Patent Publication Number: US-2019171406-A1

Title: Information processing apparatus and method of controlling the same

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a system in which an information processing apparatus and a video image display apparatus are connected via a network. 
     Description of the Related Art 
     A video image transfer system is known in which information processing apparatuses such as personal computers (“PCs” hereinafter) and video image display apparatuses such as projectors are connected via a network as opposed to a system in which PCs and projectors are connected via connection cables such as HDMI (r) cables. Such video image transfer systems are provided with functions such as the function of simultaneously causing a plurality of projectors to project a video image from a single PC and the function of causing a single projector to project video images from a plurality of PCs on multiple screens. 
     Japanese Patent Laid-Open No. 2014-127915 discloses a technology in which a work group is constructed from a plurality of PCs and a plurality of projectors, and the projectors display video images from the PCs in free layouts. 
     In a conventional system in which connection is made via video cables, when a PC and a projector are connected, the PC can automatically recognize the projector as an external display, and the desktop of the PC can be extended or replicated. In particular, when the desktop is extended, it is possible to treat the area recognized as an external display and spanning the display of the PC and the projector as a desktop area to work in. In this way, the display screen of the PC being used by the presenter may be different from the video image, which is projected by the projector, that the audience is viewing, as is widely practiced in presentations. 
     However, in a system in which a PC and a projector are connected via a network, as the PC is unable to automatically recognize the projector as an external display, the projector can only display the same video image as that on the display of the PC. 
     Moreover, if the desktop of the PC is to be extended or replicated, extension or replication needs to be performed at an appropriate timing because extending or replicating the desktop consumes PC resources. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in consideration of the aforementioned problems, and realizes a system capable of generating video images to be displayed on a device connected via a network at an appropriate timing. 
     In order to solve the aforementioned problems, the present invention provides an information processing apparatus which displays a video image on a display unit, comprising: a communication unit configured to communicate with a display apparatus via a network; and a control unit configured to generate a video image of an extended display to be displayed on the display apparatus displays when the communication unit establishes a connection with the display apparatus, the video image being different from the video image displayed on the display unit. 
     In order to solve the aforementioned problems, the present invention provides a method of controlling an information processing apparatus that includes a communication unit configured to communicate with a display apparatus via a network and display a video image on a display unit, the method comprising: generating a video image of an extended display to be displayed on the display apparatus displays when the communication unit establishes a connection with the display apparatus, the video image being different from the video image displayed on the display unit. 
     In order to solve the aforementioned problems, the present invention provides a non-transitory computer-readable storage medium storing a program for causing a computer to execute a method of controlling an information processing apparatus that includes a communication unit configured to communicate with a display apparatus via a network and display a video image on a display unit, the method comprising: generating a video image of an extended display to be displayed on the display apparatus displays when the communication unit establishes a connection with the display apparatus, the video image being different from the video image displayed on the display unit. 
     According to the present invention, it is possible to generate video images to be displayed on a device connected via a network at an appropriate timing. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing a system configuration according to an embodiment of the present invention. 
         FIG. 2  is a block diagram showing a configuration of the apparatuses according to the embodiment shown in  FIG. 1 . 
         FIG. 3  is a flowchart showing processing for generating an extended display according to the embodiment shown in  FIG. 1 . 
         FIG. 4  is a sequence diagram of the processing for generating an extended display according to the embodiment shown in  FIG. 1 . 
         FIGS. 5A-5L  are diagrams illustrating UI screens according to the embodiment shown in  FIG. 1 . 
         FIGS. 6A-6C  are diagrams showing alternative system configurations according to the embodiment shown in  FIG. 1 . 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Embodiments of the present invention will be described in detail below. The following embodiments are merely examples for practicing the present invention. The embodiments should he properly modified or changed depending on various conditions and the structure of an apparatus to which the present invention is applied. The present invention should not be limited to the following embodiments. Also, parts of the embodiments to be described later may he properly combined. 
     First Embodiment 
     A video image transfer system according to a first embodiment will be described hereinafter with reference to  FIGS. 1 and 2 . 
     In the present embodiment, while a case in which a PC is used as an exemplary information processing apparatus and a projector is used as an exemplary video image display apparatus, the present invention is not limited to this. For example, a mobile phone, a digital camera, or a so-called tablet terminal may be used as the information processing apparatus of the present invention. Furthermore, a display, a digital TV set, or a so-called tablet terminal may be used as the video image display apparatus of the present invention. Also, for example, any other type of display apparatus that can display video images transferred from a PC may be used as the video image display apparatus. 
     In  FIG. 1 , a PC  100  and a projector  200  of the present embodiment are connected via a communication network  150  such as a LAN (Local Area Network). Upon establishing communication between the PC  100  and the projector  200 , the PC  100  generates, in addition to a video image  10  on the main display, a video image  20  of an extended display and transfers the video image as a video image  30  that is compatible with the resolution of the projector  200 . The projector  200  projects the video image  30  of the extended display transferred from the PC  100  onto a screen, etc. In this way, the user operating the PC  100  (the presenter) can display, using the projector  200 , the presentation video image  30  intended for an audience while, displaying on the PC  100 , the video image  10  which could be supplemental materials for the presenter, that is different from the video image  30 . 
     As used in the present embodiment, the term “extended display” refers to an area outside of the range of the main display of the PC  100  that is created when the desktop UI displayed on the main display of the PC  100  is extended exceeding the main display resolution of the PC  100 . Referring to  FIG. 1  as an example, the main display of the PC  100  displays the video image as indicated by the reference numeral  10 , and the desktop area, while not being shown on the main display, is connected to the right side of the main display as indicated by the reference numeral  20 . This area  20  is referred to as the extended display (virtual display). 
     Referring now to  FIG. 2 , the configurations of the PC  100  and the projector  200 , which constitute the video image transfer system of the present embodiment, will be described hereinafter. 
     First, the configuration and function of the PC  100  will be described hereinafter. 
     The CPU  101  performs overall control of the PC  100 , such as display control, recording control, video image processing control, communication control, by controlling its components according to input signals and programs. A RAM  102  is the main memory for storing data. The RAM  102  is mainly used as an area for storing various types of data, such as an area for storing or deploying programs executed by the CPU  101  or a work memory for programs being executed. A VRAM  103  stores video image data displayed on a display unit  106 . If the RAM  102  is sufficiently fast, the RAM  102  may be used as the VRAM  103 . A ROM  104  stores the boot program that is executed when the CPU  101  is initialized. The boot program deploys and starts, on the RAM  102 , the OS (Operating System) stored in the recording medium  105 . The recording medium  105  is a memory card or a hard disk drive for storing data and various programs, such as the video image transfer program described below and the OS. 
     The display unit  106  displays the video image data specified by a display control unit  107 . The display unit  106 , for example, is a liquid crystal panel or an organic EL panel. The display control unit  107  reads out the video image data stored in the VRAM  103  and displays it on the display unit  106 . An operation unit  108  comprises operation members, such as a keyboard, a mouse, and a touch panel, to accept input made by a user and transmit the input to the CPU  101 . If a touch panel is used, the touch panel is provided integrated with the display unit  106  so that operations can be input by touching the display surface. A communication unit  109  communicates with external apparatuses, such as the projector  200 , via the communication network  150 . The communication unit  109  is a communication interface module, such as a Gigabit Ethernet (r) or wireless LAN module. The communication unit  109  is, however, not limited to these, and various communication systems can also be used. An internal bus  110  connects the above-described components, The PC  100  may not necessarily be controlled by a single piece of hardware. For example, a plurality of pieces of hardware may share the load of processing to implement the various functions of the PC  100 . 
     The following describes basic operations of the PC  100  of the present embodiment. 
     An application program for transferring video images (to be referred to as the video image transfer program hereinafter) is installed in the PC  100 . The video image transfer program executed by the CPU  101  controls the display control unit  107  and captures the video image data displayed on the display unit  106  from the VRAM  103 , and encodes it in a predetermined format (for example, JPEG) that the projector  200  is capable of projecting. The video image transfer program executed by the CPU  101  transmits the encoded video image data to the projector  200  via the communication unit  109 . The video image transfer program executed by the CPU  101  accepts various types of operations such as selection of the projector to be connected to and starting/stopping of video image data transfer, via the GUI provided by the video image transfer program. The video image transfer program converts such operations into control commands and transmits the commands to the projector  200  via the communication unit  109 . 
     Next, the configuration and functions of the projector  200  will be described hereinafter. 
     The functions of a CPU  201 , a RAM  202 , a ROM  203 , a VRAM  204 , an operation unit  208 , a communication unit  209 , and an internal bus  210  as hardware are the same as those in the PC  100 , description of these components is omitted. 
     The ROM  203  stores the programs and parameters required for the projector  200  to operate, and the CPU  201  operates according to the programs stored in the ROM  203 . The VRAM  204  stores the video image data projected by the projection unit  206 . The decoder  205  decodes the encoded video image data transferred from the PC  100 . The projection unit  206  has a liquid crystal panel, a lens, a light source, etc., to project the decoded video image. The projection control unit  207  reads out the video image data held in the VRAM  204  and causes the projection unit  206  to project the data. Alternatively, the CPU  201  may operate as the projection control unit  207 . The projector  200  may not necessarily be controlled only by the above-described hardware. For example, a plurality of pieces of hardware may share the load of processing to implement the various functions of the PC  100 . 
     The operation unit  208  comprises buttons provided on the main body of the apparatus and a remote controller reception unit for accepting user operations from a remote controller (not shown) and transmitting them to the CPU  201 . 
     The following describes basic operations of the projector  200  of the video image transfer system of the present embodiment. 
     The CPU  201  of the projector  200  receives, via the communication unit  209 , the encoded video image data transferred from the PC  100 , decodes the data using the decoder  205 , and deploys the decoded data on the VRAM  204 . The CPU  201  also controls the projection control unit  207 , reads out the video image data deployed on the VRAM  204 , and projects the data using the projection unit  206 . Additionally, if the projector  200  is selected as the projector to be connected to in the PC  100 , the CPU  201  receives control commands from the PC  100  via the communication unit  209 , such as a connection request and starting/stopping of video image data transfer, and executes processing according to the commands received. 
     Description of System Operation 
     Next, the operations of a system according to the present embodiment will be described with reference to  FIGS. 3, 4, 5A to 5L and 6A to 6C . 
       FIG. 3  shows a procedure followed by the PC  100  to generate an extended display.  FIG. 4  is a sequence diagram showing the processing performed by the user, the PC, and the projector.  FIGS. 5A to 5L  show exemplary UI screens of the video image transfer program of the PC.  FIGS. 6A and 6C  show alternative system configurations. 
     The following describes the processing to generate an extended display in the cases shown in  FIGS. 6A and 6B .  FIG. 6A  shows a case in which the video image transfer program of the PC  100   a  generates a group consisting of projectors  200   a  and  200   b  (referred to as a session hereinafter).  FIG. 6B  shows a case in which a new PC  100   b  participates in an already generated session (a Meeting X). Although not described in detail, a logical connection has been established between all of the PCs and all of the projectors involved in a session. This makes it possible to start and stop the transfer of video image data via the network to each of the projectors selected via the video image transfer program of the PC  100   a.  This also makes it possible to simultaneously transmit the screens of the PCs to all the projectors generating a session. It is also possible for one PC to instruct another PC to start and stop the transfer of video image data. 
     Description of Session Generation Sequence 
     First, the sequence in which the video image transfer program of the PC  100   a  is operated to generate a session formed by the projectors  200   a  and  200   b  will be described with reference to  FIGS. 4 and 5A to 5L . The following description refers to a user operating the PC  100   a  as a user A. 
     When the user A activates the video image transfer program of the PC  100   a,  the UI shown in  FIG. 5A  is displayed to prompt the user to select whether generate a session or participate in a session that has already been generated. 
     In step S 400 , the user A instructs the video image transfer program of the PC  100   a  to generate a new session. In other words, the user A presses a button  500  shown in  FIG. 5A . 
     In step S 401 , the video image transfer program of the PC  100   a  displays the list of projectors shown in  FIG. 5B  for selecting projectors to generate a session with. The projector list includes a projector information command to be broadcast by the projectors via the network. 
     In the present embodiment, the projectors  200   a  and  200   b  are on the network, and thus the projectors  200   a  and  200   b  broadcast a projector information command over the network in steps S 402  and S 404 . A projector information command includes the IP address of the projector and the projector name, for example. In this example, to simplify the description, a projector information command is transmitted when an instruction to generate a session is made. However, before being sessionized, each projector transmits a projector information command at regular intervals. 
     In steps S 403  and S 405 , the video image transfer program of the PC  100   a  updates the projector list because projector information commands have been received. In particular, as shown in  FIG. 5B , information regarding the projectors  200   a  and  200   b  is displayed in a projector list display area  502  as projectors that can be selected when generating a session. The UI shown in  FIG. 5B  displays a list of pieces of information regarding the projectors that can be selected for sessionization and includes check boxes  503  for selecting the projectors. 
     In step S 406 , the user A selects the projectors  200   a  and  200   b  from the projector list of the video image transfer program of the PC  100   a  to issue an instruction to generate a session. This operation corresponds to the selection of the projectors  200   a  and  200   b  made by checking the appropriate check boxes  503  shown in  FIG. 5B . This also corresponds to entering the name of the session to a session name entry area  504  (“Meeting X” in this example) and pressing a confirmation button  505 . 
     In steps S 407  and S 408 , the video image transfer program of the PC  100   a  establishes a logical connection with the projectors  200   a  and  200   b,  which are to be sessionized, and the PC  100   a.  Upon establishing a connection, the PC  100   a  transmits its own IP address and name (“PC  100   a ” in this example) to the projectors  200   a  and  200   b.  As described above, data transfer is enabled between the PC that has established a connection and the sessionized projectors. Although a detailed description is omitted, password verification may additionally be required for each projector before establishing a connection. 
     In steps S 409  and S 410 , the video image transfer program of the PC  100   a  transmits a sessionization request command to each of the projectors  200   a  and  200   b,  with which a connection has been established. A sessionization request command includes at least the number of projectors selected from the projector list display area  502  of  FIG. 5B  with which a session is generated and information regarding each projector (the IP address and the projector name). Furthermore, the sessionization request command includes the session name entered in the session name entry area  504  shown in  FIG. 5B . 
     In steps S 411  and S 412 , upon receiving a sessionization request command, the projectors  200   a  and  200   b  enter a sessionized state. In these steps, the CPU  201  of each of the projectors  200   a  and  200   b  stores, in the RAM  202 , information regarding each projector (the IP address and the projector name), the name of the session, and information regarding the PC participating in the session (the IP address and the PC name). 
     In step S 413 , the video image transfer program of the PC  100   a  performs the processing to generate an extended display, which will be described below. 
     Extended Display Generation Processing 
     Referring now to  FIG. 3 , the processing performed in step S 413  of  FIG. 4  to generate an extended display will be described hereinafter. The processing shown in  FIG. 3  is implemented by the CPU  101  of the PC  100  executing the video image transfer program. 
     In step S 301 , the CPU  101  uses the display control unit  107  to determine whether or not a sub-display exists in addition to the main display. If a sub-display exists, the processing is terminated, and if there is no sub-display, the process proceeds to step S 302 . If a sub-display exists in the setup, it is possible, for example, to display presentation materials to the audience on the main display while displaying auxiliary materials to the presenter on the sub-display. In other words, without applying the present embodiment, the user can cause the projector to project the presentation materials and cause the display at hand to display the auxiliary materials simply by specifying that the main display is to be transferred to the projector. 
     In step S 302 , the CPU  101  determines, via the display control unit  107 , whether or not it is possible to generate an extended display. If it is possible to generate an extended display, the process proceeds to step S 303 , otherwise the process is terminated. In this example, the display control unit  107  is already controlling the display operation of the display unit  106 . In this processing, in addition to causing the display unit  106  (the main display) to display information, the video image transfer program also makes an inquiry to the display driver as to whether or not it is possible to generate an extended display via the API (Application Programming Interface) provided by the OS. 
     In step S 303 , the CPU  101  acquires the resolution corresponding to the extended display from the display control unit  107  and stores it in the RAM  102 , and the process proceeds to step S 304 . 
     In step S 304 , the CPU  101  controls the communication unit  109  to request each of the projectors with which connection has been established to transmit its resolution, and stores the resolution received from each projector in the RAM  102 , and the process proceeds to step S 305 . 
     In step S 305 , the CPU  101  determines the resolution of the extended display based on the resolution corresponding to the extended display stored in the RAM  102  in step S 303  and the resolutions of the connected projectors stored in the RAM  102  in step S 304 , and the process proceeds to step S 306 . In this case, as the resolution at which the extended display can be generated, the CPU  101  applies, for example, the resolution closest to the lowest resolution of the resolutions of the plurality of connected projectors (including the resolution equivalent to the smallest resolution). In this way, the network bandwidth can be minimized when simultaneously displaying the video image of the extended display using all of the plurality of the connected projectors. In addition, as the video image received by the projectors need not be reduced, it is possible to reduce character blurring and the like. 
     Alternatively, as the resolution at which the extended display can be generated, the CPU  101  may apply, for example, the resolution closest to the largest resolution of the resolutions of the plurality of connected projectors (including the resolution equivalent to the largest resolution). As this allows for transfer of an optimum video image for the projector that has the highest resolution of the resolutions of the plurality of connected projectors, the optimized projector is capable of projecting the video image at high resolution. 
     In step S 306 , the CPU  101  instructs the display control unit  107  to generate an extended display at the resolution determined at step S 305 , and the extended display is generated. 
     Continued Description of Session Generation Sequence 
     Returning to  FIG. 4 , the description of the sequence in which a session is generated is resumed. To simplify the following description, in this example, the PC  100   a  is determined as being able to generate an extended display in step S 302 , and an extended display has been already generated. 
     In step S 414 , the video image transfer program of the PC  100   a  displays the projection control UI shown in  FIG. 5C  to control the projection operations of the sessionized projectors. 
     The projection control UI includes a session name display area  506 , sessionized projector selection tabs  507  and  508 , an own PC information display area  509  that shows information regarding the PC that is executing this particular video image transfer program, and a separate PC information display area  510 . In addition, the projection control UI includes a projection layout setting area  511 , a projection start button  512 , and a projection stop button  513 . 
     In the present embodiment, as the PC  100   a  has sessionized the projectors  200   a  and  200   b  under the session name of “Meeting X,” the two sessionized projector selection tabs  507  and  508  are displayed. By selecting the tab  507  or  508 , the user can display and control the projection layout setting area  511  of the projector that corresponds to the selected tab. A tab is displayed for each sessionized projector. As this session is named “Meeting X”, this session name is displayed in the session name display area  506 . The own PC information display area  509  displays information regarding the PC itself that is currently executing the video image transfer program (that is, information regarding the PC  100   a ). The separate PC information display area  510  displays information regarding PCs belonging to a session other than the own PC. However, as this step of the present example comes immediately after the generation of a session, nothing is shown in this area as there are no other participating PCs. 
     Description of Session Participation Sequence 
     Next, as shown in  FIG. 6B , the sequence in which the video image transfer program of the PC  100   b  participates in the session generated by the PC  100   a  to which the projectors  200   a  and  200   b  belong will be described with reference to  FIGS. 4 and 5A to 5L . In the following description, the user who operates the PC  100   b  is referred to as the user B. 
     First, When the user B activates the video image transfer program of PC  100   b,  the UI shown in  FIG. 5A  is displayed to prompt the user to select whether to generate a session or participate in a session that has already been generated. In step S 420 , the user B instructs the video image transfer program of the PC  100   b  to participate in a session. In other words, the user A presses a button  501  shown in  FIG. 5A . 
     In step S 421 , the video image transfer program of the PC  100   b  displays the session list shown in  FIG. 5D  for selecting the session to participate in. The session list includes a session information command to be broadcasted by the projectors via the network. 
     In the present embodiment, the projectors  200   a  and  200   b  are sessionized on the network in steps S 411  and S 412 . Therefore, in steps S 422  and S 424 , each of the projectors  200   a  and  200   b  reads session information from the RAM  202  and broadcasts it over the network as a session information command. A session information command includes the number of projectors generating the session, the IP address of each projector, the name of each projector, the session name, the IP addresses of the PCs, and the names of the PCs. In addition, the aforementioned information is included in the information transmitted to the projectors  200   a  and  200   b  upon the PC  100   a  making a connection request in steps S 407  and S 408  and in the sessionization request command transmitted by the PC  100   a  in steps S 409  and S 410 . As the information transmitted by the PC  100   a  to the projector  200   a  is the same as the information transmitted by the PC  100   a  to the projector  200   b,  the session information commands transmitted by the projectors  200   a  and  200   b  are also the same. The projectors to be sessionized are the two projectors  200   a  and  200   b,  the session name is “Meeting X”, and the PC that is participating in the session is the PC  100   a.    
     The video image transfer program of the PC  100   b  has received session information commands, and thus the program updates the session list in steps S 423  and S 425 . Specifically, the session list display area  514  indicates the session name “Meeting X” as the session to participate in as shown in  FIG. 5D . As the session information commands received in steps S 423  and S 425  are the same, no update is performed in step S 425 . The session list is provided with a radio button  515  for selecting a session to participate in, allowing the user to select one session to participate in. 
     In step S 426 , from the session list of the video image transfer program of the PC  100   b,  the user B selects the session to which the projectors  200   a  and  200   b  belong as the session to participate in. This operation corresponds to selecting “Meeting X” using the radio button  515  shown in  FIG. 5D  and pressing an OK button  516 . 
     In steps S 427  and S 428 , the video image transfer program of the PC  100   b  establishes a logical connection with the projectors  200   a  and  200   b  to be sessionized and the PC  100   b.  The PC  100   b  transmits its own IP address and name (“PC  100   b ” in this example) to the projectors  200   a  and  200   b.    
     In steps S 429  and S 430 , the projectors  200   a  and  200   b  connected to the new PC  100   b  update the PC information regarding the PC that is already participating in the session, the PC information being managed as session information, and also notify the PC that is participating in the session (the PC  100   a ) of this fact. 
     In step S 431 , the video image transfer program of the PC that has received the notification made in step S 430  (the PC  100   a ) updates the projection control UI as shown in  FIG. 5E  based on the received session information. As the session information includes the name of the PC  100   b,  which has newly participated in the session, the video image transfer program of the PC  100   b  updates the separate PC information display area  510  to show information regarding the PC  100   b.    
     In step S 432 , the video image transfer program of the PC  100  performs the processing to generate an extended display as described in connection with step S 413  in  FIG. 4 . 
     In step S 433 , the video image transfer program of the PC  100   b  shows the projection control UI shown in  FIG. 5F  to control the projection operations of the sessionized projectors. The content in the own PC information display area  509  and the content in the separate PC information display area  510  of the UI shown in  FIG. 5F  are the reverse of those in the UI of the video image transfer program of the PC  100   a  shown in  FIG. 5E . 
     Projection Control After Sessionization 
     With reference to  FIGS. 5E to 5L . the following describes the procedure in which after sessionization the user transfers, via the projection control UI of the video image transfer program of the PC  100   a,  the video image of the extended display of the PC  100   a  to the projector  200   a  and the video image of the extended display of the PC  100   b  to the projector  200   b  as shown in  FIG. 6C . 
     Transfer of Extended Display Generated by PC  100   a  to Projector  200   a    
     First, the procedure by which the video image transfer program of the PC  100   a  transfers the video image of the extended display generated by the PC  100   a  to the projector  200   a  will be described hereinafter. 
     As a result of the processing described so far, the projection control UI of the video image transfer program of the PC  100   a  is as shown in  FIG. 5E . In this state, the tab  507  is selected from the sessionized projector tabs, as shown in  FIG. 5G , in order to operate the projection layout of the projector  200   a.  Moreover, in  FIG. 5G , when the own PC information display area  509  indicating the PC  100   a  is dragged and dropped in the projection layout setting area  511 , the projection control UI changes to that shown in  FIG. 5H . The own PC information display area  509  is grayed out to indicate the own PC is in the projection layout. Furthermore, the projection layout setting area  511  indicates, with the icon  517 , that the display to be projected of the PC  100   a,  or the own PC, is the main display. By clicking on the icon  517 , the projection control UI changes to that shown in  FIG. 5I . 
     In this way, the display to be projected can be switched to the sub-display as indicated by the icon  518  as shown in  FIG. 5I . In the PC  100   a,  the extended display generated in step S 413  of  FIG. 4  is the display to be projected. It should be noted that, if it is determined in step S 301  of  FIG. 3  that a sub-display exists, the sub-display is the display to be projected. 
     By pressing the projection start button  512  in this state, the video image transfer program of the PC  100   a  controls the display control unit  107  to capture the video image data that corresponds to the extended display from the VRAM  103  and encode the data. Subsequently, the encoded video image is transmitted via the communication unit  109  to the projector  200   a  (selected in step S 407  of  FIG. 4 ), which in turn receives, decodes, and projects the video image as described above. As a result, as shown in  FIG. 6C , the projector  200   a  projects the extended display  30   a  of the PC  100   a.    
     Transfer by PC  100   a  of Extended Display Generated by Other PC (PC  100   b ) to Projector  200   b    
     The following describes the procedure in which the video image transfer program of the PC  100   a  transfers the video image of the extended display generated by the PC  100   b  to the projector  200   b.    
     The tab  508  shown in  FIG. 5J  is selected, from among the sessionized projector tabs in the state shown in  FIG. 5I , in order to operate the projection layout of the projector  200   b.  At this point, as projection layout has not vet been set for the projector  200   b,  no settings have been made in the projection layout setting area  511  as shown in  FIG. 5J . Moreover, in  FIG. 5J , when the separate PC information display area  510  showing the PC  100   b  is dragged and dropped in the projection layout setting area  511 , the projection control UI changes to that shown in  FIG. 5K . The separate PC information display area  510  is grayed out to indicate the PC  100   b,  which is the separate PC, is already in the projection layout. Furthermore, the projection layout setting area  511  indicates, with the icon  517 , that the display of the PC  100   b  to be projected is the main display. By clicking on the icon  517 , the projection control UI changes to that shown in  FIG. 5L . 
     In this way, the display to be projected can be switched to the sub-display as indicated with the icon  518  shown in  FIG. 5L . As an extended display was generated in the PC  100   b  in step S 432  of  FIG. 4 , the extended display is the display to be projected. It should be noted that, if it is determined in step S 301  of  FIG. 3  that a sub-display exists, the sub-display will be the display to be projected. 
     By pressing the projection start button  512  in this state, the video image transfer program of the PC  100   a  transmits a layout notification of the fact that the extended display of the PC  100   b  is to be projected, to the projector  200   b  via the communication unit  109 . Upon receiving this layout notification, the CPU  201  of the projector  200   b  reads out the information regarding the PC  100   b  from the session information managed by the RAM  202  and transmits, to the IP address of the PC  100   b,  a transmission start request to start transmission of the extended display video image. 
     Upon receiving the request to start transmission of the extended display video image, the video image transfer program of the PC  100   b  controls the display control unit  107  to capture the video image data that corresponds to the extended display from the VRAM  103  and encode the data. Subsequently, the encoded video image is transmitted via the communication unit  109  to the projector  200   b  (i.e., the source of the request to start transmission of the extended display video image), which in turn receives, decodes, and projects the video image as described above. As a result, as shown in  FIG. 6C , the projector  200   b  projects the extended display  30   b  of the PC  100   b.    
     In the foregoing embodiment, to simplify the description, a technique has been described in which the video image transfer program of the PC  100   a  is used to control projection. It should be noted, however, that the video image transfer program of the PC  100   b  is capable of performing the same control. The same applies if more PCs participate in the session. 
     Although not shown in  FIG. 3 , when user operation is made instructing termination of the video image transfer program, the CPU  101  may show a UI for selecting whether to leave the session in which the user is participating or to terminate the session in which the user is participating. 
     If the user issues an instruction to leave the session in which the user is participating, that is, if the connection with the projectors with which this PC is logically connected is interrupted, the display control unit  107  may be controlled to discard the extended display generated in step S 306 . 
     If the user issues an instruction to terminate the session in which the user is participating, the connection with the projectors with which this PC is logically connected may also be interrupted and the extended display may be discarded as described above. Moreover, if an instruction to terminate a session is issued, the other PC that is participating in the session also detects the termination of the session. In this case, the logical connection with the projectors may also be interrupted and the extended display may also be discarded. 
     Also, in addition to the normal processing flow described above, the video image transfer program may also interrupt a logical connection with the projectors and discard extended displays if it is detected that it is no longer possible to communicate with any of the projectors forming the session. 
     To confirm that communication with the projectors is valid, the video image transfer program may use, for example, the projector information command transmitted at regular intervals described in connection with steps S 402  and S 404  of  FIG. 4 . That is, if it is detected that a projector information command has not been received from any of the projectors forming the session for a predetermined period of time, the video image transfer program can determine that communication with that projector has ceased. 
     As described above, in the video image transfer system of the present embodiment, extended displays of PCs can be transferred to projectors after sessionization. 
     An extended display can be invalidated when a user leaves the session, when a session is terminated, when termination of a session is detected, or upon detecting that the communication path to a projector forming the session has been cut off. Furthermore, as a PC generates an extended display using the display driver that controls the main display, a display different from the main display can be generated and transferred without installing a virtual display driver. A virtual display driver cannot be installed to a PC if the version of Windows is Windows Vista or later. If the video image transfer program of the present embodiment is used, however, an extended display (a virtual display) can be generated at the PC and transferred to projectors. 
     Other Embodiments 
     Embodiment(s) of the present invention can also be realized by a computer of a system or apparatus that reads out and executes computer executable instructions (e.g., one or more programs) recorded on a storage medium (which may also be referred to more fully as a ‘non-transitory computer-readable storage medium’) to perform the functions of one or more of the above-described embodiment(s) and/or that includes one or more circuits (e.g., application specific integrated circuit (ASIC)) for performing the functions of one or more of the above-described embodiment(s), and by a method performed by the computer of the system or apparatus by, for example, reading out and executing the computer executable instructions from the storage medium to perform the functions of one or more of the above-described embodiment(s) and/or controlling the one or more circuits to perform the functions of one or more of the above-described embodiment(s). The computer may comprise one or more processors (e.g., central processing unit (CPU), micro processing unit (MPU)) and may include a network of separate computers or separate processors to read out and execute the computer executable instructions. The computer executable instructions may be provided to the computer, for example, from a network or the storage medium. The storage medium may include, for example, one or more of a hard disk, a random-access memory (RAM), a read only memory (ROM), a storage of distributed computing systems, an optical disk (such as a compact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™) a flash memory device, a memory card, and the like. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2017-231928, filed Dec. 1, 2017 which is hereby incorporated by reference herein in its entirety.