As a combination of traditional video technology and modern communication technology, video surveillance has attracted more and more attention at home and abroad. In recent years, with the popularization of broadband, the development of computer technology, and the improvement of image processing technology, video surveillance is being widely used in security fields. It is an important means to assist public security departments in combating crime and maintaining social stability.
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The basic business function of video surveillance is to provide real-time monitoring and video recording of the monitored images for later playback. On this basis, the advanced video surveillance system can remotely control the monitoring device and receive alarm signals for alarm triggering and linkage. The earliest video surveillance system is a full-simulation video surveillance system. The image information is transmitted by analog cable. The general transmission distance cannot be too far. It is mainly used for monitoring in a small range. The surveillance image can only be viewed in the control center.
With the development of digital technology, digital video surveillance systems began to appear in the mid-1990s, replacing the original analog video matrix with a digitally controlled video matrix, replacing the original long-delay analog video recorder with a digital DVR DVR. The tape storage mode is converted to digital storage recording, which converts analog video to digital video. The DVR combines functions such as a video recorder and a picture splitter to take the first step in digital surveillance. On this basis, an all-digital video surveillance system is generated, which can be based on PC or embedded devices to form a monitoring system and multimedia management. Such systems are the mainstream of the current video surveillance market.
With the popularization of broadband networks, video surveillance has gradually evolved from local monitoring to remote monitoring. A remote network video surveillance system represented by a network video server has emerged. The network video server solves the problem of video stream transmission on the network, and digitally processes and transmits from the image acquisition, so that the selection of the transmission line is more diverse, and as long as there is a network, the image transmission possibility is provided.
The development of computer technology makes video surveillance technology more intelligent. By establishing a mapping relationship between images and image descriptions, computers can understand the content in video images through digital image processing and analysis. The foundation of networked and intelligent video surveillance technology is digital. And intelligence is the highest level of "three-oriented". The transformation of the system from visual interpretation to automatic machine interpretation is a leap in video surveillance technology and is the inevitable development of security technology. The following briefly discusses the key video technologies in security systems from four aspects.
First, image sensor technology
The core part of the video surveillance system is image sensing technology. At present, the image sensor of the surveillance camera is gradually changing from the traditional CCD to the CMOS. These two sensors have their own lengths, but the shortcomings of CMOS sensors have been decreasing. The low cost and high integration of CMOS image sensors are the main features, and the image quality is not lost to CCD. Compared to CCD-based probes, CMOS probes are more integrated because CMOS sensors integrate many peripheral processing functions, require fewer devices than CCD probes, and consume much less power from CMOS probes. From the perspective of the entire system, CMOS sensors can greatly reduce the cost.
CMOS sensor and CCD sensor comparison CCD (ChargeCoupledDevice), that is, "charge coupled device", in megapixel units. How many megapixels in a digital camera specification refers to the resolution of the CCD. The CCD is a light-sensitive semiconductor chip used to capture graphics and is widely used in scanners, copiers, and filmless cameras. Similar to the principle of film, light passes through a lens and projects graphic information onto the CCD. But unlike film, CCD has neither the ability to record graphical data nor the ability to be permanently stored, or even "exposure" capabilities. All graphics data is sent to an "analog-to-digital" converter, a signal processor and a storage device (such as a memory chip or memory card). CCDs come in a variety of sizes and shapes, up to 2 x 2 square inches. In 1970, Bell Labs invented the CCD. Twenty years later, people used this technology to make digital cameras, pushing the image processing industry to a whole new field.
CMOS (Complementary Metal Oxide Semiconductor), that is, "complementary metal oxide semiconductor". It is an important chip in a computer system, which preserves a large amount of data needed for system booting. It has been found that CMOS processing can also be used as a sensitized sensor in digital cameras, which is convenient for mass production and low-cost features that merchants dream of.
From a technical point of view, CCD and CMOS have the following four differences:
1. Information reading mode: The charge information stored by the CCD charge coupler needs to be read one bit after the synchronization signal control. The charge information transfer and read output need to have a clock control circuit and three different sets. The power supply is matched, and the whole circuit is complicated. The CMOS photoelectric sensor directly generates a current (or voltage) signal after photoelectric conversion, and the signal reading is very simple.
2. Speed: The CCD charge coupler needs to output information one bit at a time in the behavior unit under the control of the synchronous clock, and the speed is slow; while the CMOS photoelectric sensor can take out the electric signal while collecting the optical signal, and can simultaneously process The image information of each unit is much faster than the CCD charge coupler.
3. Power supply and power consumption: Most of the CCD charge couplers need three sets of power supply, which consumes a large amount of power. The CMOS photoelectric sensor only needs one power supply, and the power consumption is very small, only 1/8 of the CCD charge coupler. By 1/10, CMOS photoelectric sensors have great advantages in terms of energy saving.
4. Imaging quality: CCD charge coupler fabrication technology started early, the technology is mature, and the noise is isolated by PN junction or silicon dioxide (SiO2) isolation layer. The imaging quality has certain advantages over CMOS photoelectric sensors. Due to the high integration of CMOS photoelectric sensors, the distance between each photoelectric sensing element and circuit is very close, and the optical, electrical and magnetic interference between them is serious. The noise has a great influence on the image quality, making the CMOS photoelectric sensor for a long time. Unable to enter practical. In recent years, with the continuous development of CMOS circuit noise reduction technology, it has provided good conditions for the production of high-density and high-quality CMOS image sensors.
At present, CCD technology is mainly in the hands of Sony, Canon, Olympus and other major manufacturers. The mainstream digital cameras use CCD as the photosensitive sensor, and the number of pixels is generally about 3 million. The manufacturing process is complicated, the power consumption is large, and the cost is high. In the future, digital cameras using CCD sensors will continue to improve the number of pixels, increase the shooting function, and improve the quality of photos, and strive to reach the standards of traditional cameras as soon as possible on various indicators.
Digital cameras using CMOS sensors are generally less than 1.3 million pixels, mainly for low-end markets dominated by home and personal users. Its advantages of fashion, versatility and low price have been welcomed by ordinary consumers. Domestic digital camera manufacturers have placed great enthusiasm for CMOS digital cameras, including Seagull, SAST, and Himalayan. CMOS plasticity is high, and in addition to digital cameras, it will be widely used in fax machines, scanners, digital cameras, and security detection systems. At present, there are not many CMOS products on the market, but in the United States, many companies including Intel and ATI are actively developing related products. In July of this year, IMEC, an independent semiconductor research organization in Europe, announced two R&D projects related to CMOS, among which the "AdvancedDeviceImplementationProgram", which explores the limits of CMOS technology, aims to establish the latest version of the International Semiconductor Technology Plan (ITRS) and proposes to face 60nm. ~30nm technology.
Second, streaming media technology
Real-time video surveillance and video playback are two important basic services of video surveillance. The essence is to transmit multimedia data on the video source to the video receiver. Real-time video surveillance requires real-time transmission of video, which has strong real-time performance; video playback is similar to VOD service, with certain real-time (but not very strong), requiring clear and smooth picture, and can complete various playback control operations. .
We can think of the front-end camera as a real-time A/V source and the video file as a stored A/V file. So a good way to solve this kind of problem is to use streaming media technology.
We know that streaming and streaming (StreamingMedia) was developed to solve the problem of real-time information transmission. Streaming mainly refers to the general term for transmitting media (such as audio, video, etc.) through the network. The specific meaning is that when audio, video and other information is transmitted to the user terminal through the network, it is not necessary to wait for all the files to be downloaded before playing. The continuous audio and video information is compressed and placed on the server. When the user terminal plays, the content of the beginning part is stored in its memory, and the remaining data streams are continuously received and played by the user terminal in the background until the playback is completed or the user suspends the operation. In this way, the waiting time for the user to play the media will be significantly reduced, and there is no need to cache too much. Streaming media refers to continuous time-based media using streaming technology.
Streaming is primarily intended to be distinguished from download transmissions. There are two basic conditions for the traditional download and transfer method. One is based on file operations, and the other is that files must be downloaded before they can be used (played). For real-time video surveillance, there is no concept of a file, so it cannot be implemented as a "download". For the video service, the video data can exist as a file. However, if the video data cannot be played after it has been completely downloaded, it will bring a lot of delay and the user cannot bear it. Therefore, the ideal way is to use streaming.
Streaming has two methods: Progressive Streaming and Realtime Streaming. The video surveillance service mainly uses real-time streaming.
The network camera can be regarded as a server that provides real-time A/V source. When the user requests real-time monitoring, the network camera transmits the monitoring picture to the user terminal by using real-time streaming. Considering that multiple users accessing the network camera at the same time will cause traffic bottlenecks, etc., you can use a video server to transfer, allowing the video server to provide strong load capacity.
The above is just a brief description of the principle. The above solution can meet a small video surveillance system. However, in a large-scale video surveillance system, the number of monitoring front-end devices and user terminals is very large. In addition to increasing the consideration of multicast and broadcasting, a complete set of media distribution is needed. Scheduling mechanism to ensure efficient delivery of media. In this regard, there is no ready-made mature solution, and China Communications Standards Organization (CCSA) is actively researching this to provide a standard media delivery mechanism for future video surveillance systems.
Third, infrared thermal imaging technology
The wavelength of visible light that the human eye can perceive is 0.38 to 0.78 microns. Infrared rays are electromagnetic waves having a wavelength greater than 0.78 microns. In nature, all objects radiate infrared light of different wavelengths. Therefore, a special detection device can be used to detect the infrared wavelength between the monitoring target itself and the background, so that different infrared images can be obtained. This infrared image is called a thermal image.
A device that uses infrared thermal imaging technology to detect infrared radiation of a target object and converts the temperature distribution image of the target object into a video image by means of photoelectric conversion, signal processing, etc. is called an infrared thermal imager.
Examples of applications of infrared thermal imaging cameras in video surveillance:
1. Target monitoring at night and in harsh weather conditions
At night, equipment that requires visible light is no longer working properly, and if artificial lighting is used, it is easy to expose the target. If a low-light-level night vision device is used, it also works in the visible light band and still requires external light illumination. The infrared thermal imager passively accepts the target's own infrared heat radiation, which works well day and night, and does not expose itself. Also in the harsh weather conditions such as rain and fog, because the wavelength of visible light is short, the ability to overcome obstacles is poor, so the observation effect is poor, but the wavelength of infrared rays is long, especially for thermal imagers operating at 8 to 14 um. The ability to rain and fog is strong, so at night and in severe weather conditions, infrared thermal imaging monitoring equipment can still monitor various targets.
2. Fire monitoring
Since the infrared thermal imager is a device that reflects the surface temperature of the object and is imaged, it can be used as an effective fire alarm device in addition to being used as a field monitor at night. Many fires are often caused by inconspicuous idling fires. With the existing common methods, it is difficult to find such hidden fire signs. The application of infrared thermal imager can quickly and effectively detect these hidden fires, and can accurately determine the location and extent of the fire, and find the fire point through the smoke, so as to know early, prevent early, and extinguish early.
3. Identification of camouflage and hidden targets
Camouflage is mainly based on anti-visible observation. Criminals usually hide in grass and woods when committing crimes. Due to the harshness of the wild environment and the visual illusion of people, it is easy to make false judgments. Infrared thermal imager passively accepts the target's own thermal radiation. The temperature and infrared radiation of the human body and the vehicle are generally much larger than the temperature of the vegetation and the infrared radiation, so it is not easy to disguise, and it is not easy to make a wrong judgment.
Fourth, intelligent video surveillance technology
Intelligent Video (IV, IntelligentVideo) is derived from Computer Vision (CV) technology. Computer vision technology is one of the branches of artificial intelligence (AI) research, which can establish a mapping relationship between image and image description, so that the calculation can understand the content in the video picture through digital image processing and analysis.
The intelligent video technology mentioned in video surveillance mainly refers to: “automatic analysis and extraction of key information in the video source.†If the camera is regarded as the human eye, the intelligent video system or device can be regarded as the human brain. .
The purpose of building a video surveillance system is to extend the visually--the picture that is in other places is brought closer to the front through the network and the device, so there is remote monitoring; the second is for the intellectual extension--the system Automatically analyzes and solves problems for us, so we have intelligent monitoring. Of course, the latter is a higher level requirement, but it is also an inevitable requirement for the future development of video surveillance.
The lack of intelligence in traditional video surveillance systems relies heavily on human judgment. However, human beings have weaknesses that are difficult to overcome themselves, such as: (1) limited manpower, limited human response and processing speed, resulting in limited locations where we can monitor for a specified period of time. This means that each monitored point is not monitored at all times. (2) People are not an observer who can be completely trusted. Whether watching real-time video streaming or watching video playback, due to their physical weaknesses, we often fail to detect security threats, which leads to false negatives. .
From the above analysis, after the large-scale video surveillance, intelligent monitoring is actually not an optional decoration, but an essential capability of the system.
Otherwise, huge investments will become a waste due to lack of human resources follow-up and human weaknesses.
Intelligent video technology can be applied in many places. such as:
(1) Advanced video motion detection: accurately detect and recognize the motion of a single object or multiple objects in a complex weather environment (such as rain, snow, fog, strong wind, etc.), including the direction of motion, motion characteristics, and the like.
(2) Object tracking: After detecting the moving object, the PTZ control command is automatically sent according to the motion of the object, so that the camera can automatically track the object. After the object exceeds the monitoring range of the camera, the camera in the area where the object is located is automatically notified to continue. track.
(3) Face recognition: The face features of the person are automatically recognized, and the identity of the person is identified or verified by comparison with the database file. Such applications can be subdivided into two categories: "cooperative" and "non-cooperative". A "cooperative" application requires the monitored person to stay in front of the camera for a period of time, usually in conjunction with an access control system. “Non-cooperative†can identify specific individuals in the crowd, and such applications can play a large role in security applications such as airports, train stations, and stadiums.
(4) Vehicle identification: Identify the shape, color, license plate number and other characteristics of the vehicle and feed it back to the monitor. Such applications can be used in scenarios such as stolen vehicle tracking.
(5) Illegal stay: When an object (such as a box, parcel, vehicle, person, etc.) stays in a sensitive area for too long, or exceeds a predefined length of time, an alarm is generated. Typical application scenarios include airports, train stations, subway stations, etc.
(6) Traffic flow control: used to monitor traffic conditions on the road, such as counting the number of cars passing, average speed, illegal docking, faulty vehicles, etc.
From the previous analog monitoring to the current digital monitoring; from backward on-site monitoring to advanced remote monitoring; from manned monitoring to unattended monitoring, video surveillance is booming in the direction of digital, networked and intelligent. Regardless of the development of the industry or the development of technology, the video surveillance industry will have a broader market and greater development space.
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