Operational requirements for CCTV systems

The article is based on the resources published by British Home Office. It describes the features of CCTV system which are important for its users. With many years of experience, the Home Office has developed a set of requirements on the use of monitoring systems by the police in various investigations. To be able to effectively use the material obtained through a CCTV system, it must meet the requirements set out below, collected in four sections:

• Quality,
• Recording,
• Export,
• Playback.

An important group of these requirements are the rules for the selection of the equipment.
What image resolution is suitable for a specific application? Which kind of compression should be used for transmitting and recording the video? How many frames per second are to be saved? These questions form the basis for the list of quality guidelines:

Before ordering and installing CCTV system the user should know what is to be observed and how precisely. For example, whether the system should allow to recognize the face of a person passing through an entrance or read a car registration plate, or it is sufficient to notice one's presence.
There are no clear criteria for collecting evidence for the court. If the judge rejects the material because of insufficient quality, it becomes useless. Therefore a good idea is to check the quality of images from the cameras by testing the ability to distinguish details in similar conditions in which the cameras will operate.
When testing the quality, it should be noted that live images usually look better than those played back from the recorded material.
A very important issue for the court is time synchronization of all recorded material.
Another thing that cannot be disregarded is the capacity of the archives. The storage capacity has to be matched to the image quality and archive period.
Finally, it is good to remember that the quality of the material also depends on the maintenance of the system. It includes regular focusing of the cameras, cleaning lens and housings etc.

Modern city video surveillance systems are equipped with day/night, fixed, PTZ, and megapixel cameras. The main parameters include angle of view (depending on the lens), sensitivity correlated with the ability to work at low light conditions (depending mainly on the image sensor), video resolution, and frame rate (the number of frames transmitted per second). It should be noted that PTZ cameras should ensure higher frame rates, because it has an impact on the accuracy of camera control. In addition, the optical zoom can help to capture interesting details. Unfortunately, PTZ control can be effectively performed only by the operator.

A good alternative is use of megapixel camera, which, although has no optical zoom, enables multiple digital zooming. This allows to view details of the image both live and when analyzing archives. As the amount of data transmitted from megapixel cameras is much greater than that from standard-resolution cameras, the frame rates are lower than in the case of typical analog systems. In practice, however, there is no need to record 25 frames per second, with the exception of specific systems.

Megapixel camera - IQeye 755 K1431

Modern CCTV management software allows full configuration of recording images from individual cameras. The data can be recorded on several servers, so that there is no need to match the quality of material to the capacity of hard drive - the disc space is practically unlimited.

After defining sufficient image quality the next step is choice of the video that has to be recorded and proper archiving of the video data. The main requirements for modern archiving system:

Access to the archives has to be strictly limited to authorized persons. All sessions have to be registered in system log. However, the precautions should not interfere with normal operation of the system.
One of the most important requirements is a defined period of time when the data is safely stored and protected against deleting.

Modern IP CCTV systems are managed by software that allows to configure access rights according to the needs of the administrator. The administrator can limit the rights of particular users to access individual cameras, to control some PTZ devices, to view archives from specified locations etc. The system may be made accessible only from defined locations, within specified time windows.

Configuration of access rights in Netstation

A very important feature of CCTV system is possibility of exporting the recorded material. The efficiency of the system can be measured by the kind (format) and amount of exported data.

The system will not be used optimally if the operator has not sufficient knowledge about playback and export of recorded material. The monitoring center should be equipped with a short instruction manual on the subject. In addition, the operators should be able to estimate how long does it take to export files of different size.
The composition of exported material will depend on the type of investigation. For example, in the case of a theft from a shop, it may be enough to provide a few pictures or short video. More serious crimes will require to provide the entire contents of the archive. So the system should allow export of data onto various media, from flash memory to external hard drives. In some cases the export may take a longer time, so it should not have any impact on the operation of the entire system.
It is also worth mentioning that the exported data should have the same quality as the recorded material in the archive. Additional compression or conversion to other formats cannot undermine the credibility of the evidence.

The becoming very popular IP CCTV systems enable export of the recorded material to the standard .avi format. The export of the data is performed via typical video codecs, which allows for collecting and playing back the material on other devices/computers.

Export of archives in Netstation

Finally - the requirements for playback functions and the management software. Is it possible to quickly find and playback some selected material? The system should have the following functions:

The software for playback of the previously recorded material must allow quick and effective searching of some interesting fragments. The video has to include all additional information, first of all the time stamps. It should be possible to playback any exported material directly on external devices.

The real test of the functionality of CCTV system is the usability of the recorded data. The standard playback functions include searching the video by date and time, simultaneous playback of several channels, searching by events (usually motion detection) in a certain area, frame-by-frame analysis.

The archives of Netstation

This short review of the basic requirements for professional video surveillance systems can be an incentive to take advantage of the wealth of information available at http://www.homeoffice.gov.uk/