- What is CCTV?
- What are Common Applications for CCTV?
- Analog or Digital?
- Color vs. Black and White?
- CCTV Components:
- Automatic Cameras
- How to Choose a CCTV Camera?
What is CCTV?
A video monitoring system is more commonly known as Closed Circuit Television Systems (CCTV). A CCTV system is an on premises system consisting of a television camera, video monitor, and a transmission medium (Cable, fiber or wireless) connecting the two. It is used to monitor the premises.
What are Common Applications for CCTV?
Probably the most widely known use of CCTV is in security systems and such applications as retail shops, banks, government establishments, etc. The true scope for applications is almost unlimited. Some examples are listed below.
Security Applications:
Analog or Digital?
In the past, all CCTV Cameras were attached to a Multiplexer (A device which can split multiple camera pictures onto 1 CCTV Monitor). The Multiplexer then sends the camera images to a Time Lapse Video Player (A device which unlike a normal VCR, can prolong video recording for up to 960 hours on a 3 hour tape by missing out frames). This method is still used today for simple CCTV installations but the quality of recording is usually very low (1 Frame Per 12.8 Seconds). Nowadays, most CCTV systems are Digital. Digital Surveillance uses current PC technology to digitize camera images, compress them into a PC friendly format and store them on a PC's Hard Disk Drive. CCTV pictures are stored on a computer Hard Drive which means you can save lots of CCTV footage and access them very easily and quickly. By using a PC to store CCTV footage, you are able to take advantage of today's powerful PC technology and capture CCTV images in High Resolution and Real Time.
Color vs. Black and White?
Color cameras generally require higher levels of lighting than their monochromatic (B/W) counterparts. Color produces a more natural, richer image than black and white and may keep the operator's interest for longer periods of time. It also makes it easier to detect subjects. For example, with a color system a viewer can easily distinguish a red car from a green one, while on a black and white system both cars would appear a similar shade of grey. In retail applications, a color system can help security personnel identify shoplifters and their clothing more easily and convincingly. Color accuracy is extremely important in gambling casinos, where hundreds of dollars can ride on the ability to recognize the difference between maroon chips and red ones.
While the use of color cameras is growing, black and white cameras continue to offer some distinct advantages. Black and white cameras are better suited for extremely low light situations. The ability to capture good quality images in low light situations increase the cost of both black and white and color cameras. Before purchasing cameras, you should consider the crossover points between lighting costs and camera costs. It's possible that low-light cameras will cost less than paying to increase the lighting level of a parking lot.
Cameras:
The starting point for any CCTV system must be the camera. The camera creates the picture that will be transmitted to the control position. Apart from special designs CCTV cameras are not fitted with a lens. The lens must be provided separately and screwed onto the front of the camera. There is a standard screw thread for CCTV cameras, although there are different types of lens mounts.
Cameras come is a variety of shapes and sizes. Some are mounted to be visible for ease of installation and deterrent effect. Others are concealed to enhance detection.
Versatile surveillance cameras are designed to suit almost any application requiring a view of a given location. With the broad selection of available lenses, cameras can be configured to cover broad areas such as parking lots or waiting areas, or tighter, up-close views of entrances and access points.
Lenses:
The lens is an optical device for focussing a desired scene onto the imaging device in a CCTV camera.
Selecting the most appropriate lens can be a complex task because lenses have a number of characteristics that must be considered to match a particular requirement with the best lens for the job.
Lenses are also categorized according to size format. As Camera technology has advanced, sensor chips have reduced in size, requiring lenses to produce smaller images at the focal point. This has made smaller lenses possible (less glass resulting in less physical size and weight) although the requirements of precision manufacturing doesn't permit a proportional price reduction - the component materials of a Lens being a very small proportion of the overall manufacturing cost. The quoted format of the Lens (1", 1/2", 1/3" and now even 1/4") is derived from the ratio of diameter to the viewing image produced. Whilst it is often most cost effective to match the lens format to the camera sensor size, it is possible to use a larger lens on a smaller size camera since the image only needs to be at least as large as the sensor. Using a larger lens can often be advantageous, since it offers greater depth of field (the range of distances from the lens before objects are too close or too far away to be in focus). Larger lenses also mean that the area of the image that is used is taken entirely from the central, flatter part of the lens causing much less corner distortion and better focus.
A lens with a manually adjusted iris can be used in indoor applications, where the lighting level is controllable and consistent. Both manual and fixed iris lenses can be used with cameras which offer a feature known as 'electronic iris' - an on-board technology to effectively reduce the sensor exposure to compensate for the lack of iris control. This can be cost effective, but does not provide the increased depth of field offered by a correctly sized iris.
For external use (where conditions generally vary the most), an automatic iris lens offers the best performance, as the iris aperture automatically adjusts to create the optimum image by monitoring the output signal from the camera. There are a number of different lens types offering this method of iris control. The original design for automatic iris lenses was wholly self-contained, with the image analysing technology built into the lens and an iris that was adjusted by servomotors.
The final lens characteristic to take account of is the light-gathering speed of the lens-expressed as an f-stop number. This literally measures the amount of light captured by the lens in a given period of time; the lower the f-stop range, the more light that can be transmitted.
Monitors:
The monitor receives the transmitted electronic video signal from the camera from the paints it across a cathode ray tube (CRT) to display an image to a viewer. Although similar in function to a TV, a CCTV monitor provides higher lines of resolution (better picture quality) and accepts only video signals rather than RF/antenna signals.
Lines of resolution refers to the total number of horizontal lines the camera or monitor is able to reproduce. The more lines on a screen, the better or sharper the video picture will appear. CCTV monitors can provide up to 1000 lines of resolution compared to an average of 300 lines provided by some TV sets.
Several factors can affect the monitoring function: Size of the monitor, its positioning and angle relative to the viewer, and the quality (resolution) of the monitor itself. In all cases, sufficient growth must be factored into any console design. It's also important to note that all monitors generate heat. Whether on a table or enclosed in a console, be sure to provide adequate ventilation and air-conditioning.
Most CCTV systems use both dedicated monitors and call-up (switchable) monitors. A dedicated monitor displays the video from only one camera. A call-up or switchable monitor enables the operator to call or switch different or multiple cameras into view. Generally call-up/switchable monitors are larger than dedicated monitors and give operators the ability to view multiple images simultaneously (multiplexed) as well as scrutinize the camera image more closely.
Recording Devices:
Time-lapse VCRs have been used as a storage medium for some time. VCRs have some drawbacks including, introduction of noise, wear and tear and the simple requirement that the tape needs to be rewound to access information. In a practical situation the reviewing of tapes to secure the important face shot or scene of crime can involve long and tedious work.
Digital Video Recorder (or DVR) uses a computer hard disk memory to store images and are excellent at reproducing high quality images with little noise or picture degradation and are extremely useful in calling up an alarmed picture. In addition to they may offer a number of additional features:.
PC Based Digital Video Surveillance Capture Cards use a card installed in computer along software to allow you to view your CCTV Cameras, search through previously recorded footage, backup footage to CD/DVD, control pan tilt and zoom cameras either on the PC system or remotely and much much more.
Pan, Tilts and Zoom:
CCTV cameras can be fixed or have pan, tilt, and zoom (PTZ) capabilities. Fixed cameras are mounted on a fixed bracket and cannot move in response to operator commands. PTZ cameras are motor driven and can pan left or right, tilt up or down, and use the lens to zoom in and out. A camera housing protects the camera and lens from vandalism and the environment. It also can enhance the appearance of the camera installation and conceal the equipment from the casual observer. All outdoor cameras require a housing of some type. Protection from cold, heat, dust, dirt, or other elements is needed to ensure optimal performance and extend the life of the camera. Broadly categorized into internal and external usage, pan/tilts are normally selected on the basis of the maximum load they can take.
Transmission Methods:
The purpose of the transmission medium is to carry the video signal from the camera to the monitor. Today, many video transmission methods exist: coaxial cable, fiber optic, phone lines, microwave, and radio frequency. Due to varying application technologies in use within the same CCTV system. The choice of transmission mediums depends on factors such as distance, environments, cost and facility layout. In addition nearly all methods of transmission suffer from various forms of interference or loss. The essence of good design is to minimize this impact. Examples of current video transmission include:
Switchers:
A video switcher enables different cameras to be switched to call-up monitors. In a smaller, cost-conscious applications, a manual switcher allows users to select the camera they want to see by pressing the appropriate button. The most popular type of switcher, a sequential switcher, contains circuitry that will switch one camera to another automatically. The operator can set the length of time (dwell time) that a scene remains on the monitor before sequencing automatically to the next camera. This allows operators to keep tabs on numerous cameras with only one monitor.
Matrix Switcher:
A matrix switcher is a more complex design enabling the user to switch any video signal to any call-up monitor in a large-scale system. They normally incorporate pan, tilt and zoom control and other features such as preset and alarm inputs and outputs.
Multiplexers:
Unlike conventional recording systems, a video multiplexers collects full-screen pictures from several cameras and displays them simultaneously on a monitor. Operators have the option of displaying any camera full screen or multiple cameras in reduced sizes. Multiplexers also can record all cameras in the system onto a single videotape or DVR. The cameras are recorded sequentially at a high rate of speed. As mentioned earlier, a standard video signal is comprised of 30 separate frames each second. In a video system containing 15 cameras, the multiplexers selects two frames from each camera and records them to a single videotape. The result is an effective frame rate of 2 frames per second, instead of the standard 30.
Most multiplexers today contain motion detection features that enables the system to record more frames of video from cameras showing motion than from those not showing any motion. The multiplexer does this by reallocating frames from one camera to another as needed. The net result is higher quality recordings of scenes that are more likely to be important to security personnel.
Quads:
The main feature of a quad is the ability to compress images from four separate cameras and simultaneously display them on a single monitor screen. When four cameras are displayed, each occupies a quarter of the screen. A single camera can be selected and displayed full screen as well. Unlike multiplexers recording, quad recordings yield only what appears on the monitor at the time of recording. If the VCR is recording in quad mode, then the playback is in quad mode.
Safety Applications:
Management Tools
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