Camera system and method for controlling the camera system

Abstract

To provide a camera system capable of preventing data loss and problems such as video stopping on the monitor due to data loss.SOLUTION: The camera system includes multiple cameras. The multiple cameras output video data in GOP format. The multiple camera outputs video data whose I-frame generation timings do not overlap with each other.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a camera system and a method for controlling a camera system. [Background technology]

[0002] Ensuring the safety of passengers when getting on and off trains is an important issue for train operations. As part of such safety measures, a train monitoring system has been developed that uses a camera attached to the side of the vehicle to capture images of the area around the doors and displays the camera images on a monitor in the driver's cab (see, for example, Patent Document 1).

[0003] By using such a system, train drivers can check passengers getting on and off on the monitor in the driver's cab when the train stops at a station, and continue operating the train. Traditionally, real-time monitoring of passenger safety required analog systems with no delays, but in recent years, advances in IP technology have made low-latency transmission possible, so all equipment is now connected to IP networks. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-113602 Summary of the Invention [Problem to be solved by the invention]

[0005] However, because the communication bandwidth of the network within the vehicle is limited, when attempting to simultaneously display video data from multiple cameras on a monitor device, the communication bandwidth may be exceeded along the communication path, resulting in data loss.

[0006] An object of the present invention is to provide a technique for preventing data loss and problems such as video freeze on a monitor due to data loss. [Means for solving the problem]

[0007] In order to solve the above problem, one representative camera system of the present invention is a camera system equipped with multiple cameras, each of which outputs video data in GOP format, and the multiple cameras output video data in which the I-frame generation timing does not overlap with each other. [Effects of the Invention]

[0008] According to the present invention, it is possible to prevent problems such as data loss and video freeze on a monitor due to data loss.

[0009] Problems, configurations, and effects other than those described above will become apparent from the following description of the preferred embodiment of the invention. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram illustrating an example of the configuration of a camera system according to an embodiment. [Figure 2] FIG. 2 is a diagram illustrating functional blocks of the network camera according to the embodiment. [Figure 3] 10A and 10B are diagrams illustrating operations performed by the network camera according to the embodiment when the timing for generating an I frame is set by the system control device. [Figure 4] FIG. 2 is a diagram illustrating functional blocks of a system control device according to an embodiment. [Figure 5] 10A and 10B are diagrams illustrating operations performed by the system control device of the embodiment when setting I-frame generation timing for each network camera. [Figure 6] FIG. 10 is a diagram showing the operation of a modified system control device when setting I-frame generation timing for each network camera. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that the present invention is not limited to this embodiment. In addition, in the description of the drawings, the same parts are designated by the same reference numerals.

[0012] A system to which the video data traffic smoothing technology of this embodiment is applied comprises a network camera equipped with a network interface such as a LAN, a network switch, a monitor device that decodes video data and displays the video, a system control device that controls each device connected to the system, and a network cable that connects these devices. In a system composed of these devices, the system control device individually sets the I-frame generation timing for each network camera based on the time managed by the system, thereby controlling the traffic of video data flowing over the network to be smoothed.

[0013] Some network cameras output video data in a compressed, encoded stream in GOP (Group of Picture) format, such as H.264 or H.265. GOP format video data consists of multiple consecutive frames of images in either I-frame (Intra-coded Frame), P-frame (Predicted Frame), or B-frame (Bi-directional predicted Frame) format. I-frames are images coded independently without using temporal prediction, P-frames are images coded using forward prediction, and B-frames are images coded in either a forward, backward, or bidirectional manner.

[0014] As mentioned above, I-frames are images that are coded independently without using temporal prediction, so they are generally known to have a much larger amount of data than P-frames or B-frames. Therefore, if there are multiple network cameras on a system and the video data output by these cameras passes through the same route, there is a possibility that the bandwidth of the communication route will be momentarily exceeded if the timing of the I-frame video data overlaps.

[0015] In this embodiment, in order to intentionally shift the timing of generating the I frames, the network camera under control has the function of generating I frames according to a set timing, and the system control device that performs the control has the function of automatically setting individual I frame generation timing for each camera according to the bandwidth of the communication path and the number of network cameras.

[0016] Alternatively, a GPS signal may be used as the time reference for the system. In this case, after the system control device synchronizes with the GPS, each network camera may be synchronized with the GPS using NTP or the like, or each device may synchronize with the GPS independently.

[0017] In this embodiment, a case where the present invention is used for monitoring train doors will be described. Fig. 1 shows an example of the configuration of a camera system according to this embodiment.

[0018] The camera system 100 in FIG. 1 is mounted on a train made up of six cars, cars 111 to 116. When the train travels leftward in the drawing, the first car 111 shown on the left end is the front car, and the sixth car 116 shown on the right end is the rear car. Conversely, when the train travels rightward in the drawing, the sixth car 116 shown on the right end is the front car, and the first car 111 shown on the left end is the rear car. The following describes an example in which a driver is on board the front car in the train's direction of travel (for example, the first car 111) and operates the train alone (driving, opening and closing the doors, etc.).

[0019] The camera system 100 includes a network camera 121, a monitor device 122, a recording device 123, a system control device 124, a host system 125, and a network switch 126, but may also include other elements. These devices are connected using network cables. Furthermore, these devices are connected to power supply cables, and are supplied with power from a power supply unit (not shown) in each vehicle.

[0020] Each of the cars 111 to 116 is equipped with four network cameras 121-1 to 121-4 and a network switch 126. The first car 111 and the sixth car 116 each have a driver's cab, and two monitor devices 122-1 to 122-2 are installed in the driver's cab. The network camera 121 and monitor device 122 of each car are connected to the network switch 126 of that car by a network cable. The first car 111 is also equipped with a recording device 123, a system control device 124, and a host system 125. The recording device 123 and the system control device 124 are connected to the network switch 126 by a network cable, and the host system 125 is connected to the system control device 124 by a network cable. The sixth car 116 may also be equipped with a system control device 124 and a host system 125, similar to those of the first car 111, and these devices may be multiplexed.

[0021] Furthermore, the network switch 126 in each car is connected to the network switch 126 in an adjacent car by a network cable. In this way, by connecting the network switches 126 mounted on adjacent cars, a single network is formed within the train. These network cables are connected to a jumper box (not shown), for example, via under the car floor, and between cars, the jumper wires connect the jumper boxes of adjacent cars.

[0022] The host system 125 is, for example, a device that manages train operations. As an example of the host system 125, a TMS (Train Management System) is used. The host system 125 can output train operation information to the system control device 124 at a predetermined cycle while the train is in operation. The train operation information includes train speed information, door opening / closing information (for example, information indicating the open / closed state of the doors), boarding / alighting information at the platform of the next station or the station where the train is currently stopped (for example, information indicating whether the door that should be opened is on the right or left side of the train), the number of cars, train traveling direction information, etc.

[0023] The network camera 121 of each vehicle can capture images within a predetermined field of view (angle of view) at a predetermined frame rate (for example, 30 fps). The network camera 121 of each vehicle encodes the captured images to obtain GOP format video data, which is then transmitted to the monitor device 122 and the recording device 123 via the network switch 126 and a network cable.

[0024] The recording device 123 can constantly record the video data received from the network camera 121 of each vehicle, associating it with camera identification information that identifies the source of the video data and the time of capture. The video data recorded in the recording device 123 is mainly used as analytical material or evidence in the event of an emergency such as an accident or crime.

[0025] The monitor device 122 in the driver's cab can display live video data transmitted from the network camera 121 of each vehicle. The monitor device 122 in the driver's cab can also display past video data recorded in the recording device 123. The driver can use the monitor device 122 to check the camera video captured by the network camera 121 of each vehicle.

[0026] The two monitor devices 122-1 and 122-2 are preferably arranged side by side, either vertically or horizontally, so that the driver can view these displays simultaneously. In this embodiment, the display area of ​​monitor device 122-1 is divided into 12 sections, 2 sections vertically and 6 sections horizontally, and the same is true for monitor device 122-2. Therefore, monitor device 122-1 alone can simultaneously display camera images of a train consisting of 6 cars (images from a total of 12 cameras on one side of the train). Furthermore, by using monitor device 122-2 in combination, camera images of a train consisting of up to 12 cars can also be simultaneously displayed. Furthermore, each monitor device can be used for other purposes, such as enlarging and displaying an image selected by the driver from the multiple camera images displayed on monitor device 122-1 on monitor device 122-2.

[0027] The system control device 124 can control the display of the monitor device 122 in response to instructions received from the driver or in response to the operating status of the train. For example, the system control device 124 controls the display of the monitor device 122 so that it is turned on when the train is stopped at a station and turned off when the train is running. Such display control can be performed, for example, based on train speed information that can be acquired from the upper system 125. Note that the display may be turned on / off depending on whether the train speed is zero or not, or depending on whether the train speed is equal to or less than a predetermined threshold.

[0028] The system control device 124 also controls switching of the network cameras 121 to be displayed by the monitor device 122. For example, when the right door of the train opens at a station, the network cameras 121-1 and 121-2 installed on the right side of the train are the display targets, and when the left door of the train opens, the network cameras 121-3 and 121-4 installed on the left side of the train are the display targets. The network cameras 121 to be displayed can be identified based on, for example, entrance / exit information and train traveling direction information.

[0029] Here, the system control device 124 of this embodiment is configured to transmit I-frame generation timing to each network camera 121. This allows the monitor device 122 to receive video data from each network camera 121 so that the I-frame generation timings do not overlap, making it possible to display camera video without any problems such as video freezes.

[0030] 2 shows functional blocks of the network camera 121 of this embodiment. The network camera 121 of this embodiment includes an imaging unit 1211, an encoding unit 1212, a main memory unit 1213, a control unit 1214, and a network interface (I / F) 1215, which are connected to one another via a bus 1216.

[0031] The imaging unit 1211 can convert optical signals imaged on an imaging surface through an optical system such as a lens into electrical signals and output them as digital data (RAW data). The encoding unit 1212 can compress and encode the digital data output from the imaging unit using a predetermined method to generate video data in a GOP format including I frames, P frames, and B frames. The main memory unit 1213 can store digital data captured by the imaging unit 1211 and video data encoded by the encoding unit 1212. The control unit 1214 can control the operation of the encoding unit 1212, as described below. The network I / F 1215 is an interface for transmitting video data from the main memory unit 1213 to an external device via a network and for receiving various control signals transmitted from an external device.

[0032] 3 shows the operation of the network camera 121 of this embodiment when the I-frame generation timing is set by the system control device 124. The network camera 121 generates a new I-frame at the time of the I-frame generation timing received from the system control device 124, and thereafter continues the GOP structure based on that timing. This operation causes the I-frame generation timing to move on the time axis from t2, t3, and t4 to t2', t3', and t4' before and after receiving control from the system control device 124.

[0033] 4 shows functional blocks of the system control device 124 of this embodiment. In the system control device 124 of this embodiment, a GPS antenna 1241 and a GPS receiver 1242 are connected by a high-frequency coaxial cable 1243, and the GPS receiver 1242, a main memory unit 1244, a control unit 1245, and a network interface (I / F) 1246 are connected to one another via a bus 1247.

[0034] The GPS antenna 1241 can receive GPS signals from GPS satellites and send them to the GPS receiver 1242. The GPS receiver 1242 can synchronize with the received GPS signals and send time information to the main memory unit 1244. The main memory unit 1244 can store the time information synchronized with the GPS signals, the number of network cameras 121, the GOP period, etc. As will be described later, the control unit 1245 can calculate the I-frame generation timing to be set for each network camera 121 based on the information stored in the main memory unit 1244 and set it for each camera. The network I / F 1246 is an interface for transmitting the I-frame generation timing on the main memory unit 1244 to each camera via a network.

[0035] 5 shows the operation of the system control device 124 of this embodiment when setting the I-frame generation timing for each network camera 121. The system control device 124 calculates the I-frame generation timing to be set for each camera from the time synchronized with GPS, the number of network cameras 121, and the GOP period. As a simple example, if there are 10 network cameras 121 and the GOP period of all cameras is 10 seconds, the system control device 124 sets the I-frame generation timing for each camera so that the I-frame generation timing for each camera is shifted by 1 second. If there are 10 network cameras and the GOP period of all cameras is 1 second, the system control device 124 sets the I-frame generation timing for each camera so that the I-frame generation timing for each camera is shifted by 100 milliseconds.

[0036] In this way, according to the video data communication volume smoothing technology of this embodiment, the video data communication volume, which conventional systems were unable to handle, is smoothed and controlled to fit within a limited communication bandwidth, thereby preventing data loss and problems such as the video freezing on the monitor due to data loss.

[0037] <Modification> In the above embodiment, the multiple network cameras 121 were configured to output video data that all had the same GOP period, but the multiple network cameras 121 can also be configured to include a network camera 121 that outputs video data that has a GOP period different from that of the other network cameras 121.

[0038] 6 shows the operation of the system control device of this modified example when setting the I-frame generation timing for each network camera 121. For example, the GOP period of the network camera 121 that captures a door through which many people get on and off (a door that should be checked especially carefully) is shortened, and the GOP period of the network camera 121 that captures a door through which few people get on and off is lengthened instead. This smooths the overall video data. Specifically, for example, the GOP period of camera 1 that captures a door through which many people get on and off is set to 5 seconds, the GOP period of cameras 2 through 8 is set to 10 seconds, and the GOP period of cameras 9 and 10 that capture doors through which few people get on and off is set to 20 seconds. The number of people getting on and off may be stored in advance for each station and each door, or may be detected by image processing, a sensor, or the like; any specific means is not limited.

[0039] In the above-described embodiment, the present invention is described as being used for monitoring train doors. However, the application field of the present invention is not limited to this. The present invention is applicable to general camera systems equipped with multiple cameras that output video data in GOP format.

[0040] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the gist of the present invention. [Explanation of symbols]

[0041] 100: camera system, 111 to 116: vehicle, 121: network camera, 122: monitor device, 123: recording device, 124: system control device, 125: upper system, 126: network switch, 1211: imaging unit, 1212: encoding unit, 1213: main memory unit, 1214: control unit, 1215: network I / F, 1216: bus, 1241: GPS antenna, 1242: GPS receiver, 1243: high frequency coaxial cable, 1244: main memory unit, 1245: control unit, 1246: network I / F, 1247: bus.

Claims

1. A camera system comprising a plurality of cameras and a system control device, The plurality of cameras output video data in a GOP format, the plurality of cameras output video data whose I-frame generation timings do not overlap; the plurality of cameras are synchronized with a time managed by the camera system, and generate I frames based on the synchronized time; the system control device specifies an I-frame generation timing for each of the plurality of cameras based on a time managed by the camera system; the plurality of cameras generate a new I frame at the time of the I frame generation timing designated by the system control device, and thereafter continue the GOP structure based on that timing; Used to monitor train doors, The camera that photographs a door where many people get on and off outputs video data with a short GOP period, The camera that photographs a door where few people get on and off outputs video data with a long GOP period. Camera system.

2. A camera system according to claim 1, The number of passengers getting on and off is memorized in advance for each station and door. Camera system.

3. A camera system according to claim 1, Detecting the number of people getting on and off Camera system.

4. 4. The camera system according to claim 1, The time managed by the camera system is synchronized with a GPS signal. Camera system.

5. 1. A method for controlling a camera system including a plurality of cameras and a system control device, comprising: The plurality of cameras output video data in a GOP format, the plurality of cameras output video data whose I-frame generation timings do not overlap; the plurality of cameras are synchronized with a time managed by the camera system, and generate I frames based on the synchronized time; the system control device specifies an I-frame generation timing for each of the plurality of cameras based on a time managed by the camera system; the plurality of cameras generate a new I frame at the time of the I frame generation timing designated by the system control device, and thereafter continue the GOP structure based on that timing; Used to monitor train doors, The camera that photographs a door where many people get on and off outputs video data with a short GOP period, The camera that photographs a door where few people get on and off outputs video data with a long GOP period. A method for controlling a camera system.

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