Modern closed-circuit television systems.
Modern closed-circuit television systems
Closed-circuit television systems (CCTVS) are increasingly used to ensure safety and security. This is due to both the continuing increase in crime and abuse, and the increased efficiency and quality of these systems, associated with the influence of new advanced technologies.
The security equipment industry has grown significantly in recent years and continues to expand. It is now effectively divided into several sectors: CCTV, access control systems, perimeter protection systems, etc., and only a few large companies produce and supply products related to all of these sectors. This division has contributed to a clearer specialization of companies in individual sectors and to overall progress in the field of security equipment.
A characteristic feature of the CCTV sector is that many new developments created specifically for security systems are also used in other television systems. This applies in particular to image sensors, black-and-white and color video cameras, and thermal imagers. Preference is given to CCTV where their use makes it possible to reduce the number of personnel.
In the leading countries of the world, television cameras on semiconductor devices are successfully used for security systems and commercial purposes. There is a tendency for continuous improvement of their characteristics: spatial resolution and increase in their sensitivity to radiation at lower frequencies of the optical spectrum (up to the near infrared part). In the field of thermal imaging devices, the possibilities of their non-military applications and prospects for growth in demand for them are being studied. Their development is associated with solving the problems of cost, resolution and reliability.
The expansion of the use of ZTVS and other video equipment in security systems has been facilitated and is being facilitated by the creation by the computer industry of a number of effective hardware and software for processing and using video images, which were unavailable several years ago due to their high cost.
The predominant application in ZTVS is video cameras on semiconductor devices with charge coupling (CCD). Their resolution has now been increased to 470 TV lines for color cameras, sensitivity has been increased, and dimensions have been reduced. The use of these cameras together with the RS232 communication interface has increased the quality of ZTVS, since this makes it possible to automatically set a number of parameters using new matrices programmable by a microprocessor. At present, there are cameras of this type from Hitachi (Japan), using a varifocal lens with a magnification from x 12 to x 100 (in the future).
CCD matrices and microchips are expected to appear, which will simplify camera control even to the level of image elements (pixels). This is the last opportunity to integrate the functions performed by cameras into the circuits for processing signals about the movement of intruders. This requires that industrial companies join forces and reach an agreement on the format of the digital output of cameras. The reliability of video cameras has been significantly increased.
Of great importance for the ZTVS are the functions of receiving, storing, searching and transmitting received video data. The low cost of video data carriers in combination with inexpensive accessible devices for compression and transmission of video data opens up wide possibilities for including video data in various security systems. In recent years, a large number of systems have appeared on the market designed to transmit ZTVS images with acceptable resolution over telephone lines.
Currently, the most common format for recording video images is the format adopted for home video recorders. But this format does not provide high definition of reproduced images with an acceptable signal-to-noise ratio. Existing video cameras produce images with a resolution of 470 lines, and home cassette video recorders can record them with a clarity of about 320 lines, and even super video recorders with a recording clarity of up to 400 lines do not use the capabilities of existing video cameras.
Digital recording on hard magnetic disks is becoming increasingly widespread, but this is associated with its own problems:
— firstly, hard video discs are just beginning to compete with video cassettes, so their recording clarity is lower;
— secondly, the capacity of hard drives is limited. When using the most advanced video compression system, a single frame of video will occupy about 10 kb of disk capacity; the recording speed will reach 30 Mbps, 1.8 Gbps, or 43.2 Gbps per day for one camera. The problem can only be solved by using video recorders with limited recording time or with short-term recording;
— thirdly, most video recording systems use video compression, which gives good results, but this is associated with certain disadvantages, expressed in deterioration of clarity with fast target movement, and the need to play several consecutive frames to select one of them in freeze frame mode;
— fourthly, digital video recording allows for easier manipulation of data than analog, and an experienced engineer can recreate a convincing video recording of an event that did not actually happen. This means that in the future, judicial authorities will be forced to verify the authenticity of the video recording.
Some digital video recorders use tape for both video and audio recording, but they retain the speed required for recording video data, which affects the quality of the audio recording.
Therefore, such tapes are more suitable for archiving data, rather than for real-time playback. This also applies to optical discs. Even digital optical discs, which are currently entering the consumer video market, only allow two hours of video recording per disc using video compression technology and with low-definition playback images.
Digital video recorders are made by companies such as Panasonic and JVC, but they are still very expensive (up to £7,000). However, they have a recording time of 3 hours or more per tape in real time. Their price will obviously fall, and therefore it can be assumed that they will be the “standard for digital video recording in the near future”.
This means that emerging video recording systems will displace analog video recording systems on magnetic tapes and hard disks. New video recording devices will probably contain semiconductor devices and use holographic technology and even high-capacity electronic memory. They will have no moving parts, which will significantly increase their reliability. In the coming years, they will find application in commercial ZTVS. This will be preceded by their use in military ZTVS.
Developers and manufacturers of video equipment and ZTVS will follow the trend of supplying “systems in cases” that require minimal technical knowledge from users or even do not require such a minimum. Examples of such devices are:
– multiplexers combined with telemetry;
— video cameras with motion sensors;
— monitors with built-in multiplexers.
Following this trend, manufacturers of video equipment take into account the requirements and interests of end users, and not suppliers who are intermediaries between them.
The sizes of ZTVS have increased somewhat in recent years (up to 256) due to the increase in the number of signals received and issued by them. Accordingly, the sizes of communication and control devices have increased. Such ZTVS have greater functionality. For example, they can display maps of the area, graphics and text on the touch screen of the display, they can be combined with other systems in the access control complex, with alarm systems and even with control systems for engineering and technical means of buildings (heating, fire alarm, water supply, etc.).
Control of video signals and other signals combined with them, such as alarm systems, is taking an increasingly important place in the development of video surveillance systems. The use of multiplexers in them has become almost mandatory, which is accompanied by a decrease in the prices of these devices. New devices have appeared – real-time multiplexers, distinguished by a higher (by 30%) speed in comparison with previous models, an increased volume of transmitted data, the ability to identify and even interface with motion sensors and telemetry devices. But although digital control is widely used in all these multiplexers, they still deal with analog signals.
The possibilities of transition to digital video technology here have not yet been fully studied, and such modulation methods as phase-pulse and various versions of phase modulation, widely used in telephony, remain unexplored. In the future, they can significantly affect the technology of multiplexers for video surveillance systems, especially the compression of digital video signals, their recording and transmission.
The control of video signals will also be affected by the motion detection technology of the switching system. The implementation of these possibilities depends only on the emergence of new digital video cameras.
The need for video transmission systems is not yet fully apparent, but the potential for labor reduction through long- and short-distance remote surveillance with video transmission may make video transmission an important part of the surveillance technology. This requires lowering the cost and increasing the reliability of transmission.
Digital video transmission systems are divided into two categories:
— with the transmission of signals in free space, which can be optical, for example, infrared. Such systems require a line of sight, the length of which is limited to 1.5 km under favorable conditions. But they allow the transmission of signals in real time, and their use does not require a license. The ultra-high-frequency radio systems usually used require, as a rule, official) permission. They also provide real-time transmission, and the range for all practical applications is limited in the UK by licensing conditions to a few kilometers. Similar restrictions apply in the countries of the European Union. But less stringent restrictions are allowed in countries of Africa and Asia. In the future, the transmission of digital video signals via space radio communication lines is predicted;
— Cable transmission systems can be more or less complex, depending on budgetary possibilities. The most basic Di-Cam system, costing a few hundred pounds, can transmit black and white images over a PSTN line with an update period of a few seconds. Systems of this type can perform useful security functions in various applications and provide a return channel for remote control of systems.
The use of the “conditional update” method, in which only the changed part of the image is transmitted, significantly increases the transmission rate of one frame from 30 s in the system proposed several years ago by Robot to several seconds in modern systems. This acceleration provides the same increase in the efficiency of transmission systems as the compression technique of video signals. But even with the use of optimal compression, the transmission of one frame in less than 0.5 s over dial-up telephone lines cannot be implemented for practical purposes.
Intermediate-type systems, such as those proposed by Hitachi, are intended for use in integrated service digital networks (ISDN) and allow continuous transmission of video images for 24 hours.
This technology allows us to hope for the possibility of real-time surveillance with video signal transmission via ISDN telephone lines or even the “Internet”. However, the problem of transmission range remains. Further development of video signal compression technology based on such methods as MP-EG3 or fragment compression will make practical application of ZTVS for solving various problems an everyday occurrence.
There are, of course, big differences between free-space and cable signal transmission systems, but, as a rule, the user chooses one or another type of system taking into account their specific application conditions.
Video transmission systems are becoming increasingly digital, and in the future it may be possible to use satellite communication lines for this.
Digital video signal compression technology has its own specific features. Currently, there are several projects of digital video signal compression standard, but none of them take into account the specificity of using this technology in DTVS, which differs significantly from applications in television broadcasting systems. The possibility of adopting an international standard seems unrealistic, and therefore, obviously, several systems will operate for some time. This will lead to increased competition between the leading companies in the DTVS sector (Panasonic, JVS, Hitachi) and the creation of incompatible systems by them, which will primarily harm the end users of such systems.
The analysis shows that DTVS are becoming more digital and computerized. This entails the emergence of new systems based on the use of DTVS with broader functional capabilities.
