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The basic business function of video surveillance is to provide means for real-time monitoring and video storage of the monitored images for later playback. On this basis, the advanced video surveillance system can remotely control the monitoring device, and can receive alarm signals and trigger alarms and linkages. The earliest video surveillance system is a full-simulation video surveillance system. Image information is transmitted via video cable in analog mode. The general transmission distance cannot be too far. It is mainly used in small-scale surveillance. 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. Digital control video matrix replaces the original analog video matrix, and digital video recorder DVR replaces the original long-delay analog video recorder. The tape storage mode is converted into digital storage video, enabling the conversion of analog video to digital video. The DVR integrates functions such as video recorders and picture splitters to take the first step of digital surveillance. On this basis, a full-digital video surveillance system is created, which can be based on PCs or embedded devices to form a monitoring system and multimedia management. Such systems are currently the mainstream of the video surveillance market.
With the popularity of broadband networks, video surveillance has gradually evolved from local surveillance to remote surveillance, and a remote network video surveillance system represented by network video servers has emerged. The network video server solves the problem of video stream transmission on the network. Digital processing and transmission are started from image acquisition. This makes the selection of transmission lines more diverse. As long as there are networks, it provides the possibility of image transmission.
The development of computer technology makes the video surveillance technology more intelligent, and establishes a mapping relationship between images and image descriptions, so that the computer can understand the content of the video images through digital image processing and analysis. The networked and intelligent video surveillance technology is based on digitization. And intelligence is the highest level of "threeizations." The change from visual interpretation of the system to the automatic interpretation of the machine is a leap forward in the video surveillance technology and is an inevitable development of the security technology. The following briefly discusses key video technologies in security systems from four aspects.
First, the image sensor technology
The core part of the video surveillance system is the image sensing technology. At present, the image sensor of the surveillance camera is gradually changing from the traditional CCD to the CMOS. Both sensors have their own lengths, but the disadvantages of CMOS sensors have been gradually reduced. The low cost and high integration of CMOS image sensors are their main features, and the image quality is not lost to CCD. CMOS probes are more integrated than CCD-based probes because the CMOS sensor integrates many peripheral processing functions, requires fewer devices than the CCD probe, and the power consumption of the CMOS probe is much lower. From the point of view of the entire system, CMOS sensors can greatly reduce the cost.
Comparison of CMOS sensor and CCD sensor CCD (Charge Coupled Device), or "charge coupled device", in megapixels. The number of megapixels in a digital camera specification refers to the resolution of the CCD. The CCD is a light-sensitive semiconductor chip that is used to capture graphics and is widely used in scanners, copiers, and filmless cameras. Similar to the principle of the film, light passes through a lens and projects the graphic information onto the CCD. Unlike film, however, CCDs have neither the ability to record graphical data nor the ability to be permanently stored or even have "exposure" capabilities. All graphic data will be sent to an "analog-digital" converter without stopping.
A signal processor and a storage device (such as a memory chip or memory card). CCDs come in a variety of sizes and shapes, the largest being 2 x 2 square inches. 1970 American Bell Labs invented the CCD. Twenty years later, people have used this technology to manufacture digital cameras and advance the image processing industry to a whole new field.
CMOS (Complementary Metal Oxide Semiconductor), or "Complementary Metal Oxide Semiconductor." It is an important chip in the computer system, and it saves a lot of data needed for system guidance. It has been found that CMOS processing can also be used as a sensitometric sensor in digital cameras. Its ease of mass production and low cost features are what merchants dream of.
From a technical point of view, CCD and CMOS have the following four differences:
1. Information reading method: The charge information stored in the CCD charge coupler needs to be read after bit shifting under the control of the synchronization signal. The charge information transfer and read output need to have a clock control circuit and three different groups. With the power supply, the entire circuit is more 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 unit of the line under the control of the synchronous clock, and the speed is relatively slow; while the CMOS photoelectric sensor can collect the optical signal and can take out the electrical signal, it can also process at the same time. The image information of each unit is much faster than the CCD charge coupler.
3. Power supply and power consumption: CCD charge couplers mostly need three sets of power supply, which consumes a large amount of power; CMOS photoelectric sensors use only one power supply and consume very little power, only 1/8 of the CCD charge coupler. To 1/10, CMOS photoelectric sensors have great advantages in energy saving.
4. Image quality: The CCD charge coupler fabrication technology started early and the technology is mature. The PN junction or silicon dioxide (SiO2) isolation layer is used to isolate the noise. The imaging quality has certain advantages over the CMOS photoelectric sensor. Due to the high degree of integration of CMOS photosensors, the distance between each photoelectric sensor element and the circuit is very close, and the optical, electrical, and magnetic interference between them is more serious. The noise has a great influence on the image quality, making the CMOS photoelectric sensor a long time. Unable to enter practicality. In recent years, with the continuous development of CMOS circuit noise reduction technology, it has provided favorable conditions for the production of high-density and high-quality CMOS image sensors.
At present, CCD technology is mainly in the hands of several major manufacturers such as Sony, Canon and Olympus. The mainstream digital cameras use CCDs as photosensitive sensors, and the number of pixels is generally about 3 million. Its manufacturing process is complicated, power consumption is high, and costs are high. In the future, digital cameras adopting CCD sensors will continue to move toward increasing the number of pixels, increasing the shooting function, and improving the direction of photo quality, and strive to achieve the standards of traditional cameras as soon as possible on various indicators.
Digital cameras with CMOS sensors are generally lower than 1.3 million pixels, and are mainly aimed at low-end markets that are mainly for home and individual users. Its fashionable, versatile and low-cost advantages have been welcomed by the average consumer. Domestic digital camera manufacturers have been extremely enthusiastic about CMOS digital cameras, including Seagull, Yushchenko, and Himalayan. CMOS has higher plasticity. In addition to digital cameras, it will be widely used in fax machines, scanners, digital cameras, and security detection systems. Currently, there are not many CMOS products in the market, but in the United States, companies including Intel and ATI are actively researching and developing related products. In July of this year, IMEC, an independent semiconductor research institute in Europe, announced two R&D projects related to CMOS, including the “Advanced Device Implementation Program†that explores the limits of CMOS technology. Its goal is to establish the latest version of the International Semiconductor Technology Plan (ITRS) and propose that it be oriented to 60nm. ~30nm technology.
Second, streaming media technology
Real-time video surveillance and video playback are two important basic services of video surveillance. Its essence is to transmit multimedia data from the video source to the video receiver. Real-time video surveillance requires real-time video transmission, with strong real-time performance; video playback is similar to VOD service, with certain real-time (but not very strong), requires clear and smooth pictures, and can complete a variety of playback control operations .
We can think of a front-end camera as a real-time A/V source and a video file as a stored A/V file. A good solution to this problem is to use streaming media technology.
We know that streaming and streaming media (StreamingMedia) was developed to solve the problem of real-time transmission of information. Streaming mainly refers to the technical term for transmitting media (such as audio, video, etc.) over a network. Its specific meaning is that when audio and video information is transmitted to a user terminal through a network, it is not necessary to wait until all files have been downloaded before playing. The continuous audio and video information is compressed and put on the server. When the user terminal plays, only the content of the beginning part is stored in its memory, and the rest of the data stream is continuously received and played by the user terminal in the background until the playing is completed or the user stops the operation. In this way, the waiting time for the user to play the media will be significantly reduced without having to cache too much. Streaming media refers to continuous time-based media using streaming technology.
Streaming is primarily made to distinguish it from downloading transmissions. There are two basic conditions for the traditional download transfer method. One is based on file operations, and the other is that files can only be downloaded (played) after they have been downloaded. For real-time video surveillance, there is no concept of a file and therefore cannot be implemented in a "download" manner. For video recording services, video data may exist in the form of files. However, if the video data can only be played after it is completely downloaded, it will cause a lot of delays and users cannot tolerate it. So, the ideal way is to use streaming.
There are two methods of streaming: Progressive Streaming and Realtime Streaming. The video surveillance business mainly uses real-time streaming.
Network camera can be seen as a server providing real-time A / V source when the user requests real-time monitoring, network cameras using real-time streaming mode monitor screen transmitted to the user terminal. Taking into account multiple users to simultaneously access the network camera will bring traffic bottlenecks and other issues, can be used to transfer video server, video server allows to provide a strong load capacity.
The above is only a brief description of the principle. The above solution to meet small-scale video surveillance system, but in the large-scale video surveillance system, the number of monitoring front-end equipment and user terminals are very large, in addition to increasing consideration multicast, broadcast and other programs, but also need a comprehensive media distribution , scheduling mechanism to ensure the efficient delivery of media. In this respect, there is no ready-made mature solution at present. The China Communications Standards Organization (CCSA) is actively studying 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 sense is 0.38 to 0.78 micrometers. Infrared is an electromagnetic wave with a wavelength greater than 0.78 μm. In nature, all objects radiate infrared light of different wavelengths, so it is possible to detect the infrared wavelengths between the monitoring target itself and the background using a special detection device, so that different infrared images can be obtained. This infrared image is called a thermal image.
The use of infrared thermal imaging technology to detect the infrared radiation of a target object and convert the temperature distribution image of the target object into a video image through photoelectric conversion, signal processing, etc. is called an infrared thermal imager.
Example of application of infrared thermal imager in video surveillance:
1. Target monitoring at night and in adverse weather conditions
At night, devices that require visible light cannot work properly. If artificial lighting is used, the target is easily exposed. If low-vision night vision equipment is used, it also works in the visible light range and still requires external light illumination. The infrared thermal imager passively accepts the target's own infrared thermal radiation, and can work normally both during the day and night, and will not expose itself. Also in rain, fog, and other harsh weather conditions, due to the short wavelength of visible light, poor ability to overcome obstacles, so the observation is poor, but the infrared wavelength is longer, especially in the thermal imager working on 8 ~ 14um, through The ability of rain and fog is strong, so at night and in bad weather conditions, infrared thermal imaging monitoring equipment can still monitor various targets normally.
2. Fire monitoring
Since the infrared thermal imager is a device that reflects the surface temperature of an object and is imaged, it can be used as an effective fire alarm device in addition to being used as a site monitor at night. Many fires are often triggered by hidden fires. With existing common methods, it is difficult to find such hidden fire signs. The use of infrared thermal imager can quickly and effectively find these hidden flames, and can accurately determine the location and scope of the fire, through the smoke found that the fire point, so that as early as possible, early prevention and early extinguishing.
3. Disguise and covert target recognition
Camouflage is mainly based on the prevention of visible light observations. Criminals often hide in grass and woods when committing crimes. Due to the harsh environment and human visual illusions, criminals are prone to misjudgement. The infrared thermal imager passively receives the target's own thermal radiation, and the human body and the vehicle's temperature and infrared radiation are generally much larger than the temperature and infrared radiation of the vegetation, so it is not easy to disguise, and it is not easy to produce erroneous judgments.
Fourth, intelligent video surveillance technology
Intelligent Video (IV, IntelligentVideo) is derived from computer vision (CV, Computer Vision) technology. Computer vision technology is one of the branches of Artificial Intelligence (AI) research. It can establish a mapping relationship between images and image descriptions, so that computing can understand the content of video images through digital image processing and analysis.
The intelligent video technology mentioned in video surveillance mainly refers to “automatically analyzing and extracting key information from 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 vision visually - to "bring" the screens in other places to the front through the network and equipment, so that remote monitoring is in place; secondly, for the purpose of intellectual extension - let the system Automatically analyze problems and solve 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 their own insurmountable weaknesses. For example: (1) Manpower is limited, and people's response and processing speed is limited, resulting in limited locations where we can conduct surveillance within a specified time. This means that each monitored point is not monitored at all times. (2) People are not an observer who can completely trust. Whether watching real-time video streaming or viewing video playback, due to their own physical weaknesses, we often fail to detect security threats, resulting in missed notifications. .
From the above analysis, after large-scale video surveillance, intelligent surveillance is actually not an optional ornament, but an ability necessary for the system.
Otherwise, the huge investment may become a waste because of the lack of follow-up of human resources and the weaknesses of human beings.
Smart video technology can be applied in many places. such as:
(1) Advanced video motion detection: Accurately detects and recognizes the motion of a single object or multiple objects in a complex weather environment (such as rain, snow, fog, or wind), including the direction of motion, motion characteristics, and the like.
(2) Object tracking: After detecting a moving object, a PTZ control instruction 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 that automatically notifies the area in which the object is located continues to perform. track.
(3) Character facial recognition: Automatically recognize the character's facial features, and identify or verify the identity of the character by comparing with the database file. Such applications can be subdivided into two major categories: "cooperative" and "non-cooperative." "Cooperative" applications require 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. Such applications can play a significant role in security applications such as airports, train stations, and stadiums.
(4) Vehicle identification: The vehicle's shape, color, license plate number, and other characteristics are identified and fed back to the monitor. Such applications can be used in scenarios such as stolen vehicle tracking.
(5) Illegal detention: 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: It is used to monitor traffic conditions on highways, such as the number of vehicles passing through, the average speed of vehicles, whether there is illegal parking, whether there is a faulty vehicle, and so on.
From the previous analog surveillance to the current digital surveillance; from behind-the-scene monitoring to advanced remote monitoring; from on-duty monitoring to the current unattended monitoring, video surveillance is moving toward digital, network, and intelligent direction. No matter from the perspective of industrial development or the development of technology, the video surveillance industry will have a broader market and more room for development.
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 has become more and more widely used in the field of security. It is an important means to assist public security agencies in cracking down on crimes and maintaining social stability.