may be possible to specify the external display  20  as the main-display to change the screen destination of the output while enabling the main body screen and retaining the enabled display of the external display  20 . Hence, the contents that have been displayed on the external display  20  may be retained on the external display  20  while being displayed. According to the present embodiment, when the screen display in the present embodiment is switched back to the original screen display, a user may continue stable operation on the main-display without changing work environment on the external screen, by setting the external display  20  as a main-display. 
       FIGS. 10A and 10B  represent examples of operations. The tablet terminal  10  is coupled to the external display  20 . In the example of  FIG. 10A , a screen is output only on the external display  20 , and the tablet terminal  10  is disabled. In this example, a window W 1  and an icon Q are displayed on a desktop screen displayed on the external display  20 . In this screen status, a user clicks the icon Q with a mouse to select a specific application  1  to activate the application  1 . In this case, when the function of the screen output control process according to the present embodiment is implemented in the application  1 , the screen output destination is changed according to the definition of the extended display ( 2 ). This enables the main body screen. Next, as depicted in  FIG. 10B , an image R generated by the application  1  is displayed in the rendering area of the main body screen. Note that the contents displayed on the external display  20  retain their original display on the external display  20 . 
     In the examples depicted in  FIGS. 11A and 11B , the external display  20  is coupled to the tablet terminal  10 , and duplicated display is set to the external display  20  and the tablet terminal  10 , which enables images of the same contents to be displayed on the main body screen and the external screen. In this case, the specific application  1  indicated by the icon Q is selected from the desktop screen displayed on the external display  20 , whereby the application  1  is activated. At that time, similar to the example of  FIGS. 10A and 10B , after changing the screen output destination to the extended display ( 2 ), the image R generated by the application  1  is displayed in the rendering area of the main body screen. 
     Accordingly, it is possible to prevent the screen of the application  1  designed to be optimum according to the screen size of the tablet terminal  10  from being displayed as small on the external display  20  or from being displayed outside the display area due to a difference in resolution between the tablet terminal  10  and the external display  20 . Further, the screen generated by the application  1  is displayed on the main body screen by enabling the disabled main body screen. This makes it possible for a user to perform an input operation via the screen on the touch panel of the tablet terminal  10 . In addition, when a user performs some work on the external display, display contents on the external display may still be retained as they are. Thus, the user may continue operation without being interrupted. 
     Further, when the screen output destination is switched by the image output control process of the present embodiment upon activation of the application  1 , an end process depicted in  FIG. 12  is executed upon ending the application  1 . In the ending process of the application  1 , the rendering area specifying unit  14  determines whether the screen output destination has been changed upon activation of the application  1  (step S 22 ). When the rendering area specifying unit  14  determines that the screen output destination has been changed, the rendering area specifying unit  14  returns the screen output destination to the original status of the screen before activation of the application  1  (step S 24 ), based on information about the original screen output destination recorded in the main memory  201 , and ends the process. When the rendering area specifying unit  14  determines that the screen output destination has not been changed, the rendering area specifying unit  14  immediately ends the process. 
     Modification 
     Implementation on Launcher: Second Method 
     Finally, a screen output control process according to a modification of the present embodiment will be described with reference to  FIGS. 13 and 14 . In the modification, a description is given of an example of the screen output control function that is implemented on the launcher. 
     In this case, the screen output control function is implemented on the launcher for activating the application  1 . Hence, it is not necessary for the application  1  designed for the tablet terminal  10  to be activated to implement the screen output control function. Accordingly, all the applications included in the launcher may be provided with the same effect by the screen output control. 
     The launcher is a tool for displaying a list of multiple applications frequently used by a user registered in advance to enable the user to immediately activate these applications. For example, the tablet terminal  10  of  FIG. 13  registers a launcher displaying a list of icons L 1  to L 12  for activating the multiple applications frequently used by the user. 
     To register an application in the launcher, display attribute information such as an application name  52 , an installation folder  53 , and the like may need to be registered in the registration table  5 . An icon  51  may be registered according to the application name  52 . In this modification, activation screen information  54  indicating whether to activate an application to be registered on the main body screen is added to the display attribute information. In a case where a user desires to activate an application to be registered in the launcher on the main body screen without failing, the user registers the application by specifying the main body screen in the activation screen information  54 . 
       FIG. 14  illustrates a flow of selecting an application from the launcher and starting activation of the selected application. First, based on the registration table  5 , the launcher determines whether to activate an application on the main body screen according to display attribute information (application name  52 , installation folder  53 ) of the application that is linked to the icon  51  specified by the user (step S 30 ). Note that in a case of an application being not registered to be activated on the main body screen, the function of the image output control process needs not to be executed; hence, the specified application is thus directly activated (step S 14 ), and the process then ends. 
     However, in a case of an application being registered to be activated on the main body screen, step S 10  and steps subsequent to step S 10  are executed. Steps subsequent to step S 10  are provided with the same step numbers as those given to the screen output control process depicted in  FIG. 9 . Since these are similar processors, a duplicated description will be omitted here. 
     In a case of implementing an application in the launcher as similar to that in the above-described embodiment, when the screen destination of the output is switched upon activation of the specified application, the output destination (original output destination) before being switched is recorded. Then, a process of returning the screen output destination to the original screen output destination as before the activation of the application will be executed upon ending the application. In this case, the screen switching process ( FIG. 12 ) is executed upon recognizing the ending of the process of the application specified by a launcher. 
     As described above, according to the screen output control method according to the modification of the present embodiment, when the application registered in the launcher is activated, an application generation screen will be displayed invariably on the main body screen of the tablet terminal  10  without failing. As a result, even when a screen is displayed on an external display having a large screen or a projector, disordering a layout of the screen and degrading the touch operation on the external display  20 , a user may be able to perform touch operation on the main body screen of the tablet terminal  10 . In addition, displaying the application generation screen invariably on the main body without failing may secure an input operation by touching the screen even when the touch panel is not installed on the external display  20 . 
     Further, even when the operation to switch the screen output destination is executed in order to change the main screen from the disabled status to the enabled status, the display content of the external display  20 , on which the user has been working, will be retained. As a result, the above-described advantageous effect may be provided without disturbing the user&#39;s work. 
     As described above, according to the screen output control method according to the present embodiment and the modification of the present embodiment, it is possible to improve an output process of an image on the multiple display devices having different screen functions. 
     The image output control method, the image output control program, and the display device have been described in the above embodiment and modification; however, the image output control method, the image output control program, and the display device according to the present invention are not limited to the above embodiments; various modifications and improvements may be made within the scope of the present invention. Further, when there are two or more embodiments and modifications, these embodiments and modifications may be combined within a scope of these embodiments and modifications having no contradiction. 
     For example, the configuration of the display device according to the above embodiment and its modification is merely an example, and the scope of the present invention is not limited this example. It is needless to say that there are various system configuration examples according to an application or purpose. For example, the number of display devices to which a tablet terminal is coupled is not limited to one, and multiple display devices may be coupled to the tablet terminal. 
     In the above embodiment and its modification, among the multiple display devices having different screen functions, one of the display devices is used as the external display acting as a display device, and the other is used as the other display device acting as the tablet terminal, such that when a screen function is unable to be implemented in one display device, screen function is implemented on the other display device. However, the present invention is not limited to this example. One of display devices may be one of a plurality of display devices having different screen functions, and another display device from a plurality of display devices may be another one of the display devices having different screen functions. 
     According to one aspect of embodiments, it is possible to improve an image output process upon outputting an image to a plurality of display devices having different screen functions. 
     All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority or inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.