Overview

The principles of security are to deter, detect, delay and respond to criminal and anti-social behaviour. CCTV is a highly effective technology which contributes to the deter and detect objectives of the security function. Its use as a crime fighting tool is becoming increasingly widespread in the communities of the Western World. The technological developments in this area are occurring at an astonishing rate and the capabilities of CCTV are escalating significantly. A typical CCTV system consists of the cameras, the signal transmission medium, the monitoring station and the recording capability. Each of these components is important and the way in which they are integrated influences the overall effectiveness of the CCTV system. The purpose of this article is to provide an overview of the components of a CCTV system and to provide some insight into the variables which can be manipulated to achieve the desired outcomes for each particular system.
 

Light Conditions

Light plays a crucial role in video surveillance because without it a picture can not be obtained. Therefore the area to be viewed must be illuminated either naturally, by the sun, or by artificial light sources. The colour, texture and physical shape of the object being viewed will affect the intensity of the reflected light and, in turn, the quality of the picture. Both low light and extremely bright conditions will result in poor image quality as will a lack of contrast between moving objects and the background.

CCTV Cameras

CCTV cameras are responsible for capturing the picture and they achieve this as a result of the light reflecting from an object which is then focused by a lens and captured by what is known as a charged coupled device (CCD) image sensor. The purpose of the camera lens is to focus incoming light onto the sensor producing a picture. The type of lens which is selected depends on the surveillance application for which it is required. Once the light is received by the camera's image sensor it is converted into an electronic signal and transmitted, via the transmission medium, to the display monitor. The most common type of image sensor found in CCTV cameras is the CCD which typically is available in different sizes: ½", 1/3"and 1/4".

The three types of common lenses are fixed focal, vari-focal and zoom lenses. Cameras can be either 'fixed' or 'pan, tilt and zoom' (PTZ). Fixed cameras can be used for both internal and external applications and require manual adjustment of the lens. The PTZ cameras are able to be moved up and down and from side to side by an operator. The operator is also able to zoom in and out. PTZ cameras are best suited to surveillance of large open areas such as car parks, airports and city precincts. This type of surveillance also requires the ability for the camera to zoom in on particular areas or incidents as they occur. PTZ cameras are generally more expensive than fixed due to the larger amount of components that are required for their operation.

Signal Transmission

The most common forms of transmission for CCTV data are 'coaxial cable', 'twisted pair' and 'fibre optics'. 'Coaxial cable' consists of a central core which transmits the signal and an external shield which serves to reduce the effect of electromagnetic interference on the signal transmission. Coaxial can be used for cable runs up to 300m. Where cable runs of greater distances are required 'twisted pair' provides a good alternative to 'coaxial cable' and can be used for cable runs up to 600m without any line repeaters. 'Twisted pair', as the name suggests, consists of a pair of wires twisted around each other repeatedly which serves to reduce the amount of electromagnetic interference, over large distances, resulting in high quality video signal at the receiving end. Another advantage of 'twisted pair' is that four pairs of wires are incorporated into the one cable and so four cameras can be connected on the one cable run. The most effective form of video transmission is achieved through the use of 'fibre optic' cable. 'Fibre optics' provides the best quality and the most secure form of signal transmission and can be used for far greater distances than both 'coaxial' and 'twisted pair'.

System Architecture

CCTV systems are either analogue or digital or a combination of the two. Analogue is the older format and more recent developments have been in the area of digital technology. The digital transmission standard is Internet Protocol (IP) which enables the video signals to be sent over the internet. This can congest an organisation's IT network if not managed carefully. The IP CCTV infrastructure is considerably cheaper to install than a purely analogue system. Where analogue cameras are used instead of IP cameras, streamers or video encoders are used to convert the analogue signal to digital which is then stored on a network video recorder (NVR) or high capacity storage array.

Methods of Storage

There are a number of recording methods available for the storage of CCTV images and each of them has advantages and disadvantages over the others. The coding formats which are commonly used include: 'Motion JPEG', 'Motion JPEG2000', 'H.26x', 'MPEG-1', 'MPEG-2' and 'MPEG-4' as well as the 'Common Intermediate Format' (CIF). CIF refers to the number of horizontal and vertical lines in the video picture frame (the resolution) and the frame rate. The official CIF size is 352 x 288 lines at 25 frames per second', but video can also be transmitted and displayed at 2CIF and 4CIF.

'Motion JPEG' records a very high quality image because it records a full frame image of the video stream. This is great for viewing the video, but is not practical for storage, given the large amount of hard disk space which is required. 'Motion JPEG 2000' enables better compression which results in a good quality image but with a smaller storage requirement than 'Motion JPEG'.

'MPEG' uses what is known as a key frame, at the beginning of the video sequence, which involves recording a full frame of the picture and using that, as a reference, for succeeding images. For each additional frame only those parts of the image which have moved are recorded which results in a reduction in the storage requirements and enables a longer sequence of video to be recorded. 'MPEG-2' uses advances in technology to produce a better video image than 'MPEG-1' but with the same bandwidth and storage space requirements.

The release of the 'MPEG-4' (Part 2) standard, in 2000, enabled video to be encoded at lower bit rates while maintaining a high quality image. It was designed to be suitable for a wider range of video encoding applications, from movies to mobile phones, but it offers very little advantage over 'MPEG-2' for security surveillance applications. 'MPEG-4' (Part 10) is also referred to as 'H.264' and is currently the highest performing video coding format available on the market. 'MPEG-4' (Part 10) can provide the same quality recordable image as 'MPEG-2' but at half the bit rate.

Real-time video surveillance applications require high performing compression standards such as 'MPEG-2' (Part2), 'MPEG-4'(Part2) and 'MPEG-4' (Part10), which offer a higher level of performance than their predecessors. An added advantage of these standards is the fact that it is possible to adjust the compression ratio. This means that by adjusting the compression rate, and therefore the quality and size of the image, various qualities of video can be used.

CCTV Technology

Electronic security systems have become a mainstay of any comprehensive and cohesive security management program. Closed Circuit Television (CCTV) technology has developed extensively over the past decade and enhanced the surveillance capabilities of security departments in both the private and public sectors. While the technology and its capabilities have changed in recent years, the basic system requirements that are outlined in this paper remain. While future articles will focus more specifically on recent technological advances in CCTV technology, the purpose of this article is to provide an overview of the various components that comprise a basic CCTV system. A standard CCTV system consists of the cameras, a data transmission medium, monitors for viewing the footage, keyboards and other equipment for controlling the system and computer hard drives for storing recorded images.

The hardware item that is most representative of a CCTV system due to its visibility is the camera. The cameras are clearly visible in most instances and, along with appropriate signage, aim to deter people from engaging in illegal or inappropriate behaviour, although opinions relating to the effectiveness of CCTV as a crime deterrent vary. CCTV cameras are either fixed focus or Pan, Tilt, Zoom (PTZ), by design and each type serves a different purpose. Fixed focus cameras are employed in areas where the required field of view generally remains unchanged, although fixed cameras can be fitted with manual zoom lenses. These cameras can be found in foyers and waiting areas in facilities such as banks, hospitals and airport lounges, for example. Where fixed cameras are mounted in outdoor areas they are usually encased in a dome type housing to protect the camera from the elements. PTZ cameras are designed to pan (move from side to side), tilt (move up and down) and to zoom (in and out) as directed by the control room operator. These cameras are generally employed outdoors, cover larger areas than the average fixed camera and enable the operator to zoom in on an item, or individual, and track moving vehicles or persons on foot that are of particular interest. Systems incorporating PTZ cameras are generally monitored and operated by security personnel, while smaller CCTV systems, with only a few cameras, may not require constant monitoring and may simply record the images for evidentiary purposes.

While the original CCTV cameras were analogue, and these can still be seen in operation today, the most recent technological advances have been in the development of Internet Protocol (IP) cameras and systems. A network IP camera is a stand-alone device which allows a user to view live, full motion video from anywhere on a computer network, and over the Internet, using a standard web-browser. These network cameras can be connected directly to existing IP networks, eliminating the need for separate and expensive coaxial cable installations. IP cameras have individual IP addresses that enable CCTV images to be viewed over the Internet from anywhere in the world on any Internet ready computer or smart phone. One of the many advantages of IP technology is that it allows the user to record the images that are captured by the camera to a secure location that is situated remotely from the site where the camera is located, thus providing an added level of security against the threat of data interception and theft. IP systems also support additional analytical functions like Video Motion Detection.

Where non IP CCTV systems are installed, the communication medium is one of a number of different cables, depending upon the scale of the system and the distances between the cameras and the CCTV servers. The most common and the cheapest of the transmission media is coaxial cable which is used for cable runs up to a maximum of about 400m, depending on the coaxial type. If the cable run is more than a few hundred metres twisted pair is a good alternative that can be utilised up to about 600m without line repeaters. Another benefit of twisted pair cables is that they typically have four pairs per cable which means that it is possible to connect up to four cameras at the one location using just the one cable run. Fibre optic is the most secure of the CCTV transmission media; however its use is generally limited to very long cable runs, or sensitive installations, due to its higher cost. Fibre optics use light to transmit the data rather than electrical signals that are typically used in other copper based transmission cable types.

Some of the advantages of fibre include:

• Very high data carrying capacity;
• Cables can be installed over very large distances with no loss of data;
• It is difficult to intercept, making it more secure;
• The light signal travels entirely within the fibre causing no interference to the adjacent wires or other optical fibres and is immune to electrical interference; and
• Fibre optic cables are very small and light and are becoming increasingly cost effective to install.

Conversely, terminating fibre optic cables requires special tools and a higher degree of precision in their installation than with any other cable. In addition, switching and routing of fibre optic signals is difficult and the cables are fragile and can, therefore, be easily damaged. All these positives and negatives should be considered when it comes to the use of fibre as a method of data transmission for CCTV installations.

In large commercial settings CCTV cameras are usually monitored by a security guard force that can provide a physical response in the event of an incident. The security guards are either located in a control room, or stand alone building, that contains all the necessary equipment that is required for them to monitor the CCTV system, perhaps in addition to an electronic access control (EAC) and/or intrusion detection system. A typical security control room or monitoring centre consists of a number of monitors for viewing CCTV footage and administering any other appropriate security and building management systems. The more advanced monitoring facilities will have numerous monitors of varying sizes which enable the operator/s to observe multiple cameras at any point in time or watch the footage from one particular camera of interest if they are tracking an individual person, or vehicle, or watching an incident unfold. Other monitors will display additional information including intruder alarm and duress alarm interfaces and emergency management systems, for example.

Whether monitored or not, the data captured by the camera in the form of video footage is generally recorded so it can be used to review incidents and provide evidence at a later date, if required. The recording capabilities and hardware required will vary depending on the number of cameras in the system and the length of time that the recorded images are required to be stored. It is common for recorded images to be stored for up to thirty days in commercial settings and many sites have in excess of 100 cameras. Understandably, large systems such as this have extensive data storage requirements which must be considered in the design of the CCTV system. The storage for smaller systems is usually achieved by installing a digital video recorder (DVR) which typically has up to 16 camera inputs. A separate DVR is used for each of the multiples of 16 cameras that is attached to the system, however, where very large numbers of cameras are installed a network attached storage (NAS) device may be utilised. A NAS device is a server that has large storage capabilities due to the size of the hard drive (generally measured in Terabytes) and is often used in instances where the sheer size of the system means that the number of DVRs required is too extensive to be housed in the security control room due to space restrictions.

As mentioned earlier the most significant recent developments in the field of CCTV have been in relation to IP CCTV technology. In addition, CCTV systems are now becoming increasingly integrated with other security and building management systems to provide a more comprehensive facilities management function in commercial applications.