Patent Publication Number: US-2020293785-A1

Title: Information processing apparatus, information processing method, and medium

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to an information processing apparatus, an information processing method, and a medium and particularly to a technique of displaying results of monitoring in a video monitoring system. 
     Description of the Related Art 
     In recent years, large-scale monitoring systems using a plurality of cameras have emerged. As an example of a monitoring system, proposed is a system that detects positions of a tracking target and tracks the tracking target by performing video analysis and recognition processing on a video captured by a camera. In such a system, a previously registered tracking target such as an object or a person is detected by video analysis. Upon the detection of the tracking target, a monitoring person is notified of the detection, and tracking is started. Japanese Patent Laid-Open No. 2018-32994 proposes a system that displays, for a tracking target detected in such a tracking system, a list of thumbnail images acquired from a video of each camera, together with image capture time arranged in a time series. Such a configuration facilitates determining the stay time and the movement path of the tracking target at each location. 
     SUMMARY OF THE INVENTION 
     According to an embodiment of the present invention, an information processing apparatus comprises: an acquisition unit configured to acquire detection locations of a tracking target and detection times of the tracking target; a display control unit configured to cause a display device to display a plurality of detection results of the tracking target sequentially acquired based on images captured by an image capturing unit, wherein the plurality of detection results are displayed in a display style where two or more of the plurality of detection results are grouped in accordance with detection locations of the tracking target and detection times of the tracking target. 
     According to another embodiment of the present invention, an information processing method comprises: causing a display device to display a plurality of detection results of a tracking target sequentially acquired based on images captured by an image capturing unit, wherein the plurality of detection results are displayed in a display style where two or more of the plurality of detection results are grouped in accordance with detection locations of the tracking target and detection times of the tracking target. 
     According to still another embodiment of the present invention, a non-transitory computer-readable medium stores a program which, when executed by a computer comprising a processor and a memory, causes the computer to: cause a display device to display a plurality of detection results of a tracking target sequentially acquired based on images captured by an image capturing unit, wherein the plurality of detection results are displayed in a display style where two or more of the plurality of detection results are grouped in accordance with detection locations of the tracking target and detection times of the tracking target. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an example of hardware configuration of an information processing apparatus according to an embodiment; 
         FIG. 2  illustrates an example of the functional configuration of an image processing apparatus according to an embodiment; 
         FIG. 3  is a flowchart of a processing example in an information processing method according to an embodiment; 
         FIG. 4  is a flowchart illustrating a processing example in grouping processing; 
         FIG. 5  is a flowchart illustrating a processing example in displaying processing; 
         FIGS. 6A to 6D  illustrate presentation examples of detection information; 
         FIG. 7  illustrates an example of detection information; and 
         FIGS. 8A to 8B  illustrate examples of group information of a camera and group information of detection information. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, embodiments will be described in detail with reference to the attached drawings. Note, the following embodiments are not intended to limit the scope of the claimed invention. Multiple features are described in the embodiments, but limitation is not made an invention that requires all such features, and multiple such features may be combined as appropriate. Furthermore, in the attached drawings, the same reference numerals are given to the same or similar configurations, and redundant description thereof is omitted. 
     In a case where a tracking target is not moving or the movement speed is slow in a tracking system, the information of the tracking target (e.g., thumbnail image) acquired from a same camera may be successively displayed. For example, in a case where the monitoring area is congested, the tracking target may be obstructed from view by irrelevant people, repeatedly causing a state of the tracking target being detected and a state of the tracking target not being detected. In a case where tracking is started such that the detection of the tracking target is started in the monitoring area and in a case where tracking is terminated such that the tracking target can no longer be detected, the same tracking target is successively detected at the same detection location for a certain time period, and the information of the tracking target is also successively displayed. A similar problem arises in a configuration that displays the information of the tracking target at a predetermined time interval. 
     A monitoring person, using the tracking system, may occasionally analyze the behavior of a tracking target in order to know “how long the tracking target stayed in a certain location” or “from which location the tracking target moved to which location”. However, there has been a problem that successively displaying information about the same tracking target at the same detection location makes it difficult to determine the stay time and the movement path of the tracking target at each location. 
     An embodiment of the present invention can make it easier for a user to check the behavior of the tracking target in a tracking system. 
       FIG. 1  is a block diagram illustrating an example of a hardware configuration of an information processing apparatus according to an embodiment. An information processing apparatus  100  has a processor, the processor being a CPU  101  (Central Processing Unit) in the example of  FIG. 1 . The processor can perform arithmetic operations and logical determination for various processes and can control respective components connected to a system bus  108 . 
     The information processing apparatus  100  has a memory including a program memory and a data memory. The program memory stores programs that define controls, which are performed by the processor, including various processing procedures described below. The data memory can provide a loading area and a work area for such a program and also provide a save area for data during error handling. Note that such a program may be loaded on the data memory from an external storage device or the like connected to the information processing apparatus  100 . In the example of  FIG. 1 , the information processing apparatus  100  includes a ROM  102  (Read-Only Memory) as the program memory and a RAM  103  (Random Access Memory) as the data memory. 
     The information processing apparatus  100  can have a storage medium that stores electronic data, programs, and the like. The storage medium may be a storage device such as a hard disk or an SSD or may be an external storage device. The external storage may be media (recording medium), and the media can be accessed via an external storage drive. As such media, there are known, for example, a flexible disk (FD), a CD-ROM, a DVD, a USB memory, MO, a flash memory, or the like. In addition, the external storage device may be an external information processing apparatus such as a server connected via a network. In the example illustrated in  FIG. 1 , the information processing apparatus  100  has an HDD  104 , which is a hard disk, as a storage medium. 
     An input device  105  is a device for receiving information indicating an operation made by a user, such as a mouse or a keyboard. An image capturing device  106  is a device for acquiring an image or a video. An output device  107  is a device, such as a display, having a display screen that outputs a presentation to a user. Note that the information processing apparatus  100  may be an information processing system including a plurality of devices, such as a server having the CPU  101 , the ROM  102 , the RAM  103 , and the HDD  104 ; and also a plurality of the image capturing devices  106 . 
       FIG. 2  is a block diagram illustrating an example of the functional configuration of the information processing apparatus according to an embodiment. The information processing apparatus  100  can the cause the display unit to display a plurality of detection results of the tracking target which have been sequentially acquired based on the image captured by the image capturing unit. The information processing apparatus  100  has a determination unit  204 , a grouping unit  205 , and a display unit  206  as components for performing such display control. In addition, the information processing apparatus  100  may have an image capturing unit  201 , an input unit  202 , a detection unit  203 , and a storage unit  207 . Each of the functional units can be realized by the CPU  101  that expands a program stored in the ROM  102  into the RAM  103 , and performs a process according to each flowchart described below in accordance with the program. In the aforementioned configuration, the storage unit  207  can be realized by the RAM  103 . However, in an embodiment, at least some of the functional units included in the information processing apparatus  100  may be realized by dedicated hardware. 
     The determination unit  204 , the grouping unit  205 , and the display unit  206  can perform display control that causes the display unit to display one or more detection results in a display style being grouped in accordance with the detection location of the tracking target and the detection time of the tracking target. In an embodiment illustrated in  FIG. 2 , the determination unit  204  determines whether or not to treat a detection result as a grouping target. In addition, the grouping unit  205  performs grouping processing on the detection results. Furthermore, the display unit  206  causes the output device  107  to display the detection results in accordance with the results of processing by the grouping unit  205 . 
     Although the type of the tracking target is not particularly limited, the tracking target may be a predetermined subject such as, for example, a specific person. Detection results of such a tracking target can be acquired based on captured images. For example, such detection results can be acquired by performing the detection processing of the tracking target, on each of the sequentially acquired captured images, e.g., on each frame of the video, for example. 
     The image capturing unit  201  can acquire such a captured image. In the present embodiment, the image capturing unit  201  performs the image capturing of a predetermined area. The image capturing unit  201  is therefore realized by the plurality of image capturing devices  106  each having a different image capturing range. The number of the image capturing devices  106  being used is not particularly limited. In addition, the information processing apparatus  100  may acquire a captured image from an external image capturing device. Hereinafter, the image capturing unit  201  is supposed to acquire a video for a predetermined area formed of a plurality of captured images (frames) successively acquired by each of the image capturing devices  106 . 
     The detection unit  203  can perform the detection processing of the tracking target on a plurality of captured images that are sequentially captured. For example, the detection unit  203  can detect a tracking target appearing in the video captured by performing image analysis processing, for example. In addition, the detection unit  203 , when detecting the tracking target, can acquire detection information as a detection result of the tracking target. The detection information refers to information relating to the tracking target. The detection information may include information for identifying the tracking target. As the information for identifying the tracking target, the following are given: identification information of the tracking target, such as an ID or name; and an image of the tracking target (e.g., a thumbnail image extracted from the video image) acquired from the captured image. In addition, the detection information may include information indicating the detection status of the tracking target. As the information indicating the detection status, the following are given: the detection time or the detection location. The detection information may include other information, without being limited to aforementioned information. 
     In the following example, the detection unit  203  acquires, as the detection information, an image, a detection time, and a detection location of the tracking target. The detection location may be a two-dimensional or three-dimensional position of the tracking target or may be a two-dimensional or three-dimensional position of the image capturing device  106  having captured a video in which the tracking target appears. Furthermore, the detection location may be a name or an ID of the image capturing device  106  having captured a video in which the tracking target appears or may be a name or an ID indicating an area which is a target to be captured by the image capturing device  106 . Furthermore, the detection location may be a name or an ID of an image capturing unit group (camera group) to which belongs the image capturing device  106  having captured the video in which the tracking target appears. In this case, for example, the image capturing devices can be grouped such that the plurality of image capturing devices that are intended to take a specific region as a target to be captured are included in a single camera group. Information indicating a camera group to which each of the image capturing devices belongs can be held by the storage unit  207 , for example. In addition, the detection time may be the image capture date of an image (or a video frame) in which the tracking target is detected. 
     In the present embodiment, the detection unit  203  can determine whether or not the tracking target has been detected in each of the videos captured by the image capturing devices  106 . Subsequently, when the detection of the tracking target is started in a video captured by one of the image capturing devices  106 , the detection unit  203  can store, in the storage unit  207 , the detection information of the tracking target acquired from the video by the one of the image capturing devices  106 . In this embodiment, the detection information of the tracking target is recorded when the tracking target has entered the image capturing range of one of the image capturing devices  106 . On the other hand, in this embodiment, there is a possibility that the detection information of the tracking target is also recorded in a case where an object which had been obstructing the tracking target from view has moved within an image capturing range of one of the image capturing devices  106 . Note that the timing of acquiring the detection information is not limited to this example. For example, the detection unit  203  may store, in the storage unit  207 , the detection information of the tracking target acquired from a video captured by each of the image capturing devices  106  at a constant time interval. In addition, the detection unit  203  may store, in the storage unit  207 , after the tracking target has entered the image capturing range of one of the image capturing devices  106 , the detection information of the tracking target acquired from the video by the image capturing device  106  at a predetermined time interval. 
     In addition, the detection unit  203  can determine whether or not the detection of the tracking target in a video by any of the image capturing devices  106  is started. When the detection of the tracking target is started, the detection unit  203  can notify, via the output device  107 , the user that the tracking target has been detected or the tracking of the tracking target is started. 
     In the present embodiment, the detection unit  203  acquires detection information indicating sequential detection results of the tracking target, based on the image captured by the image capturing unit  201 . Subsequently, the display control of such detection results is performed by the determination unit  204 , the grouping unit  205 , and the display unit  206 . In the present embodiment, detection information is displayed on the output device  107  as the detection results. Herein, the detection results may be referred to as detection information. However, the present invention is not limited to such examples. For example, detection processing may be performed such that each of the plurality of image capturing devices acquires a captured image and detects the tracking target in the acquired captured image. In this case, the information processing apparatus  100  can acquire detection information from each of the plurality of image capturing devices. In addition, the information processing apparatus  100  may acquire such detection information from another information processing apparatus such as a server; or from a storage device. 
     The input unit  202  accepts user input via the input device  105 . As user input, the following are given: position input using a mouse pointer or the like; and selection input by clicking or the like. 
     The storage unit  207  can store detection information acquired by the detection unit  203 . In addition, the storage unit  207  may store camera group information indicating a camera group to which each of the image capturing devices belongs. Furthermore, the storage unit  207  may store tracking target information for identifying the tracking target detected by the detection unit  203 . The tracking target information may include the image characteristic amount of the tracking target to be used by the detection unit  203  to detect the tracking target, for example. In addition, the tracking target information may include the ID or the name of the tracking target or may include the registration date and time of the tracking target. In the present embodiment, such tracking target information is preliminarily generated and stored in the storage unit  207 . 
     In the following, referring to  FIG. 3 , described is a flow of an information processing method performed by the information processing apparatus according to the present embodiment.  FIG. 3  is a flowchart illustrating an example of processing performed by the information processing apparatus  100 . In the present embodiment, the image capturing devices are grouped by each room in which the image capturing devices are installed. An example of camera group information indicating such grouping is illustrated in  FIG. 8A . However, the criterion for camera grouping is not limited thereto. In  FIG. 8A , image capturing devices having particular camera IDs and camera names are classified into one of camera groups A to D. Additionally, in the present embodiment, the detection information includes, as the detection location, the name of the camera group to which belongs the image capturing device which has detected the tracking target. However, the detection location may be different information, as has been described above. 
     At step S 301 , the image capturing unit  201  acquires a live video. Here, the plurality of image capturing devices  106  can simultaneously perform image capturing in each of the image capturing ranges, and the image capturing unit  201  can acquire respective live videos. At step S 302 , the detection unit  203  detects the tracking target by performing video analysis processing on the videos acquired at step S 301 . Upon detecting the tracking target, the detection unit  203  stores, in the storage unit  207 , the detection information acquired as a result of the video analysis processing. 
     At step S 303 , the input unit  202  acquires an operation event indicating a user input. The input unit  202  can acquire, for example, an operation event specifying the display style. In the present embodiment, the display style of grouped detection results is specified by the user. As a specific example, the input unit  202  can detect an operation event that instructs to display only the representative piece of detection information among the grouped detection information; and an operation event that instructs to display all the grouped detection information. Hereinafter, the display style where only the representative piece of detection information is displayed is referred to as a collapsed style, and a display style where all the grouped detection information is displayed is referred to as an expanded style. The input unit  202  stores, in the storage unit  207 , the operation events detected in such a manner. However, it is not essential to modify the display style in accordance with user instructions. 
     At step S 304 , the determination unit  204  and the grouping unit  205  perform grouping processing on the detection results in accordance with the detection location of the tracking target and the detection time of the tracking target. At step S 305 , the display unit  206  causes the output device  107  to display one or more detection results in a display style according to the result of the grouping processing at step S 304 . The processes of steps S 304  and S 305  are described below. 
     The detection unit  203  may perform such video analysis processing on a video that lasts for a predetermined time length, i.e., on a plurality of frames, or may perform such video analysis processing on the latest video, i.e., on the latest frame. In the present embodiment, at step S 301 , the image capturing unit  201  sequentially acquires frames, and at step S 302 , the detection unit  203  generates a new piece of detection information by performing the detection processing on the tracking target on a newly acquired frame. Subsequently, at step S 304 , the determination unit  204  and the grouping unit  205  perform a grouping control on the new piece of detection information, and at step S 305 , the display unit  206  causes the output device  107  to display the newly acquired detection information. In other words, repeating the processes illustrated in  FIG. 3  causes the display of the output device  107  to be successively updated. On the other hand, the detection unit  203  may perform the video analysis processing on the video acquired in the past and stored in the storage device. 
     In addition, in a case where there exists a plurality of tracking targets to be tracked by the information processing apparatus  100 , the processes of steps S 302  to S 305  may be performed for each of the tracking targets. In this case, the detection information can be displayed along a time series for each of the tracking targets, similarly to  FIGS. 6A to 6D . 
       FIG. 4  is a flowchart illustrating an example of the grouping processing at step S 304 . As described below, the determination unit  204  controls, at step S 404 , whether or not to group the tracking targets in accordance with the detection time of the tracking targets. In addition, at steps S 405  to S 411 , the grouping unit  205  groups the tracking targets determined by the determination unit  204  as a grouping target, in accordance with the detection locations of the tracking targets. In the following, the process of step S 304  is described referring to a specific example. 
     First, described is a case where the grouping processing of step S 304  is performed at 2018 Feb. 1 12:26. At step S 401 , the determination unit  204  determines whether or not there exists, among the pieces of detection information stored in the storage unit  207 , any piece of detection information not belonging to a group. In a case where there exists one or more pieces of detection information not belonging to a group, the process flow proceeds to step S 402 , otherwise the process flow terminates. 
     Here, described is a case where the storage unit  207  has stored therein the detection information illustrated in  FIG. 7 . The detection information illustrated in  FIG. 7  includes: the detection ID which is the ID of the detection information; the ID of the tracking target; the detection time of the tracking target; the detection location of the tracking target; the image file name of the detected tracking target; and the group ID which is the ID of the group (detection result group) to which the detection information belongs. In the example of  FIG. 7 , the detection information includes the group ID in order to associate the detection information and the group information. The storage unit  207  can store group information with regard to such a group of detection information. Although the example of group information illustrated in  FIG. 8B  indicates the association between respective group IDs and the generation date and time of the group of detection information, the group information in the detection information is not limited to that illustrated in  FIG. 8B . Additionally, in the example of  FIG. 7 , detection information not belonging to a group is provided with “−1” as the group ID. 
     In this example, the storage unit  207  has stored therein two pieces of detection information (detection IDs  8  and  9 ) not belonging to a group. Accordingly, the process flow proceeds to step S 402 . 
     At step S 402 , the determination unit  204  determines whether or not the processes at and after step S 403  have been performed on all the pieces of detection information not belonging to a group. In a case where the aforementioned processes have been performed, the entire process terminates. In a case where the aforementioned processes have not been performed, the process flow proceeds to step S 403 . In this example, the processes have not been performed on the two pieces of detection information (detection IDs  8  and  9 ) and therefore the process flow proceeds to step S 403 . 
     At step S 403 , the determination unit  204  selects a piece of detection information having the oldest detection time, among the pieces of detection information which do not belong to a group and have not been subjected to the processes at and after step S 403 . In this example, the determination unit  204  selects the piece of detection information having the detection ID  8 . 
     At step S 404 , the determination unit  204  determines whether or not to select the piece of detection information selected at step S 403  as a grouping target, in accordance with the detection time (detection time included in the detection information in the example of  FIG. 7 ) of the tracking target. In the present embodiment, the determination unit  204  performs the aforementioned determination further based on the current time. For example, the determination unit  204  can select the piece of detection information as a grouping target when the difference between the current time and the detection time is equal to or greater than a predetermined threshold value, in which case the process flow proceeds to step S 405 . On the other hand, the determination unit  204  does not select the piece of detection information as a grouping target when the difference is less than the predetermined threshold value, in which case the process flow returns to step S 402 . Here, a piece of detection information which has not been selected as a grouping target remain unattached to a group (i.e., group ID=−1). 
     In this example, the threshold value is set to 5 minutes. The difference between the current time and the detection time of the piece of detection information having the detection ID  8  is less than 5 minutes, and therefore the process flow returns to step S 402 . Subsequently, at step S 403 , the determination unit  204  selects a piece of detection information including the detection ID  9 . Also in this case, the aforementioned piece of detection information is not selected as a grouping target at step S 404 . Subsequently, the process flow returns to S 402  and processes at and after step S 403  are performed on all the pieces of detection information not belonging to a group, and therefore the process flow of  FIG. 4  terminates. 
     In such an example, the display unit  206  can perform, at step S 305 , a display control described below.  FIG. 5  is a flowchart illustrating an example of the display control processing at step S 305 . As described below, the display unit  206  causes, at step S 305 , the output device  107  to display a list of detection results along a time series in the display style according to the result of the grouping processing performed at step S 304 . 
       FIGS. 6A to 6D  illustrate presentation examples of detection results on the output device  107  in accordance with the display control performed at step S 305 . In the examples of  FIGS. 6A to 6D , pieces of detection information are displayed for each tracking target. In  FIG. 6A , the tracking target information is displayed in an area  601 . In the example of  FIG. 6A , although the ID of the tracking target, the name of the tracking target, and the registration date and time of the tracking target are displayed as the tracking target information, things to be displayed are not limited thereto. In addition, in an area  600 , the pieces of detection information for the tracking target indicated in the area  601  are displayed in chronological order. 
     In the following, the process of step S 305  is described referring to a specific example. At step S 501 , the display unit  206  determines whether or not there exists, among the pieces of detection information stored in the storage unit  207 , one or more pieces of detection information not belonging to a group of detection information. In a case where there exists any, the process flow proceeds to step S 502 , otherwise, the process flow proceeds to step S 503 . In this example, the storage unit  207  has stored therein two pieces of detection information (detection IDs  8  and  9 ) not belonging to a group. Accordingly, the process flow proceeds to step S 502 . 
     At step S 502 , the display unit  206  causes the output device  107  to display a list of pieces of detection information not belonging to a group, in a manner arranged in a time series. In an embodiment, the piece of detection information having the latest detection time is displayed on the left end, with pieces of detection information having earlier detection times being displayed rightward. For example, in the example of  FIG. 6A , detection information  602  with the detection ID  9  is displayed on the left side and detection information  603  with the detection ID  8  is displayed on the right side. 
     At step S 503 , the display unit  206 , referring to the group information acquired from the storage unit  207 , determines whether or not there exists one or more groups of detection information. In a case where there exists any, the process flow proceeds to step S 504 , otherwise the process flow of  FIG. 5  terminates. In this example, there exist four groups (group IDs  1  to  4 ) as illustrated in  FIG. 8B , and therefore the process flow proceeds to step S 504 . 
     At step S 504 , the display unit  206  determines whether or not the processes at and after step S 505  have been performed on all the groups. In a case where the aforementioned processes have been performed, the process flow of  FIG. 5  terminates, otherwise the process flow proceeds to step S 505 . In this example, none of the groups has been processed, and therefore the process flow proceeds to step S 505 . 
     At step S 505 , the display unit  206 , referring to the group information acquired from the storage unit  207 , selects the group information with the latest generation date and time, among the groups of detection information which have not been subjected to the processes at and after step S 505 . In the example of  FIGS. 6A to 6D , at step S 508  or S 509 , detection information belonging to the group selected at step S 505  is displayed on the output device  107 . Repeating the processes of step S 504  to S 509  causes each group to be displayed along a time series in recent order of generation date and time, following the detection information not belonging to the group displayed at step S 502 . In other words, each group is displayed along a time series in order of the latest detection time of detection information belonging to the group. In this example, the display unit  206  selects a group having the group ID  4 . 
     At step S 506 , the display unit  206  determines whether or not two or more pieces of detection information belong to the group selected at step S 505 . In a case where two or more pieces of detection information belong to the group, the process flow proceeds to step S 507 , or the process flow proceeds to step S 509  in a case where one or less piece of detection information belongs thereto. In this example, there exist four pieces of detection information belonging to the group having the group ID  4  (detection IDs  4  to  7 ), and therefore the process flow proceeds to step S 507 . 
     At step S 507 , the display unit  206  determines to cause the output device  107  to display the detection information belonging to the group selected at step S 505  in a grouped display style. In the present embodiment, at subsequent step S 508 , the display unit  206  acquires, from the storage unit  207 , the detection information belonging to the group selected at step S 505  and causes the output device  107  to display the information in a display style according to user instructions. 
     As an example, the display style used by the display unit  206  may include the collapsed style. In the collapsed style, only a part of the plurality of pieces of detection information grouped into one group of detection information are displayed. For example, as illustrated in  FIG. 6A , the display unit  206  can cause the output device  107  to display detection information  604  having the detection ID  7  with the latest detection time among the pieces of detection information belonging to a group having the group ID  4 . On this occasion, the display unit  206  can control the presentation in a manner recognizable that a plurality of pieces of detection information belong to one group. For example, in a case where two or more pieces of detection information are grouped into one group, the display unit  206  can cause the output device  107  to display the so-grouped detection results in a manner distinguishable from detection results not grouped as such. Specifically, the display unit  206  can cause the output device  107  to display the aforementioned detection information in a style distinguished from detection information not belonging to a group and from detection information not having other detection information belonging to the same group. For example, in  FIG. 6A , the detection information  604  displayed in the collapsed style is displayed so that a plurality of pieces of detection information overlap one another. Additionally, in  FIG. 6A , the detection information  604  displayed in the collapsed style is provided with an icon  608  indicating that only the representative piece of detection information among the plurality of pieces of detection information is displayed. 
     As another example, the display style used by the display unit  206  may include the expanded style. In the expanded style, displayed are all the pieces of detection information among the plurality of pieces of detection information grouped in one group of detection information. For example, as illustrated in  FIG. 6B , the display unit  206  can cause the output device  107  to display all detection information  609  to  612  (detection IDs  7  to  4 ) belonging to a group having the group ID  4 . Also in the expanded style, the display unit  206  can cause the output device  107  to display the aforementioned detection information in a style distinguished from detection information not belonging to a group and from detection information not having other detection information belonging to the same group. For example, in  FIG. 6B , the detection information  609  to  612  displayed in the expanded style is provided with an icon  613  indicating that all the plurality of pieces of detection information are displayed. 
     The display style on the display unit  206  may be switchable. In other words, the display unit  206  may select one from a plurality of display styles. On this occasion, the display unit  206  may switch the display style based on user instructions. Furthermore, display styles may be individually set for each of the plurality of groups of detection results, and the storage unit  207  may store information indicating a display style for each of the plurality of groups. For example, it is possible to register the information indicating the display style in the group information stored in the storage unit  207 . 
     For example, upon a user clicking on the icon  608  while  FIG. 6A  is displayed on the output device  107 , the input unit  202  detects, at step S 303 , an operation event specifying the expanded style for the group of detection information having the group ID  4 . On this occasion, the storage unit  207  can register, in the group information of the detection information having the group ID  4 , information indicating that the expanded style is instructed. At step S 508 , the display unit  206  can retrieve, from the storage unit  207 , such information indicating the display style of the group selected at step S 505 . Subsequently, the display unit  206  can perform display control such that the group of detection information having the group ID  4  is displayed in the expanded style. 
     Similarly, upon the user clicking on the icon  613  while  FIG. 6B  is displayed on the output device  107 , the input unit  202  detects an operation event specifying the collapsed style for the group of detection information having the group ID  4 . In this case, the display unit  206  can perform, at step S 508 , display control such that the group of detection information having the group ID  4  is displayed in the collapsed style. 
     In this example, the process flow returns to S 505  through steps S 508  to S 504 . At step S 505 , the display unit  206  selects a group having the group ID  3  with the latest generation date and time after the group of detection information having the group ID  4 . Since only one piece of detection information belongs to the aforementioned group (detection ID  3 ), the process flow proceeds from step S 506  to S 509 . 
     At step S 509 , the display unit  206  acquires, from the storage unit  207 , the detection information belonging to the group selected at step S 505  and causes the output device  107  to display the detection information. In this example, the display unit  206  causes the output device  107  to display detection information  605  having the detection ID  3 . In this example, repeating the processes of step S 504  to S 509  causes detection information  606  (detection ID  2 ) belonging to the group having the group ID  2  to be similarly displayed. In addition, detection information  607  (detection ID  1 ) belonging to a group having the group ID  1  is also displayed. 
     Next, described is a case where the grouping processing of step S 304  is performed again at the time 2018Feb. 1 12:30 after having performed the grouping processing of step S 304  at 2018 Feb. 1 12:26. Steps S 401  to S 403  are performed in a similar manner. At step S 404 , the difference between the current time and the detection time of the detection information having the detection ID  8  is equal to or greater than 5 minutes, and therefore the process flow proceeds to step S 405 . 
     At steps S 405  to S 411 , the pieces of detection information selected at step S 403  are grouped. At step S 405 , the grouping unit  205  determines whether or not there exists one or more groups of detection information. In a case where there exists any, the process flow proceeds to step S 406 , otherwise the process flow proceeds to step S 410 . In this example, the group illustrated in  FIG. 8B  has already been generated, the process flow proceeds to step S 406 . 
     At steps S 406  to S 408 , the grouping unit  205  determines whether or not to attach the piece of detection information selected at step S 403  to the already generated group of detection information. In the present embodiment, the grouping unit  205  determines whether or not to attach the piece of detection information selected at step S 403  to the group containing the latest piece of detection information. Although the determination criterion is not particularly limited, the grouping unit  205  performs determination in the following example in accordance with the detection location of the tracking target indicated by the piece of detection information selected at step S 403  and the detection time of the tracking target. 
     At step S 406 , the grouping unit  205  selects the latest piece of detection information among the pieces of detection information belonging to the group. For example, the grouping unit  205  can select detection information having a detection time closest to the current time among the pieces of detection information belonging to the group. In this example, a piece of detection information having the detection ID  7  is selected. 
     At step S 407 , the grouping unit  205  determines whether or not to group the pieces of detection information in accordance with the detection time of the tracking target indicated by the piece of detection information selected at step S 403 ; and in accordance with the detection time of the tracking target indicated by the piece of detection information selected at step S 406 . In the present embodiment, the grouping unit  205  determines whether or not the difference between the detection time indicated by the piece of detection information selected at step S 406  and the detection time indicated by the piece of detection information selected at step S 403  is less than a predetermined threshold value. In a case where the difference is less than the predetermined threshold value, the process flow proceeds to step S 408 , or the process flow proceeds to step S 410  in a case where the difference is equal to or greater than the predetermined threshold value. The predetermined threshold value can be set as appropriate and is set to one hour in this example. In this example, the difference between the detection time indicated by the detection information having the detection ID  7  and the detection time indicated by the detection information having the detection ID  8  is one minute, as illustrated in  FIG. 7 , and therefore the process flow proceeds to step S 408 . 
     At step S 408 , the grouping unit  205  determines whether or not to group the pieces of detection information in accordance with the detection location of the tracking target indicated by the piece of detection information selected at step S 403 ; and in accordance with the detection location of the tracking target indicated by the piece of detection information selected at step S 406 . In the present embodiment, the grouping unit  205  determines whether or not the detection location indicated by the piece of detection information selected at step S 403  matches the detection location indicated by the piece of detection information selected at step S 406 . In a case where the locations match, the process flow proceeds to step S 409 , otherwise the process flow proceeds to step S 410 . 
     In the present embodiment, the detection location refers to a camera group to which the image capturing device having detected the tracking target belongs. Accordingly, the grouping unit  205  determines that the detection location matches, in a case where the detection results have been acquired based on images captured by image capturing devices included in the same camera group. According to such a configuration, even in a case where the tracking target is being simultaneously captured by two or more image capturing devices included in the same camera group covering an overlapping image capturing area, it is possible to group the pieces of detection information acquired from images captured by each of the image capturing devices. In this example, as illustrated in  FIG. 7 , both the detection location indicated by the detection information having the detection ID  7  and the detection location indicated by the detection information having the detection ID  8  correspond to Camera A, and therefore the process flow proceeds to step S 409 . 
     At step S 409 , the grouping unit  205  groups the piece of detection information selected at step S 403  with the piece of detection information selected at step S 406 . In the present embodiment, the grouping unit  205  stores, in the storage unit  207 , information indicating the group including the piece of detection information selected at step S 403 , in a manner of attaching the former piece of information to the group including the detection information selected at step S 406 . In this example, the grouping unit  205  updates the group ID related to the detection information having the detection ID  8  to the group ID  4 , which is the group ID of the group to which the detection information having the detection ID  7  belongs. 
     In this example, the process flow subsequently returns to step S 402  from step S 409 . Subsequent processes are performed in a similar manner, whereby a piece of detection information having the detection ID  9  is selected at step S 403  and it is determined at step S 404  that the piece of detection information is to be grouped. At step S 406 , a piece of detection information having the detection ID  8  is selected. and the process flow proceeds to step S 408  through step S 407 . In this example, the detection location indicated by the detection information having the detection ID  7  corresponds to Camera A, the detection location indicated by the detection information having the detection ID  8  corresponds to Camera B, and therefore the process flow proceeds to step S 410  from step S 408 . 
     At steps S 410  and S 411 , the grouping unit  205  generates a new group including only the pieces of detection information selected at step S 403 . In the present embodiment, the grouping unit  205  generates a new group of detection information at step S 410 . In this example, the grouping unit  205  generates a group having the group ID  5 . In addition, the grouping unit  205  stores, in the storage  207 , group information which is similar to that of  FIG. 8B  for the generated group. As described above, it is possible to register the information indicating the display style in the group information. In this example, the display style is either the collapsed style or the expanded style, the initial value being the collapsed style. 
     At step S 411 , the grouping unit  205  stores, in the storage unit  207 , information indicating the group including the piece of detection information selected at step S 403 , in a manner attaching the former piece of information to the group generated at step S 410 . In this example, the grouping unit  205  updates the group ID related to the detection information having the detection ID  9  to the group ID  5 , which is the group ID of the newly generated group. 
     In such an example, at step S 305 , the display unit  206  can cause the output device  107  to perform the presentation illustrated in  FIG. 6C , according to the flowchart of  FIG. 5 . As illustrated in  FIG. 6C , the detection information having the detection ID  8  is included in the group having the group ID  4 , and the detection information  603  with the detection ID  8  is displayed in the collapsed style. 
     According to the present embodiment, in a case where the same tracking target has been detected a plurality of times at the same detection location at or less than a predetermined interval, the detection information is grouped. Such a technique facilitates providing a user with a presentation which is easy to check the behavior of tracking target. 
     Modification 
     The grouping unit  205  according to an embodiment can determine, such as at steps S 406  to S 408 , whether or not to group two or more detection results acquired at successive detection times. In the above example, two detection results are grouped in a case where the difference between the detection times is less than a threshold value (S 407 ) and the detection locations match (S 408 ). However, the method for determining whether or not to group is not limited to such an example. 
     In an embodiment, the grouping unit  205  can determine whether or not to group two or more detection results obtained at successive detection times, in accordance with the detection location of the tracking target. In particular, the grouping unit  205  may determine whether or not to group two or more detection results in accordance with whether or not the detection locations match. According to such a configuration, it is possible to group the detection information of the tracking target detected at the same or close detection location, whereby it becomes easier to check the behavior of the tracking target. Accordingly, it is not essential to consider the difference between the detection times when performing grouping in accordance with the detection location of the tracking target and the detection time of the tracking target. 
     The display style is not limited to those described above. For example, as a display style, there may be displayed only two or more pieces of detection information which are a part of a plurality of pieces of detection information belonging to one group. In addition, as another display style, there may be displayed a summary of a plurality of pieces of detection information belonging to one group. As a specific example, the following are given: information common to a plurality of pieces of detection information, information selected from mutually different pieces of detection information, information acquired by analysis of a plurality of pieces of detection information, and information calculated from a plurality of pieces of detection information and being different from items included in the detection information. 
       FIG. 6D  illustrates one of such examples. In  FIG. 6D , an area  701  is a presentation example of a group having the group ID  4  in the expanded style. In the area  701 , there are displayed the detection information  603  having the detection ID  8  and the detection information  609  having the detection ID  7 . In addition, as illustrated in  FIG. 6D , further displayed is summary information  702  related to the detection information belonging to the group having the group ID  4 . The summary information  702  includes the detection location (common to each detection information), the detection start time (i.e., the detection time indicated by the detection information having the oldest detection ID  4 ), and the number of detections (the number of pieces of detection information). Accordingly, detailed information about old detection information may be omitted and a summary may instead be displayed, while displaying detailed information about new detection information. In addition, a link  703  for referencing detailed information about old detection information may be displayed. For example, a click on the  703  by a user displays all the pieces of detection information belonging to a group. Note that  FIG. 6D  is merely an example and the method for displaying a summary is not limited thereto. 
     The aforementioned example displays, in the collapsed style, detection information with the latest detection time among the pieces of detection information belonging to the group. However, the detection information to be displayed may be selected based on another criterion, or a summary such as described above for a plurality of pieces of detection information belonging to a group may be displayed instead of the detection information. As an example, detection information selected based on the recognition reliability of the tracking target acquired during video analysis may be displayed. 
     Additionally, in the above example, whether or not to treat a piece of detection information as a grouping target is determined in accordance with the difference between the current time and the detection time. However, the method for determining a grouping target is not limited to the aforementioned method. In an embodiment, the determination unit  204  determines whether or not to treat a piece of detection information as a grouping target, further based on a later detection result than the aforementioned detection result. For example, the determination unit  204  may determine whether or not to treat a piece of detection information as a grouping target, based on another piece of detection information not yet belonging to a group. 
     As a specific example, the determination unit  204  can perform the aforementioned determination based on the detection location indicated by the piece of detection information selected at step S 403 ; and based on the detection location indicated by a piece of detection information whose detection time is later than that of the former piece of detection information. For example, the determination unit  204  can determine, as a grouping target, the piece of detection information selected at step S 403  regardless of the detection time, in a case where the detection locations do not match. For example, the detection location indicated by the detection information having the detection ID  8  does not match the detection location indicated by the detection information having the detection ID  9 . Therefore, in a case having selected at step S 403  the detection information having the detection ID  8 , the determination unit  204  can determine, as a grouping target, the piece of detection information having the detection ID  8 . 
     As another specific example, the determination unit  204  can perform the aforementioned determination based on the detection time indicated by the piece of detection information selected at step S 403 ; and based on the detection time indicated by the detection information whose detection time is later than that of the former piece of detection information. For example, the determination unit  204  can determine, as a grouping target, the piece of detection information selected at step S 403  regardless of the current time, in a case where there exists a piece of detection information whose detection time is later than the detection time of the piece of detection information selected at step S 403 . According to such a configuration, there is a possibility that only the latest piece of detection information is excluded from the grouping targets, and all the other pieces of detection information turn out to be grouping targets. 
     Other Embodiments 
     Embodiment(s) of the present invention can also be realized by a computer of a system or apparatus that reads out and executes computer executable instructions (e.g., one or more programs) recorded on a storage medium (which may also be referred to more fully as ‘non-transitory computer-readable storage medium’) to perform the functions of one or more of the above-described embodiment(s) and/or that includes one or more circuits (e.g., application specific integrated circuit (ASIC)) for performing the functions of one or more of the above-described embodiment(s), and by a method performed by the computer of the system or apparatus by, for example, reading out and executing the computer executable instructions from the storage medium to perform the functions of one or more of the above-described embodiment(s) and/or controlling the one or more circuits to perform the functions of one or more of the above-described embodiment(s). The computer may comprise one or more processors (e.g., central processing unit (CPU), micro processing unit (MPU)) and may include a network of separate computers or separate processors to read out and execute the computer executable instructions. The computer executable instructions may be provided to the computer, for example, from a network or the storage medium. The storage medium may include, for example, one or more of a hard disk, a random-access memory (RAM), a read only memory (ROM), a storage of distributed computing systems, an optical disk (such as a compact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™), a flash memory device, a memory card, and the like. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2019-046384, filed Mar. 13, 2019 which is hereby incorporated by reference herein in its entirety.