Abstract:
A data delivery device that switches picture data to be delivered so that pictures different in quality can be efficiently grasped without missing information of a high importance level is provided. The data delivery device receives picture data from multiple cameras through a network using a picture reception program. It determines whether or not to display each image frame of the picture data by accumulating the frequency of viewpoint switching or the importance level information of an image from each viewpoint by a picture selection program. In addition, it delivers a selected image frame through an interface by a picture transmission program. The display time for each frame is varied according to the importance level information of the image to enhance the viewability of an important frame.

Description:
CLAIM OF PRIORITY 
       [0001]    The present application claims priority from Japanese Patent Application JP2008-203831 filed on Aug. 7, 2008, the content of which is hereby incorporated by reference into this application. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to data delivery devices and in particular to a data delivery device in surveillance systems that switches and delivers pictures. 
         [0004]    2. Description of Related Art 
         [0005]    There are viewpoint-switching surveillance systems in which multiple cameras, sensors, and the like installed on the street are connected together through a communication network to monitor security or watch children. To efficiently monitor security or watch children with such a system, a technology for selecting important information from pictures from cameras or information from sensors and switching display. 
         [0006]    As a system for switching picture display, there are multi-viewpoint picture systems for sports broadcasting or the like. In these multi-viewpoint picture systems, viewpoints are selected to the taste or preference of an individual. For example, Japanese Patent Application Laid-Open Publication No. 2003-179908 discloses a delivery device that controls pictures to be delivered based on information on the taste of a viewer. 
         [0007]    In monitoring security or watching children, delivery may be controlled sometimes by assigning an importance level to each picture according to the situation of an object to be monitored. For example, Japanese Patent Application Laid-Open Publication No. 2004-80560 discloses a system in which a priority is assigned to each picture input from multiple picture shooting devices or image pickup devices and input pictures to be selected are sequentially switched based on these priorities. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    When pictures are selected to the taste or preference of an individual with the device disclosed in Japanese Patent Application Laid-Open Publication No. 2003-179908, an importance level is not objectively assigned to each picture and thus these pictures are equal in quality. For monitoring security or watching children, a criterion for picture selection is clarified to some degree. Therefore, to reduce the amount of transmitted and received information, a picture in which movement is not observed at all or the like may fluctuate the quality of a picture transmitted from the camera side sometimes. In the device disclosed in Japanese Patent Application Laid-Open Publication No. 2004-80560, picture inputs to be selected are sequentially switched based on the priorities of multiple picture inputs to increase the frequency with which a picture input high in importance level is selected. However, the device cannot instantaneously display information of a high importance level among picture inputs so that a viewer will not miss it. 
         [0009]    It is an object of the invention to provide a data delivery device that switches and delivers pictures so that pictures different in quality can be reliably grasped without missing information of a high importance level. 
         [0010]    To solve the above problem, the invention provides a data delivery device that receives picture data picked up by multiple image pickup devices through a network and selects an image frame from the received multiple pieces of picture data and delivers it. The data delivery device includes: interfaces that are connected to the network and transmit and receive picture data; a processing unit that processes picture data; and a storage unit that stores picture data. This processing unit selects picture data from multiple image pickup devices that picked up picture data, received through the interface, based on a cumulative value of the number of times of switching the multiple image pickup devices and delivers the picture data. This processing unit preferably delivers picture data from an image pickup device when the cumulative value of the number of times of switching thereof exceeds a preset threshold value(hereinafter, threshold). 
         [0011]    To solve the above problem, further, the invention provides a data delivery device that receives picture data picked up by multiple image pickup devices through a network and selects an image frame from the received multiple pieces of picture data and delivers it. The data delivery device includes: interfaces that are connected to the network and transmit and receive picture data; a processing unit that processes picture data; and a storage unit that stores picture data. This processing unit selects picture data from multiple image pickup devices based on the number of image frames from each image pickup device in a predetermined number of consecutive image frames of picture data received through the interface and delivers the picture data. The processing unit preferably compares the numbers of image frames from the individual image pickup devices with one another and selects picture data from an image pickup device largest in the number of image frames and delivers the picture data. 
         [0012]    To solve the above problem, furthermore, the invention provides a data delivery device that receives picture data picked up by an image pickup device through a network and delivers the received picture data. The data delivery device includes: an interface that is connected to the network and transmits and receives an image frame containing importance level information as picture data; a storage unit that stores picture data received through the interface; and a processing unit that carries out delivery processing on the image frame based on the importance level information. This processing unit controls a display time for an image frame based on the importance level information of the image frame. When there are multiple image pickup devices, the processing unit controls the image frame to be displayed based on the cumulative value of the importance level information from each of the image pickup devices in a predetermined number of the consecutive image frames from the image pickup devices. This control is carried out based on the cumulative value of importance level information from each image pickup device in a predetermined number of consecutive image frames. The processing unit preferably determines image data to be delivered this time by comparing the following information: the importance level information of the image frame delivered last and the importance level information of the image frame selected this time based on the cumulative value of importance level information. 
         [0013]    That is, in this invention, the following processing is carried out to instantaneously display important information: whether or not to display a picture is evaluated when each image frame is received, not at specific time intervals, by accumulating the frequency of viewpoint switching or the number of image frames from each viewpoint. In addition, the display time for each image frame is varied according to importance level information and the viewability of an important frame is thereby enhanced. 
         [0014]    The configuration of this invention makes it possible to provide a data delivery device in which important information is not missed and can be instantaneously viewed. 
         [0015]    Thus pictures different in quality can be efficiently grasped and information of a high importance level, even though the information is shown in only one frame of picture, is not missed and can be grasped. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  illustrates the basic configuration of a system to which the invention is applied; 
           [0017]      FIG. 2A  illustrates an example of the format of picture data flowing between a camera and a data delivery device in each embodiment; 
           [0018]      FIG. 2B  illustrates another example of the format of picture data flowing between a camera and a data delivery device in each embodiment; 
           [0019]      FIG. 3  illustrates the format of picture data flowing between a data delivery device in each embodiment and a data display device; 
           [0020]      FIG. 4  illustrates the basic configuration of a data delivery device in each embodiment; 
           [0021]      FIG. 5  illustrates a picture management DB in each embodiment; 
           [0022]      FIG. 6  illustrates an example of control based on the number of times of camera switching in a first embodiment; 
           [0023]      FIG. 7  illustrates a processing flow in control based on the number of times of camera switching in the first embodiment; 
           [0024]      FIG. 8  illustrates an example where control based on the number of times of camera switching cannot be carried out; 
           [0025]      FIG. 9  illustrates an example of control based on the number of frames from each camera included in multiple received frames in a second embodiment; 
           [0026]      FIG. 10  illustrates a processing flow in control based on the number of frames from each camera included in multiple received frames in the second embodiment; 
           [0027]      FIG. 11  illustrates a first example where control based on the number of frames from each camera included in multiple received frames cannot be carried out; 
           [0028]      FIG. 12  illustrates an example where control is carried out by combining the following controls in a third embodiment: control based on the number of times of camera switching and control based on the number of frames from each camera included in multiple received frames; 
           [0029]      FIG. 13  illustrates a processing flow in control carried out by combining the following controls in the third embodiment: control based on the number of times of camera switching and control based on the number of frames from each camera included in multiple received frames; 
           [0030]      FIG. 14  illustrates a second example where control based on the number of frames from each camera included in multiple received frames cannot be carried out; 
           [0031]      FIG. 15  illustrates an example of control based on the importance level of a frame from each camera included in multiple received frames in a fourth embodiment; 
           [0032]      FIG. 16  illustrates a processing flow in control based on the importance level of a frame from each camera included in multiple received frames in the fourth embodiment; 
           [0033]      FIG. 17  illustrates an example of control carried out by combining the following controls in a fifth embodiment: control based on the number of times of camera switching and control based on the importance level of a frame from each camera included in multiple received frames; 
           [0034]      FIG. 18  illustrates a processing flow in control carried out by combining the following controls in the fifth embodiment: control based on the number of times of camera switching and control based on the importance level of a frame from each camera included in multiple received frames; 
           [0035]      FIG. 19  illustrates an example where a frame of a high importance level is kept displayed in a sixth embodiment; 
           [0036]      FIG. 20  illustrates a processing flow in control in which a frame of a high importance level is kept displayed in the sixth embodiment; 
           [0037]      FIG. 21  illustrates an example of control carried out by combining the following controls in a seventh embodiment: control based on the number of times of camera switching, control based on the importance level of a frame from each camera included in multiple received frames, and control in which a frame of a high importance level is kept displayed; and 
           [0038]      FIG. 22  illustrates a processing flow in control carried out by combining the following controls in the seventh embodiment: control based on the number of times of camera switching, control based on the importance level of a frame from each camera included in multiple received frames, and control in which a frame of a high importance level is kept displayed. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0039]    Hereafter, description will be given to embodiments of the invention with reference to the drawings. In the following description, importance level information, or information indicating the importance level of an image frame, may be simply referred to as “importance level” sometimes. 
         [0040]      FIG. 1  illustrates the overall configuration of a viewpoint-switching surveillance system as an example of the embodiments of the invention. 
         [0041]    In the example in the drawing, a first camera  101 , a second camera  102 , and a third camera  103  as image pickup devices respectively deliver picked-up pictures to a data delivery device  104  through a line  111 , a line  112 , and a line  113 . The data delivery device  104  extracts a relevant picture, for example, a picture embracing a viewed object  107 , from the received pictures in accordance with a request from a viewer  106  and delivers the picture to a data display device  105  through a line  114 . 
         [0042]      FIGS. 2A and 2B  illustrate examples of the format of picture data flowing through the lines  111  to  113  between the cameras  101  to  103  and the data delivery device  104  in the configuration illustrated in  FIG. 1 . When the cameras  101  to  103  transmit picture data as an IP packet to the data delivery device  104 , the cameras  101  to  103  can be identified by transmission source IP  202 , or the IP address of a camera as the transmission source of the IP packet as indicated by format  201  in  FIG. 2A . A reference numeral  203  denotes transmission destination IP, or the IP address of the data delivery device as the destination of transmission. A picture information header  204  indicating the contents of picture data  205  contains information indicating a viewed object  107  and its importance level (importance level information). 
         [0043]    When picture data from the cameras  101  to  103  is transmitted to the data delivery device  104  with an intermediate device intervening, a format  206  illustrated in  FIG. 2B  is used. When an intermediate device, not shown, exists as indicated in the drawing, the cameras  101  to  103  cannot be identified by the transmission source IP  207  of the IP packet. Therefore, information for identifying the cameras  101  to  103  is included in a picture information header  209  indicating the contents of picture data  210 . 
         [0044]      FIG. 3  illustrates an example of the format of picture data flowing through the line  114  between the data delivery device  104  and the data display device  105  in the configuration illustrated in  FIG. 1 . Similarly with the formats in  FIGS. 2A and 2B , a reference numeral  302  denotes transmission source IP indicating the data delivery device; a reference numeral  303  denotes transmission destination IP indicating the data display device; a reference numeral  304  denotes picture information header; and a reference numeral  305  denotes picture data. 
         [0045]      FIG. 4  is a functional block diagram illustrating the basic configuration of the data delivery device  104  in the viewpoint-switching surveillance system illustrated in  FIG. 1 . In  FIG. 4 , the data delivery device  401  includes interfaces  402 ,  403  and a picture processing unit  404  that processes picture data. The picture processing unit  404  includes a picture processing memory  405  and a picture processing processor  406 . The picture processing memory  405  has therein a picture reception program  407 , a picture transmission program  408 , and a picture selection program  409  executed by the picture processing processor  406 . The picture processing memory  405  includes a picture management DB  410 , a picture storage area  411 , and an interim storage area  412  for storing picture data. The picture reception program  407  and the picture transmission program  408  are respectively programs for receiving and transmitting picture data through the interfaces  402 ,  403 . The picture selection program  409  is a program for selecting picture data to be delivered and displayed on the data display device of the viewer from among picture data received from the image pickup devices. 
         [0046]    When the picture processing unit  404  of the data delivery device  401  receives a picture data delivery request from the viewer through the interfaces  402 ,  403 , it carries out the following processing by the picture reception program  407 : the picture processing unit stores information on the received picture in the picture management DB  410  and stores the received picture data in the picture storage area  411 . Further, when the data delivery device  401  receives a picture data delivery request from the viewer through the interfaces  402 ,  403 , it carries out the following processing: the data delivery device extracts a picture corresponding to the picture data delivery request from the picture management DB  410  by the picture selection program  409  and delivers it by the picture transmission program  408 . The interim storage area  412  holds temporary information required for processing in accordance with the picture selection program  409 . Examples of such information include the cumulative values of varied data described later, the number of times of switching, and the like. The above-mentioned functional configuration can be obtained by an ordinary computer system, such as a server, including a central processing unit (CPU), a storage unit (memory), and a network interface, needless to add. 
         [0047]      FIG. 5  illustrates an example of the picture management DB  410  in  FIG. 4 . The picture management DB  410  is comprised of: shooting time  501  at which picture data was picked up; an identifier  502  of the picture data; camera information  503  on a camera that picked up the picture data; viewed object information  504  on a viewed object contained in the picture data; and importance level information  505  on the importance level of the picture data. When the shooting time  501  is contained in the picture information headers  204 ,  209  in  FIG. 2A  or  2 B, it is generated from the contents of the picture information header. When it is not contained in the picture information header, it is generated from time when the data delivery device  104 ,  401  received the picture data. 
       First Embodiment 
       [0048]      FIG. 6  schematically illustrates an example of control based on the cumulative value of the number of times of camera switching, one of picture selection methods in a first embodiment. The input of the delivery device that receives a picture  601  from camera  1  and a picture  602  from camera  2  equal in frame rate is denoted by a reference numeral  603 . Since camera  1  and camera  2  are equal to each other in frame rate, pictures from these cameras are alternately repeated. If these pictures are directly outputted, they are very difficult to view. The number of times of camera switching in the input  603  to the delivery device is denoted by a reference numeral  604 . “3” will be taken as the threshold of the number of times of switching. At time  606  when this threshold is exceeded, a camera whose picture should be outputted by the delivery device is fixed. The output of the delivery device is denoted by a reference numeral  605 . As denoted by this reference numeral, the pictures from camera  1  and from camera  2  are prevented from being alternately displayed and this makes the displayed picture easy to view. 
         [0049]      FIG. 7  illustrates a processing flow in the first embodiment illustrated in  FIG. 6 . In the drawing, reference numerals  701  to  715  denote the individual steps of the processing flow. This is the same with the following processing flowcharts. When the data delivery device  104  receives an image ( 702 ), it extracts camera information ( 703 ) and determines whether or not the extracted camera information is identical with stored camera information ( 704 ). When they are identical with each other, the number of times of camera switching is decremented ( 705 ). When they are not identical with each other, the number of times of camera switching is incremented ( 706 ). 
         [0050]    When the number of times of camera switching is decremented at Step  705 , it is determined whether or not the number of times of camera switching has fallen below a threshold ( 707 ). When it has fallen below the threshold, the fixation of the camera is canceled ( 708 ). When the number of times of camera switching is incremented at Step  706 , it is determined whether or not the number of times of camera switching has exceeded a threshold ( 709 ). When it has exceeded the threshold, the fixation of the camera is started ( 710 ). Subsequently, the camera information of the received image is stored ( 711 ) and it is determined whether or not a camera whose image is displayed is fixed ( 712 ). When the camera is not fixed and when the camera is fixed but it is matched with the camera information of the received image, the received image is displayed ( 714 ). When the camera is fixed and it is not matched with the camera information of the received image, the received image is not displayed and this series of processing is terminated ( 715 ). 
         [0051]      FIG. 8  illustrates an example where delivered pictures cannot be controlled based on the number of times of camera switching as in the first embodiment illustrated in  FIG. 6  and  FIG. 7 . The input to the delivery device  104  that receives a picture  801  from camera  1  and a picture  802  from camera  2 , different in frame rate, is denoted by a reference numeral  803 . At this time, the number of times of camera switching is as denoted by a reference numeral  804 . Since a certain number of times of camera switching is maintained and the threshold of  3  is not exceeded, the following takes place under the same control as illustrated in  FIG. 6  and  FIG. 7 : the output of the delivery device  104  is as denoted by a reference numeral  805  and a picture from camera  1  and a picture from camera  2  is continuously mixed into a picture from camera  1 . 
       Second Embodiment 
       [0052]      FIG. 9  illustrates a picture selection method in a second embodiment. To control the case illustrated in  FIG. 8 , in this embodiment, control is carried out based on the number of frames from each camera included in multiple received frames, that is, a predetermined number of multiple consecutive received image frames. As in the case illustrated in  FIG. 8 , the input of the delivery device  104  that receives a picture  901  from camera  1  and a picture  902  from camera  2  is as denoted by a reference numeral  903 . At this time, the number of frames from camera  1  included in newly received five frames is as denoted by a reference numeral  904  and the number of frames from camera  2  included in the same frames is as denoted by a reference numeral  905 . When the number of frames from a camera is larger than that from the other camera and the number of frames from the camera is equal to or larger than the threshold of 3, a frame is outputted. In this case, the output of the delivery device  104  is as denoted by a reference numeral  906  and unlike the case illustrated in  FIG. 8  pictures are prevented from being mixed. 
         [0053]      FIG. 10  illustrates a processing flow in the picture selection method in the second embodiment illustrated in  FIG. 9 . When the data delivery device  104  receives a picture ( 1002 ), it extracts camera information ( 1003 ) and computes the number of frames from each camera included in the preset number of frames ( 1004 ). Subsequently, it is determined whether or not the camera from which the image is received has exceeded a threshold of the number of frames with respect to image display ( 1005 ). When the camera has exceeded the threshold, it is determined whether or not the camera from which the image is received is largest in the number of frames from each camera among all the cameras ( 1006 ). When the camera is largest in the number of frames from each camera, the image received from the camera is displayed ( 1007 ). 
         [0054]      FIG. 11  illustrates an example where delivered pictures cannot be controlled based on the number of frames from each camera included in multiple received frames unlike the case illustrated in  FIG. 9  and  FIG. 10 . Similarly with the example illustrated in  FIG. 6 , the input of the delivery device that receives a picture ( 1101 ) from camera  1  and a picture ( 1102 ) from camera  2 , equal in frame rate, is as denoted by a reference numeral  1103  and pictures from camera  1  and from camera  2  are alternately repeated. At this time, the number of frames from camera  1  included in five received frames is as denoted by a reference numeral  1104  and the number of frames from camera  2  included in the same frames is as denoted by a reference numeral  1105 . Thus the same values are alternately repeated. Under the same control as illustrated in  FIG. 9 , therefore, the output of the delivery device is as denoted by a reference numeral  1106  and a picture from camera  1  and a picture from camera  2  are alternately repeated. 
       Third Embodiment 
       [0055]      FIG. 12  illustrates a picture selection method in a third embodiment. To make it possible to control the case illustrated in  FIG. 11 , in this embodiment, control is carried out by combining the following controls: control based on the number of times of camera switching (cumulative value) in the first embodiment; and control based on the number of frames from each camera included in multiple received frames in the second embodiment. Similarly with the example illustrated in  FIG. 11 , the input of the delivery device  104  that receives a picture  1201  from camera  1  and a picture  1202  from camera  2  is as denoted by a reference numeral  1203 ; and the number of frames from camera  1  included in the five received frames is as denoted by a reference numeral  1204  and the number of frames from camera  2  included in the same frames is as denoted by a reference numeral  1205 . The frame selected by control based on the five received frames is as denoted by a reference numeral  1206  and at this time the number of times of camera switching is as denoted by a reference numeral  1207 . “3” will be taken as the threshold of the number of times of switching  1207 . At time  1209  when this threshold is exceeded, a camera whose picture should be outputted is fixed. As a result, the output of the delivery device is as denoted by a reference numeral  1208 . 
         [0056]      FIG. 13  illustrates a processing flow in the third embodiment illustrated in  FIG. 12 . When the data delivery device  104  receives a picture ( 1302 ), it extracts camera information ( 1303 ) and computes the number of frames from each camera included in a preset number of frames ( 5  in this example) ( 1304 ). Subsequently, it is determined whether or not the camera from which the image is received has exceeded a threshold of the number of frames with respect to image display ( 1305 ). When the camera has exceeded the threshold, it is determined whether or not the camera from which the image is received is largest in the number of frames from each camera among all the cameras ( 1306 ). When the camera is largest in the number of frames from each camera, it is determined whether or not the extracted camera information is identical with stored camera information ( 1307 ). When they are identical with each other, the number of times of camera switching  1207  is decremented ( 1308 ). When they are not identical with each other, the number of times of camera switching is incremented ( 1309 ). When the number of times of camera switching is decremented at Step  1308 , it is determined whether or not the number of times of camera switching has fallen below a threshold ( 1310 ). When it has fallen below the threshold, the fixation of the camera is canceled ( 1311 ). When the number of times of camera switching is incremented at Step  1309 , it is determined whether or not the number of times of camera switching has exceeded a threshold ( 1312 ). When it has exceeded the threshold, the fixation of the camera is started ( 1313 ). Subsequently, the camera information of the received image is stored ( 1314 ) and it is determined whether or not a camera whose image is displayed is fixed ( 1315 ). When the camera is not fixed and when the camera is fixed but it is matched with the camera information of the received image, the received image is displayed ( 1317 ). When the camera is fixed and it is not matched with the camera information of the received image, the received image is not displayed and this series of processing is terminated ( 1318 ). The camera information of the received image stored at Step  1314  is the information of the image in the selected frame  1206  in  FIG. 12 . 
         [0057]      FIG. 14  illustrates a second example where delivered pictures cannot be desirably controlled based on the number of frames from each camera included in multiple received frame unlike the case illustrated in  FIG. 9  and  FIG. 10 . Similarly with the example illustrated in  FIG. 9 , the input of the delivery device that receives a picture  1401  from camera  1  and a picture  1402  from camera  2 , different in frame rate, is as denoted by a reference numeral  1403 ; the number of frames from camera  1  included in the five received frames is as denoted by a reference numeral  1404  and the number of frames from camera  2  included in the same frames is as denoted by a reference numeral  1405 . The pictures  1401 ,  1402  from camera  1  and camera  2  contain information on importance level (importance level information) indicated by parenthesized numerals. At this time, the output of the delivery device  104  is as denoted by a reference numeral  1406  and a frame  1407  of a high importance level (frame of importance level ( 10 ) from camera  2 ) is not displayed. 
       Fourth Embodiment 
       [0058]      FIG. 15  illustrates a fourth embodiment. To make it possible to control the case illustrated in  FIG. 14 , in this embodiment, control is carried out based on importance level information contained in each frame received from each camera. Similarly with the example illustrated in  FIG. 14 , the input of the delivery device  104  that receives a picture  1501  from camera  1  and a picture  1502  from camera  2  is as denoted by a reference numeral  1503 . At this time, the importance level of a frame from camera  1  included in newly received five frames is as denoted by a reference numeral  1504  and the importance level of a frame from camera  2  included in the same frames is as denoted by a reference numeral  1505 . A frame is outputted when both the following conditions are met: the importance level information of a frame from a camera included in the five received frames should be higher than that of a frame from the other camera; and the importance level information of a frame from the camera should be equal to or higher than a threshold of (6). In this case, the output of the delivery device is as denoted by a reference numeral  1506  and a frame  1507  of a high importance level (frame of importance level ( 10 ) from camera  2 ) is displayed. 
         [0059]      FIG. 16  illustrates a processing flow in the fourth embodiment illustrated in  FIG. 15 . When the data delivery device  104  receives a picture ( 1602 ), it extracts camera information ( 1603 ) and extracts importance level ( 1604 ). Then it computes the importance level of a frame from each camera included in the preset number of frames ( 1605 ). Subsequently, it is determined whether or not the camera from which the image is received has exceeded a threshold of importance level with respect to image display ( 1606 ). When the camera has exceeded the threshold, it is determined whether or not the camera from which the image is received is highest in the importance level of a frame from each camera among all the cameras ( 1607 ). When the camera is highest in the importance level of a frame from each camera, the received image is displayed ( 1608 ). 
       Fifth Embodiment 
       [0060]      FIG. 17  illustrates a picture selection method in a fifth embodiment. In this embodiment, control is carried out by combining control based on the number of times of camera switching and control based on the importance level information of a frame from each camera included in multiple received frames. The input of the delivery device that receives a picture  1701  from camera  1  and a picture  1702  from camera  2  is as denoted by a reference numeral  1703 . At this time, the importance level of a frame from camera  1  included in five received frames is as denoted by a reference numeral  1704 ; and the importance level of a frame from camera  2  included in the same frames is as denoted by a reference numeral  1705 . Similarly with the above embodiment, a frame is outputted when both the following conditions are met: the importance level of a frame from a camera included in five received frames should be higher than that of a frame from the other camera; and the importance level information of a frame from the camera should be equal to or higher than a threshold of (6). In this case, the selected frame is as denoted by a reference numeral  1706  and at this time the number of times of camera switching is as denoted by a reference numeral  1707 . “3” will be taken as the threshold of the number of times of switching  1707 . At time  1711  when the threshold of (6) is exceeded, a camera whose picture should be outputted is fixed. As denoted by a reference numeral  1708 , as a result, a frame  1709  of a high importance level is outputted from the delivery device  104 . 
         [0061]      FIG. 18  illustrates a processing flow in the fifth embodiment illustrated in  FIG. 17 . When the data delivery device  104  receives a picture ( 1802 ), it extracts camera information ( 1803 ) and extracts importance level ( 1804 ). Then it computes the importance level of a frame from each camera included in the preset number of frames ( 1805 ). Subsequently, it is determined whether or not the camera from which the image is received has exceeded a threshold of importance level with respect to image display ( 1806 ). When the camera has exceeded the threshold, it is determined whether or not the camera from which the image is received is highest in the importance level of a frame from each camera among all the cameras ( 1807 ). When the camera is highest in the importance level of a frame from each camera, it is determined whether or not the extracted camera information is identical with stored camera information ( 1808 ). When they are identical with each other, the number of times of camera switching is decremented ( 1809 ). When they are not identical with each other, the number of times of camera switching is incremented ( 1810 ). When the number of times of camera switching is decremented at Step  1809 , it is determined whether or not the number of times of camera switching has fallen below a threshold ( 1811 ). When it has fallen below the threshold, the fixation of the camera is canceled ( 1812 ). When the number of times of camera switching is incremented at Step  1810 , it is determined whether or not the number of times of camera switching has exceeded a threshold ( 1813 ). When it has exceeded the threshold, the fixation of the camera is started ( 1814 ). Subsequently, the camera information of the received image is stored ( 1815 ) and it is determined whether or not a camera whose image is displayed is fixed ( 1816 ). When the camera is not fixed and when the camera is fixed but it is matched with the camera information of the received image, the received image is displayed ( 1818 ). When the camera is fixed and is not matched with the camera information of the received image, the received image is not displayed and this series of processing is terminated ( 1819 ). The camera information of the received image stored at Step  1815  is the information of the image in the selected frame  1706  in  FIG. 17 . 
         [0062]    In the fifth embodiment in  FIG. 17 , the output  1708  of the delivery device  104  containing a frame of a high importance level is obtained. However, the display of a frame  1709  of a high importance level is overwritten with the display of a frame  1710  of a low importance level from the same camera. This shortens the display time for the frame  1709  of a high importance level and it can be missed. 
       Sixth Embodiment 
       [0063]      FIG. 19  illustrates a picture selection method in a sixth embodiment. In this embodiment, a frame of a high importance level is kept displayed based on the difference in importance level information between an outputted frame and a received frame. The possibility of the display of the frame of a high importance level being missed is thereby reduced. The input of the delivery device that receives a picture  1901  from camera  1  is as denoted by a reference numeral  1902 . At this time, the difference in importance level between the frame outputted last by the delivery device  104  and the received frame is as denoted by a reference numeral  1903 . When a frame is outputted with the difference in importance level of the received frame equal to or higher than a threshold of (−5), the output of the delivery device  104  is as denoted by a reference numeral  1904 . Thus a frame  1905  of a high importance level is kept displayed until a frame having a predetermined condition of the importance level is received, namely, a frame  1908  of  FIG. 19  is received and displayed. In addition, the importance level of the stored image is decremented by a certain value (for example, −2). That is, the delivery period of a frame is controlled based on information on the importance level of the frame. With respect to a frame of a high importance level, it is possible to lengthen the delivery period for which it is delivered and the display time for which it is displayed. 
         [0064]      FIG. 20  illustrates a processing flow in the fifth embodiment illustrated in  FIG. 19 . When the data delivery device  104  receives a picture ( 2002 ), it extracts importance level ( 2003 ). Then it is determined whether or not the difference in importance level between the received image and a stored image is greater than the threshold of (−5) ( 2004 ). When the threshold is exceeded, the received image is stored ( 2005 ) and the received image is displayed ( 2006 ). When the threshold is not exceeded, the importance level of the stored image is decremented by a certain value ( 2007 ). 
       Seventh Embodiment 
       [0065]      FIG. 21  illustrates a picture selection method in a seventh embodiment. In this embodiment, control is carried out by combining the following controls: control based on the number of times of camera switching; control based on the importance level information of a frame from each camera included in multiple received frames; and control based on the difference in importance level information between an outputted frame and a received frame. The input of the delivery device that receives a picture  2101  from a camera  1  and a picture  2102  from camera  2  is as denoted by a reference numeral  2103 . At this time, the importance level of a frame from camera  1  included in five received frames is as denoted by a reference numeral  2104  and the importance level of a frame from camera  2  included in the same frames is as denoted by a reference numeral  2105 . A frame is outputted when both the following conditions are met: the importance level of a frame from a camera included in five received frames should be higher than that of a frame from the other camera; and the importance level of a frame from the camera should be equal to or higher than a threshold of (6). In this case, the selected frame is as denoted by a reference numeral  2106 ; and the difference in importance level between the frame outputted last by the delivery device  104  and the selected frame is as denoted by a reference numeral  2107 . 
         [0066]    When this difference  2107  in importance level is equal to or larger than a second threshold of (+4), the number of times of camera switching ( 2108 ) is initialized to zero and the fixture of the camera is canceled. When the difference in importance level ( 2107 ) is equal to or larger than a first threshold of (−4), the following processing is carried out: “3” will be taken as the threshold of the number of times of camera switching ( 2108 ); and at time  2114  when this threshold is exceeded, the camera whose picture is outputted is fixed. As denoted by a reference numeral  2109 , as the result of the above processing, frames  2110  and  2115  of a high importance level are outputted from the delivery device  104 . 
         [0067]      FIG. 22  illustrates a processing flow in the seventh embodiment illustrated in  FIG. 21 . When the data delivery device  104  receives a picture ( 2202 ), it extracts camera information ( 2203 ) and extracts importance level ( 2204 ). Then it computes the importance level of a frame from each camera included in a preset number of frames ( 2205 ). Subsequently, it is determined whether or not the camera from which the image is received has exceeded a threshold of importance level with respect to image display ( 2206 ). When the camera has not exceeded the threshold, this series of processing is terminated ( 2224 ). When the camera has exceeded the threshold, it is determined whether or not the camera from which the image is received is highest in the importance level of a frame from each camera among all the cameras ( 2207 ). When the camera is not highest, this series of processing is terminated ( 2224 ). 
         [0068]    When the camera is highest in the importance level of a frame from each camera, it is determined whether or not the difference in importance level between the received image and a stored image is greater than the second threshold of (+4) ( 2208 ). When the second threshold is exceeded, the number of times of camera switching is initialized ( 2209 ) and the fixation of the camera is canceled ( 2215 ). When the second threshold is not exceeded, it is determined whether or not the difference in importance level between the received image and the stored image is greater than the first threshold of (−4) ( 2210 ). When the first threshold is not exceeded, the importance level of the stored image is decremented by a certain value (−2) ( 2211 ) and this series of processing is terminated ( 2224 ). 
         [0069]    When the second threshold is exceeded, it is determined whether or not the extracted camera information is identical with stored camera information ( 2212 ). When they are identical with each other, the number of times of camera switching is decremented ( 2213 ). When they are not identical with each other, the number of times of camera switching is incremented ( 2216 ). When the number of times of camera switching is decremented at Step  2213 , it is determined whether or not the number of times of camera switching has fallen below a threshold ( 2214 ). When it has fallen below the threshold, the fixation of the camera is canceled ( 2215 ). When the number of times of camera switching is incremented at Step  2216 , it is determined whether or not the number of times of camera switching has exceeded a threshold ( 2217 ). When it has exceeded the threshold, the fixation of the camera is started ( 2218 ). Subsequently, the camera information of the received image is stored ( 2219 ) and it is determined whether or not a camera whose image is displayed is fixed ( 2220 ). When the camera is not fixed and when the camera is fixed but it is matched with the camera information of the received image, the received image is stored ( 2222 ) and displayed ( 2223 ). When the camera is fixed and it is not matched with the camera information of the received image, the received image is not displayed and this series of processing is terminated ( 2224 ). 
         [0070]    The invention described in detail up to this point can be used for picture display control in, for example, monitoring systems and surveillance systems.