Patent Publication Number: US-2021168411-A1

Title: Storage medium, video image generation method, and video image generation system

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based on and claims the benefit of priority of the prior Japanese Patent Application No. 2019-217050, filed on Nov. 29, 2019, the entire contents of which are incorporated herein by reference. 
     FIELD 
     The embodiments discussed herein are related to a storage medium and so on. 
     BACKGROUND 
       FIG. 23  is a diagram illustrating an example of a related-art broadcasting system. In the related-art broadcasting system, plural pieces of video information are captured by cameras C 1 , C 2 , and C 3 , respectively. By way of example, the case of broadcasting a basketball game over the Internet will now be described. In the related-art broadcasting system, the cameras C 1  to C 3  capture images when operated by the respective camera operators. 
     The camera C 1  is a camera that captures bird&#39;s-eye view video images of a court  1 . The camera C 2  is a camera that captures video information on a scene close to a player or the like. The camera C 3  is a camera that captures video information on an area under the goal. The respective pieces of video information of the cameras C 1  to C 3  are output to a switcher  2 . The switcher  2  is coupled to a server  3 . The server  3  transmits video information to terminal devices (not illustrated) of viewers. 
       FIG. 24  illustrates video information captured by each camera. Video information M 1 - 1 , M 1 - 2 , or M 1 - 3  is video information captured by the camera C 1 . A camera operator operates the camera C 1  to change the camera shooting direction and to zoom in or out the camera C 1 . For example, when the camera operator moves the camera C 1  horizontally, video information changes from the video information M 1 - 1  to the video information M 1 - 2 . When the camera operator performs a zoom-up operation, video information changes from the video information M 1 - 2  to the video information M 1 - 3 . 
     The video information M 2  is video information captured by the camera C 2 . The camera operator operates the camera C 2  so that a specific player appears. For example, when confirming that the specific player has scored a goal, the camera operator captures a close-up video image of the specific player. 
     The video information M 3  is video information captured by the camera C 3 . The camera operator operates the camera C 3  to capture video information of an area under the goal. 
     The switcher  2  is a device that selects video information to be output to the server  3 , among the respective pieces of video information output from the cameras C 1  to C 3 , and is operated by an administrator. For example, by operating the switcher  2 , the administrator first selects the video information of the camera C 1 , and thus outputs, to the server  3 , the pieces of video information M 1 - 1 , M 1 - 2 , and M 1 - 3  representing motions of both the offensive players and the defensive players. Subsequently, when confirming that a specific player has scored a goal, the administrator selects the video information of the camera C 2  and outputs, to the server  3 , the video information M 2  of the player who has scored a goal. This enables viewers to sequentially view the pieces of video information M 1 - 1 , M 1 - 2 , M 1 - 3 , and M 2 . 
     There is another related-art technique that detects a crowd of people included in a video image, using video information, and automatically controls a photographic apparatus so that the crowd of people is included in the video information. Related-art techniques are disclosed in, for example, Japanese Laid-open Patent Publication Nos. 2006-312088, 2010-183301, 2015-070503, 2001-230993, and 2009-153144. 
     SUMMARY 
     According to an aspect of the embodiments, a non-transitory computer-readable storage medium storing a program that causes a computer to execute a process, the process includes receiving first positional information of each of a plurality of players, the first positional information being identified based on first video information captured by a plurality of first cameras installed in a field where the plurality of players play a competition; acquiring second video information from a second camera that captures a video image of the competition; when accepting identification information of a specific player among the plurality of players, converting first positional information of the specific player when and after the identification information is accepted, to second positional information in the second video information; generating third video information that is a partial area cut out from the second video information based on the second positional information obtained by the conversion; and outputting the third video information. 
     The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  illustrates an example of a video image generation system according to a first embodiment; 
         FIG. 2  is a diagram illustrating processing of a second server according to the first embodiment; 
         FIG. 3  is a functional block diagram illustrating a configuration of a first server according to the first embodiment; 
         FIG. 4  depicts an example of a data structure of a first video buffer; 
         FIG. 5  depicts an example of a data structure of a tracking table; 
         FIG. 6  is a functional block diagram illustrating a configuration of a second server according to the first embodiment; 
         FIG. 7  depicts an example of a data structure of a tracking information buffer; 
         FIG. 8A  depicts an example of a data structure of a second video buffer; 
         FIG. 8B  depicts an example of a data structure of a bird&#39;s-eye view video information buffer; 
         FIG. 8C  depicts an example of a data structure of a conversion table; 
         FIG. 8D  depicts an example of a data structure of a third video information buffer; 
         FIG. 9  is a diagram illustrating processing of generating bird&#39;s-eye view video information; 
         FIG. 10  is a diagram (1) illustrating processing of generating third video information, the processing being performed by a generation unit; 
         FIG. 11  is a diagram (2) illustrating processing of generating third video information, the processing being performed by a generation unit; 
         FIG. 12  is a functional block diagram illustrating a configuration of a video distribution server according to the first embodiment; 
         FIG. 13  is a flowchart illustrating a processing procedure of a first server according to the first embodiment; 
         FIG. 14A  is a flowchart illustrating a processing procedure of a second server according to the first embodiment; 
         FIG. 14B  is a flowchart illustrating a processing procedure of a video distribution server according to the first embodiment; 
         FIG. 15  is a diagram illustrating processing of a detection unit; 
         FIG. 16  illustrates an example of a video image generation system according to a second embodiment; 
         FIG. 17  is a functional block diagram illustrating a configuration of a second server according to the second embodiment; 
         FIG. 18  is a functional block diagram illustrating a configuration of a video distribution server according to the second embodiment; 
         FIG. 19A  is a flowchart illustrating a processing procedure of a second server according to the second embodiment; 
         FIG. 19B  is a flowchart illustrating a processing procedure of a second server according to the second embodiment; 
         FIG. 20  illustrates an example of a hardware configuration of a computer that achieves functions similar to those of a first server; 
         FIG. 21  illustrates an example of a hardware configuration of a computer that achieves functions similar to those of a second server; 
         FIG. 22  illustrates an example of a hardware configuration of a computer that achieves functions similar to those of a video distribution server; 
         FIG. 23  is a diagram illustrating an example of a related-art broadcasting system; and 
         FIG. 24  illustrates video information captured by each camera. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     In the related-art techniques described above, however, a problem arises in that it may not be possible to automatically generate video information on a specific player from video information on the entire area of the field where a plurality of players play a competition. 
     For example, in the related-art broadcasting systems, video information on a specific player is generated when a camera operator, who operates a camera, autonomously captures video images of the specific player. For example, a camera operator who operates the camera C 2  determines to capture a close-up video image of a player who has scored a goal, so that a close-up video image of the specific player is generated. For example, video information on the specific player is not automatically generated from video information on the entire area of the field where a plurality of players play a competition. Even using the related-art technique of detecting a crowd of people, it may not be possible to automatically generate video information representing the specific player. 
     In view of the above, it is desirable that video information on the specific player be automatically generated from video information on the entire area of the field where a plurality of players play a competition. 
     Embodiments of a video image generation program, a video image generation method, and a video image generation system disclosed in the present application will be described in detail below with reference to the accompanying drawings. The present disclosure is not limited to the embodiments. 
     First Embodiment 
       FIG. 1  illustrates an example of a video image generation system according to a first embodiment. As illustrated in  FIG. 1 , the video image generation system includes first cameras  4   a  to  4   i,  second cameras  5   a,    5   b,  and  5   c,  third cameras  6   a  and  6   b,  a fourth camera  7 , and a fifth camera. The video image generation system also includes a first server  100 , a second server  200 , and a video distribution server  300 . 
     The first cameras  4   a  to  4   i  are coupled to the first server  100 . The first cameras  4   a  to  4   i  are collectively referred to as “first cameras  4 ”. The second cameras  5   a  to  5   c  are coupled to the second server  200 . The second cameras  5   a  to  5   c  are collectively referred to as “second cameras  5 ”. The third cameras  6   a  and  6   b  are coupled to the second server  200 . The third cameras  6   a  and  6   b  are collectively referred to as “third cameras  6 ”. The fourth camera  7  is coupled to the second server  200 . The first server  100  and the second server  200  are coupled to each other. The second server  200  and the video distribution server  300  are coupled to each other via a network (closed network)  50 . 
     In the court  1 , a plurality of players (not illustrated) play a competition. In the first embodiment, a description will be given of the case in which players play a basketball game in the court  1 . However, the present disclosure is not limited to this. For example, the present disclosure may be applied to, in addition do basketball, athletic events such as soccer, volleyball, baseball, and track and field, dances, and so on. 
     The first camera  4  is a camera (such as a 2K camera) that outputs, to the first server  100 , video information in a shooting range captured at a certain frame rate (frames per second (FPS)). Hereafter, video information captured by the first camera  4  will be referred to as “first video information”. The first video information is used for identifying the positional information of each of players. The positional information of each of the players indicates a three-dimensional position in the reference space. The first video information is provided with a camera identifier (ID), which uniquely identifies the camera  4  that has captured the first video information, and the time point information of each frame. 
     The second camera  5  is a camera (such as a 4K camera or an 8K camera) that outputs, to the second server  200 , video information in the shooting range captured at the certain frame rate (FPS). Hereafter, video information captured by the second camera  5  will be referred to as “partial video information”. The shooting range made of a combination of the shooting range of the second camera  5   a,  the shooting range of the second camera  5   b,  and the shooting range of the second camera  5   c  is assumed to cover the entire area of the court  1 . The partial video information is provided with a camera ID, which uniquely identifies the camera  5  that has captured the partial video information, and the time point information of each frame. Bird&#39;s-eye view video information is generated by coupling together pieces of partial video information. The bird&#39;s-eye view video information corresponds to “second video information”. 
     The third camera  6  is a camera (2K camera) that is installed under the goal of the court  1  and outputs, to the second server  200 , video information in a shooting range captured at a certain frame rate (FPS). Hereafter, video information captured by the third camera  6  will be referred to as “under-goal video information”. 
     The fourth camera  7  is a camera that includes, in the shooting range, a timer  7   a  and a scoreboard  7   b.  The timer  7   a  is a device that displays the current time point and the elapsed time of a game. The scoreboard  7   b  is a device that displays the score in a game. Hereafter, video information captured by the fourth camera  7  will be referred to as “score video information”. The timer  7   a  and the scoreboard  7   b  may be an integrated device. 
     The first server  100  is a device that acquires first video information from the first cameras  4 , and sequentially identifies the positional information of each of a plurality of players, based on the first video information. The positional information of each of the plurality of players identified by the first server  100  is referred to as “first positional information”. The first positional information indicates a three-dimensional position in the reference space. The first server  100  transmits “tracking information” in which information identifying time, such as frame rates, the first positional information, and identification information uniquely identifying a player are associated with each other, to the second server  200 . 
     The second server  200  acquires tracking information from the first server  100  and acquires plural pieces of partial video information from the second cameras  5 . The second server  200  generates bird&#39;s-eye view video information from the plural pieces of partial video information. When accepting the identification information of a specific player among a plurality of players, using the tracking information, the second server  200  sequentially converts the positional information of the specific player when and after the identification information is accepted, to the positional information in the bird&#39;s-eye view video information (hereafter referred to as second positional information). The second server  200  generates third video information that is a partial area cut out from the bird&#39;s-eye view video information, in accordance with the second positional information. The second server  200  transmits the generated third video information to the video distribution server  300 . The second positional information is a two-dimensional position in the reference plane. 
       FIG. 2  is a diagram illustrating processing of a second server according to the first embodiment. The bird&#39;s-eye view video information  10 A illustrated in  FIG. 2  is video information obtained by coupling together the respective pieces of partial video information captured by the second cameras  5 . For example, the case where the second server  200  has accepted the identification information of a player P 1  will be described. The second server  200  compares the identification information of the player P 1  with tracking information and identifies first positional information corresponding to the player P 1 . The second server  200  converts the first positional information corresponding to the player P 1  to second positional information (x P1 , y P1 ) in the bird&#39;s-eye view video information  10 A. 
     The second server  200  cuts out a partial area Al from the bird&#39;s-eye view video information  10 A, in accordance with the second positional information (x P1 , y P1 ). The second server  200  generates the video information on the cut-out area Al as third video information  10 B. For example, the resolution of the bird&#39;s-eye view video information  10 A is 4K, and the resolution of the third video information  10 B is 2K or high definition (HD). After the identification information of a specific player has been specified, the second server  200  sequentially identifies the second positional information of the specific player for a predetermined time period using tracking information, and cuts out a partial area of the bird&#39;s-eye view video information  10 A in accordance with the second positional information to generate the third video information. 
     The video distribution server  300  is a device that receives third video information from the second server  200  and distributes the third video information to terminal devices (not illustrated) of viewers. 
     In such a way, in the video image generation system according to the first embodiment, the first server  100  generates tracking information based on the first video information. When accepting the identification information of a specific player, the second server  200  converts the first positional information of the specific player who may be identified using tracking information, to the second positional information in the bird&#39;s-eye view video information. The second server  200  generates third video information, which is a partial area cut out from the bird&#39;s-eye view video information in accordance with the second positional information of the specific player. Thus, third video information on the specific player may be automatically generated from the second video information on the entire area of the court  1  where a plurality of players play a competition. For example, the video information on a specific player has been generated by a camera operator or the like who operates the camera C 2 . The camera operator or the like takes a close-up video image and the like of the specific player to generate the video information on the specific player. However, the video image generation system according to the present embodiment may automatically generate the video information on the specific player. 
     An example of a configuration of the first server  100  illustrated in  FIG. 1  will now be described.  FIG. 3  is a functional block diagram illustrating a configuration of a first server according to the first embodiment. As illustrated in  FIG. 3 , the first server  100  includes a communication unit  110 , an input unit  120 , a display unit  130 , a storage unit  140 , and a control unit  150 . 
     The communication unit  110  is a processing unit that performs information communication with the first cameras  4  and the second server  200 . The communication unit  110  corresponds to a communication device, such as a network interface card (NIC). For example, the communication unit  110  receives first video information from the first camera  4 . The control unit  150  described later exchanges information with the first cameras  4  and the second server  200  via the communication unit  110 . 
     The input unit  120  is an input device that inputs various types of information to the first server  100 . The input unit  120  corresponds to a keyboard, a mouse, a touch panel, and the like. 
     The display unit  130  is a display device that displays information output from the control unit  150 . The display unit  130  corresponds to a liquid crystal display, an organic electro-luminescence (EL) display, a touch panel, or the like. 
     The storage unit  140  includes a first video buffer  141  and a tracking table  142 . The storage unit  140  corresponds to a semiconductor memory element, such as a random-access memory (RAM) or a flash memory, or a storage device, such as a hard disk drive (HDD). 
     The first video buffer  141  is a buffer that holds first video information captured by the first camera  4 .  FIG. 4  depicts an example of a data structure of a first video buffer. As illustrated in  FIG. 4 , the first video buffer  141  associates a camera ID with first video information. The camera ID is information that uniquely identifies the first camera  4 . For example, the camera IDs corresponding to the first cameras  4   a  to  4   i  are camera IDs “C 4   a  to C 4   i ”, respectively. The first video information is video information captured by the first camera  4  of interest. 
     The first video information includes a plurality of image frames arranged in the time sequence. An image frame is data of one frame of a still image. An image frame included in the first video information is referred to as a “first image frame”. Each first image frame is provided with the time point information. 
     The tracking table  142  is a table that holds information on positional coordinates (paths of travel) at time points for players.  FIG. 5  is a table of a data structure of a tracking table. As illustrated in  FIG. 5 , the tracking table  142  associates identification information, team identification information, a time point, and coordinates with each other. 
     The identification information is information that uniquely identifies a player. The team identification information is information that uniquely identifies a team to which the player belongs. The time point is information indicating the time point of a first image frame in which the player is detected. 
     The coordinates indicate the coordinates of the player and correspond to the first positional information. For example, a player with player identification information “H 101 ” belonging to team identification information “A” is positioned at coordinates “xa 11 , ya 11 ” at a time point “T 1 ”. 
     Referring back to  FIG. 3 , the control unit  150  includes an acquisition unit  151 , an identification unit  152 , and a transmitting unit  153 . The control unit  150  may be implemented as a central processing unit (CPU), a microprocessor unit (MPU), or the like. The control unit  150  may be implemented as a hard-wired logic circuit, such as an application-specific integrated circuit (ASIC) or a field-programmable gate array (FPGA). 
     The acquisition unit  151  is a processing unit that acquires first video information from the first cameras  4 . The acquisition unit  151  stores the acquired first video information in the first video buffer  141 . The acquisition unit  151  stores first video information in the first video buffer  141  in such a manner that the first video information is associated with the camera ID of the first camera  4 . The acquisition unit  151  corresponds to a “first acquisition unit”. 
     The identification unit  152  is a processing unit that sequentially identifies the first positional information of each of a plurality of players based on first video information stored in the first video buffer  141 . Based on an identified result, the identification unit  152  registers the identification information, team identification information, time points, and coordinates of players in association with each other in the tracking table  142 . A description will be given below of an example of processing in which the identification unit  152  identifies the first positional information of some player included in the first video information (first image frame). The first video information is first video information captured by the first camera  4   a.  The processing of identifying the first positional information of a player is not limited to the processing described below. 
     The identification unit  152  generates a difference image between a first image frame at a time point T 1  and a first image frame at a time point T 2 , from the first video information in the first video buffer  141 . The identification unit  152  compares the area of a region remaining in the difference image with a template that defines the area of a player, and detects, as a player, a region in the difference image where the difference of the area of this region from the area of the template is less than a threshold. 
     The identification unit  152  converts the coordinates (coordinates in the first image frame) of a player calculated from the difference image, to the entire coordinates using a conversion table (not illustrated). The conversion table is a table that defines correspondence relationship between the coordinates in the first image frame captured by one first camera  4  (for example, the first camera  4   a ) and the entire coordinates common to all the first cameras  4   a  to  4   i,  and is assumed to be set in advance. The position indicated by such entire coordinates becomes the first positional information of a player. 
     The identification unit  152  assigns the identification information of a player detected from the first image frame. For example, the identification unit  152  assigns the identification information of a player, using features of the uniform (the uniform number and the like) of each player set in advance. The identification unit  152  identifies the team identification information of the player detected from the first image frame, using the features of the uniform of each team set in advance. 
     The identification unit  152  performs the processing described above and registers the identification information, team identification information, time points, and coordinates (entire coordinates) of the player in association with each other in the tracking table  142 . The identification unit  152  performs the processing described above for each player by using the other first cameras  4   b  to  4   i  and thus registers the identification information, team identification information, time points, and coordinates of each player in association with each other in the tracking table  142 . The identification unit  152  performs the processing described above repeatedly at each time point. 
     The transmitting unit  153  is a processing unit that transmits, to the second server  200 , tracking information including the first positional information of each player. The tracking information includes the identification information, team identification information, information (such as time points, frame rates, and the like) for identifying a time period, coordinates (first positional information) of each player. 
     In the tracking table  142 , for each player, a time point and the coordinates (first positional information) indicating the position where the player is at the time point are registered by the identification unit  152 . The transmitting unit  153  generates, at each time point, tracking information including the identification information, team identification information, and time points, coordinates (first positional information) of each player who has been newly registered, and sequentially transmits the generated tracking information to the second server  200 . 
     An example of a configuration of the second server  200  illustrated in  FIG. 1  will now be described.  FIG. 6  is a functional block diagram illustrating a configuration of a second server according to the first embodiment. As illustrated in  FIG. 6 , the second server  200  includes a communication unit  210 , an input unit  220 , a display unit  230 , a storage unit  240 , and a control unit  250 . 
     The communication unit  210  is a processing unit that performs data communication with the second cameras  5 , the third cameras  6 , the fourth camera  7 , the first server  100 , and the video distribution server  300 . The communication unit  210  corresponds to a communication device, such as an NIC. For example, the communication unit  210  receives partial video information from the second camera  5 . The communication unit  210  receives under-goal video information from the third camera  6 . The communication unit  210  receives score video information from the fourth camera  7 . The communication unit  210  receives tracking information from the first server  100 . The control unit  250  described later exchanges information with the second cameras  5 , the third cameras  6 , the fourth camera  7 , the first server  100 , and the video distribution server  300  via the communication unit  210 . 
     The input unit  220  is an input device that inputs various types of information to the second server  200 . The input unit  220  corresponds to a keyboard, a mouse, a touch panel, and the like. As described later, the administrator may operate the input unit  220  to input the identification information of a specific player. The administrator may operate a switch unit  345  of the video distribution server  300  to specify a specific player. In this case, the communication unit  210  of the second server  200  receives the identification information of the specific player selected by the administrator, from a communication unit  310  of the video distribution server  300 . 
     The display unit  230  is a display device that displays information output from the control unit  250 . The display unit  230  corresponds to a liquid crystal display, an organic EL display, a touch panel, or the like. 
     The storage unit  240  includes a tracking information buffer  241 , a second video buffer  242 , a bird&#39;s-eye view video information buffer  243 , a conversion table  244 , and a third video information buffer  245 . The storage unit  240  corresponds to a semiconductor memory element, such as a RAM or a flash memory, or a storage device, such as an HDD. 
     The tracking information buffer  241  is a buffer that holds tracking information transmitted from the first server  100 .  FIG. 7  depicts an example of a data structure of a tracking information buffer. As depicted in  FIG. 7 , the tracking information buffer  241  associates a time point, identification information, team identification information, and coordinates with each other. The time point is information indicating the time point of a first image frame in which a player is detected. The identification information is information that uniquely identifies a player. The team identification information is information that identifies a team. The coordinates indicate the coordinates of a player and correspond to the first positional information. 
     The second video buffer  242  is a buffer that individually holds the partial video information captured by the second camera  5 , the under-goal video information captured by the third camera  6 , and the score video information captured by the fourth camera  7 .  FIG. 8A  depicts an example of a data structure of a second video buffer. As illustrated in  FIG. 8A , the second video buffer  242  includes camera IDs and video information. 
     The camera ID is information that uniquely identifies the second camera  5 , the third camera  6 , or the fourth camera  7 . For example, the camera IDs corresponding to the second cameras  5   a  to  5   c  are assumed as camera IDs “C 5   a  to C 5   c ”, respectively. The camera IDs corresponding to the third cameras  6   a  and  6   b  are assumed as camera IDs “C 6   a  and C 6   b ”, respectively. The camera ID corresponding to the fourth camera  7  is assumed as a camera ID “C 7 ”. 
     The video information captured by the second camera  5  is partial video information. The partial video information includes image frames arranged in the time sequence. An image frame included in the partial video information is referred to as a “partial image frame”. Each partial image frame is provided with the time point information. 
     The video information captured by the third camera  6  is under-goal video information. The under-goal video information includes image frames arranged in the time sequence, and each of the image frames is provided with the time point information. The video information captured by the fourth camera  7  is score video information. The score video information includes image frames arranged in the time sequence, and each of the image frames is provided with the time point information. 
     The time point information of an image frame of the first video information (a first image frame), the time point information of an image frame of the partial video information (a partial image frame), the time point information of an image frame of the under-goal video information, and the time point information of an image frame of the score video information are assumed to be in synchronization with each other. 
     Referring back to  FIG. 6 , the bird&#39;s-eye view video information buffer  243  is a buffer that stores bird&#39;s-eye view video information. The bird&#39;s-eye view video information includes image frames arranged in the time sequence. An image frame included in the bird&#39;s-eye view video information is referred to as a “bird&#39;s-eye view image frame”.  FIG. 8B  depicts an example of a data structure of a bird&#39;s-eye view video information buffer. As depicted in  FIG. 8B , in the bird&#39;s-eye view video information buffer  243 , a time point and a bird&#39;s-eye view image frame are associated with each other. For example, the bird&#39;s-eye view image frame at a time point Tn is an image frame in which the partial image frames captured at the time point Tn by the second cameras  5  are coupled together. The character n denotes a natural number. 
     The conversion table  244  is a table that defines the relationship between the first positional information and the second positional information.  FIG. 8C  depicts an example of a data structure of a conversion table. As depicted in  FIG. 8C , in the conversion table  244 , the first positional information and the second positional information are associated with each other. The first positional information corresponds to the coordinates of a player included in the tracking information transmitted from the first server  100 . The second positional information corresponds to the coordinates in a bird&#39;s-eye view image frame (bird&#39;s-eye view video information). For example, first positional information “xa 11 , ya 11 ” is associated with second positional information “xb 11 , yb 11 ”. 
     The third video information buffer  245  is a buffer that stores third video information. The third video information includes image frames arranged in the time sequence. An image frame included in the third video information is referred to as a “third image frame”.  FIG. 8D  depicts an example of a data structure of a third video information buffer. As depicted in  FIG. 8D , in the third video information buffer  245 , a time point and a third image frame are associated with each other. 
     The control unit  250  includes a receiving unit  251 , an acquisition unit  252 , a conversion unit  253 , a generation unit  254 , and an output control unit  255 . The control unit  250  may be implemented as a CPU, an MPU, or the like. The control unit  250  may be implemented as a hard-wired logic circuit, such as an ASIC or an FPGA. 
     The receiving unit  251  is a processing unit that sequentially receives tracking information from the first server  100 . The receiving unit  251  sequentially stores the received tracking information in the tracking information buffer  241 . As described above, the tracking information includes the identification information, team identification information, time points, and coordinates (first positional information) of each player. 
     The acquisition unit  252  is a processing unit that acquires partial video information from the second camera  5 . The acquisition unit  252  stores the acquired partial video information in the second video buffer  242 . In the case of storing partial video information in the second video buffer  242 , the acquisition unit  252  stores the partial video information and the camera ID of the second camera  5  in association with each other. The acquisition unit  252  corresponds to a “second acquisition unit”. 
     The acquisition unit  252  acquires under-goal video information from the third camera  6 . In the case of storing the acquired under-goal video information in the second video buffer  242 , the acquisition unit  252  stores the under-goal video information and the camera ID of the third camera  6  in association with each other. 
     The acquisition unit  252  acquires score video information from the fourth camera  7 . In the case of storing the acquired score video information in the second video buffer  242 , the acquisition unit  252  stores the score video information and the camera ID of the fourth camera  7  in association with each other. 
     The acquisition unit  252  generates bird&#39;s-eye view video information from plural pieces of partial video information stored in the second video buffer  242 .  FIG. 9  is a diagram illustrating processing of generating bird&#39;s-eye view video information. Referring to  FIG. 9 , a description is given using partial image frames FT 1 - 1 , FT 1 - 2 , and FT 1 - 3 , by way of example. The partial image frame FT 1 - 1  is a partial image frame at the time point T 1  included in partial video information captured by the second camera  5   a.  The partial image frame FT 1 - 2  is a partial image frame at the time point T 1  included in partial video information captured by the second camera  5   b.  The partial image frame FT 1 - 3  is a partial image frame at the time point T 1  included in partial video information captured by the second camera  5   c.    
     The acquisition unit  252  generates a bird&#39;s-eye view image frame FT 1  at the time point T 1  by coupling the partial image frames FT 1 - 1 , FT 1 - 2 , and FT 1 - 3  together. By repeatedly performing the processing described above at each time point, the acquisition unit  252  generates bird&#39;s-eye view image frames in the time sequence to generate bird&#39;s-eye view video information. The acquisition unit  252  stores the bird&#39;s-eye view video information in the bird&#39;s-eye view video information buffer  243 . 
     The acquisition unit  252  may correct the distortion of each of the partial image frames and then couple partial image frames together, thereby generating a bird&#39;s-eye view image frame. For example, it is assumed that the second camera  5   b  includes, in the shooting range, the center portion of the court  1 , and the second cameras  5   a  and  5   c  include, in the shooting ranges, areas on the left and right of the center of the court  1 . In this case, distortions may occur at ends of partial image frames captured by the second cameras  5   a  and  5   c.  The acquisition unit  252  corrects distortions at the ends of partial image frames captured by the second cameras  5   a  and  5   c,  using a distortion correction table (not illustrated). The distortion correction table is a table that defines the relationship between the position of a pixel before distortion correction and the position of a pixel after the distortion correction. The information of the distortion correction table is assumed to be set in advance. 
     The conversion unit  253  is a processing unit that, when accepting identification information of a specific player among a plurality of players, sequentially converts the first positional information of the specific player when and after the identification information is accepted, to the second positional information. The conversion unit  253  outputs the second positional information obtained by the conversion to the generation unit  254 . Hereafter, the identification information of a specific player will be referred to as “specific identification information”. The conversion unit  253  accepts specific identification information via a network from the video distribution server  300  described later. The administrator may input specific identification information by operating the input unit  220 , and the conversion unit  253  may accept the specific identification information. When the first server  100  has a function of automatically recognizing that a goal has been scored, in recognizing that a goal has been scored, the first server  100  may transmit the identification information of a player who has scored the goal, to the second server  200 , and thus the conversion unit  253  may accept the identification information of the specific player. The processing of recognizing a goal is performed, for example, by the following method. Using the first video information, the first server  100  tracks the position of a ball and tracks the position of each player. The first server  100  detects the scored goal when a ball has passed through a goal area (area set in advance). After detecting the scored goal, the first server  100  tracks back the path of the ball so as to determine which player has been at the position of the ball shooting. The first server  100  thus recognizes that the player who shot the ball has scored the goal. The first server  100  transmits the identification information of the player to the second server  200 . 
     For example, the case where, at the time point T 1 , the conversion unit  253  has accepted specific identification information “H 101 ” will be described. The conversion unit  253  references the tracking information buffer  241  and acquires the coordinates (first positional information) of specific identification information “H 101 ” at the time point T 1 . The conversion unit  253  compares the acquired first positional information with the conversion table  244  and identifies second positional information corresponding to the first positional information. After accepting the specific identification information, the conversion unit  253  sequentially converts the first positional information to the second positional information for a predetermined time period (from the time point T 1  to a time point Tm) and time-sequentially outputs the second positional information to the generation unit  254 . The character m is a numerical value set in advance. 
     The conversion unit  253  identifies the positional information crowded with players. The positional information crowded with players is referred to as “crowded positional information”. 
     An example of the processing of identifying crowded positional information will be described below. If specific identification information is not accepted at the time point Tn, the conversion unit  253  acquires the respective pieces of first positional information of all the players at the time point Tn from the tracking information buffer  241 . The conversion unit  253  assigns players who are close in distance to each other, to the same cluster, based on the respective pieces of first positional information of all the players, such that the players are classified into a plurality of clusters. 
     The conversion unit  253  selects a cluster including the largest number of players among the plurality of clusters and calculates, as crowded positional information, the center of the respective pieces of first positional information of players included in the selected cluster. The conversion unit  253  compares the crowded positional information with the conversion table  244  and identifies second positional information corresponding to the crowded positional information. Hereafter, the second positional information corresponding to the crowded positional information will be referred to as “crowded second positional information”. The conversion unit  253  sequentially calculates the crowded second positional information and time-sequentially outputs the calculated crowded second positional information to the generation unit  254 . 
     The generation unit  254  is a processing unit that generates third video information. The third video information is a partial area cut out from the bird&#39;s-eye view video information in accordance with the second positional information obtained by the conversion sequentially performed by the conversion unit  253 . Third video information related to a crowded area is an example of different video information. The generation unit  254  stores the generated third video information in the third video information buffer  245 . Hereafter, a partial area of bird&#39;s-eye view video information (bird&#39;s-eye view image frames) in accordance with the second positional information will be referred to as a “target area”. 
       FIG. 10  is a diagram (1) illustrating processing of generating third video information, the processing being performed by a generation unit. A description will now be given using the bird&#39;s-eye view image frame FT 1  at the time point T 1  included in the bird&#39;s-eye view video information. The player corresponding to the specific identification information is a player P 2 , and the second positional information of the player P 2  at the time point T 1  is (x P2 , y P2 ). 
     The generation unit  254  cuts out a target area A 2  from the bird&#39;s-eye view image frame FT 1 , in accordance with the second positional information (x P2 , y P2 ). The generation unit  254  generates the information on the cut-out target area A 2  as a third image frame F 3 T 1 . The size of the target area is set in advance. The generation unit  254  aligns the center of the target area with the coordinates of the second positional information to identify the location of the target area. The generation unit  254  may perform magnification control within a magnification range set in advance so that the size of a player corresponding to the specific identification information is as large as possible. The generation unit  254  generates third image frames by repeatedly performing the processing described above for a predetermined time period during which the generation unit  254  accepts the second positional information from the conversion unit  253 , and sequentially stores the third image frames in the third video information buffer  245 . 
     The generation unit  254  accepts the crowded second positional information from the conversion unit  253 . In accordance with the crowded second positional information, the generation unit  254  sets a partial area to be cut out in the bird&#39;s-eye view image frame. Hereafter, a partial area to be cut out, which is set in accordance with the crowded second positional information, is referred to as a “crowded area”. The generation unit  254  generates a third image frame by cutting out information on a crowded area from a bird&#39;s-eye view image frame. 
       FIG. 11  is a diagram (2) illustrating processing of generating third video information, the processing being performed by a generation unit. A description will now be given using a bird&#39;s-eye view image frame FTn at the time point Tn included in the bird&#39;s-eye view video information. The crowded second positional information is designated as (X 1 , Y 1 ). 
     In accordance with the crowded second positional information (X 1 , Y 1 ), the generation unit  254  cuts out a crowded area A 3  in the bird&#39;s-eye view image frame FTn. The generation unit  254  generates the information on the cut-out crowded area A 3  as a third image frame F 3 Tn. The size of the crowded area A 3  is set in advance. The generation unit  254  may perform magnification control within a magnification range set in advance so that as many players as possible are included in the crowded area A 3 . 
     The generation unit  254  aligns the center of the crowded area with the coordinates of the crowded second positional information to identify the location of the target area. If a predetermined time period has elapsed since the specific identification information was accepted, or if the specific identification information has not been accepted, the generation unit  254  generates third image frames and sequentially stores the third image frames in the third video information buffer  245 . 
     The output control unit  255  is a processing unit that outputs the third video information stored in the third video information buffer  245 , to the video distribution server  300 . The output control unit  255  may output the under-goal video information and score video information stored in the second video buffer  242  to the video distribution server  300 . 
     The output control unit  255  may generate video information in which the first positional information of each player and the identification information of the player are associated with each other, by using the tracking information buffer  241 , and output the generated video information to the display unit  230  for display on the display unit  230 . Output of such video information by the output control unit  255  allows the administrator to support a task of inputting specific identification information. 
     An example of a configuration of the video distribution server  300  illustrated in  FIG. 1  will now be described.  FIG. 12  is a functional block diagram illustrating a configuration of a video distribution server according to the first embodiment. As illustrated in  FIG. 12 , the video distribution server  300  includes the communication unit  310 , an input unit  320 , a display unit  330 , a storage unit  340 , and a control unit  350 . 
     The communication unit  310  is a processing unit that performs information communication with the second server  200 . The communication unit  310  corresponds to a communication device, such as an NIC. For example, the communication unit  310  receives third video information, under-goal video information, and score video information from the second server  200 . The control unit  350  described later exchanges information with the second server  200  via the communication unit  310 . 
     The input unit  320  is an input device that inputs various types of information to the video distribution server  300 . The input unit  320  corresponds to a keyboard, a mouse, a touch panel, and the like. The administrator references third video information, under-goal video information, and the like displayed on the display unit  330  and operates the input unit  320  so as to switch the video information to be distributed to viewers. The administrator may reference third video information related to a crowded area, and select a specific player included in the third video information by operating the input unit  320 . 
     The display unit  330  is a display device that displays information output from the control unit  350 . The display unit  330  corresponds to a liquid crystal display, an organic EL display, a touch panel, or the like. For example, the display unit  330  displays third video information, under-goal video information, score video information, and the like. 
     The storage unit  340  includes a video buffer  341  and CG information  342 . The storage unit  340  corresponds to a semiconductor memory element, such as a RAM or a flash memory, or a storage device, such as an HDD. 
     The video buffer  341  is a buffer that holds third video information, under-goal video information, and score video information. 
     The CG information  342  is information of computer graphics (CG) of a timer and scores. The CG information  342  is created by a creation unit  352  described later. 
     The control unit  350  includes a receiving unit  351 , the creation unit  352 , a display control unit  353 , a switching unit  354 , and a distribution control unit  355 . The control unit  350  may be implemented as a CPU, an MPU, or the like. The control unit  350  may be implemented as a hard-wired logic circuit, such as an ASIC or an FPGA. 
     The receiving unit  351  is a processing unit that receives third video information, under-goal video information, and score video information from the second server  200 . The receiving unit  351  stores the received third video information, under-goal video information, and score video information in the video buffer  341 . The receiving unit  351  receives the positional information of each player in the third video information from the second server  200 , and stores the received positional information in the video buffer  341 . 
     Using the score video information stored in the video buffer  341 , the creation unit  352  reads a numerical value displayed on the timer  7   a  and a numerical value displayed on the scoreboard  7   b.  Using the read numerical values, the creation unit  352  creates CG of a timer and scores. The creation unit  352  stores information on the created CG of a timer and scores (CG information  342 ) in the storage unit  340 . The creation unit  352  performs the processing mentioned above repeatedly at each time point. 
     The display control unit  353  is a processing unit that outputs the third video information, under-goal video information, and score video information stored in the video buffer  341  to the display unit  330  and displays such information on the display unit  330 . When outputting third video information related to a crowded area to the display unit  330  and displaying the third video information, the display control unit  353  causes a cursor for specifying a player included in the third video information to be superimposed to correspond to any player in the third video information, using the positional information of each player in the third video information related to the crowded area. 
     The switching unit  354  is a processing unit that acquires video information selected by the administrator who operates the input unit  320 , from the video buffer  341 , and outputs the acquired video information to the distribution control unit  355 . For example, when third video information is selected by the administrator, the switching unit  354  outputs the third video information to the distribution control unit  355 . When under-goal video information is selected by the administrator, the switching unit  354  outputs the under-goal video information to the distribution control unit  355 . 
     When any player included in third video information is selected by the administrator who operates the input unit  320 , for example, by cursor manipulation, the switching unit  354  identifies the identification information of the player. The switching unit  354  transmits the identified identification information of the player, as specific identification information, to the second server  200 . 
     The distribution control unit  355  is a processing unit that distributes video information output from the switching unit  354 , to the terminal devices of viewers. In distributing video information, the distribution control unit  355  may distribute video information in such a manner that the CG information  342  is superimposed on the video information. Although not described, the distribution control unit  355  may distribute predetermined background music (BGM), audio information by a commentator, caption information, and the like in a superimposed manner on video information. 
     An example of the processing procedure of the first server  100  according to the first embodiment will now be described.  FIG. 13  is a flowchart illustrating the processing procedure of a first server according to the first embodiment. As illustrated in  FIG. 13 , the acquisition unit  151  of the first server  100  starts to acquire first video information from the first cameras  4  and stores the acquired first video information in the first video buffer  141  (step S 101 ). 
     The identification unit  152  of the first server  100  identifies the first positional information of each player based on the first video information (step S 102 ). The identification unit  152  stores the identification information, team identification information, time points, and coordinates (first positional information) of each player in the tracking table  142  (step S 103 ). 
     The transmitting unit  153  of the first server  100  transmits tracking information to the second server  200  (step S 104 ). When the first server  100  continues the process (Yes in step S 105 ), the process proceeds to step S 102 . However, when the first server  100  does not continue the process (No in step S 105 ), the process terminates. 
     An example of the processing procedure of the second server  200  according to the first embodiment will now be described.  FIG. 14A  is a flowchart illustrating the processing procedure of a second server according to the first embodiment. As illustrated in  FIG. 14A , the receiving unit  251  of the second server  200  starts to receive tracking information from the first server  100  and stores the received tracking information in the tracking information buffer  241  (step S 201 ). 
     The acquisition unit  252  of the second server  200  starts to acquire partial video information from the second cameras  5  and stores the acquired partial video information in the second video buffer  242  (step S 202 ). The acquisition unit  252  starts to acquire under-goal video information from the third cameras  6  and stores the acquired under-goal video information in the second video buffer  242  (step S 203 ). The acquisition unit  252  starts to acquire score video information from the fourth camera  7  and stores the acquired score video information in the second video buffer  242  (step S 204 ). The acquisition unit  252  couples plural pieces of partial video information together to generate bird&#39;s-eye view video information and stores the generated bird&#39;s-eye view video information in the bird&#39;s-eye view video information buffer  243  (step S 205 ). 
     The conversion unit  253  of the second server  200  determines whether the identification information of a specific player (specific identification information) has been accepted (step S 206 ). When the specific identification information has not been accepted (No in step S 206 ), the conversion unit  253  converts the crowded positional information to crowded second positional information (step S 210 ). In accordance with the crowded second positional information, the generation unit  254  sets a crowded area in the bird&#39;s-eye view video information (step S 211 ). The generation unit  254  cuts out information on the crowded area to generate third video information (third image frame) and stores the generated third video information (third image frame) in the third video information buffer  245  (step S 212 ), and the process proceeds step S 213 . For example, third video information for the crowded area is generated until the specific player is specified from the video distribution server  300 . After a certain time period has elapsed since the specific player was specified from the video distribution server  300 , third video information on the crowded area is generated. 
     However, when the specific identification information has been accepted (Yes in step S 206 ), the conversion unit  253  converts first positional information corresponding to the specific identification information to second positional information (step S 207 ). 
     The generation unit  254  of the second server  200  sets a target area in the bird&#39;s-eye view video information (bird&#39;s-eye view image frame) in accordance with the second positional information (step S 208 ). The generation unit  254  generates third video information (third image frame) by cutting out information on the target area and stores the generated third video information (third image frame) in the third video information buffer  245  (step S 209 ), and the process proceeds to step S 213 . If Yes is determined in step S 206  until a predetermined time period has elapsed since the specific identification information was accepted, a close-up video image of a specific player (the third video information including the target area of the specific player) is generated. 
     The output control unit  255  of the second server  200  transmits the third video information, the under-goal video information, and the score video information to the video distribution server  300  (step S 213 ). The output control unit  255  of the second server  200  transmits the positional information of each player in the third video information related to the crowded area, together with the above pieces of information, to the video distribution server  300 . When the second server  200  continues the process (Yes in step S 214 ), the process proceeds to step S 206 . However, when the second server  200  does not continue the process (No in step S 214 ), the process terminates. 
     An example of the processing procedure of the video distribution server  300  in the case where specific identification information is specified on the side of the video distribution server  300  will now be described.  FIG. 14B  is a flowchart illustrating the processing procedure of a video distribution server according to the first embodiment. As illustrated in  FIG. 14B , the receiving unit  351  of the video distribution server  300  starts to receive, from the second server  200 , third video information related to a crowded area and the positional information of each player in the third video information related to the crowded area, and stores these pieces of information in the video buffer  341  (step S 250 ). Although the example in which the video distribution server  300  accepts the third video information extracted from a bird&#39;s-eye view video image is described, the video distribution server  300  may accept a bird&#39;s-eye view video image or a low-resolution bird&#39;s-eye view video image obtained from the bird&#39;s-eye view video image. 
     The display control unit  353  of the video distribution server  300  starts to display third video information related to the crowded area (step S 251 ). In accordance with the positional information of each player in the third video information related to the crowded area, the display control unit  353  displays a cursor such that the cursor is placed over any of players included in the third video information (step S 252 ). In the initial state, the cursor is displayed, for example, such that the cursor is placed over a player wearing uniform number  4  of any team, or the like. 
     When the switching unit  354  of the video distribution server  300  accepts the movement and determination of a cursor (selection of a player), the switching unit  354  identifies the specific identification information of the player for whom the selection is accepted (step S 253 ). The switching unit  354  transmits the identified specific identification information to the second server  200  by using the communication unit  310  (step S 254 ). When the video distribution server  300  continues the process (Yes in step S 255 ), the process proceeds to step S 252 . However, when the video distribution server  300  does not continue the process (No in step S 255 ), the process terminates. Thereafter, in response to step S 213  in the second server  200 , the video distribution server  300  receives third video information related to a target area on a specific player for a certain time period. The video distribution server  300  distributes the video information selected by the administrator. 
     The effects of the video image generation system according to the first embodiment will now be described. In the video image generation system according to the first embodiment, the first server  100  sequentially identifies the first positional information of each of a plurality of players, based on the first video information captured by the first cameras  4 , and transmits tracking information including the first positional information of each player to the second server  200 . When the second server  200  accepts specific identification information, the second server  200  sequentially converts the first positional information of a player corresponding to the specific identification information to second positional information. The second server  200  generates third video information, which is a partial area cut out from the bird&#39;s-eye view video information in accordance with the second positional information obtained by sequential conversion, and outputs the generated third video information to the video distribution server  300 . Thus, video information on the specific player may be automatically generated from video information on the entire area of the field where a plurality of players play a competition. 
     The second server  200  generates bird&#39;s-eye view video information from plural pieces of partial video information captured by the second cameras  5 . This enables bird&#39;s-eye view video information including the entire area of the court  1  to be generated even when the shooting ranges of the second cameras  5  are fixed. 
     The second server  200  further corrects distortions in plural pieces of partial video information, and generates bird&#39;s-eye view video information from plural pieces of partial video information in which the distortions are corrected. This enables generation of bird&#39;s-eye view video information in which the effects of distortions are reduced. 
     In the first embodiment, plural pieces of partial video information are captured by a plurality of second cameras  5  and are coupled together, so that bird&#39;s-eye view video information is generated. However, the present disclosure is not limited to this. For example, in the case where the entire area of the court  1  is included in the shooting range of a single second camera, the acquisition unit  252  of the second server  200  may store partial video information captured by the single second camera (for example, the second camera  5   b ), as bird&#39;s-eye view video information, in the bird&#39;s-eye view video information buffer  243 . In this case, the partial video information captured by the single second camera may correspond to second video information. 
     The conversion unit  253  of the second server  200  calculates the second positional information at each time point, and outputs the second positional information at each time point, as is, to the generation unit  254 . However, the present disclosure is not limited to this. For example, the conversion unit  253  may calculate an average (moving mean) of the pieces of second positional information included for a predetermined time period and output the calculated average, as second positional information, to the generation unit  254 . 
     Alternatively, the conversion unit  253  calculates a difference in the vertical direction between ytn and ytn+1 of the second positional information (xtn, ytn) at the time point Tn and the second positional information (xtn+1, ytn+1) at a time point Tn+1. If the difference is less than a threshold, the conversion unit  253  may output (xtn+1, ytn) as the second positional information at a time point Tn+1, to the generation unit  254 . This enables the target area to be suppressed from vertically vibrating at each time point. Thus, third video information in which vertical vibrations are reduced may be generated. 
     In the first embodiment, a description has been given of the case where the second server  200  accepts specific identification information from an outside device or the input unit  220 . However, the present disclosure is not limited to this. For example, the second server  200  may include a detection unit (not illustrated) that detects a predetermined event, and automatically detect, as specific identification information, the identification information of a player for whom the event has occurred. 
       FIG. 15  is a diagram illustrating processing of the detection unit. Although not illustrated, the detection unit is to be coupled to the fifth camera. The fifth camera is to be a camera (stereo camera) that includes, in the imaging range, a periphery including a basketball hoop  20   b.    
     In image frames captured by the fifth camera, a partial region  20   a  through which only a ball shot by a player would pass is set in advance. For example, the partial region  20   a  is set adjacent to the basketball hoop  20   b.    
     The detection unit determines whether a ball is present in the partial region  20   a.  For example, the detection unit uses a template defining the shape and size of a ball to determine whether a ball is present in the partial region  20   a.  In the example illustrated in  FIG. 15 , the detection unit detects a ball  25  from the partial region  20   a.  When detecting the ball  25  in the partial region  20   a,  the detection unit calculates the three-dimensional coordinates of the ball  25  based on the principle of stereoscopy. 
     When detecting the ball  25  from the partial region  20   a,  the detection unit acquires an image frame  21 , which precedes the image frame  20  by one or two frames, and detects the ball  25  from the image frame  21 . The detection unit calculates the three-dimensional coordinates of the ball  25  detected from the image frame  21 , based on the principle of stereoscopy. 
     Using, as a clue, the position of the ball  25  detected in the image frame  20 , the detection unit may detect the ball  25  from the image frame  21 . The detection unit estimates a path  25   a  of the ball  25  from the respective three-dimensional coordinates of the ball  25  detected from the image frames  20  and  21 . Using the path  25   a,  the detection unit estimates a start position  26  of the path  25   a  and a time point at which the ball  25  is present at the start position  26 . Hereafter, the time point at which the ball  25  is present at the start position  26  will be appropriately referred to as a “start time point”. 
     The detection unit acquires an image frame  22  corresponding to the start time point and detects the ball  25  from the start position  26 . The detection unit calculates the three-dimensional coordinates of the ball  25  detected in the image frame  22 , based on the principle of stereoscopy. The detection unit identifies a player  27  who is present at the three-dimensional coordinates of the ball  25 . The detection unit detects the identification information of the player  27  in such a case, as specific identification information, and outputs the specific identification information to the conversion unit  253 . 
     With reference to  FIG. 15 , by way of example, a description has been given of the case where an event “shooting” is detected and the identification information of a player who has shot is detected as specific identification information. However, the event is not limited to shooting but may be dribbling, passing, rebounding, assisting, or the like. The detection unit may use any related art technique to detect dribbling, passing, rebounding, assisting, or the like. 
     In the first embodiment, by way of example, the case where the first server  100  and the second server  200  are separate devices has been described. However, the present disclosure is not limited to this, and the first server  100  and the second server  200  may be the same device. 
     Second Embodiment 
     An example of a video image generation system according to a second embodiment will now be described.  FIG. 16  illustrates an example of a video image generation system according to the second embodiment. As illustrated in  FIG. 16 , the video image generation system includes the first cameras  4 , the second cameras  5 , the third cameras  6 , the fourth camera  7 , and the fifth camera. The video image generation system includes the first server  100 , a second server  400 , and a video distribution server  500 . 
     The description here of the first cameras  4 , the second cameras  5 , the third cameras  6 , and the fourth camera  7  is similar to the description in the first embodiment of the first cameras  4 , the second cameras  5 , the third cameras  6 , and the fourth camera  7 . 
     The first server  100  is a device that acquires the first video information from the first cameras  4 , and sequentially identifies the first positional information of each of a plurality of players based on the first video information. The first server  100  transmits tracking information in which the first positional information is associated with identification information uniquely identifying a player, to the second server  400 . A description of the first server  100  is similar to the description of the first server  100  given in the first embodiment. 
     The second server  400  acquires tracking information from the first server  100  and acquires plural pieces of partial video information from the second cameras  5 . The second server  400  generates bird&#39;s-eye view video information from the plural pieces of partial video information. When accepting specific identification information, using the tracking information, the second server  400  sequentially converts the first positional information of the player of the specific identification information to the second positional information in bird&#39;s-eye view video information. The second server  400  generates third video information, which is a partial area cut out from the bird&#39;s-eye view video information in accordance with the second positional information. The second server  400  transmits the generated third video information to the video distribution server  500 . 
     The second server  400  calculates crowded positional information from the first positional information of each player and sequentially converts the crowded positional information to second crowded positional information. In accordance with the second crowded positional information, the second server  400  generates fourth video information that is a partial area cut out from the bird&#39;s-eye view video information. For example, the fourth video information is video images representing a plurality of players. The second server  400  transmits the generated fourth video information to the video distribution server  500 . The fourth video information is an example of different video information. 
     The second server  400  may transmit bird&#39;s-eye view video information, instead of the fourth video information, to the video distribution server  500 . 
     The video distribution server  500  is a device that receives third video information and fourth video information (or bird&#39;s-eye view video information) from the second server  400 , selects either the received third video information or the received fourth video information, and distributes the selected video information to the terminal devices (not illustrated) of viewers. 
     In this way, in the video image generation system according to the second embodiment, an area in accordance with the second positional information is cut out from bird&#39;s-eye view video information, and an area in accordance with the second crowded positional information is also cut out. Thus, the third video information on a specific player and the fourth video information including a plurality of players may be automatically generated from the bird&#39;s-eye view video information of the entire area of the court  1  where a plurality of players play a competition. 
     An example of a configuration of the second server  400  illustrated in  FIG. 16  will now be described.  FIG. 17  is a functional block diagram illustrating a configuration of a second server according to the second embodiment. As illustrated in  FIG. 17 , the second server  400  includes a communication unit  410 , an input unit  420 , a display unit  430 , a storage unit  440 , and a control unit  450 . 
     The communication unit  410  is a processing unit that performs data communication with the second cameras  5 , the third cameras  6 , the fourth camera  7 , the first server  100 , and the video distribution server  500 . The communication unit  410  corresponds to a communication device, such as an NIC. For example, the communication unit  410  receives partial video information from the second camera  5 . The communication unit  410  receives under-goal video information from the third camera  6 . The communication unit  410  receives score video information from the fourth camera  7 . The communication unit  410  receives tracking information from the first server  100 . The control unit  450  described later exchanges information with the second cameras  5 , the third cameras  6 , the fourth camera  7 , the first server  100 , and the video distribution server  500  via the communication unit  410 . 
     The input unit  420  is an input device that inputs various types of information to the second server  400 . The input unit  220  corresponds to a keyboard, a mouse, a touch panel, and the like. As described later, the administrator may operate the input unit  220  to input the identification information of a specific player. 
     The display unit  430  is a display device that displays information output from the control unit  450 . The display unit  430  corresponds to a liquid crystal display, an organic EL display, a touch panel, or the like. 
     The storage unit  440  includes a tracking information buffer  441 , a second video buffer  442 , a bird&#39;s-eye view video information buffer  443 , a conversion table  444 , a third video information buffer  445 , and a fourth video information buffer  446 . The storage unit  440  corresponds to a semiconductor memory element, such as a RAM or a flash memory, or a storage device, such as an HDD. 
     The tracking information buffer  441  is a buffer that holds tracking information transmitted from the first server  100 . The data structure of the tracking information buffer  441  is similar to the data structure of a tracking information buffer  241  depicted in  FIG. 7 . 
     The second video buffer  442  is a buffer that holds each of the partial video information captured by the second camera  5 , the under-goal video information captured by the third camera  6 , and the score video information captured by the fourth camera  7 . The data structure of the second video buffer  442  is similar to the data structure of the second video buffer  242  depicted in  FIG. 8A . 
     The bird&#39;s-eye view video information buffer  443  is a buffer that stores bird&#39;s-eye view video information. Other description regarding the bird&#39;s-eye view video information buffer  443  is similar to that regarding the bird&#39;s-eye view video information buffer  243  in the first embodiment. 
     The conversion table  444  is a table that defines the relationship between the first positional information and the second positional information. The first positional information corresponds to the coordinates of a player included in the tracking information transmitted from the first server  100 . The second positional information corresponds to the coordinates in a bird&#39;s-eye view image frame (bird&#39;s-eye view video information). 
     The third video information buffer  445  is a buffer that stores third video information. The third video information includes third image frames arranged in the time sequence. 
     The fourth video information buffer  446  is a buffer that stores fourth video information. The fourth video information includes image frames arranged in the time sequence. An image frame included in the fourth video information is referred to as a “fourth image frame”. Each fourth image frame is provided with the time point information. 
     The control unit  450  includes a receiving unit  451 , an acquisition unit  452 , a conversion unit  453 , a generation unit  454 , and an output control unit  455 . The control unit  450  may be implemented as a CPU, an MPU, or the like. The control unit  450  may be implemented as a hard-wired logic circuit, such as an ASIC or an FPGA. 
     The receiving unit  451  is a processing unit that sequentially receives tracking information from the first server  100 . The receiving unit  451  sequentially stores the received tracking information in the tracking information buffer  441 . As described above, the tracking information includes the identification information, team identification information, time points, and coordinates (first positional information) of each player. 
     The acquisition unit  452  is a processing unit that acquires partial video information from the second camera  5 . The acquisition unit  452  stores the acquired partial video information in the second video buffer  442 . The acquisition unit  452  stores the partial video information in the second video buffer  442  in such a manner that the partial video information is associated with the camera ID of the second camera  5 . 
     The acquisition unit  452  acquires under-goal video information from the third camera  6 . The acquisition unit  452  stores the acquired under-goal video information in the second video buffer  442  in such a manner that the under-goal video information is associated with the camera ID of the third camera  6 . 
     The acquisition unit  452  acquires score video information from the fourth camera  7 . The acquisition unit  452  stores the acquired score video information in the second video buffer  442  in such a manner that the score video information is associated with the camera ID of the fourth camera  7 . 
     The acquisition unit  452  generates bird&#39;s-eye view video information from plural pieces of partial video information stored in the second video buffer  442 . The processing in which the acquisition unit  452  generates bird&#39;s-eye view video information is similar to the processing of the acquisition unit  252  in the first embodiment. The acquisition unit  452  stores the bird&#39;s-eye view video information in the bird&#39;s-eye view video information buffer  443 . 
     The conversion unit  453  is a processing unit that, when accepting identification information (specific identification information) of a specific player among a plurality of players, sequentially converts the first positional information of the specific player when and after the identification information is accepted, to the second positional information. The processing in which the conversion unit  453  converts first positional information to second positional information is similar to the processing of the conversion unit  253  in the first embodiment. After accepting the specific identification information, the conversion unit  453  sequentially converts the first positional information to the second positional information for a predetermined time period (from the time point T 1  to the time point Tm) and time-sequentially outputs the second positional information to the generation unit  254 . 
     The conversion unit  453  identifies second crowded positional information. The processing in which the conversion unit  453  identifies the second crowded positional information is similar to the processing in which the conversion unit  253  in the first embodiment identifies the second crowded positional information. The conversion unit  453  sequentially calculates the crowded second positional information and time-sequentially outputs the calculated crowded second positional information to the generation unit  254 . 
     The generation unit  454  is a processing unit that generates third video information, which is a partial area cut out from the bird&#39;s-eye view video information in accordance with the second positional information obtained by the conversion sequentially performed by the conversion unit  453 . The processing in which the generation unit  454  generates the third video information is similar to the processing of the generation unit  254  in the first embodiment. The generation unit  454  stores the third video information in the third video information buffer  445 . 
     The generation unit  454  accepts crowded second positional information from the conversion unit  453 . In accordance with the crowded second positional information, the generation unit  454  sets a partial area to be cut out (crowded area) in the bird&#39;s-eye view image frame. The generation unit  454  generates a fourth image frame by cutting out information on a crowded area from a bird&#39;s-eye view image frame. 
     The generation unit  454  generates fourth image frames by repeatedly performing the processing described above for a predetermined time period during which the generation unit  454  accepts the crowded second positional information from the conversion unit  453 , and sequentially stores the fourth image frames in the fourth video information buffer  446 . 
     The output control unit  455  is a processing unit that outputs the third video information stored in the third video information buffer  445  and the fourth video information stored in the fourth video information buffer  446 , to the video distribution server  500 . The output control unit  455  may output the under-goal video information and the score video information stored in the second video buffer  442 , to the video distribution server  500 . 
     An example of a configuration of the video distribution server  500  illustrated in  FIG. 16  will now be described.  FIG. 18  is a functional block diagram illustrating a configuration of a video distribution server according to the second embodiment. As illustrated in  FIG. 18 , the video distribution server  500  includes a communication unit  510 , an input unit  520 , a display unit  530 , a storage unit  540 , and a control unit  550 . 
     The communication unit  510  is a processing unit that performs information communication with the second server  400 . The communication unit  510  corresponds to a communication device, such as an NIC. For example, the communication unit  510  receives third video information, fourth video information, under-goal video information, and score video information from the second server  400 . The control unit  550  described later exchanges information with the second server  400  via the communication unit  510 . 
     The input unit  520  is an input device that inputs various types of information to the video distribution server  500 . The input unit  520  corresponds to a keyboard, a mouse, a touch panel, and the like. The administrator references third video information, fourth video information, under-goal video information, and the like displayed on the display unit  530  and operates the input unit  520  so as to switch video information to be distributed to viewers. 
     The display unit  530  is a display device that displays information output from the control unit  550 . The display unit  530  corresponds to a liquid crystal display, an organic EL display, a touch panel, or the like. For example, the display unit  530  displays third video information, fourth video information, under-goal video information, score video information, and the like. 
     The storage unit  540  includes a video buffer  541  and CG information  542 . The storage unit  540  corresponds to a semiconductor memory element, such as a RAM or a flash memory, or a storage device such as an HDD. 
     The video buffer  541  is a buffer that holds third video information, fourth video information, under-goal video information, and score video information. 
     The CG information  542  is information of CG of a timer and scores. The CG information  542  is created by a creation unit  552  described later. 
     The control unit  550  includes a receiving unit  551 , the creation unit  552 , a display control unit  553 , a switching unit  554 , and a distribution control unit  555 . The control unit  550  may be implemented as a CPU, an MPU, or the like. The control unit  550  may be implemented as a hard-wired logic circuit, such as an ASIC or an FPGA. 
     The receiving unit  551  is a processing unit that receives third video information, fourth video information, under-goal video information, and score video information from the second server  400 . The receiving unit  551  stores the received third video information, fourth video information, under-goal video information, and score video information in the video buffer  541 . The receiving unit  551  receives the positional information of each player in the fourth video information related to a crowded area from the second server  200  and stores the received positional information in the video buffer  541 . 
     Using the score video information stored in the video buffer  541 , the creation unit  552  reads a numerical value displayed on the timer  7   a  and a numerical value displayed on the scoreboard  7   b.  Using the read numerical values, the creation unit  552  creates CG of a timer and scores. The creation unit  552  stores information on the created CG of a timer and scores (CG information  542 ) in the storage unit  540 . The creation unit  552  performs the processing mentioned above repeatedly at each time point. 
     The display control unit  553  is a processing unit that outputs the third video information, fourth video information, under-goal video information, and score video information stored in the video buffer  541  to the display unit  530  and displays such information on the display unit  530 . When outputting fourth video information related to a crowded area to the display unit  530  and displaying the fourth video information, the display control unit  553  causes a cursor for specifying a player included in the fourth video information to be superimposed to correspond to any player in the fourth video information, using the positional information of each player in the fourth video information related to the crowded area. 
     The switching unit  554  is a processing unit that acquires video information selected by the administrator who operates the input unit  520 , from the video buffer  541 , and outputs the acquired video information to the distribution control unit  555 . For example, when third video information is selected by the administrator, the switching unit  554  outputs the third video information to the distribution control unit  555 . When fourth video information is selected by the administrator, the switching unit  554  outputs the fourth video information to the distribution control unit  555 . When under-goal video information is selected by the administrator, the switching unit  554  outputs the under-goal video information to the distribution control unit  555 . 
     When any player included in fourth video information is selected by the administrator who operates the input unit  520 , for example, by cursor manipulation, the switching unit  554  identifies the identification information of the player. The switching unit  554  transmits the identified identification information of the player, as specific identification information, to the second server  400 . 
     The distribution control unit  555  is a processing unit that distributes video information output from the switching unit  554 , to the terminal devices of viewers. In distributing video information, the distribution control unit  555  may distribute video information in such a manner that the CG information  542  is superimposed on the video information. Although not described, the distribution control unit  555  may distribute predetermined background music (BGM), audio information by a commentator, caption information, and the like in a superimposed manner on video information. 
     An example of the processing procedure of the second server  400  according to the second embodiment will now be described.  FIG. 19A  and  FIG. 19B  are a flowchart illustrating a processing procedure of a second server according to the second embodiment. As illustrated in  FIG. 19A  and  FIG. 19B , the receiving unit  451  of the second server  400  starts to receive tracking information from the first server  100  and stores the received tracking information in the tracking information buffer  441  (step S 301 ). 
     The acquisition unit  452  of the second server  400  starts to acquire partial video information from the second cameras  5  and stores the acquired partial video information in the second video buffer  442  (step S 302 ). The acquisition unit  452  starts to acquire under-goal video information from the third cameras  6  and stores the acquired under-goal video information in the second video buffer  442  (step S 303 ). The acquisition unit  452  starts to acquire score video information from the fourth camera  7  and stores the acquired score video information in the second video buffer  442  (step S 304 ). The acquisition unit  452  couples plural pieces of partial video information together to generate bird&#39;s-eye view video information and stores the generated bird&#39;s-eye view video information in the bird&#39;s-eye view video information buffer  443  (step S 305 ). 
     The second server  400  determines whether the second server  400  has accepted specific identification information (step S 306 ). When the specific identification information has been accepted (Yes in step S 306 ), the generation unit  454  generates third video information and stores the generated third video information in the third video information buffer  445  (step S 307 ). The generation unit  454  generates fourth video information and stores the generated fourth video information in the fourth video information buffer  446  (step S 308 ). The output control unit  455  of the second server  400  transmits the third video information, the fourth video information, the under-goal video information, and the score video information to the video distribution server  500  (step S 309 ), and the process proceeds to step S 312 . 
     However, when the specific identification information has not been accepted (No in step S 306 ), the generation unit  454  generates fourth video information and stores the generated fourth video information in the fourth video information buffer  446  (step S 310 ). The output control unit  455  transmits the fourth video information, the under-goal video information, and the score video information to the video distribution server  500  (step S 311 ), and the process proceeds to step S 312 . When the second server  400  continues the process (Yes in step S 312 ) the process proceeds to step S 306 . However, when the second server  400  does not continue the process (No in step S 312 ), the process terminates. 
     The effects of a video image generation system according to the second embodiment will now be described. In this way, in the video image generation system according to the second embodiment, an area in accordance with the second positional information is cut out from bird&#39;s-eye view video information, and an area in accordance with the second crowded positional information is also cut out from the bird&#39;s-eye view video information. Thus, the third video information on a specific player and the fourth video information including a plurality of players may be automatically generated from the bird&#39;s-eye view video information of the entire area of the court  1  where a plurality of players play a competition. 
     The following describes an example of the hardware configuration of a computer that achieves functions similar to those of the first server  100  described above in the embodiments.  FIG. 20  illustrates an example of a hardware configuration of a computer that achieves functions similar to those of a first server. 
     As illustrated in  FIG. 20 , a computer  600  includes a CPU  601  that executes various types of arithmetic processing, an input device  602  that accepts input of data from a user, and a display  603 . The computer  600  includes a reading device  604  that reads a program or the like from a storage medium, and a communication device  605  that exchanges data with the first cameras  4 , the second server  200 , or the like via a wired or wireless network. The computer  600  includes a RAM  606  that temporarily stores various types of information, and a hard disk device  607 . Each of the devices  601  to  607  is coupled to a bus  608 . 
     An acquisition program  607   a,  an identification program  607   b,  and a transmission program  607   c  are in the hard disk device  607 . The CPU  601  reads the programs  607   a  to  607   c  into the RAM  606 . 
     The acquisition program  607   a  functions as an acquisition process  606   a.  The identification program  607   b  functions as an identification process  606   b.  The transmission program  607   c  functions as a transmitting process  606   c.    
     The processing of the acquisition process  606   a  corresponds to the processing of the acquisition unit  151 . The processing of the identification process  606   b  corresponds to the processing of the identification unit  152 . The processing of the transmitting process  606   c  corresponds to the processing of the transmitting unit  153 . 
     The programs  607   a  to  607   c  may not be stored in the hard disk device  607  from the beginning. For example, the programs may be stored in a “portable physical medium” to be inserted into the computer  600 , such as a floppy disk (FD), a compact disk read-only memory (CD-ROM), a digital versatile disk (DVD), a magneto-optical disk, or an integrated circuit (IC) card. The computer  600  may read and execute the programs  607   a  to  607   c.    
     The following describes an example of the hardware configuration of a computer that achieves functions similar to those of the second server  200  ( 400 ) described above in the embodiments.  FIG. 21  illustrates an example of a hardware configuration of a computer that achieves functions similar to those of a second server. 
     As illustrated in  FIG. 21 , a computer  700  includes a CPU  701  that executes various types of arithmetic processing, an input device  702  that accepts input of data from a user, and a display  703 . The computer  700  includes a reading device  704  that reads a program or the like from a storage medium, and a communication device  705  that exchanges data with the second cameras  5 , the third cameras  6 , the fourth camera  7 , the first server  100 , the video distribution server  300 , or the like via a wired or wireless network. The computer  700  includes a RAM  706  that temporarily stores various types of information, and a hard disk device  707 . Each of the devices  701  to  707  is coupled to a bus  708 . 
     A receiving program  707   a,  an acquisition program  707   b,  a conversion program  707   c,  a generation program  707   d,  and an output control program  707   e  are in the hard disk device  707 . The CPU  701  reads the programs  707   a  to  707   e  into the RAM  706 . 
     The receiving program  707   a  functions as a receiving process  706   a.  The acquisition program  707   b  functions as an acquisition process  706   b.  The conversion program  707   c  functions as a conversion process  706   c.  The generation program  707   d  functions as a generation process  706   d.  The output control program  707   e  functions as an output control process  706   e.    
     The processing of the receiving process  706   a  corresponds to the processing of the receiving unit  251 . The processing of the acquisition process  706   b  corresponds to the processing of the acquisition unit  252 . The processing of the conversion process  706   c  corresponds to the processing of the conversion unit  253 . The processing of the generation process  706   d  corresponds to the processing of the generation unit  254 . The processing of the output control process  706   e  corresponds to the processing of the output control unit  255 . 
     The programs  707   a  to  707   e  may not be stored in the hard disk device  707  from the beginning. For example, the programs may be stored in a “portable physical medium” to be inserted into the computer  700 , such as an FD, a CD-ROM, a DVD, a magneto-optical disk, or an IC card. The computer  700  may read and execute the programs  707   a  to  707   e.    
     The following describes an example of the hardware configuration of a computer that achieves functions similar to those of the video distribution server  300  ( 500 ) described above in the embodiments.  FIG. 22  illustrates an example of a hardware configuration of a computer that achieves the functions similar to those of a video distribution server. 
     As illustrated in  FIG. 22 , a computer  800  includes a CPU  801  that executes various types of arithmetic processing, an input device  802  that accepts input of data from a user, and a display  803 . The computer  800  includes a reading device  804  that reads a program or the like from a storage medium, and a communication device  805  that exchanges data with the second server  200  or the like via a wired or wireless network. The computer  800  includes a RAM  806  that temporarily stores various types of information, and a hard disk device  807 . Each of the devices  801  to  807  is coupled to a bus  808 . 
     A receiving program  807   a,  a creation program  807   b,  a display control program  807   c,  a switching program  807   d,  and a distribution control program  807   e  are in the hard disk device  807 . The CPU  801  reads the programs  807   a  to  807   e  into the RAM  806 . 
     The receiving program  807   a  functions as a receiving process  806   a.  The creation program  807   b  functions as a creation process  806   b.  The display control program  807   c  functions as a display control process  806   c.  The switching program  807   d  functions as a switching process  806   d.  The distribution control program  807   e  functions as a distribution control process  807   e.    
     The processing of the receiving process  806   a  corresponds to the processing of the receiving unit  351 . The processing of the creation process  806   b  corresponds to the processing of the creation unit  352 . The processing of the display control process  806   c  corresponds to the processing of the display control unit  353 . The processing of the switching process  806   d  corresponds to the processing of the switching unit  354 . The processing of the distribution control process  806   e  corresponds to the processing of the distribution control unit  355 . 
     The programs  807   a  to  807   e  may not be stored in the hard disk device  807  from the beginning. For example, the programs may be stored in a “portable physical medium” to be inserted into the computer  800 , such as an FD, a CD-ROM, a DVD, a magneto-optical disk, or an IC card. The computer  800  may read and execute the programs  807   a  to  807   e.    
     All examples and conditional language provided herein are intended for the pedagogical purposes of aiding the reader in understanding the invention and the concepts contributed by the inventor to further the art, and are not to be construed as limitations to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although one or more embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.