Design of video surveillance systems
The Russian security systems market, despite its youth, has already come a long way from using simple, disparate systems to the period of formation and understanding of the need for an integrated approach to security systems.
This necessitates the selection of equipment for integrated security systems that ensure the stable operation of each facility, taking into account its features. This approach places increased demands on the quality of security system design.
Most often, video surveillance systems are integrated with fire alarm systems, access control systems, and security and alarm or perimeter alarm systems. Currently, all video surveillance systems are equipped with built-in motion detectors based on software comparison of each frame with the previous one.
If there is a difference, the alarm mode is activated, which highlights the alarm camera on the monitor screen, can turn on the sound notification, record, pre-record and subsequent record with the appropriate system settings. Often, security sensors are connected to the alarm inputs of the video surveillance system, which similarly transfer the video surveillance system to an alarm state. Fire sensors are connected to the video surveillance system in the same way. Of course, all of the listed systems can also operate autonomously.
Currently, the Russian market mainly features video surveillance systems based on:
1. Cameras with analog output and analog recording devices.
This is the previous generation equipment, but it has a number of advantages, such as the lowest inertia in signal transmission, low cost, absence of distortions introduced by processing. Analog video surveillance systems include, in addition to video cameras, tape recorders, monitors, analog switches or quads that allow you to adjust the sequence of output to the monitor of video signals from several cameras or multiplex the image from several cameras and have alarm inputs for various security and fire sensors, which in the event of an emergency give an alarm signal and the image from the corresponding camera appears on the monitor.
2. Analog cameras with digital signal processing and video servers, video recorders.
3. Digital cameras with IP output with an internal processor that digitizes the video signal and transmits it to the network in compressed form, and servers that process the archive from several such cameras.
4. Hybrid video surveillance systems for the simultaneous connection of analog video cameras and cameras with IP output. These systems provide the unification of cameras with analog and digital outputs into a single network with the creation of a common archive and the ability to access the cameras of several remote operators.
In cameras with digital signal processing, the signal is sent to the camera output in analog form, but inside the camera, digital signal processing occurs using a digital processor (DSP = Digital Signal Processor) to implement the following functions: automatic control of the electronic shutter, automatic gain control (AGC), bright background compensation, automatic white balance, camera synchronization, bright spot suppression mode, etc. In cameras with an IP output or digital cameras, the signal is internally converted to digital form and transmitted from the camera output to the network in compressed digital form.
An analog signal is a continuous stream, characterized by changes in frequency and amplitude. When a signal fades, its amplitude must be increased. An amplifier increases the overall signal level in the line, including the noise level. Each conversion, each intermediate storage, each transmission over cable or air degrades the analog signal.
Digital signals consist of discrete values. Some deviations from their magnitude are allowed. For example, voltage can take two values: from 0 to 0.5 V (zero level) or from 2.5 to 5 V (one level). Since there are always zones of permissible deviations, a digital signal is better protected from the effects of noise, interference, and interference.
When considering video surveillance systems, it is very important to use the correct terminology, not only when describing the types of video cameras, but also when defining the goals and objectives to be achieved using video surveillance systems. A clear formulation of the purpose of video surveillance systems ensures the correct selection of equipment to perform the desired tasks.
At the current stage of development of the regulatory framework, security video surveillance most often does not prevent the commission of the offenses recorded by it. Of course, at any facility you can place a unit of security guards who watch the monitors and are ready to detain violators at any time. However, this is a very expensive solution, usually used at special facilities. Video surveillance systems most effectively solve search tasks when, based on the analysis of the archive, you can understand what happened at a particular moment at the protected facility. Taking into account the tasks performed by video surveillance systems, the choice of equipment for a particular facility is made.
For example, stores need video surveillance systems that can record a continuous flow of information, analyze it and filter out all unnecessary information (personal identification functions, the presence of missing/abandoned items are very useful). For a warehouse, the option is when the system is in standby mode and is activated when an emergency situation occurs. In an office, it is advisable to conduct full-fledged surveillance during the day, and at night, switch the system to standby mode, i.e., camera operation due to an alarm event. To create a video surveillance system for large facilities, such as airports and train stations, high-reliability video surveillance systems are used, including hundreds of monitors and video cameras with the ability to access the cameras of several remote operators on a priority basis and create an archive. This is ensured by the use of expensive world-class equipment, such as matrix microprocessor switches and video recorders simultaneously. Also, such facilities require the selection of systems with functions for personal identification, missing/abandoned items, identification of sudden movements (running, jumping), identification of car numbers, etc. This is done by digitalizing the signal using video recorders or video servers with an activity detector and developed software for unification into a common network with the ability to control cameras, highlight an alarm event, operate cameras according to a schedule, create a single archive and have several remote operators access cameras on a priority basis.
To work in conditions of changing illumination, it is necessary to use video cameras with internal digital signal processing, which provide for the suppression of glare, for example, from car headlights, video cameras with an electronic shutter with automatic adjustment of the aperture, white balance, etc.When organizing perimeter security, the entire perimeter is divided into zones. Video cameras are placed along the perimeter or inside the perimeter at high points of the building or on masts on rotary devices that view the entire perimeter. In addition, security sensors are installed in each zone. When an alarm signal is generated, additional lighting is turned on, and the cameras on rotary devices turn to the zone of the sensor that generated the alarm signal. In cases where it is necessary to recognize the identity of a person who has entered the camera's field of view, or to read license plates, the camera's range must be selected accordingly, and video cameras with high sensitivity must be used.
If the system must distinguish colors, equipment capable of perceiving and recording information in color is used. This is relevant in cases where it is necessary to single out violators from a crowd, such as, for example, if a person in a yellow jacket jumps over a turnstile in the subway, then information about him can be more easily transmitted to the nearest security point. If such identification is not required, then black and white cameras have a higher resolution and greater sensitivity.
The main difficulty of video surveillance in train cars with data transmission to the driver's cabin and then to the monitoring center is associated with ensuring noise immunity of the networks transmitting data.
High-resolution video cameras are required to integrate cash registers with video surveillance systems. When creating such systems, the customer at the cash register with a purchase is visible on the monitor screen. At the same time, the punched check is visible on the monitor screen of the video surveillance system. This is very important in shopping centers, where the customer pays for the selected goods at the cash register.
Chicago has developed video surveillance systems with software for recording shots. The video cameras have built-in acoustic sensors. If a shot is fired near the video camera, it is aimed at the place where the shot was fired from. In addition, the operator immediately receives an alarm signal. The video cameras are able to recognize shots within a radius of 350 m, and the video system software instantly provides a close-up image of both the place where the shot was fired and the shooter himself. Immediately after the shot is fired, the police receive a notification about it in a matter of seconds.
When placing a system or part of it outdoors, it is necessary to take into account the peculiarities of our changeable climate and ensure operation at different temperatures, rain, snow, sun, dust, etc. Video cameras with IP 68 protection rating are adapted for such conditions.
A number of industries associated with explosive substances and the possibility of their ignition are forced to use explosion-proof video equipment capable of operating in a wide range of temperatures, in an environment of aggressive explosive mixtures of gases and dust, allowing for remote visual monitoring of the equipment condition and the passage of technological processes. The Russian market has a list of not only explosion-proof video cameras, but also other components of video systems. However, such products are distinguished by their high cost due to the complexity of circuit and design solutions and high costs for testing in testing organizations to obtain a certificate of conformity.
There are video surveillance systems that are resistant to ionizing radiation. Such resistance is achieved both by selecting radiation-resistant video camera chips and by the design of the system itself. Such systems are mainly used at special industrial facilities. To correctly build such video surveillance systems, it is important to clearly identify the main destabilizing factor.
Such a wide distribution of video surveillance systems is associated with progress in the development of video cameras, first of all, which have the main element — the eye of the video camera — a photosensitive matrix. During this time, the cost of video cameras has decreased by an order of magnitude, and their size, perhaps, by two orders of magnitude. Very often, camera sellers focus on the matrix type, attributing certain properties to cameras thanks to the matrices. However, due to the fairly high level of development of modern solid-state electronics, the quality of CCD and CMOS matrices of the latest generations is almost the same. Difficulties arise at another stage. Since the modern market of video surveillance systems is quite young, developers and suppliers of video surveillance cameras have successfully managed to avoid the strict influence of regulatory documents when declaring a particular sensitivity level of their products. This allows misleading consumers about the real sensitivity level of the cameras they purchase. Firstly, the signal/noise value is not indicated at a given sensitivity, and secondly, the manufacturer often implies that the camera gives an acceptable signal at such and such illumination. But what is meant by an acceptable signal is not specified. Thirdly, sensitivity is often given in the so-called charge accumulation mode, i.e. with a sufficiently open electronic shutter. However, in this mode, the camera's performance is significantly reduced, and the camera cannot be used to record fast-moving objects in this mode. In general, when choosing cameras, it is better for the designer to familiarize himself with the entire set of parameters.
IP-output video surveillance cameras have already firmly established themselves on our market. The built-in processor provides signal processing and digital output with the transmission of video images in compressed form.
Advantages of IP-output video cameras:
high stability of the digital signal;
easy installation;
megapixel resolution;
progressive scanning;
power supply via a network cable (Power Ethernet).
Very often, IP-output cameras load the network much less than standard systems based on analog-output cameras and video recorders. This is due to the fact that IP-output cameras have a built-in recording buffer, which stores current information. Only when the motion detector is turned on and a signal is received about the need for pre-recording and recording by the motion detector, this information begins to be transmitted to the central video server. This can be very important for building systems with a large number of video cameras without creating powerful broadcast networks.