JP2006217326A - Network camera system, camera apparatus and method for synchronizing picture - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a network camera system, camera apparatuses and a method for synchronizing pictures where pictures photographed respectively by a plurality of camera apparatuses can be synchronized with each other without regard to a communication status of a communication network in the case of transmitting the pictures photographed by the plurality of camera apparatuses to a separated place through the communication network. <P>SOLUTION: The plurality of camera apparatuses 2 and 3 obtain reference time information through the communication network, synchronize time of an internal clock of one camera apparatus 2 or 3 with that of the other camera apparatus 3 or 2 based on the obtained reference time information, photograph each picture frame at the same timing as that of the other camera apparatus 3 or 2 based on the time of the internal clock, and transmit data of each photographed picture frame to a video recorder 1 through the communication network. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a network camera system, a camera device, and an image synchronization method for transmitting images taken by a plurality of camera devices to a place separated by a communication network.

  Conventionally, an analog transmission method and a digital transmission method are known as methods for transmitting images taken by a plurality of surveillance cameras to a remote place. As shown in FIG. 5, in the analog transmission system, analog video signals of, for example, NTSC (National Television Standards Committee) system, which are captured by a plurality of analog cameras 101 and 102, are transmitted to a recording unit 100 at a remote location. In this case, the image frames of the analog cameras 101 and 102 are inevitably recorded in synchronization with the clock frequency of the recording unit 100 of the transmission destination, so that the time axis of the video shot by the analog cameras 101 and 102 is shifted. The problem does not occur.

  On the other hand, as shown in FIG. 6, in the digital transmission method, each image frame photographed as digital data by the digital cameras 201 and 202 is transmitted to the remote recording unit 200, and each transmission destination recording unit 200 transmits each image frame. The image frame is recorded as it is (see Patent Document 1 for an example of another digital transmission method). At this time, due to the difference in the transmission path, the arrival time of the data of each image frame of each digital camera 201, 202 to the recording unit 200 may be different, and the time axis of each video may be shifted.

  For example, as shown in FIG. 6, when the digital camera 201 and the recording unit 200 are connected by a wireless network 203 and the digital camera 202 and the recording unit 200 are connected by a wired network 204, the electronic camera If a device that generates an interference wave such as the range 205 exists nearby, a communication failure may occur in the wireless network 203, and it may take time for each image frame of the digital camera 201 to reach the recording unit 200.

  That is, even if each image frame is photographed at the same timing by the digital cameras 201 and 202, as shown in FIG. 7, until each image frame reaches the recording unit 200 from each digital camera 201 and 202. A time difference occurs. Therefore, when each image frame of each digital camera 201, 202 is recorded with reference to the internal clock of the recording unit 200, a shift occurs in each image frame recorded in the recording unit 200.

On the other hand, when recording each image frame of each digital camera 201, 202 with the internal clock of the digital camera 201, 202 as a reference, transmission is performed by attaching time information to each captured image frame and transmitting it to the recording unit 200. It is possible to prevent a shift of each image frame due to a difference in path. However, when the internal clocks of the digital cameras 201 and 202 are deviated from each other, even if each image frame is actually captured at the same timing, a deviation occurs by the time difference between the internal clocks (see FIG. 8). ).
JP-A-8-171691

  Therefore, in the present invention, when images captured by a plurality of camera devices are transmitted to a place distant by a communication network, images captured by each camera device can be synchronized regardless of the communication status of the communication network. An object of the present invention is to provide a network camera system, a camera device, and an image synchronization method that can be used.

  In order to solve the above-described problem, the present invention provides a plurality of camera devices that acquire reference time information via a communication network, and synchronize the time of the internal clock with other camera devices based on the acquired reference time information. Each image frame is captured at the same timing as other camera devices with reference to the time of the internal clock, and the data of each captured image frame is transmitted to the recording device via a communication network.

  According to the present invention, the data of each image frame captured at the same timing is synchronized with the time of the internal clocks of the plurality of camera devices, and is transmitted to the recording device. It is possible to record images captured by each camera device in synchronization.

  A first invention of the present application includes a recording device that records image data, and a plurality of camera devices connected to the recording device via a communication network. The camera device receives reference time information via the communication network. Means for acquiring, synchronization means for synchronizing the time of the internal clock with other camera devices based on the acquired reference time information, and taking each image frame at the same timing as other camera devices based on the time of the internal clock A network camera system having imaging means for performing transmission, and transmission means for transmitting data of each image frame taken by the imaging means to a recording apparatus via a communication network. According to the present invention, the data of each image frame captured at the same timing is synchronized with the time of the internal clocks of the plurality of camera devices, and is transmitted to the recording device. It is possible to record images captured by each camera device in synchronization.

  According to a second aspect of the present invention, there is provided a network camera system in which the camera device acquires the reference time information by referring to a time server that provides the reference time information by a network time protocol (NTP). According to the present invention, it is possible to synchronize the times of the internal clocks of a plurality of camera devices by referring to the reference time information of the time server by the network time protocol.

  A third invention of the present application is the network camera system in which the synchronization means sets the time of the internal clock for each update interval calculated from the frame rate, the clock frequency accuracy, and the frame shift target accuracy. According to the present invention, it is possible to maintain the shift of each image frame within the set frame shift target accuracy according to the frame rate and clock frequency accuracy of the camera device.

  In the fourth invention of the present application, when the update interval is Rf (frame / second), the clock frequency accuracy is Rc, and the frame shift target accuracy is A, T = A / (2 × Rc × Rf) This is a network camera system with an interval less than the required time. According to the present invention, it is possible to maintain the shift of each image frame within the set frame shift target accuracy A according to the frame rate Rf (frame / second) and the clock frequency accuracy Rc of the camera device.

  A fifth aspect of the present invention is a network camera system in which the camera device has means for providing the acquired reference time information to another camera device. According to the present invention, the time of the internal clock of the other camera device is synchronized with the time of the internal clock of one camera device among the plurality of camera devices, and each image photographed at the same timing by these camera devices. Since the frame is transmitted to the recording device, it is possible to record the images captured by the plurality of camera devices in synchronization with each other regardless of the communication status of the communication network.

  A sixth aspect of the present invention is a network camera system in which the transmission means transmits the data of each image frame and the time data when each image frame is taken to the recording apparatus as one package. According to the present invention, since the recording apparatus can record the data of each image frame based on the time data when each image frame is captured, the timing of each image frame does not conflict.

  A seventh invention of the present application is a camera device connected to a recording device for recording image data via a communication network, the means for acquiring reference time information via the communication network, and the acquired reference time information A synchronization unit that synchronizes the time of the internal clock with the other camera device based on the time, a photographing unit that photographs each image frame at the same timing as the other camera device based on the time of the internal clock, and each of the images captured by the photographing unit It is a camera device having transmission means for transmitting image frame data to a recording device via a communication network. According to the camera device of the present invention, the time of the internal clocks of a plurality of camera devices can be synchronized with each other so that each image frame can be captured and transmitted to the recording device at the same timing. Instead, it is possible to record images captured by a plurality of camera devices in a synchronized manner.

  An eighth invention of the present application is an image synchronization method by a network camera system including a recording device for recording image data and a plurality of camera devices connected to the recording device via a communication network. Acquires the reference time information via the communication network, the camera device synchronizes the time of the internal clock with other camera devices based on the acquired reference time information, and the camera device uses the time of the internal clock as a reference. The image synchronization method is characterized in that each image frame is captured at the same timing as other camera devices, and the camera device transmits data of each captured image frame to the recording device via a communication network. According to the present invention, the time of the internal clocks of a plurality of camera devices can be synchronized with each other, and each image frame can be captured and transmitted to the recording device at the same timing. It is possible to record images captured by each camera device in synchronization.

  Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment)
FIG. 1 is a schematic configuration diagram of a network camera system according to an embodiment of the present invention.

  In FIG. 1, the network camera system in the embodiment of the present invention comprises a recording device 1 for recording image data, and a plurality of camera devices 2 and 3 connected to the recording device 1 via a communication network. The The recording device 1 and the camera devices 2 and 3 are connected via a router device 4 and the Internet 5 as a communication network.

  In the present embodiment, it is assumed that the camera device 2 and the router device 4 are connected by a wireless LAN (local area network) 6 as a communication network. The camera device 3 and the router device 4 are connected by a wired LAN 7 as a communication network.

  FIG. 2 is a block diagram of the recording device 1 and the camera devices 2 and 3 of FIG.

  As shown in FIG. 2, the recording apparatus 1 includes a storage unit 10 such as a hard disk or a flash memory, and a recording unit 11 that records image data in the storage unit 10. The recording apparatus 1 also has a time server function 12 that provides reference time (time) information by NTP (Network Time Protocol).

  The camera device 2 includes a time information acquisition unit 21 that acquires reference time information from the recording device 1, a synchronization unit 22 that sets the internal clock 20 based on the reference time information acquired by the time information acquisition unit 21, and an internal clock 20 The image capturing means 23 for capturing each image frame at a predetermined timing based on the time of the image, the temporary storage means 24 as a buffer for temporarily storing the data of each image frame captured by the image capturing means 23, and the image capturing means 23 Transmission means 25 for transmitting the data of each image frame to the recording apparatus 1.

  The synchronization unit 22 sets the internal clock 20 based on the reference time information acquired by the time information acquisition unit 21 in order to synchronize the internal clock 20 with another camera device (for example, the camera device 3). At this time, the synchronization unit 22 updates the update interval T calculated by the following equation (1) from the frame rate Rf (frame / second), the clock frequency accuracy Rc, and the frame shift target accuracy A of each image frame captured by the imaging unit 23. Every time (seconds), the time information acquisition means 21 acquires accurate reference time information and sets the time of the internal clock.

T = A ÷ (2 × Rc × Rf) (1)
The reason why “2” is entered in the denominator of the expression (1) is that when the internal clocks of the camera devices 2 and 3 are shifted in the opposite directions (forward and backward directions), the time difference is double. It is to become.

  For example, when the frame rate Rf = 30 (frames / second), the clock frequency accuracy Rc = 100 (ppm), and the frame shift target accuracy A = 5 (%), the update interval T is T = 0.05 ÷ (2 × 0.0001 × 30) = 8.3333 (seconds).

  The frame shift target accuracy A is set with a target of what percentage of the frame interval the frame shift is allowed (see FIG. 3B). The update interval may be smaller than T calculated by Expression (1). When the update interval is smaller than T, the actual frame shift accuracy is realized with higher accuracy than the target value.

  The photographing unit 23 photographs each image frame at the same timing as the other camera device 3 with reference to the time of the internal clock 20 synchronized with the other camera device 3 by the synchronization unit 22. This is because the timing for driving the photographing means 23 is unified between the camera devices 2 and 3 even if the internal clock 20 synchronized with each other between the camera devices 2 and 3 records the frame photographing date and time without any deviation in the time axis. Otherwise, the maximum deviation of half the frame period occurs (see FIG. 3A).

  The photographing unit 23 stores the data of each captured image frame and information (time data) indicating the shooting date and time when each image frame was captured in the temporary storage unit 24 as one package. For example, when the data of each captured image frame is a still image file, information indicating the shooting date and time is embedded in the header information portion of the image file. Alternatively, an image file name including shooting order information may be used, and the shooting time interval and the shooting date and time of the first frame may be stored as separate files. In addition, the shooting date and time may be recorded not only at the first frame but every plural frames.

  The transmission means 25 transmits the data of each image frame imaged by the imaging means 23 and stored in the temporary storage means 24 to the recording device 1 as needed. Since the data of each image frame is temporarily stored in the temporary storage means 24 and then transmitted, all the image frames photographed by the photographing means 23 are transmitted to the recording device 1 as long as the temporary storage means 24 is not full. Is done. As the still image file, specifically, a file in JPEG (Joint Photographic Experts Group) format or the like can be used.

  The camera device 3 has the same configuration as the camera device 2.

  In the network camera system configured as described above, the synchronization means 22 of the camera apparatuses 2 and 3 acquire accurate reference time information from the recording apparatus 1 by the time information acquisition means 21 at each update interval T (seconds). The time of the internal clock 20 is synchronized. As a result, photographing is performed at the same timing by the respective photographing means 23 of each camera device 2, 3, and data of each photographed image frame is transmitted to the recording device 1 by the transmission means 25 and stored by the recording means 11. Recorded in means 10.

  Since the data of each image frame recorded in this manner is taken by the camera devices 2 and 3 based on the time of the internal clock 20 synchronized with each other, the wireless LAN 6 of the camera device 2 and the camera device 3 Regardless of the communication status of the wired LAN 7, the time axis of each image frame is not shifted.

  In the present embodiment, the recording device 1 is arranged outside the wireless LAN 6 and the wired LAN 7 constituted by the router device 4, that is, on the WAN (wide area network) side. The wireless LAN 6 and the wired LAN 7 side may be arranged. The time server function 12 may be provided in the router device 4. Alternatively, one of the plurality of camera devices 2 and 3 may include a time server function 12 that provides the reference time information acquired by the time information acquisition unit 21 to the other camera devices 2 and 3.

  Next, the case where the image photographed by the photographing unit 23 is a video in a format (for example, MPEG (Moving Picture Experts Group) format) in which a plurality of image frames are stored in the temporary storage unit 24 as one file will be described. .

  As shown in FIG. 4 (a), one image frame of an MPEG video has only an "I picture" of the compressed single image and a difference signal of a portion different from the previous I picture. There are three types of data: a “picture” and a “B picture” that predicts motion based on the preceding and following I and P pictures and fills in the gaps. In this case, the transmission means 25 transmits the data (moving image file) of each image frame composed of a plurality of pictures and the time data (shooting date / time file) of shooting the I picture of each image frame to the recording apparatus 1 as one package. .

  FIG. 4B shows the contents of the shooting date file. As shown in the drawing, a list of I picture shooting date and time of each image frame is recorded in the shooting date and time file. Further, as shown in FIG. 4C, the storage unit 10 of the recording apparatus 1 records a moving image file (for example, CAM1_001.mpeg) and a shooting date / time file (for example, CAM1_001.tim) as one package. The

  It is not necessary to record the shooting date and time of all I pictures. The picture for recording the shooting date and time may be other than the I picture. The video may be in a format other than the MPEG format. Also, the moving image file and the shooting date / time file need not be separate files, and may be a single file. In short, it suffices if the shooting date and time of each image frame is recorded in a format that can be read out when reproducing a moving image.

  INDUSTRIAL APPLICABILITY The present invention is useful as a network camera system, a camera device, and an image synchronization method that transmit images taken by a plurality of camera devices to a place separated by a communication network. In particular, according to the present invention, when images taken by a plurality of camera devices are transmitted to a place separated by a communication network, the images taken by each camera device can be synchronized regardless of the communication status of the communication network. It is suitable as a simple network camera system, camera device, and image synchronization method.

Schematic configuration diagram of a network camera system in an embodiment of the present invention 1 is a block diagram of the recording device and camera device of FIG. (A) The figure which shows a mode that the shift | offset | difference of the half of a frame period generate | occur | produced, (b) The figure which shows a frame shift | offset | difference target precision. (A) The figure which shows the structure of the MPEG moving picture file, (b) The figure which shows the contents of the photographing date file, (c) The figure which shows the moving picture file recorded as one package and the photographing date file The figure which shows the example which transmits the image image | photographed with the some surveillance camera to the place distant by the analog transmission system The figure which shows the example which transmits the image image | photographed with several surveillance cameras to the place distant by a digital transmission system The figure which shows a mode that the image image | photographed with several surveillance cameras shifts by the problem of a transmission path. The figure which shows a mode that the image image | photographed with several surveillance cameras shifts by the problem of the internal clock of the surveillance camera

Explanation of symbols

1 Recording device 2, 3 Camera device 4 Router device 5 Internet 6 Wireless LAN
7 Wired LAN
DESCRIPTION OF SYMBOLS 10 Memory | storage means 11 Recording means 12 Time server function 20 Internal clock 21 Time information acquisition means 22 Synchronization means 23 Imaging | photography means 24 Temporary storage means 25 Transmission means

Claims (8)

A recording device that records image data, and a plurality of camera devices connected to the recording device via a communication network,
The camera device is
Means for obtaining reference time information via the communication network;
Synchronization means for synchronizing the time of the internal clock with another camera device based on the acquired reference time information;
Photographing means for photographing each image frame at the same timing as other camera devices based on the time of the internal clock;
A network camera system comprising: transmission means for transmitting data of each image frame photographed by the photographing means to the recording device via the communication network. The network camera system according to claim 1, wherein the camera device acquires the reference time information by referring to a time server that provides the reference time information using a network time protocol. 3. The network camera system according to claim 1, wherein the synchronization means sets the time of an internal clock for each update interval calculated from a frame rate, a clock frequency accuracy, and a frame shift target accuracy. . The update interval is an interval equal to or shorter than the time obtained by T = A / (2 × Rc × Rf), where Rf (frame / second) is the frame rate, Rc is the clock frequency accuracy, and A is the frame shift target accuracy. The network camera system according to claim 3, wherein: 5. The network camera system according to claim 1, wherein the camera device has means for providing the acquired reference time information to another camera device. 6. 6. The transmission unit according to claim 1, wherein the transmission unit transmits the data of each image frame and time data of capturing each image frame to the recording apparatus as one package. Network camera system. A camera device connected via a communication network to a recording device for recording image data,
Means for obtaining reference time information via the communication network;
Synchronization means for synchronizing the time of the internal clock with another camera device based on the acquired reference time information;
Photographing means for photographing each image frame at the same timing as other camera devices based on the time of the internal clock;
And a transmission unit configured to transmit data of each image frame photographed by the photographing unit to the recording device via the communication network. An image synchronization method by a network camera system comprising a recording device for recording image data and a plurality of camera devices connected to the recording device via a communication network,
The camera device acquires reference time information via the communication network,
The camera device synchronizes the time of the internal clock with other camera devices based on the acquired reference time information,
The camera device shoots each image frame at the same timing as other camera devices based on the time of the internal clock,
The image synchronization method, wherein the camera device transmits data of each captured image frame to the recording device via the communication network.

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