KR20220135745A - Camera, method and computer program for operating syncronization between a plurality of cameras - Google Patents

Abstract

A camera for performing synchronization between a plurality of cameras may include: a reception part for receiving a first synchronization signal and a second synchronization signal generated based on a predetermined period from a main camera; a first determination part for determining network validity between the main camera and the camera based on the reception time of the first synchronization signal and the reception time of the second synchronization signal; and a second determination part for determining the validity of the internal frame of the camera based on the first frame generation time.

Description

CAMERA, METHOD AND COMPUTER PROGRAM FOR OPERATING SYNCRONIZATION BETWEEN A PLURALITY OF CAMERAS

The present invention relates to a camera, method and computer program for performing synchronization between a plurality of cameras.

Referring to FIG. 1A , in the conventional photography synchronization method, a camera controller generates a synchronization signal and transmits the generated synchronization signal to the camera to perform camera synchronization. At this time, the synchronization signal is transmitted to the camera through an optical cable in order to exclude a signal delay.

As described above, in a wired environment, it is necessary to construct an optical cable to synchronize shooting of a camera and receive image data. Accordingly, an expensive optical cable installation cost is high, and the optical cable installation may be subject to environmental restrictions.

In the case of the current broadcast service, since shooting synchronization between cameras is not essential, the image data after shooting can be compressed and transmitted through a Wi-Fi network or a cellular network. Service is not available.

Meanwhile, an image capturing environment in a wireless environment may be configured as shown in FIG. 1B . Referring to FIG. 1B , each camera 120 is connected to the AP device 110 to configure the same network, and is configured to communicate with the camera controller 100 . Here, the camera controller 100 transmits commands to start and stop shooting of the cameras to each camera 120 .

≤β와 같이 나타난다. Looking at the characteristics of image capturing in such a wireless environment, a delay occurs due to interference of radio signals, a delay occurs due to a packet collision higher than that in a wired environment, and a delay occurs due to switching of the AP device 110 . In addition, in consideration of a photographing synchronization condition (eg, 1/2 ms) between cameras required for image photographing, synchronization of photographing between cameras in a wireless environment is almost impossible. Furthermore, the conditions for checking the synchronization of shooting between cameras are difficult. Specifically, for shooting synchronization, a command should be transmitted from the camera controller 100 to each camera 120 at the same time so that each camera can take a picture at the same time. In the case of a wired environment, since the camera controller 100 transmits a shooting command to each camera 120 through an optical cable, the phase difference is not large. However, in the case of a wireless environment, there is a difference in the reception time of the photographing command according to radio wave interference or distance. Referring to FIG. 1C , the delay time from the transmission time of the shooting command to the reception time is α≤

It appears as ≤β.

)이 목표가 되어야 한다. In order to synchronize shooting, the minimum(

) should be the goal.

)을 측정할 방법이 없다. 실제 지연 시간을 측정하기 방법은 다음의 ①과 ②를 이용한다. However, in a wireless environment, the transmission/reception delay time (

), there is no way to measure To measure the actual delay time, use ① and ② below.

=

-

①

=

-

=

-

②

=

-

를 측정하고 이를 저장하더라도

은 카메라 컨트롤러(100)에서 발생한 시각이기에 이 둘의 차이는 카메라 컨트롤러(100)와 카메라 1이 동기화 되었다는 전제하에 의미가 있다. In case of ①, the delay time cannot be measured unless the transmitting device and the receiving device are absolutely synchronized. For example, in order to measure a synchronization signal between the camera controller 100 and the camera 1, the camera 1

Even if you measure and store it

Since is a time generated by the camera controller 100 , the difference between the two is meaningful on the premise that the camera controller 100 and the camera 1 are synchronized.

)과 카메라 1이 촬영 명령어의 수신 여부를 다시 카메라 컨트롤러(100)에게 응답해서 이를 수신한 시각(

)의 차이를 카메라 컨트롤러(100)에서 확인하는 방식이다. 하지만, 지연 시간이 촬영 명령어가 카메라 1로 전달되는 과정에 의해 발생했는지 카메라 1의 촬영 명령어에 대한 응답에 의해 발생했는지 판단이 불가능하다. 또한, 지연 시간이 요구 조건(②)에 만족한다 하더라도 무선 환경의 차이에 따른 불확실성이 높아 동기화 판단은 불가능하다. In the case of ②, the absolute time (

) and the time (

) is a method of checking the difference in the camera controller 100 . However, it is impossible to determine whether the delay time is caused by a process in which the shooting command is transmitted to the camera 1 or is caused by the response to the shooting command of the camera 1. In addition, even if the delay time satisfies the requirement (②), it is impossible to determine the synchronization due to the high uncertainty due to the difference in the wireless environment.

시각 이후, 카메라 1이 실제 촬영하는 시각은

+

이다. 문제는 지연 시간(

)이 각 카메라마다 동일하지 않다.On the other hand, even if the shooting command is transmitted to each camera at the same time by solving the network problem, synchronization is not possible due to the internal delay of each camera. Referring to FIG. 1D , the camera 1 receives a shooting command for starting shooting.

After the time, the time at which camera 1 actually shoots is

+

to be. The problem is the latency (

) is not the same for each camera.

Meanwhile, communication with the camera controller is essential for shooting synchronization in a wireless environment. In order to communicate with the camera controller, each camera must connect to the AP device. Accordingly, each camera is inevitably limited to a distance that must be located within an accessible distance to the AP device.

Japanese Laid-Open Patent Publication No. 2006-227245 (published on August 31, 2006)

The present invention is to solve the problems of the prior art described above, and to perform synchronization between a plurality of cameras connected wirelessly. Specifically, the present invention intends to perform synchronization between cameras based on whether the network between the cameras is valid and whether the internal frame of the camera is valid.

However, the technical problems to be achieved by the present embodiment are not limited to the technical problems described above, and other technical problems may exist.

As a technical means for achieving the above technical problem, the camera performing synchronization between a plurality of cameras according to the first aspect of the present invention is a first synchronization signal and a second synchronization signal generated based on a preset period from a main camera a receiving unit for receiving; a first determination unit configured to determine network validity between the main camera and the camera based on a reception time of the first synchronization signal and a reception time of the second synchronization signal; and a second determination unit that determines the validity of the internal frame of the camera based on the initial frame generation time.

A method for performing synchronization between a plurality of cameras performed by a camera according to a second aspect of the present invention comprises: receiving a first synchronization signal and a second synchronization signal generated based on a preset period from a main camera; determining network validity between the main camera and the camera based on a reception time of the first synchronization signal and a reception time of the second synchronization signal; and determining the validity of the internal frame of the camera based on the initial frame generation time.

A computer program stored in a computer-readable recording medium including a sequence of instructions for performing synchronization between a plurality of cameras by a camera according to the third aspect of the present invention is executed by a computing device based on a preset period from the main camera to receive a first synchronization signal and a second synchronization signal generated by and a sequence of instructions for determining the validity of the internal frame of the camera based on the initial frame generation time.

The above-described problem solving means are merely exemplary, and should not be construed as limiting the present invention. In addition to the exemplary embodiments described above, there may be additional embodiments described in the drawings and detailed description.

According to any one of the above-described problem solving means of the present invention, the present invention can perform synchronization between a plurality of cameras connected wirelessly. Specifically, the present invention may perform synchronization between cameras based on whether the network between cameras is valid and whether the internal frame of the camera is valid.

1A to 1D are diagrams for explaining a conventional camera synchronization method.
2 is a block diagram of a camera, according to an embodiment of the present invention.
3A to 3B are diagrams illustrating an environment configuration for camera synchronization according to an embodiment of the present invention.
4 is a diagram illustrating a camera synchronization sequence according to an embodiment of the present invention.
5 is a flowchart illustrating a camera synchronization method according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. However, the present invention may be embodied in several different forms and is not limited to the embodiments described herein. And in order to clearly explain the present invention in the drawings, parts irrelevant to the description are omitted, and similar reference numerals are attached to similar parts throughout the specification.

Throughout the specification, when a part is "connected" with another part, this includes not only the case of being "directly connected" but also the case of being "electrically connected" with another element interposed therebetween. . Also, when a part "includes" a certain component, it means that other components may be further included, rather than excluding other components, unless otherwise stated.

In this specification, a "part" includes a unit realized by hardware, a unit realized by software, and a unit realized using both. In addition, one unit may be implemented using two or more hardware, and two or more units may be implemented by one hardware.

Some of the operations or functions described as being performed by the terminal or device in this specification may be instead performed by a server connected to the terminal or device. Similarly, some of the operations or functions described as being performed by the server may also be performed in a terminal or device connected to the corresponding server.

Hereinafter, detailed contents for carrying out the present invention will be described with reference to the accompanying configuration diagram or process flow diagram.

2 is a block diagram of a camera 20, according to an embodiment of the present invention.

Referring to FIG. 2 , the camera 20 may include a receiving unit 200 , a first determining unit 210 , a second determining unit 220 , a third determining unit 230 , and a transmitting unit 240 . . However, the camera 20 shown in FIG. 2 is only one embodiment of the present invention, and various modifications are possible based on the components shown in FIG. 2 .

Hereinafter, FIG. 2 will be described with reference to FIGS. 3A to 4 .

The present invention can configure an environment in which a plurality of cameras can be connected to each AP device based on a preset number of camera connections for each of the plurality of AP devices, as shown in FIG. 3A for synchronizing cameras. Referring to FIG. 3A , when the camera controller 100 accesses the first AP device, the first AP device and each other AP device communicating with the first AP device are connected to the camera controller 100 by wire. ) can be relayed to communicate with By placing several AP devices in this way, it is possible to escape from the limitation of the distance due to the installation.

The plurality of cameras may be grouped into a plurality of groups according to preset criteria in the form of a hierarchical structure. In this case, a camera belonging to a group corresponding to the uppermost layer serves as a reference for synchronization.

For example, referring to FIGS. 3A and 3B together, {camera 1} may be included in the group corresponding to the first layer. Here, camera 1 belonging to the first layer may be set as a main camera for synchronization between cameras.

A group corresponding to the second layer mapped to camera 1 may include {camera 2, camera 3}.

Here, camera 1 corresponding to the main camera may be included in a group corresponding to an upper layer, and {camera 2, camera 3} may be included in a group corresponding to a lower layer of the layer to which camera 1 belongs.

The group corresponding to the third layer mapped to camera 2 includes {camera 4, camera 5, camera 6}, and the group corresponding to the third layer mapped to camera 3 includes {camera 7, camera 8, camera 9} may be included.

Here, {camera 4, camera 5, camera 6} and {camera 7, camera 8, camera 9} may be included in a group corresponding to a lower layer of a layer belonging to {camera 2, camera 3}.

The synchronization criterion of {camera 2, camera 3} belonging to the second layer is based on a synchronization signal generated by {camera 1} belonging to the first layer. The synchronization criteria of {camera 4, camera 5, camera 6} and {camera 7, camera 8, camera 9} belonging to the third layer are based on the synchronization signal generated by {camera 2, camera 3} belonging to the second layer do.

After synchronization between the first layer and the second layer, synchronization between the second layer and the third layer may be performed.

Hereinafter, with reference to FIGS. 2 and 3B together, the main camera is camera 1, the camera 20 is camera 2, and at least one companion camera in the lower layer mapped with the camera 20 is named camera 4 and described. decide to do

The receiver 200 may receive the first synchronization signal and the second synchronization signal generated based on a preset period from the camera 1 corresponding to the main camera. Here, the camera 1 may be included in the group corresponding to the first layer, and the camera 20 (camera 2) may be included in the group corresponding to the second layer, which is a lower layer of the first layer.

In a wireless network environment, synchronization between camera 1 and camera 2 can be performed only when camera 1 transmits a synchronization signal to camera 2 without delay.

To this end, the first determination unit 210 may determine whether the network is valid for confirming that there is no delay in reception of the synchronization signal on the wireless network.

Specifically, the first determination unit 210 determines the network validity between the camera 1 (main camera) and the camera 2 (camera 20) based on the reception time for the first synchronization signal and the reception time for the second synchronization signal. can judge about it.

) 및 제 2 동기화 신호에 대한 전송 시각(

)은 예를 들어 [수학식 1]과 같이 나타낼 수 있다. 1c, when camera 1 transmits the first synchronization signal and the second synchronization signal to the camera 2 every 1/fps period, the transmission time for the first synchronization signal (

) and the transmission time for the second synchronization signal (

) can be expressed as, for example, [Equation 1].

[Equation 1]

)을 획득할 수 있다. 예를 들어, 동기화 신호의 수신 간격은 [수학식 2] 및 [수학식 3]를 통해 계산될 수 있다. The first determination unit 210 is a synchronization signal reception interval (

) can be obtained. For example, the reception interval of the synchronization signal may be calculated through [Equation 2] and [Equation 3].

[Equation 2]

[Equation 3]

The first determination unit 210 may determine whether the difference value between the reception time for the first synchronization signal and the reception time for the second synchronization signal is less than or equal to a preset threshold to check the network validity between the camera 1 and the camera 2 have. Here, the threshold value may be set based on the delay time of the synchronization signal.

For example, when the difference value between the reception time for the first synchronization signal and the reception time for the second synchronization signal is smaller than a preset threshold value, the first determination unit 210 determines the network validity between the camera 1 and the camera 2 can admit

Thereafter, when it is determined that the network validity between the camera 1 and the camera 2 is recognized, the camera 2 may start shooting.

)이 카메라 2의 고유 특성 또는 실제 동기화 명령의 순간에 따라 다른 값을 가지게 된다. 카메라 2의 동기화를 위해서는 예를 들어 [수학식 4]와 같은 조건을 만족해야 한다. On the other hand, due to the internal factors of Camera 2, the first frame creation time (

) will have different values depending on the intrinsic characteristics of Camera 2 or the instant of the actual synchronization command. For synchronization of camera 2, for example, conditions such as [Equation 4] must be satisfied.

[Equation 4]

The second determination unit 220 may determine the validity of the internal frame of the camera 2 based on the initial frame generation time.

The second determination unit 220 derives the first frame generation time from the start of shooting, and determines whether the derived first frame generation time corresponds to a multiple of a preset number of frames per second (FPS, Frame Per Second), You can check the validity of the inner frame.

If the multiple of the preset number of frames per second does not have a natural number, the photographing of the camera 2 may be stopped.

For example, when the initial frame generation time corresponds to a multiple of a preset number of frames per second, the second determiner 220 may recognize the validity of the internal frame of the camera 2 .

When it is determined that the validity of the internal frame of the camera 2 is recognized, the transmitter 240 may transmit a synchronization signal to at least one companion camera (camera 4) mapped with the camera 2 . Here, camera 4 may be included in a group corresponding to a lower layer of the group including camera 2 .

Meanwhile, the overall synchronization sequence among a plurality of cameras having a hierarchical structure is shown in FIG. 4 . Referring to FIG. 4 , camera 1 (main camera) belonging to the first layer operates in an on state, and periodically generates synchronization signals (first synchronization signal and second synchronization signal) accordingly It is transmitted to camera 2 and camera 3 belonging to layer 2.

Each of the cameras 2 and 3 belonging to the second layer may check the network validity with the camera 1 based on the reception time for the first synchronization signal and the reception time for the second synchronization signal received from the camera 1 .

When the network validity with the camera 1 is confirmed, each of the cameras 2 and 3 belonging to the second layer may set the camera operation state to an on state and start shooting.

Each of the cameras 2 and 3 belonging to the second layer may determine the validity of the internal frame by determining whether the initial frame generation time derived from the start time of shooting corresponds to a multiple of a preset number of frames per second (FPS).

When each of camera 2 and camera 3 belonging to the second layer checks the validity of the internal frame, camera 2 periodically sends a synchronization signal (third synchronization signal, fourth synchronization signal) to each of camera 4, camera 5, and camera 6 mapped with camera 2 signal), and the camera 3 may periodically transmit a synchronization signal (a third synchronization signal and a fourth synchronization signal) to each of the cameras 7 , 8 , and 9 mapped to the camera 3 .

Each of the cameras 4, 5, and 6 belonging to the third layer may check network validity with the camera 2 based on the reception time of the third synchronization signal and the reception time of the fourth synchronization signal.

Each of the cameras 7, 8, and 9 belonging to the third layer may check network validity with the camera 3 based on the reception time of the third synchronization signal and the reception time of the fourth synchronization signal.

When the network validity with the camera 2 is confirmed, each of the cameras 4, 5, and 6 belonging to the third layer may set the camera operation state to an on state and start shooting.

Each of the cameras 4, 5, and 6 belonging to the third layer may determine the validity of the internal frame by determining whether the initial frame generation time derived from the start of shooting corresponds to a multiple of a preset number of frames per second (FPS).

When the network validity with the camera 3 is confirmed, each of the cameras 7, 8, and 9 belonging to the third layer may set the camera operation state to an on state and start shooting.

Each of the cameras 7, 8, and 9 belonging to the third layer may check the validity of the internal frame by determining whether the initial frame generation time derived from the start of shooting corresponds to a multiple of a preset number of frames per second (FPS).

Meanwhile, the third determination unit 230 may determine the synchronization validity between the camera 1 and the camera 2 based on the reception time of the synchronization validity command transmitted from the camera 1 and the frame generation time in the camera 2 .

After determining the network validity between the camera 1 and the camera 2 and the internal frame validity of the camera 2 (pre-synchronization process) is finished, the third determination unit 230 aperiodically performs the camera 1 and the camera 2 while shooting, respectively. It is possible to determine the synchronization validity between the cameras 2 (post-synchronization process).

) 및 카메라 1로부터 수신된 동기 유효성 명령을 수신한 수신 시각(

) 간의 차이값을 도출하고, 도출된 차이값이 임계 시간값(

) 이하인지 여부를 할 수 있다. 도출된 차이값이 임계 시간값(

) 이내인 경우, 제 3 판단부(230)는 카메라 1 및 카메라 2 간에 동기화가 수행되었다고 판단할 수 있다. For example, when receiving the synchronization validity command including the generation time of the 31st frame generated by the camera 1, the third determination unit 230 is the generation time of the 31st frame generated by the camera 2 (

) and the reception time (

), and the derived difference value is the critical time value (

) or not. The derived difference value is the critical time value (

), the third determination unit 230 may determine that synchronization has been performed between the camera 1 and the camera 2 .

Meanwhile, for those skilled in the art, each of the receiving unit 200, the first determining unit 210, the second determining unit 220, the third determining unit 230, and the transmitting unit 240 is implemented separately, or at least one of them It will be fully understood that this may be integrated and implemented.

5 is a flowchart illustrating a camera synchronization method according to an embodiment of the present invention.

Referring to FIG. 5 , in step S501 , the main camera 50 may transmit a first synchronization signal generated based on a preset period to the camera 20 .

In step S503 , the main camera 50 may transmit a second synchronization signal generated based on a preset period to the camera 20 .

In step S505, the camera 20 determines the network validity between the main camera 50 and the camera 20 based on the reception time for the first synchronization signal and the reception time for the second synchronization signal received from the main camera 50. can judge

When the network validity between the main camera 50 and the camera 20 is recognized in step S507, the camera 20 may start shooting in step S509.

In step S511, the camera 20 derives the first frame generation time from the start time of shooting, and determines whether the derived first frame generation time corresponds to a multiple of a preset number of frames per second to check the validity of the internal frame of the camera 20 can

When the validity of the internal frame of the camera 20 is recognized in step S513 , the camera 20 may transmit a synchronization success message to the main camera 50 in step S515 .

In step S517 , when the validity of the internal frame of the camera 20 is recognized, the camera 20 may transmit a synchronization signal to the camera 20 and the mapped fellow camera 52 .

In step S519, the camera 20 may enter the standby mode if the network validity between the main camera 50 and the camera 20 is not recognized.

In step S521 , the camera 20 may change the camera operation state to an off state when the validity of the internal frame of the camera 20 is not recognized.

In the above description, steps S501 to S521 may be further divided into additional steps or combined into fewer steps, according to an embodiment of the present invention. In addition, some steps may be omitted if necessary, and the order between steps may be changed.

An embodiment of the present invention may also be implemented in the form of a recording medium including instructions executable by a computer, such as a program module executed by a computer. Computer-readable media can be any available media that can be accessed by a computer and includes both volatile and nonvolatile media, removable and non-removable media. Also, computer-readable media may include all computer storage media. Computer storage media includes both volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules or other data.

The foregoing description of the present invention is for illustration, and those of ordinary skill in the art to which the present invention pertains can understand that it can be easily modified into other specific forms without changing the technical spirit or essential features of the present invention. will be. Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive. For example, each component described as a single type may be implemented in a distributed manner, and likewise components described as distributed may also be implemented in a combined form.

The scope of the present invention is indicated by the following claims rather than the detailed description, and all changes or modifications derived from the meaning and scope of the claims and their equivalent concepts should be construed as being included in the scope of the present invention. .

20: camera
200: receiver
210: first judgment unit
220: second judgment unit
230: third judgment unit
240: transmission unit

Claims (19)

A camera performing synchronization between a plurality of cameras, the camera comprising:
a receiver configured to receive a first synchronization signal and a second synchronization signal generated based on a preset period from the main camera;
a first determination unit configured to determine network validity between the main camera and the camera based on a reception time of the first synchronization signal and a reception time of the second synchronization signal; and
A second determination unit that determines the validity of the internal frame of the camera based on the initial frame generation time
which includes, a camera.
The method of claim 1,
The first determination unit determines whether a difference value between the reception time for the first synchronization signal and the reception time for the second synchronization signal is less than or equal to a preset threshold to check the network validity between the main camera and the camera, ,
wherein the threshold is set based on the delay time of the synchronization signal.
3. The method of claim 2,
The camera starts shooting when it is determined that the network validity between the main camera and the camera is recognized.
4. The method of claim 3,
The second determination unit derives the first frame generation time from the start time of the shooting,
The camera is to check the validity of the internal frame by determining whether the first frame generation time corresponds to a multiple of a preset number of frames per second (FPS, Frame Per Second).
5. The method of claim 4,
When it is determined that the validity of the internal frame is recognized, a transmission unit that transmits a synchronization signal to at least one fellow camera mapped with the camera
Which will further include a camera.
The method of claim 1,
A third determination unit that determines the validity of synchronization between the main camera and the camera based on a reception time of the synchronization validity command transmitted from the main camera and a frame generation time in the camera
Which will further include a camera.
6. The method of claim 5,
The plurality of cameras will be grouped into a plurality of groups according to a preset criterion in a hierarchical structure form.
8. The method of claim 7,
The main camera is included in the group corresponding to the upper layer,
The camera will be included in a group corresponding to a lower layer of the upper layer, the camera.
8. The method of claim 7,
The camera of claim 1, wherein the fellow camera is included in a group corresponding to a lower layer of the group including the camera.
A method of performing synchronization between a plurality of cameras performed by a camera, the method comprising:
Receiving a first synchronization signal and a second synchronization signal generated based on a preset period from the main camera;
determining network validity between the main camera and the camera based on a reception time of the first synchronization signal and a reception time of the second synchronization signal; and
Determining the validity of the internal frame of the camera based on the initial frame generation time
A method for performing synchronization, comprising:
11. The method of claim 10,
The step of determining the network validity between the main camera and the camera comprises:
determining whether a difference value between the reception time for the first synchronization signal and the reception time for the second synchronization signal is less than or equal to a preset threshold value to check network validity between the main camera and the camera;
Wherein the threshold is set based on a delay time of the synchronization signal.
12. The method of claim 11,
Initiating shooting when it is determined that the network validity between the main camera and the camera is recognized
Which will further include, a method of performing synchronization.
13. The method of claim 12,
The step of determining the validity of the internal frame of the camera is
deriving the first frame generation time from the starting point of the photographing;
and determining whether the initial frame generation time corresponds to a multiple of a preset number of frames per second (FPS) and checking the validity of the internal frame.
14. The method of claim 13,
When it is determined that the validity of the internal frame is recognized, transmitting a synchronization signal to at least one fellow camera mapped with the camera;
Which will further include, a method of performing synchronization.
11. The method of claim 10,
Determining the validity of synchronization between the main camera and the camera based on the reception time of the synchronization validity command transmitted from the main camera and the frame generation time in the camera
Which will further include, a method of performing synchronization.
15. The method of claim 14,
The method of performing synchronization, wherein the plurality of cameras are grouped into a plurality of groups according to a preset criterion in a hierarchical structure.
17. The method of claim 16,
The main camera is included in the group corresponding to the upper layer,
The method of performing synchronization, wherein the camera is included in a group corresponding to a lower layer of the upper layer.
17. The method of claim 16,
The method for performing synchronization, wherein the fellow camera is included in a group corresponding to a lower layer of the group including the camera.
A computer program stored in a computer-readable recording medium including a sequence of instructions for performing synchronization between a plurality of cameras by a camera, the computer program comprising:
When the computer program is executed by a computing device,
Receive a first synchronization signal and a second synchronization signal generated based on a preset period from the main camera,
Determine the network validity between the main camera and the camera based on the reception time for the first synchronization signal and the reception time for the second synchronization signal,
A computer program stored on a computer-readable medium, comprising a sequence of instructions for determining the validity of an internal frame of the camera based on an initial frame generation time.

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