Abstract:
A communication system easy to be operated upon as to the display method of images generated by image generating units of a plurality of communication terminals and as to the control of each image generating unit. The communication system has a reception unit for receiving images generated by image generating units of a plurality of communication terminals, an output unit for outputting a multi-image of images received by the reception unit to a display unit, a designation unit for designating an arbitrary image from the images constituting the multi-image, and a processing unit for controlling the output form of an image to be output to the display unit, the image being designated by the designation unit, if a designation operation by the designation unit is a first designation operation, and for setting the communication terminal as a control object, the communication terminal generating an image designated by the designation unit, if a designation operation by the designation unit is a second designation operation.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a communication system and method, and a storage medium storing programs in communication system. 
     2. Related Background Art 
     A remote monitor system using a plurality of video cameras and a synthesizer for synthesizing in an analog manner images taken with the cameras has been used in a building of a relatively small scale or the like and such as system is called a local monitor system. In contrast to such a local monitor system, a remote monitor system has been proposed in which a plurality of cameras are connected by a digital network such as LAN (local area network) and public digital line ISDN so that the more cameras at remoter sites can be controlled more flexibly. 
     Of remote monitor systems, some systems control the image display and system operations through graphical user interface (GUI) by using personal computers or work stations as monitor terminals. Use of GUI at a monitor terminal enables a computer device to operate the system easily. The operability of the system can be improved by displaying a camera control panel together with an image taken with the camera. 
     However, conventional methods of displaying images with such a system include various methods such as a glance display of images taken with a plurality of cameras. A conventional display operation and discrimination between system operations are not always good heretofore. Personal computers and work stations are directly, or via a synthesizer for image synthesis and a switcher for switching between cameras, connected to the network. The image synthesizer can select one of cameras connected thereto to display its image, or can display a plurality of images side by side at the same time. By using the switcher, any desired camera can be selected to be controlled. 
     However, the operability of the system which inputs images via the switcher/synthesizer is not so much satisfactory and there is still a room to be improved. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to solve the above problems and provide a communication system and method and a storage medium storing communication system programs, capable of providing flexible operations. 
     It is another object of the present invention to provide a communication system and method having user interface (UI) capable of being flexibly operated upon and provide a communication system and method and a storage medium storing communication system programs, capable of switching, when necessary, between a glance display mode of displaying images supplied from a plurality of communication terminals and a fine display mode of displaying a single image taken with each camera. 
     According to one aspect of the present invention achieving the above objects, a communication system comprises reception means for receiving images generated by image generating units of a plurality of communication terminals, output means for outputting a multi-image of images received by the reception means to a display unit, designation means for designating an arbitrary image from the images constituting the multi-image, and processing means for controlling the output form of an image to be output to the display unit, the image being designated by the designation means, if a designation operation by the designation means is a first designation operation, and for setting the communication terminal as a control object, the communication terminal generating an image designated by the designation means, if a designation operation by the designation means is a second designation operation. 
     It is another object of the present invention to improve the operability of the system when images are supplied via a switcher or synthesizer. 
     It is another object of the present invention to provide a communication system and method and a storage medium storing communication system programs, having novel functions. 
     The other objects and aspects of the present invention will become more apparent from the following detailed description and appended claims when read in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram briefly showing the overall structure of a system according to a first embodiment of the invention. 
     FIG. 2 is a block diagram showing the outline structure of a video transmission terminal of the first embodiment. 
     FIG. 3 is a block diagram showing the outline structure of a video reception terminal (monitor terminal) of the first embodiment. 
     FIG. 4 is a block diagram showing the configuration of software of the first embodiment. 
     FIG. 5 shows examples of the display contents on the screen of the monitor terminal of the first embodiment. 
     FIG. 6 is a diagram showing an example of a map window in which a map is displayed at the front of the window. 
     FIG. 7 illustrates an operation of starting an image display. 
     FIG. 8 is a diagram showing an example of the shape of a mouse cursor during the image display start operation. 
     FIG. 9 is a diagram showing an example of a camera icon during the image display. 
     FIG. 10 is a flow chart illustrating a power turnoff process. 
     FIG. 11 is a diagram illustrating the operation of changing a video display area. 
     FIG. 12 is a diagram illustrating the operation of stopping an image display. 
     FIG. 13 is a diagram showing an example of an image display window in a watching mode. 
     FIGS. 14A and 14B are diagrams showing examples of an image quality setting panel. 
     FIG. 15 is a block diagram briefly showing the overall structure of a system according to a second embodiment of the invention. 
     FIG. 16 is a diagram showing a display example in the glance display mode, a synthesized image of images being displayed which are supplied from a video transmission terminal connected to a plurality of video cameras via the synthesizer and switcher. 
     FIG. 17 is a diagram showing a display example in the glance display mode, a single image being displayed which is selected from images taken with a plurality of video cameras connected via the synthesizer and switcher to the video transmission terminal. 
     FIG. 18 is a block diagram showing the outline structure of the video reception terminal (monitor terminal) of the second embodiment. 
     FIG. 19 is a block diagram showing the outline structure of software of the second embodiment. 
     FIG. 20 is a diagram showing a monitor example of the monitor terminal of the second embodiment. 
     FIG. 21 is a diagram showing a display example when the single image display window is popped up. 
     FIG. 22 is a diagram showing a display example in the single image display mode, a single image being displayed which is selected from images taken with a plurality of video cameras connected via the synthesizer and switcher to the video transmission terminal. 
     FIG. 23 is a diagram showing a display example in the glance display mode, a synthesized image of images being displayed which are supplied from a video transmission terminal connected to a plurality of video cameras via the synthesizer and switcher. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     &lt;First Embodiment&gt; 
     FIG. 1 is a block diagram briefly showing the structure of an overall system according to an embodiment of the invention. A digital network  10  transfers digital signals of video data and camera control information (inclusive of status information). The digital network  10  is connected to n video transmission terminals  12  ( 12 - 1  to  12 -n). Each video transmission terminal  12  is connected via a camera controller  14  ( 14 - 1  to  14 -n) to a video camera  16  ( 16 - 1  to  16 -n). In accordance with a control signal supplied from the terminal  12 , the camera controller  14  controls panning, tilting, zooming, focussing, diaphragming, and the like of the connected video camera  16 . The video camera  16  is supplied with power from the camera controller  14  which in accordance with an external control signal received from a video reception terminal  18  ( 18 - 1  to  18 -m), turns on and off the power. 
     The network  10  is also connected to m video reception terminals  18  which receive video signals transmitted from the video transmission terminals  12  via the network  10  and display them on m monitor displays (hereinafter abbreviated as monitors)  20  ( 20 - 1  to  20 -m). 
     The video transmission terminal  12  compresses video signals output from the connected video camera  16  in a predetermined compression format such as H.261, MPEG, and Motion JPEG and transmits the compressed video signals to the video requesting video reception terminal  18  or to all the video reception terminals  18 . The video reception terminal  18  received the video signal operates to display the image in a video display area of the monitor  20 . The video reception terminal  18  can control, via the network  10 , video transmission terminal  12 , and camera controller  14 , various parameters (such as photographing direction, magnification factor, focus, and diaphragm) as well as a power supply (from on to off or vice versa) of any one or ones of desired cameras  16 . The details of this will be later described in detail. 
     A video reception terminal may be realized by providing the video transmission terminal  12  with a monitor and a video expansion device for expanding compressed video signals. Similarly, a video transmission terminal may be realized by providing the video reception terminal  18  with a camera controller, a video camera, and a video compression device. In this case, it is obvious that software for video transmission or reception is also provided. 
     FIG. 2 is a block diagram showing the outline structure of the video transmission terminal  12 . Reference numeral  22  represents a CPU for controlling the entirety of the terminal  12 , reference numeral  24  represents a main storage, reference numeral  26  represents a removable external storage unit such as a floppy disk and a CD-ROM, reference numeral  28  represents a secondary storage unit such as a hard disk, reference numeral  30  represents a mouse as a pointing device, reference numeral  32  represents a keyboard, reference numeral  34  represents an I/O board for interface with the camera controller  14  and transfer of a camera control signal, and reference numeral  36  represents a video capture board for receiving a video signal output from the video camera  16 . The video capture board  36  of this embodiment has an A/D conversion function of converting an analog video signal into a digital video signal and a function of compressing video signals. Reference numeral  38  represents a video board for displaying images on the screen of a monitor  40 , reference numeral  42  represents a network interface, reference numeral  44  represents a system bus for interconnecting devices  22  to  38 , and  42 . 
     The video board  38  and monitor  40  may be omitted for video transmission only. 
     The terminal  12  constructed as above transmits video signals via the network to a remote video reception terminal (monitor terminal) and receives a camera control signal from a remote monitor terminal to control the camera  16 . 
     FIG. 3 is a block diagram showing the outline structure of the video reception terminal (monitor terminal)  18 . Reference numeral  122  represents a CPU for controlling the entirety of the terminal  18 , reference numeral  124  represents a main storage, reference numeral  126  represents a removable external storage unit such as a floppy disk and a CD-ROM, reference numeral  128  represents a secondary storage unit such as a hard disk, reference numeral  130  represents a mouse as a pointing device, reference numeral  132  represents a keyboard, reference numeral  138  represents a video board for displaying images on the screen of a monitor  140 , reference numeral  142  represents a network interface, reference numeral  144  represents a compression decoder for expanding compressed video signals, and reference numeral  146  represents a system bus for interconnecting devices  122  to  132 ,  138 ,  142 , and  144 . 
     The video reception terminal  18  has the same structure as the video transmission terminal  12  shown in FIG. 2 excepting that it has no function of controlling the camera and receiving camera images, that it has the decoder  144  for expanding compressed video signals, and that it has different system software from that of the video transmission terminal  12 . Some or all of the video reception terminals  18  can transmit a camera control signal to any one or ones of the video transmission terminals  12  or to the terminals  12  permitted to control their cameras. The video transmission terminal  12  received the camera control signal controls its camera  16  in accordance with the contents of the camera control signal, and sends back the current status of the camera  16 . In accordance with the received status signal, the monitor terminal displays the current status of the camera on the monitor. At the same time, the monitor terminal receives video data transmitted from the video transmission terminal, expands it, and displays it in real time on the monitor screen. 
     FIG. 4 illustrates the software configuration of this embodiment. The video reception terminal (monitor terminal)  18  is installed with camera control client software  50 , video reception software  52 , and map management software  54 . The camera control client software  50  remotely controls the camera  16  via the network  10  and video transmission terminal  12 . The video reception software  52  expands compressed video data supplied from the video transmission terminal  12 . The map management software  54  displays a camera symbol representative of the current position and status of the camera  16  on a map, and also displays an operation panel for controlling the camera  16 . A set of above-described software is stored either at the video transmission terminal  12  or video reception terminal  18  in its main storage medium or secondary storage medium. 
     The video reception software  52  also manages all the cameras  16  via the network  10  and video transmission terminals  12 , and stores fixed information of each camera  16  and variable information thereof (e.g., a camera name, a host name of the computer connected to the camera, a camera status such as pan, tilt, and zoom, a controllable or uncontrollable state, a camera name under control, a camera name under display). Such fixed and variable information is also supplied to the camera control client software  50  and map management software  54  to change the display of the camera symbol or the like. 
     The video transmission terminal  12  is installed with camera control server software  56  and video transmission software  58 . The camera control server software  56  controls the camera  16  via the camera controller  14  in response to a request from the camera client software  50 , and notifies the requested terminal of the current status of the camera  16 . The video transmission software  58  compresses video data output from the camera  16  in a predetermined compression format and transmits it via the network  10  to the requested terminal. 
     FIG. 5 shows examples of the display contents of the monitor screen of the video reception terminal  18 . Reference numeral  60  represents a map window showing a layout of, for example, an office, a store, or a warehouse in which cameras  16  are installed. In this map window, a plurality of maps  60   a,    60   b,    60   c,  and  60   d  can be selectively displayed. The number of maps which can be displayed depends upon the performance of the system and is not limited to a particular number. Each map  60   a,    60   b,    60   c,    60   d  is provided with a tag. By clicking the tag with a mouse pointer, the map with the clicked tag is displayed at the front of the map window. The map displayed at the front also displays camera icons (camera symbols)  62   a,    62   b,    62   c,  and  62   d  of the cameras installed at this map. Each camera icon  62   a,    62   b,    62   c,    62   d  is displayed being directed toward the direction of the camera  16 . 
     Reference numeral  64  represents a video display window having a plurality of video display areas  66   a  to  66   f.  In this embodiment, six video display areas are used. Obviously the number of these areas is not limited to six. A trash-can icon  66   g  is displayed on the video display window  64  in order to stop displaying a camera image. A use method of the trash-can icon  66   g  will be later described. 
     The video display window  64  has two display modes, one for displaying all video display areas as shown in FIG.  5  and the other for displaying only one video image area as shown in FIG. 13 to watch the image in one video display area. The former is called a glance mode and the latter is called a watching mode. The watching mode is used when one image is viewed as a magnified image or it is viewed at high resolution. Switching between the glance mode and the watching mode will be later described. 
     Reference numeral  68  represents a camera control panel which is provided with buttons and the like for instructing the direction (pan/tilt), zoom, and the like of a designated camera, and in this embodiment, also with a camera power button  70  for instructing a power on/off of a designated camera. 
     For example, when the map  60   c  is selected in the map window  60  and displayed at the front of the window, a map such as shown in FIG. 6 is displayed and camera icons  62   e  and  62   f  representing two cameras disposed in this map are also displayed. 
     The camera control of this embodiment will be detailed. If an image of a camera  16  is to be displayed, the camera icon of the camera  16  is selected in the map window  60  by moving the mouse  130  to one of the video display areas  66   a  to  66   f  in the video display window  64  and releasing the click button (so called drag-and-drop). Usually, one of the video display areas  66   a  to  66   f  not used is selected. However, if the video display area in use is selected, a warning is issued to the effect that the camera is to be changed, and a user is urged to select either “continue” or “stop”. The basic operations of these processes are already known in the field of this art. 
     FIG. 7 illustrates a drag-and-drop operation of the camera icon  62   c  to the video display area  66   c.  An image taken with the camera represented by the camera icon  62   c  is displayed in the video display area  66   c.  While the camera icon is dragged, the mouse cursor changes to a shape shown in FIG. 8 so that the user can recognize the dragging operation for displaying an image. The map management software  54  notifies the video reception software  52  of an ID of the camera represented by the camera icon, and the video reception software  52  checks from the ID the direction, name, and host name of the camera and notifies these pieces of information to the camera control client software  50  and map management software  54 . 
     Next, the operation of controlling a camera will be described. Of the video display areas  66   a  to  66   c,  as the video display area (e.g.,  66   c ) in which the image taken with the camera is displayed by the above operations is single clicked with the mouse  130 , this designated camera enters a controllable state. At this time, a yellow frame is displayed on the video display area  66   c  to notify the user of the camera controllable state, and the camera control panel  68  is automatically displayed. 
     In accordance with the information supplied from the camera reception software  52 , the camera control client software  50  accesses over the network the camera control server software  56  of the video transmission terminal  12  connected to the selected camera. Thereafter, the camera control client software  52  transmits over the network the camera control signal designated by the user operation to the camera control server software  56 . In accordance with the received camera control signal, the camera control server software  56  notifies the current status of the camera  16  to the camera control client software  52 . The camera control client software  52  notifies the current status to the map management software  54 . 
     The map management software  54  changes the direction of the camera icon so as to match the direction of the camera  16 , displays a scope  72  shown in FIG. 9 indicating that an image is under display, and displays a control pointer  74  in the scope  72  to be used for the control of pan/tilt and zoom. As described earlier, the map management software  54  is constantly notified by the video reception software  52  of variation information (particularly of pan/tilt information) of the camera  16  under display, and in accordance with this information, the direction of the camera icon  62   a  to  62   f  is changed so as to match the direction of the camera. 
     The camera control panel  68  may be used in common by all the video display areas  66   a  to  66   f  or may be provided for each of the video display areas. If a plurality of camera control panels  68  are provided, the video display areas  66   a  to  66   f  are given specific serial numbers which are given to the corresponding ones of the camera control panels  68 . In this manner, a system can be realized which has a correspondence between images and camera control panels  68  easy to understand. Instead of serial numbers, names of cameras may be displayed or different colors may be allocated to the video display areas  66   a  to  66   f.    
     FIG. 10 is a flow chart illustrating the operation of turning off the power of any selected camera  16 . If the power of the selected camera is to be temporarily turned off, the camera icon of the camera whose power is turned off is selected and the camera power button  70  in the camera control panel  68  is pressed. The camera power button  70  is displayed in different colors and/or characters (e.g., “power off” or “power on”) in accordance with the state of the camera power. In response to the operation of the camera power button  70 , the camera control client software  52  notifies over the network  10  the camera power-off request to the camera control server software  56  of the video transmission terminal  12  connected to the corresponding camera  16  (S 1 ). 
     The camera control server software  56  causes the camera controller  14  via the I/O board  34  to turn off the power of the video camera  10  (S 2 ). The camera power button  70  changes its display shape to indicate that the power is in an off-state (S 3 ). In this manner, the user is notified that the camera power is in the off-state. 
     If the power is supplied again to the camera in the off-state, the camera icon is selected with the mouse  130  and thereafter the camera power button  70  is again pressed. In this case, a camera power-on request is issued to the camera control server software  56  to supply power to the corresponding video camera  16 . The color of the camera power button  70  is changed to indicate the power-on state. 
     In the above manner, the power supply to any camera can be controlled by the monitor terminal  18  to save power consumption. 
     In accordance with a video transmission request from the video reception software  52 , the video transmission software  58  transmits a camera image. More specifically, the video reception software  52  requests the video transmission software  58  of the video transmission terminal  12  connected to the selected camera over the network  10  to transmit video data of one frame. In response to this request, the video transmission software  58  compresses the video data of the latest frame supplied from the camera and divides it into packets which are then transmitted to the requested video reception software  52 . The video reception software  52  reconfigures the received packets to generate a frame, and expands the compressed frame to display it in the designated one of the video display areas  66   a  to  66   f.  Thereafter, the video reception software  52  issues again the video transmission request. By repeating these processes, the video reception terminal  18  receives the images at the remote camera over the network and displays them. 
     If the images of a plurality of cameras are displayed at the same time, the video transmission request is issued to the video display transmission software  58  of the video transmission terminal  12  connected to each camera, and the image is received and displayed. These operations are cyclically performed for the cameras. 
     Changing the display position of a received camera image can be performed also by the drag-and-drop operation. For example, as illustrated in FIG. 11, if the video display area  66   c  is to be changed to the video display area  66   b,  the mouse pointer is moved to the video display area  66   c.  After the mouse is clicked and maintained in this state, the mouse pointer is moved to the video display area  66   c  whereat the mouse button is released. 
     With the above operations, the video reception software  52  stops displaying an image in the first selected video display area (area  66   c  in FIG.  11 ), and starts displaying the image in the next selected video display area (area  66   b  in FIG.  11 ). During this operation, the network connection is not intercepted. 
     In order to watch an image in a particular video display area (e.g., area  66   a ) during the glance mode, this display area is double clicked with the mouse. Then, the video display window  64  is switched to the watching mode of watching the image. FIG. 13 shows the video display window in the watching mode. A window  80  is called a watching display window. Reference numeral  82  represents a mode switch button used for returning to the glance mode. Reference numerals  84   a,    84   b,    84   c,  and  84   d  represent cursors for controlling the direction of the camera to display an image in conformity with the camera direction. 
     In the watching mode, one image is displayed in a magnified scale. In this case, it is possible to select either a smooth motion display which gives a priority of a display speed (frame rate) or a high resolution display which gives a priority of an image quality by increasing the data amount per one frame. FIG. 14A shows an image quality setting window for setting the high resolution display. Reference numeral  90  represents a display speed priority button, and reference numeral  92  represents an image priority button. One of these buttons  90  and  92  can be selected at a time. The image quality setting window is displayed on the monitor upon instruction by the watching mode. When the display is selected in the image quality setting window, a corresponding image of the watching mode is displayed. 
     Next, the operation of the watching mode after the image quality priority button  92  is pressed will be detailed. First, the video reception software  52  notifies the video transmission software  58  of the corresponding video transmission terminal  12  of a high resolution request over the network  10 . Upon reception of this high resolution request, the video transmission software  58  switches the transmission image to the high resolution. The video reception software  52  receives the high resolution image and displays it in the watching display window  80 . In this case, since the high resolution image has a data amount larger than the standard resolution image, the display speed lowers in some cases. 
     As the mode switch button  82  is pressed or the watching display window  80  is double clicked with the mouse, the video display window  64  resumes the glance mode. The video reception software  52  notifies the video transmission software  52  of the corresponding video transmission terminal  12  of a standard resolution request over the network  10 . Upon reception of the standard resolution request, the video transmission software  58  changes the transmission image to the standard resolution. 
     Next, the operation of the watching mode after the display speed priority button  90  is pressed will be described. In this case, the video reception software  52  notifies nothing to the video transmission software  58 . The video reception software  52  magnifies the image transmitted at the standard resolution and displays it in the watching display window  80 . The operation of returning to the glance mode is the same as the case the image quality button  92  is selected. 
     In the mode selection, although the image resolution is controlled, an image compression ratio or an image transmission rate may be controlled. 
     Next, the operation of controlling a camera in the watching mode will be described. Similar to the glance mode, the motion of a camera can be controlled in the watching mode by using the camera control panel  68 . The camera can be controlled also by pressing the button of the mouse in the watching display window. As indicated by broken lines in FIG. 13, depending upon the position of the mouse cursor in one of the upper/lower and right/left areas in the watching display window  80 , the mouse cursor changes to one of the camera direction control cursors  84   a  to  84   d.  When the mouse button is pressed, the direction of the camera is changed to one of the upper/lower and right/left directions. 
     Although the video reception terminal does not display other images on the monitor during the watching mode, the communication with the corresponding video transmission terminals is maintained. As a result, when the watching mode is terminated, the monitor can be changed to the multi-image display state at high speed. 
     It is obvious that in response to a mode change instruction to the watching mode, communications with the other video transmission terminals may be intercepted to shift to the image quality priority mode or display speed priority mode. Alternatively, as shown in FIG. 14B, a communication keep button and a communication stop button may be provided in the image quality setting window in order to instruct, when the watching mode is designated, to keep or stop communications with the other video transmission terminals. 
     Therefore, in the watching mode, the designated terminal can be assigned a broad channel band so that an image of high resolution can be transmitted and an image of a high frame rate can be transmitted. 
     If the image display is to be terminated, the image displayed in the video display area is dragged and dropped in the trash-can icon  66   g.  FIG. 12 illustrates an operation of stopping the display of an image in the video display area  66   c.  The mouse pointer is moved to the video display area  66   c  and the mouse button is pressed. In the state of the pressed mouse button, the mouse pointer is moved to the trash-can icon  66   g  whereat pressing the mouse button is released. 
     In response to the above operations, the video reception software  54  stops issuing the video transmission request to the video transmission software  58  of the video transmission terminal connected to the camera which displays the image in the selected video display area (area  66   c  in FIG.  12 ). Furthermore, the video reception software  54  notifies the image display termination to the camera control client software  50  and map management software  54 . In response to this notice, the camera control client software  50  disconnects the network connection to the camera control server software  56  of the corresponding video transmission terminal  12  to clear its video display area (area  66   c  in FIG.  12 ). The map management software  54  erases the scope display of the camera icon (e.g., icon  62   c ) of the corresponding camera to update the map. 
     In this embodiment, the camera symbol in the map is dragged and dropped in the video display area to establish the network connection between the video reception and transmission terminals. The image display position can be changed by a drag-and-drop operation between the video display area in which a camera image is displayed and another optional video display area. An image display can be stopped by a drag-and-drop operation from the video display area in which a camera image is displayed to the display stop symbol. As above, it becomes very easy to start a camera image display, change a display position, and stop an image display. Obviously, images are not limited to only camera images, but other images may be used such as images generated from a storage medium such as a video tape. 
     &lt;Second Embodiment&gt; 
     FIG. 15 is a block diagram showing the outline structure of a video transmission terminal  112  having a switcher and a synthesizer connected thereto. Similar to the first embodiment, the video transmission terminal  112  is connected to a network  110  to which a plurality of video transmission and reception terminals are connected. 
     In the first example shown in FIG. 2, one video camera is connected to one video transmission terminal. In the second embodiment, four camera controllers  114   a  to  114   d  are connected to the switcher  101  and four video cameras  116   a  to  116   d  are connected to the synthesizer  102 . 
     The synthesizer  102  will be described. The synthesizer  102  synthesizes moving image analog signals supplied from the video cameras  116   a  to  116   d,  as indicated at  166   a  in FIG.  16 . As indicated at  66   a  in FIG. 17, an image of each video camera can be selectively displayed by sending a command from the video transmission terminal to the synthesizer  102  via the switcher  101 . 
     The switcher  101  will be described. As different from the structure shown in FIG. 2, the structure shown in FIG. 15 has four camera controllers connected to the switcher  101 . In order for the computer to control the video camera, the camera controllers  114   a  to  114   d  are required to be switched. The switcher  101  performs this function. As described before, as the command is sent to the synthesizer  102 , moving image signals from the video cameras can be selected or synthesized. 
     FIG. 18 is a block diagram showing the outline structure of the video reception terminal (monitor terminal)  118 . The video reception terminal has the same hardware structure as the first embodiment, but has different software. 
     FIG. 19 illustrates the software configuration of this embodiment. The video reception terminal (monitor terminal)  118  is installed with camera control client software  150 , video reception software  152 , and map management software  154 . The camera control client software  150  remotely controls the cameras  116   a  to  116   d  via the network  110  and video transmission terminals  112 . The video reception software  152  expands compressed video data supplied from the video transmission terminal  112 . The map management software  154  displays a camera symbol representative of the current position and status of each camera  116   a  to  116   d  on a map, and also displays an operation panel for controlling each camera  116   a  to  116   d.  Similar to FIG. 1, to the network  110  a plurality of video transmission terminals  112 - 1  to  112 -n and video reception terminals  118 -a to  118 -n are connected. 
     The video reception software  152  also manages all the cameras  116  via the network  110  and video transmission terminals  112 , and stores fixed information of each camera  116  and variable information thereof (e.g., a camera name, a host name of the computer connected to the camera, a camera status such as pan, tilt, and zoom, a controllable or uncontrollable state, a camera name under control, a camera name under display). Such fixed and variable information is also supplied to the camera control client software  150  and map management software  154  to change the display of the camera symbol or the like. A set of above-described software is stored either at the video transmission terminal  112  or video reception terminal  118  in its main storage medium or secondary storage medium. 
     The video transmission terminal  112  is installed with camera control server software  156  and video transmission software  158 . The camera control server software  156  controls the camera  116  via the camera controller  114  in response to a request from the camera client software  150 , and notifies the requested terminal of the current status of the camera  116 . The video transmission software  158  compresses video data output from the camera  116  in a predetermined compression format and transmits it via the network  110  to the requested terminal. 
     As shown in FIG. 15, for the control of the video cameras  116   a  to  116   d  via the switcher  101 , the camera control server software  156  supplies the switcher  101  with a command for selecting a video camera to be controlled, so that the switcher  101  is connected to the corresponding camera controller of the video camera. Thereafter, in response to a request from the camera control client software  150 , the video camera is controlled by the switcher  101  and camera controller  114  connected thereto. 
     FIG. 20 shows examples of the display contents of the monitor screen of the video reception terminal  118 . Like constituents to those shown in FIG. 5 are represented by identical reference numerals and the description thereof is omitted. Reference numeral  110  represents a single image display mode button. When this button is clicked, as indicated at  111  in FIG. 21, a new window is popped up and only the selected moving image is displayed. When the single image display mode button is clicked, a command for stopping image transmission is sent to the video transmission terminals other than the selected terminal, and a command for increasing a frame rate or raising a resolution is sent to the selected terminal in order to efficiently utilize the capacity of empty channels. 
     Whether the command for increasing a frame rate or raising a resolution is determined in accordance with initial setting made by a user. Obviously, with this initial setting, a balanced setting of both the frame rate and resolution may be set. 
     In FIG. 20, reference numeral  112  represents a four-image simultaneous display button, and reference numeral  113  represents a selective display button. These buttons are made valid only when the video transmission terminal is selected which is connected to the four video cameras via the synthesizer and switcher shown in FIG.  15 . Assuming that the image at  66   a  in the video display area  64  is supplied from the video transmission terminal shown in FIG. 15, the four-image simultaneous display button  112  and selective display button  113  become valid when the image  66   a  is selected by the mouse. 
     For example, if the lower right image among the four images displayed simultaneously as shown in FIG. 16 is clicked and thereafter the selective display button  113  is clicked, then the image shown in FIG. 17 is displayed. If the image  66   a  shown in FIG. 17 is clicked and thereafter the four-image simultaneous display button  112  is clicked, the images shown in FIG. 16 are displayed. 
     If the selected tag  60   a  to  60   d  has a video transmission terminal which does not use the switcher and synthesizer, the buttons  112  and  113  are not displayed. A video transmission terminal having the switcher and synthesizer is discriminated from other terminals by exchanging the current status between the video transmission and reception terminals displayed when the map is switched. 
     Next, the single image display mode will be described. As one of the image display areas  66   a  to  66   f  is clicked with the mouse  130  and thereafter the single image display mode button  113  is clicked, the single image display window  111  shown in FIG. 22 is popped up and the selected image is displayed. 
     Next, consider the switching to the single image display mode from the state that four images are displayed from the video transmission terminal having four video cameras via the synthesizer and switcher shown in FIG.  15 . The images shown in FIGS. 16 and 17 are those images supplied from the video transmission terminal shown in FIG.  15 . 
     As the single image display mode button  110  is clicked while the images shown in FIG. 16 are displayed, the single image display window  111  shown in FIG. 23 is popped up. Since these images are supplied from the video transmission terminal having four video cameras via the synthesizer and switcher, the four-image simultaneous display button  112   a  and selective display button  113   a  are displayed in the single image display window  111 . In this case, if the lower right image shown in FIG. 23 is clicked with the mouse and thereafter the selective display button  113   a  is clicked, the image shown in FIG. 22 is displayed. 
     Similar to switching to the single image display mode, the image shown in FIG. 22 has a good image quality because of the improved frame rate and resolution effected in response to the command. 
     If the single image display mode button  110  is clicked while the image shown in FIG. 17 is displayed, the single image display window  111  shown in FIG. 22 is popped up. Since this image is supplied from the video transmission terminal connected to four video camera via the synthesizer and switcher, the four-image simultaneous display button  112   a  and selective display button  113   a  are displayed in the single image display window  111 . In this case, as the four-image simultaneous display button  112   a  is clicked with the mouse, four images shown in FIG. 23 are displayed at the same time. 
     In this embodiment, even in the single image display mode, images from the video transmission terminal connected to four video cameras via the synthesizer and switcher can be synthesized or selected. Therefore, image synthesis and selection can be easily performed by a user without confirming whether the operation mode is the single image display mode or the glance image display mode. 
     &lt;Other Embodiments&gt; 
     Programs realizing the structures and functions of the above embodiments may be stored in a storage medium. In this case, a method of realizing the above embodiments with such programs and the storage medium constitutes other embodiments of this invention. 
     Such a storage medium may be a floppy disk, a hard disk, an optical disk, a magnetooptical disk, a CD-ROM, a magnetic tape, a non-volatile memory card, and a ROM. 
     Other types of embodiments of this invention include not only for the case wherein the embodiment functions are realized by executing the program stored in the storage medium but also for the case wherein the programs are executed on an OS together with other application software and functions of other expansion boards.