To best understand the needs and possibilities of modern cctv security, some terms and concepts must first be understood. The phrase closed-circuit television video system is abbreviated as CCTV. Broadcast video such as traditional television is a much more complex system in which the video images and audio tracks are converted to signals, which are transmitted and can be received by anyone within range who has the proper equipment tuned to the proper frequency. Because the video is available to anyone who is tuned to the correct frequency, broadcast television is essentially an open-circuit system. With CCTV security systems, however, signals from a video source, such as a camera, are transmitted by a direct connection to the receiving equipment, such as a monitor. This connection is usually made with coaxial cable but can also be made with fiber-optic cable or a single twisted-pair cable if the correct conversion equipment is used. This connection makes a completed closed circuit, which cannot easily be viewed from outside of the cctv security system. In theory, the only way to view the video images from the camera is with a piece of equipment that is part of the closed circuit. Modern camera systems are not always a true closed-circuit system, although they are still usually referred to as such.
The role of the camera system in security program has evolved substantially in the last decade, as has the equipment. In the past, cameras were thought of as an extreme measure, primarily for banks and large office buildings. CCTV security systems were mainly used in facilities with a 24-hour guard service. Most cctv security systems consisted of a few cameras, monitors for the guards to view, and possibly a switcher to view multiple cameras on a single monitor. These cctv security systems were not considered practical for most facilities because they were fairly costly and only beneficial for live viewing.
Advanced technology in cctv security systems brought the video recorder and eventually the timelapse recorder, which made it possible to store images for later review of any incidents that may have occurred. The recording devices expanded the possible uses of cctv security systems.
Visible cctv security cameras, mounted in the most obvious places, are considered to be a good deterrent for many crimes, such as armed robbery, burglary, and shoplifting. Although many security professionals may still argue that cctv security cameras are a great deterrent, this is not-and should not be-the primary purpose of the system. Many cities have begun installing cctv security cameras citywide based on the assumption that cameras will discourage people from performing criminal acts. The cameras may discourage some activities from happening in the immediate viewing area of the cameras, but there has not been enough evidence gathered to show that the cctv security cameras deter the crime from happening altogether. If the crime still occurs but is covered by video surveillance, it is hoped that the system has been set up properly to capture the event for future use as evidence. Home intrusion detection systems are similar. They may not make a criminal decide to stop breaking and entering but instead search for an easier target.
Insurance companies and the judicial system have also established cctv security systems as a necessity to limit or decrease potential liability. From a corporate point of view, a camera system in conjunction with other security measures, such as lighting and alarm systems, can show that a company has taken adequate and reasonable measures to protect employees, customers, and clients.
Mentioned below are some of the metrics that define the efficiency of a cctv security camera.
The most common way to specify how far a cctv security camera can see is to select an optical zoom range. Generally, this provides a good proxy for maximum distance though it suffers from 2 major limitations - variances in maximum focal lengths and differences in resolution. If a user wants a camera that can see as far as possible, it is better specify a maximum focal length rather than an optical zoom. By definition, optical zoom is comprised of a minimum and a maximum focal length. For example, a 36x optical zoom cctv security camera might have a minimum focal length of 3.5mm and a maximum of 126mm (36x greater than the minimum). However, another cctv security camera might have the same optical zoom range but a higher minimum and maximum focal length (e.g., 4mm to 144mm). This second camera, all other things equal, would be able to 'see' farther.
Pan range defines how far horizontally (left to right) a cctv security camera can move. The movement is circular and the possibilities range from 0 to 360 degrees. 360 is an especially important level for pan range. With 360 pan range, the camera can move continuously to track a subject. Anything else and the operator needs to manually move the cctv security camera back the other way to track a suspect around an area. A significant difference exists in price between cameras that support pan ranges of 350 and those that support 360. If an application will be actively monitored by a guard, we recommend requiring 360 degree camera pan ranges.
Tilt range defines how far vertically (up and down) a cctv security camera can move. The practical range offered is from 0 to 220 degrees. This attribute is commonly not specified but is important for professional monitoring applications. The key decision to make is whether the application requires a cctv security camera that tilts less than or more than 180 degrees. If a camera tilts less than 180 degrees, an operator will need to awkwardly reposition the camera when a subject walks underneath a camera.
Below are a number of common metrics that are believed to be dangerous to include in a specification. In my experience, these metrics have weak correlation with actual real world performance. All suffer from having no standards nor external validation of results.
• Lux Ratings attempt to convey how well a cctv security camera performs in low light / night time. Common ratings range from .001 lux to .1 lux to 1 lux, etc. These numbers are horribly gamed and nearly impossible to compare across manufacturers. As such, we recommend requiring mechanical cut filter as a proxy for lux rating. If you do require a minimum lux rating, do not require anything less than .5 lux. This is sufficient to ensure a camera has a mechanical cut filter but will not penalize products with more conservative self-ratings.
• Dynamic Range attempts to convey how well a cctv security camera can deal with a wide range of lighting (i.e., WDR). The scale is measured in dB. Most 'normal' cameras have dB ratings in the 60s. WDR cameras generally list dB ratings in the 110 to 120 dB range. Do not try to differentiate quality of WDR cameras by dB measurements as manufacturers self-ratings are incomparable. If you do require a minimum dynamic range for WDR, set it at no higher than 100 dB. This is high enough that it will exclude cameras that have no WDR optimizations at all but will not penalize WDR products with more conservative self-ratings.
• Signal to Noise Ratio (SNR) attempts to convey image quality. Theoretically, the higher the rating the less visible noise is displayed. We strongly recommend to leave this out as there is no standard measurement for IP cameras.
• Digital Zoom or Total Zoom: The only zoom that really counts for differentiating cameras is optical zoom. Unfortunately, many manufacturers conflate digital and optical zoom. For instance, a manufacturer might say a camera has a 216x zoom made up of 18x optical and 12x digital (i.e., 18 x 12 = 216). Only focus on the optical aspect. Digital zoom is roughly the same for all cameras and only 'enlargens' what was already captured.