A closed-circuit television camera can produce images or recordings for

surveillance Surveillance is the monitoring of behavior, many activities, or information for the purpose of information gathering, influencing, managing or directing. This can include observation from a distance by means of electronic equipment, such as ...

or other private purposes. Cameras can be either

video camera A video camera is an optical instrument that captures videos (as opposed to a movie camera, which records images on film). Video cameras were initially developed for the television industry but have since become widely used for a variety of oth ...

s, or digital stills cameras.

Walter Bruch Walter Bruch (2 March 1908 – 5 May 1990) was a German electrical engineer and pioneer of German television. He was the inventor of Closed-circuit television. He invented the PAL colour television system at Telefunken in the early 1960s. In add ...

was the inventor of the CCTV camera. The main purpose of a CCTV camera is to capture light and convert it into a video signal. Underpinning a CCTV camera is a CCD sensor (

charge-coupled device A charge-coupled device (CCD) is an integrated circuit containing an array of linked, or coupled, capacitors. Under the control of an external circuit, each capacitor can transfer its electric charge to a neighboring capacitor. CCD sensors are a ...

). The CCD converts light into an electrical signal and then signal processing converts this electrical signal into a video signal that can be recorded or displayed on the screen.

Video cameras

Video cameras are either analogue or digital, which means that they work on the basis of sending analogue or

digital Digital usually refers to something using discrete digits, often binary digits. Technology and computing Hardware *Digital electronics, electronic circuits which operate using digital signals ** Digital camera, which captures and stores digital ...

signals to a storage device such as a video tape recorder or

desktop computer A desktop computer (often abbreviated desktop) is a personal computer designed for regular use at a single location on or near a desk due to its size and power requirements. The most common configuration has a case that houses the power supply ...

or laptop computer.

Analogue

These cameras can record straight to a

video tape recorder A video tape recorder (VTR) is a tape recorder designed to record and playback video and audio material from magnetic tape. The early VTRs were open-reel devices that record on individual reels of 2-inch-wide (5.08 cm) tape. They were u ...

which can record analogue signals as pictures. If the analogue signals are recorded to tape, then the tape must run at a very slow speed in order to operate continuously. This is because to allow a three-hour tape to run for 24 hours, it must be set to run on a slow time-lapse basis, usually about four frames per second. In one second, the camera scene can change dramatically. A person for example can have walked a distance of 1 meter, and therefore if the distance is divided into four parts, i.e. four frames or "snapshots" in time, then each frame invariably looks like a blur, unless the subject keeps relatively still. Analogue signals can also be converted into a digital signal to enable the recordings to be stored on a PC as

digital recording In digital recording, an audio or video signal is converted into a stream of discrete numbers representing the changes over time in air pressure for audio, or chroma and luminance values for video. This number stream is saved to a storage ...

s. In that case, the analogue video camera must be plugged directly into a

video capture card Video capture is the process of converting an analog video signal—such as that produced by a video camera, DVD player, or television tuner—to digital video and sending it to local storage or to external circuitry. The resulting digital data a ...

in the computer, and the card then converts the analogue signal to digital. These cards are relatively cheap, but inevitably the resulting digital signals are compressed 5:1 (MPEG compression) for the video recordings to be saved on a continuous basis. Another way to store recordings on a non-analogue media is through the use of a

digital video recorder A digital video recorder (DVR) is an electronic device that records video in a digital format to a disk drive, USB flash drive, SD memory card, SSD or other local or networked mass storage device. The term includes set-top boxes with direct to ...

(DVR). Such a device is similar in functionality to a PC with a capture card and appropriate video recording

software Software is a set of computer programs and associated documentation and data. This is in contrast to hardware, from which the system is built and which actually performs the work. At the lowest programming level, executable code consist ...

. Unlike PCs, most DVRs designed for CCTV purposes are embedded devices that require less maintenance and simpler setup than a PC-based solution, for a medium to a large number of analogue cameras. Some DVRs also allow digital broadcasting of the video signal, thus acting like a network camera. If a device does allow broadcasting of the video, but does not record it, then it's called a video server. These devices effectively turn any analogue camera (or any analogue video signal) into a network TV.

Digital

These cameras do not require a video capture card because they work using a digital signal which can be saved directly to a computer. The signal is compressed 5:1, but DVD quality can be achieved with more compression (MPEG-2 is standard for DVD-video, and has a higher compression ratio than 5:1, with a slightly lower video quality than 5:1 at best, and is adjustable for the amount of space to be taken up versus the quality of picture needed or desired). The highest picture quality of DVD is only slightly lower than the quality of basic 5:1-compression DV. Saving uncompressed digital recordings takes up an enormous amount of hard drive space, and a few hours of uncompressed video could quickly fill up a hard drive. Uncompressed recordings may look fine but one could not run uncompressed quality recordings on a continuous basis.

Motion detection Motion detection is the process of detecting a change in the position of an object relative to its surroundings or a change in the surroundings relative to an object. It can be achieved by either mechanical or electronic methods. When it is done b ...

is therefore sometimes used as a workaround solution to record in uncompressed quality. However, in any situation where standard-definition video cameras are used, the quality is going to be poor because the maximum

pixel In digital imaging, a pixel (abbreviated px), pel, or picture element is the smallest addressable element in a raster image, or the smallest point in an all points addressable display device. In most digital display devices, pixels are the ...

resolution of the image chips in most of these devices is 320,000 pixels (analogue quality is measured in TV lines but the results are the same); they generally capture horizontal and vertical fields of lines and blend them together to make a single frame; the maximum frame rate is normally 30 frames per second. Multi-megapixel IP-CCTV cameras can capture video images at resolutions of several megapixels. Unlike with analogue cameras, details such as number plates are easily readable. At 11 megapixels, forensic quality images are made where each hand on a person can be distinguished. Because of the much higher resolutions available with these types of cameras, they can be set up to cover a wide area where normally several analogue cameras would have been needed.

Network

IP camera An Internet Protocol camera, or IP camera, is a type of digital video camera that receives control data and sends image data via an IP network. They are commonly used for surveillance, but, unlike analog closed-circuit television (CCTV) camera ...

s or network cameras are analogue or digital video cameras, plus an embedded video server having an

IP address An Internet Protocol address (IP address) is a numerical label such as that is connected to a computer network that uses the Internet Protocol for communication.. Updated by . An IP address serves two main functions: network interface ident ...

, capable of streaming the video (and sometimes, even audio). Because network cameras are embedded devices, and do not need to output an analogue signal, resolutions higher than closed-circuit television 'CCTV' analogue cameras are possible. A typical analogue CCTV camera has a

PAL Phase Alternating Line (PAL) is a colour encoding system for analogue television. It was one of three major analogue colour television standards, the others being NTSC and SECAM. In most countries it was broadcast at 625 lines, 50 fields (25 ...

(768x576

s) or

NTSC The first American standard for analog television broadcast was developed by National Television System Committee (NTSC)National Television System Committee (1951–1953), Report and Reports of Panel No. 11, 11-A, 12–19, with Some supplement ...

(720x480 pixels), whereas network cameras may have

VGA Video Graphics Array (VGA) is a video display controller and accompanying de facto graphics standard, first introduced with the IBM PS/2 line of computers in 1987, which became ubiquitous in the PC industry within three years. The term can no ...

(640x480 pixels), SVGA (800x600 pixels) or quad-VGA (1280x960 pixels, also referred to as "megapixel") resolutions. An analogue or digital camera connected to a video server acts as a network camera, but the image size is restricted to that of the video standard of the camera. However, optics (lenses and

image sensor An image sensor or imager is a sensor that detects and conveys information used to make an image. It does so by converting the variable attenuation of light waves (as they pass through or reflect off objects) into signals, small bursts of c ...

s), not video resolution, are the components that determine the image quality. Network cameras can be used for very cheap surveillance solutions (requiring one network camera, some

Ethernet Ethernet () is a family of wired computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN). It was commercially introduced in 1980 and first standardized in 1 ...

cabling, and one PC), or to replace entire CCTV installations (cameras become network cameras, tape recorders become DVRs, and CCTV monitors become computers with TFT screens and specialised software. Digital video manufacturers claim that turning CCTV installations into digital video installations is inherently better). Image:Inside of an EverFocus CCTV camera 20110115.jpg, Looking at the inside of a CCTV camera Image:HitachiVKC150.jpg, Hitachi CCTV color camera Image:PhilipsCCTVlens.jpg, Philips CCTV Varifocal Auto-Iris security camera lens

References

External links