Abstract:
With a conventional image-display system, a presenter sometimes has difficulty in providing every viewer with an easy-to-see picture. When projecting an image transmitted from a computer operated by the presenter and enabling the viewer to watch the image projected by the projector, the projector receives image data transmitted through two-way communication from the computer operated by the presenter, projects an image represented by the received image data and transmits the received image data to a client computer operated by the viewer through the two-way communication, and the client computer receives the image data transmitted through the two-way communication and displays the image represented by the received image data on its display.

Description:
This is a Continuation of application Ser. No. 10/788,356 filed Mar. 1, 2004, which claims the benefit of Japanese Patent Application No. 2003-080030 filed Mar. 24, 2003. The disclosure of the prior application is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to an image-display method, a projector, an image-display system, a projector-control method, an image-display program, and a projector-control program. 
     2. Description of the Related Art 
     In a conventional image-display system of this type, a presenter connects his/her computer to a projector through a network and sends the data of an image displayed on his/her computer to the projector, which projects the image on a screen (see, for example, Japanese Unexamined Patent Publication No. 2001-14135). 
     With the above image-display system, the presenter sometimes has difficulty in providing every viewer with an easy-to-see picture. For example, viewers at a distance from the screen in a large presentation hall often have difficulty in watching the screen and concentrating on the content of the presentation, particularly if letters and figures are small. 
     SUMMARY OF THE INVENTION 
     In accordance with the above, it is the object of the present invention to provide an image-display method, a projector, an image-display system, a projector-control method, an image-display program, and a projector-control program capable of providing every viewer with an easy-to-see picture. 
     To achieve the above object, image data transmitted from a computer operated by a presenter are sent to client computers operated by viewers according to the present invention. Because the image data represent images to be projected on a screen by a projector, viewers can watch the images on the displays of client computers on hand by reproducing them with client computers. Accordingly, even if viewers are seated at a distance from the screen in a large hall, they can watch images on the displays of client computers on hand. 
     Although it serves the purpose if the computer operated by the presenter can transmit image data representing images to be projected on a screen, it is preferable if the computer operated by the presenter is the same as the computer used by the presenter for presentation. In this sense, it is preferable to transmit image data for displaying computer pictures including the presenter&#39;s operation (operation of a mouse pointer, etc.). Formats of image data are not limited in particular. Various formats such as picture signals, RGB signals, and compressed data of MPEG etc. can be adopted. 
     It serves the purpose if the communication-control units of the projector and the client computers can connect the computer operated by the presenter and the client computers that can be operated by the viewers interactively, and communication lines, protocols and standards are not limited. For example, either a wire network or a radio network will do, and various protocols such as TCP and UDP can be adopted, or various standards of Ethernet (a registered trademark of Fuji Xerox Co., Ltd.), IEEE 1394, USB, etc. can be adopted. 
     It serves the purpose if the unit for projecting images can project images represented by image data on a screen; accordingly, if image data are compressed, the projecting unit decompresses them and projects images on a screen. The image data-transmitting section sends on the above image data received to client computers. If image data are processed (for example, expanded) for the display of images and then sent on to client computers, the image data become bulky and it takes time for the image data-transmitting section to send on the image data to client computers. 
     Accordingly, it is preferable for the image data-transmitting unit to send on the above image data received, just as they are, to client computers. Besides, because image data are sent on from the projector to client computers, it is unnecessary for the computer operated by the presenter to be involved in the sending on of image data to a plurality of client computers. The load due to the control of communication occurs on the projector alone. Because the computer operated by the presenter is operated in various ways, the presenter can make presentation smoothly even with a low-performance computer if extra loads are eliminated. 
     It serves the purpose if the image-displaying unit of the client computer is capable of displaying the images represented by image data fed from the projector. If the above image-data processing is made in the projector, it is preferable to do the processing and decompressing, etc. with the same algorithm so that images displayed on the displays of client computers are always the same as images displayed on the screen by the projector. If image data are stored in a hard disk, a RAM, or the like of the client computer, the viewer can review images of the presentation at any time. If a viewer cannot keep up with the presentation, he/she can pause and restart at any time. Thus, such convenient functions can be achieved. 
     As described above, the projector sends on image data representing projected images to the client computers so that viewers can watch images on the displays of client computers. On the other hand, the presenter may want to disable the client computers from displaying certain images because of the contents of the presentation or presenter&#39;s intention. To achieve this selective non-display of image, the computer operated by the presenter sends the projector  30  data indicating the permission or prohibition of the delivery of image data to the client computers, and the image data-transmitting unit of the projector handles image data in accordance with the permission/prohibition-indicating data. With regard to delivery-permitted image data, the projector permits all the client computers, which demanded connection, to connect to itself and sends on the image data to the client computers. 
     In this manner, the projector acquires permission/prohibition-indicating data from the computer operated by the presenter and handles image data in accordance with the presenter&#39;s intention. Thus, by using permission/prohibition-indicating data alone, the projector can determine whether to send on image data to a plurality of client computers or not. It is not necessary to control the delivery or nondelivery of image data to individual client computers. Thus, the delivery or nondelivery of image data to individual client computers can be controlled by very simple processing. 
     The above delivery/nondelivery control is convenient especially for the handling of image data in a presentation hall. In other words, because many viewers watch images in a presentation hall, it is often nonsense to try to control the delivery and nondelivery of image data to individual client computers. Accordingly, the delivery/nondelivery control where the presenter takes the initiative in controlling delivery and nondelivery is often sufficient. 
     The transmission of permission/prohibition-indicating data can be made in various ways. The presenter may register the permission and prohibition of delivery of image data with the computer operated by the presenter in advance, and the computer operated by the presenter may automatically transmit permission/prohibition-indicating data to the projector in response to the inquiries from the projector. When the computer operated by the presenter receives an inquiry from the projector, a pop-up menu for instruction of permission or prohibition may be displayed on the display of the computer operated by the presenter. 
     To control the delivery or nondelivery of image data, passwords to be inputted through client computers may be used. A viewer inputs a password, which is visible to only the viewers of images projected on the screen by the projector, into the image data-receiving unit of his/her client computer. When he/she demands connection to the projector, the password is sent from his/her client computer to the image data-transmitting unit and a password-checkup section determines whether the password is correct or not. If the password is correct, image data are sent on to his/her client computer. 
     Thus, it is possible to determine whether image data should be sent on to each client computer or not. Besides, because the password is visible to only the viewers of images projected on the screen by the projector, the destinations of image data can be limited to client computers operated by the viewers of images projected on the screen by the projector. Various passwords can be adopted as the password visible to only the viewers of images projected on the screen by the projector. For example, a password may be written in images projected on the screen by the projector. Accordingly, the destinations of image data can be limited to client computers operated by the viewers in the presentation hall. Alternatively, slips printed with a password may be handed over to the viewers at the entrance of the presentation hall. 
     Needless to say, the above image-display system functions by the method of executing certain steps in time series with projector and client computers; therefore, the image-display system constitutes an invention as an image-display method and an projector-control method. The image-display system may exist by itself or may be incorporated into a device. Thus, the image-display system as an idea of invention is not limited to the above embodiment, but may be embodied in other specific forms. For example, the image-display system may be made of software or may be made of hardware. 
     In the case of the embodiment of the idea of the invention as software for controlling an image-display system and a projector, there exist programs realizing such functions, of course. The software is image-display and projector-control programs which are executed in the projector and client computers to realize the above functions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of an embodiment of the image-display system of the present invention; 
         FIG. 2  is a flowchart of the processing by the transmission-control program of the image-display system of  FIG. 1 ; 
         FIG. 3  is a flowchart of the processing by the projector-control program of the image-display system of  FIG. 1 ; 
         FIG. 4  is a flowchart of the processing by the reception-control program of the image-display system of  FIG. 1 ; and 
         FIG. 5  is a schematic illustration of another embodiment of image-display system of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The preferred embodiments of the present invention will be described below in the following orders. 
     (1) Configuration of the image-display system 
     (2) Processing at the presenter PC 
     (3) Processing at the projector 
     (4) Processing at the client PCs 
     (5) Other embodiments 
     (1) Configuration of the Image-Display System 
       FIG. 1  shows a configuration of the image-display system of the present invention. The image-display system  10  comprises a presenter PC  20 , a projector  30 , and a plurality of client PCs  40 . The presenter PC  20 , projector  30 , and client PCs  40  form a LAN through UTP cables and can communicate with one another. The projector  30  receives image data from the presenter PC  20  and projects images on a screen. At the same time, the projector  30  sends on the received image data as they are to the client PCs  40  if the image data are delivery-permitted ones. Thus, the client PCs  40  receive image data from the projector  30  and display images on their displays. 
     The presenter PC  20 , projector  30 , and client PCs  40  communicate with one another by using the TCP protocol. They send and receive packets to and from one another to establish connection among them, and image data are divided into packets for transmission as the need arises. There are block diagrams in  FIG. 1  showing the configurations of a presenter PC  20 , a projector  30 , and only one client PC  40 , but a plurality of client PCs  40  can be realized by using the same configuration. 
     General-purpose computers can be adopted as a presenter PC  20  and client PCs  40  which control certain interfaces and recording media under certain operating systems. The presenter PC  20  of the image-display system  10  of the present invention comprises a network interface  21 , a communication controller  22 , a transmission-control program  23 , a hard-disk drive  24 , a presentation program  25 , a displaying section  26 , and an input device-controller  27 . 
     To make presentation by using the projector  30 , a presenter operates the presenter PC  20  and starts the presentation program  25 . The presentation program  25  reads out presentation data  24   a , which are prepared and stored in the hard-disk drive  24  in advance, and outputs image data to the displaying section  26  to display images in certain or any order. 
     The displaying section  26  controls a display such as a liquid-crystal display (not shown in  FIG. 1 ). A mouse  27   a  or the like inputs operation into the input device-controller  27 , which outputs data representing the contents of inputted operation to the presentation program  25 , which makes processing such as changing the presentation picture and moving the mouse pointer on the displaying section  26 . 
     While the presentation program  25  is running, the transmission-control program  23  is started and controls the transmission of the image data representing the images on the presentation picture of the displaying section  26  to the projector  30  in order to make the projector  30  project images on a screen which are the same as the images on the presentation picture of the displaying section  26 . Besides, the presenter PC  20  is capable of achieving two-way communication by means of the network interface  21  and the communication controller  22 . In other words, the communication controller  22  divides image dada fed from the transmission-control program  23  into packets as the need arises, makes such processing as adding data indicating proper destinations, and outputs the image data through the network interface  21 . Before being transmitted, image data may be compressed for a higher communication speed or encoded for security. 
     The transmission-control program  23  has a delivery/nondelivery-designating section  23   a . The displaying section  26  and the input device-controller  27  constitute a user interface (not shown) under the control by the delivery/nondelivery-designating unit  23   a . Thus, the presenter can designate the delivery and nondelivery of image data to the client PCs  40 . The data representing the contents of designation of delivery and nondelivery are stored in the hard-disk drive  24  and can be referred to at any step. At the time of establishing the communication with the projector  30  or at other times, a pop-up menu may be displayed on the user interface so that the presenter can designate delivery or nondelivery of image data to the client PCs  40 . And other various configurations for designation of delivery and nondelivery of image data are possible. 
     In the projector  30 , certain interface, recording medium, etc. can be controlled under an operating system and a certain program can be run. To construct the image-display system  10 , the projector  30  comprises a network interface  31 , a communication controller  32 , a projector-control program  33 , a projection controller  34 , and a projecting section  35 . The projector  30  is capable of two-way communication by means of the network interface  31  and the communication controller  32 . The communication controller  32  receives packets of image data through the network interface  31 , combines the packets in accordance with their headers, and sends the combined image data to the projector-control program  33 . Besides, the communication controller  32  receives image data from the projector-control program  33 , divides the image data into packets as the need arises, makes such processing as adding data including proper destinations and outputs the packets through the network interface  31 . 
     The projector-control program  33  sends and receives image data and controls the projection of images according to the received image data. Besides, the projector-control program  33  finds whether the image data received are delivery-permitted ones or delivery-prohibited ones and controls two-way communication with the client PCs  40 . Moreover, when projecting images, the projector-control program  33  starts the projection controller  34  and sends image data to it. The projection controller  34  processes the received image data and controls the projection of images at the projecting section  35 . 
     Thus, the projection controller  34  processes the above image data received and produces data which are fed to the projecting section  35  for the projection of images on a screen. If image data are compressed or encoded, the projection controller  34  decompresses or decodes the image data. The projecting section  35  has a mechanism to project light of three colors RGB on an external screen through a lens (not shown in  FIG. 1 ) to form images. Thus, the projecting section  35  generates RGB light for individual pixels to form images on the screen by using the above image data processed by the projection controller  34 . 
     In each client PC  40 , certain interface, recording medium, etc. can be controlled under an operating system and a certain program can be run. To construct the image-display system of the present invention, each client PC  40  comprises a network interface  41 , a communication controller  42 , a reception-control program  43 , a display controller  44 , and a displaying section  45 . Each client PC  40  is capable of two-way communication by means of the network interface  41  and the communication controller  42 . The communication controller  42  receives packets through the network interface  41 , combines the packets in accordance with their headers, and sends the combined image data to the reception-control program  43 . 
     The reception-control program  43  receives and sends image data and controls the display of images according to the received image data. To receive image data, the reception-control program  43  controls two-way communication with the projector  30 . The reception-control program  43  starts the display controller  44  and sends the image data to it. The display controller  44  processes the image data and controls the display of images at the displaying section  45 . Thus, the display controller  44  processes the above image data received and produces data to be sent to the displaying unit  45  for the display of images. The displaying section  45  has a display such as a liquid-crystal display (not shown in  FIG. 1 ) and generates RGB light for individual pixels to form images on the display. 
     The processing at the display controller  44  is equivalent to the processing at the projection controller  34 . If image data are compressed or encoded, the display controller  44  decompresses or decodes the image data by using the same algorithm as the projection controller  34 . Because the projector  30  projects images on a screen while the client PC  40  displays images on a display, the projection controller  34 &#39;s method of driving the relevant parts for the projection of images is different from the display controller  44 &#39;s method of driving the relevant parts for the display of images. In this embodiment, however, the projection controller  34  and the display controller  44  have a common point in that an image is expressed by pixels of RGB colors. Thus, the method of processing image data is common to the two controllers  34  and  44 . Therefore, the projector  30  and the client PCs  40  have many common modules and hence the image-display system  10  of the present invention can be constructed easily. 
     (2) Processing at the Presenter PC 
     The processing and workings of the presenter PC  20  are now described.  FIG. 2  is a flowchart of the processing of the transmission-control program  23  of the presenter PC  20 . In this embodiment, the presenter PC  20  communicates with the projector  30  and does not communicate with the client PCs  40 . In Step S 100 , the transmission-control program  23  demands connection to the projector  30  of the communication controller  22 . The communication controller  22  transmits a connection-demanding packet to the projector  30  through the network interface  21 . In Step S 110 , the transmission-control program  23  monitors the network interface  21  through the communication controller  22  for a connection-permitting packet from the projector  30 . 
     When the communication controller  22  receives a connection-permitting packet from the projector  30 , the transmission-control program  23  recognizes the permission in Step S 110  and monitors the network interface  21  further through the communication controller  22  to find whether there is a demand for the delivery of image data or not in Step S 120 . In other words, the transmission-control program  23  monitors the network interface  21  for a delivery-demanding packet from the projector  30 . If a demand for the delivery of image data is not found in Step S 120 , the transmission-control program  23  checks to see if a preset time has passed in Step S 125 . The transmission-control program  23  repeats the processing in and after Step S 120  until the preset time passes. 
     If the preset time has passed without receiving a delivery-demanding packet in Step S 125 , the delivery/nondelivery-designating section  23   a  designates image data as delivery-prohibited data and makes the communication controller  22  transmit a datum indicating the prohibition of delivery to the projector  30  in Step S 140 . If delivery of image data is demanded in Step S 120 , the delivery/nondelivery-designating section  23   a  checks in Step S 130  to see if the delivery is already permitted. If it is found in Step  130  that the delivery is not permitted, the delivery/nondelivery-designating section  23   a  makes the communication controller  22  transmit a datum indicating the prohibition of delivery to the projector  30  in Step S 140 . 
     If it is found in Step S 130  that the delivery is permitted, the delivery/nondelivery-designating unit  23   a  makes the communication controller  22  transmit a datum indicating the permission of delivery to the projector  30  in Step S 135 . In Step  150 , the image data representing a presentation image displayed on the displaying section  26  under the control by the presentation program  25  are transmitted to the projector  30 . Before the transmission, the image data are compressed or encoded as the need arises. In Step S 160 , the transmission-control program  23  checks to see if the presentation has been finished. The processing in and after Step S 150  is repeated until the presentation is finished. 
     By the processing described above, image data representing the presentation images to be projected by the projector  30  are outputted from the presenter PC  20 . Besides, the presenter PC  20  designates image data as ones to be delivered from the projector  30  to the client PCs  40  and ones not to be delivered from the projector  30  to the client PCs  40  and transmits data indicating the contents of the designation to the projector  30 . It serves the purpose if the data indicating the contents of designation are transmitted to the projector  30  only once. Thus, the substantial communication load on the system is only the image data-transmission load. Accordingly, when the presenter makes presentation, operating the presenter PC  20 , the resource of the presenter PC  20  is prevented from being reduced and hence the presenter can make presentation very smoothly. 
     (3) Processing at the Projector 
       FIG. 3  is a flowchart of the processing of the projector-control program  33  of the projector  30 . In this embodiment, the projector  30  makes two-way communication with the presenter PC  20  and the client PCs  40 . In Step S 200 , the projector-control program  33  checks to see if the network interface  31  has received a demand for connection through the communication controller  32 . In other words, the projector-control program  33  monitors the network interface  31  through the communication controller  32  for a connection-demanding packet to be outputted by the presenter PC  20  in Step S 100 . 
     If the reception of a connection-demanding packet was confirmed in Step S 200 , the projector-control program  33  makes the communication controller  32  transmit a connection-permitting packet through the network interface  31  to the presenter PC  20  in Step S 210 . In Step S 220 , the projector-control program  33  makes the communication controller  32  transmit a delivery-demanding packet through the network interface  31  to the presenter PC  20  in order to check to see if the delivery of image data to the client PCs  40  is permitted. 
     The presenter PC  20  recognizes the demand of delivery in Step S 120  and transmits a datum indicating the permission of delivery in Step S 135  or a datum indicating the prohibition of delivery in Step S 140  to the projector  30 . The projector  30  monitors the network interface  31  through the communication controller  32  for a datum indicating the permission or prohibition of delivery in Step S 225 . If the projector-control program  33  finds in Step S 225  that the delivery of image data to the client PCs  40  is permitted, the projector-control program  33  designates image data as delivery-permitted ones in Step S 230 . If the projector-control program  33  finds in Step S 225  that the delivery of image data to the client PCs  40  is prohibited, the projector-control program  33  designates image data as delivery-prohibited ones in Step S 235 . Various configurations can be adopted for the designation. For example, flags indicating the permission and prohibition of delivery may be stored in a RAM (not shown in  FIG. 1 ). 
     When image data has been designated as delivery-permitted or delivery-prohibited ones, the projector-control program  33  makes the communication controller  32  monitor the network interface  31 , receive the image data representing a presentation image, and store the image data temporarily in a RAM (not shown in  FIG. 1 ) in Step S 240 . In other words, the projector-control program  33  makes the communication controller  32  receive packets of image data, combine the packets, and store the combined image data in a RAM. In Step S 245 , the received image data are sent to the projection controller  34  for the projection of the presentation image. In other words, the projection controller  34  processes (decompresses or decodes as the need arises) the compressed or encoded image data temporarily stored in the RAM to produce data which the projecting section  35  uses to project the presentation image. 
     In Step S 250 , the projector-control program  33  checks to see whether image data are designated as delivery-permitted ones (in Step S 230 ) or not (in Step S 235 ). If it is confirmed in Step S 250  that image data are designated as delivery-permitted ones, the projector-control program  33  monitors the network interface  31  through the communication controller  32  for connection-demanding packets from client PCs  40  in Step S 255 . If it is confirmed in Step S 255  that some client PCs  40  have sent connection-demanding packets to the projector  30 , the projector-control program  33  permits the connection-demanding client PCs  40  to connect with the projector  30  in Step S 260 . In other words, the projector-control program  33  makes the communication controller  32  transmit a packet indicating the permission of connection to the connection-demanding client PCs  40  through the network interface  31 . 
     In Step S 265 , the projector-control program  33  sends the image data temporarily stored in the RAM to the connection-permitted client PCs  40 . In other words, the projector-control program  33  makes the communication controller  32  (i) divide the image data into packets, (ii) write data, which address the packets to the connection-permitted client PCs  40 , into the headers of packets, and (iii) transmit the packets through the network interface  31  to the connection-permitted client PCs  40 . The image data sent to the connection-permitted client PCs  40  are the same as the image data stored in the above RAM. In other words, the image data stored in the RAM are transmitted, just as they are, without undergoing the processing by the projection controller  34 , to the connection-permitted client PCs  40 ; therefore, if the image data stored in the RAM is compressed, the image data can be transmitted as a relatively light load on the network. 
     If the image data were transmitted to the connection-permitted client PCs  40  in Step S 265  or any client PCs  40  did not send connection-demanding packets to the projector  30  in Step S 255 , the projector-control program  33  checks in Step S 270  to see if the presentation has been finished. In other words, the projector-control program  33  makes the communication controller  32  monitor the network interface  31  and finds whether the final presentation image has been received or not. The processing in and after Step S 240  is repeated until the ending of the presentation is confirmed in Step S 270 . If image data were designated as delivery-prohibited ones in Step S 250 , the projector-control program  33  checks in Step S 275  to see if the presentation has been finished. If the ending of the presentation is not confirmed in Step S 275 , the processing in and after Step S 240  is made. 
     As described above, the projector  30  not only receives image data from the presenter PC  20  and projects images on a screen but also sends on image data to connection-permitted client PCs  40  if image data are designated as delivery-permitted ones. Because the projector  30  communicates with the client PCs  40  and sends image data to the client PCs  40 , the load on the presenter PC  20  is very light. Besides, because the projector  30  receives image data from the presenter PC  20  and sends on the image data just as they are to the client PCs  40 , no load of image processing occurs on the projector  30  and image data are smoothly sent to the client PCs  40  where the viewers can watch images clearly. 
     RGB cables, coaxial cables, etc. are known as technologies used for the transmission of image data. To transmit image data by using these technologies for the projection of images by the projector  30 , two lines are needed; i.e., one line of, for example, RGB for the transmission of image data and another line for two-way communication for the control of the relevant devices. In the present embodiment of this invention, however, it serves the purpose if a cable network is formed among the presenter PC  20 , the projector  30  and the client PCs  40 . Thus, the image-display system  10  can be constructed with relatively simple construction. 
     (4) Processing at the Client PC 
       FIG. 4  is a flowchart of the processing of the reception-control program  43  of the client PCs  40 . The client PCs  40  communicate with the projector  30  and not with the presenter PC  20 . In Step S 300 , the reception-control program  43  sends a demand for connection to the projector  30  through the communication controller  42 . In other words, the reception-control program  43  makes the communication controller  42  send a packet indicating a demand for connection to the projector  30  through the network interface  41 . 
     In Step  310 , the reception-control program  43  finds if the connection is permitted. In other words, the reception-control program  43  monitors the network interface  41  through the communication controller  42  to find if a connection-permitting packet to be transmitted by the projector  30  in Step S 260  has been received. If the reception-control program  43  finds in Step S 310  that the connection is permitted, the reception-control program  43  receives image data outputted by the projector  30  in Step S 320 . In other words, the reception-control program  43  makes the communication controller  42  (i) monitor the network interface  41 , (ii) receive the packets of image data representing a presentation image, (iii) combine the packets into the original image data, and (iv) store the image data in a RAM (not shown in  FIG. 1 ) temporarily. 
     In Step S 340 , the reception-control program  43  sends the image data to the display controller  44  for the display of the presentation image on the display. In other words, the display controller  44  processes (decompresses or decodes as the need arises) the decompressed or encoded image data to produce data which the displaying section  45  uses to display the presentation image. Then, in Step S 340 , the reception-control program  43  makes the communication controller  42  monitor the network interface  41  to find if the final presentation image has been received. Thus, the processing in and after step S 320  is repeated until the ending of the presentation is confirmed. 
     If the reception-control program  43  does not find in Step S 310  that the connection is permitted, the processing in and after Step  320  is skipped and image data are not received. As described above, the client PC  40  receives image data from the projector  30  and displays the presentation image on its display. Accordingly, even if viewers are seated at a distance from the screen in a large hall, they can watch images on the display of client computers on hand. 
     (5) Other Embodiments 
     The embodiment described above is an example to achieve the image-display system, projector, image-display method, projector-control method, image-display program and projector-control program of the present invention, and other configurations are also possible. For example, the destinations of image data may be limited to client PCs  40  operated by the participants, or viewers, in the presentation hall. For example, the projector permits all the client PCs  40 , which demanded connection, to connect to itself and sends on the image data to them. However, passwords to be inputted through client computers may be used to control the delivery of image data. 
     The descriptions surrounded by broken lines in  FIGS. 3 and 4  show the processing to be added when the passwords are used to control the delivery of image data, and  FIG. 5  is a schematic diagram showing workings of such an example. In this example, as shown in  FIG. 5  as an image projected on the screen by the projector  30 , a password is displayed in a part of the presentation image. Therefore, the image data sent from the presenter PC  20  are data including an image for displaying the password, and the projector  30  displays the password when projecting the image on the screen in Step S 245 . 
     At the client PC  40 , the password is inputted by an input device such as a keyboard before sending a demand for connection in Step S 300 . When sending the demand for connection in Step S 300 , together with data indicating the demand for connection, data indicating the password is sent. Before giving permission to the connection-demanding client PC  40  in Step S 260 , the projector  30  acquires the inputted data indicating the password and determines whether the password is correct or not. When it is found that the password is correct, the demand for connection is permitted in Step S 260 . When it is found that the password is not correct, the processing in Step S 270  is carried out. 
     There are various ways to determine whether the password is correct or not. For example, data indicating the correct password may be stored in advance temporarily in a RAM, etc. (not shown) of the projector  30  and the inputted password may be compared with the stored correct password. Further, the data of the password included in the image data received in the above Step S 240  may be extracted and used as the correct password, and various other ways are also possible. Either of the above configurations enables viewers of the image projected on the screen in the presentation hall to input the correct passwords, so that the destinations of image data can be limited to client PCs  40  in the presentation hall.