What is CCTV?
CCTV, Closed Circuit Television, is a TV system that does not broadcast TV signals to public but transmits them over to limited monitor(s). CCTV system usually utilizes CCD video cameras (to produce the video), cable or wireless transmitters/receivers or Internet (to transmit the video), and monitors (to see the video). CCTV system is not only applied to the security and surveillance purpose but also to the other fields like laboratory in schools or in private companies, even to production lines in factories. As the application of CCTV system increased, the CCTV industry has developed variety of CCTV equipment like Time Lapse VCRs, combiners, infrared illuminators, Pan/Tilt, etc. The most recent development is web camera server which uses the Internet for remote surveillance.
Digital Video Recorder
DVR, Digital Video Recorder, records video pictures digitally on a hard disk drive (HDD). This HDD, usually built-in, has capacity of 250 Gb, 320 Gb 1 TB or 1.5TB to store the records. You can program the picture resolution and recording speed (how many frames per second) according to the application; real-time or time lapse recording also available. Overwriting the oldest pictures is programmable.
Event alarm recording which records only when a movement is captured within the image frame is easier to program and more reliable than the Time Lapse VCR's alarm recording function. You just assign dots over the screen where you want to detect the movement. As DVR records digitally, the image quality remains the same regardless of how many times the images are stored or rerecorded. And, you can select images quickly by using time/date or alarm search, or just browsing through.
About Resolution of CCTV systems
The resolution of CCTV system is usually measured by TV lines in the field. The vertical TV lines has maximum 350 TV lines in 525-line NTSC system and is not variable. But the horizontal TV lines, which is used as the parameter of picture quality, vary depending on the quality of camera, lens, transmission and monitor.
Camera Resolution
The industry of CCD video camera sensor uses pixels (picture elements) as its quality parameter. Medium resolution of B/W camera in EIA system is 510 horizontal pixels by 492 vertical pixels and is equivalent to 380 TV lines. High resolution is 768(H) x 492(V) pixels and equivalent to 570 TV lines. Colour camera's medium resolution means 330TV lines and high resolution needs more than 460 TV lines.
Monitor Resolution
The monitors in NTSC system have 525 vertical scanning lines regardless of their size. The horizontal 700 TV lines of B/W monitors represents medium level and more than 900 TV lines means high resolution in EIA system. The colour monitor's horizontal resolution of 300 TV lines means medium quality and that of more than 450 TV lines means high resolution.
To maximize the system's resolution, it is recommended to choose a monitor which has better resolution than that of the camera.
What is CCD chip?
A CCD(charge coupled device) consists of several hundred thousand individual picture elements (pixels) on a tiny 1/2", 1/3", or 1/4" chip. Each pixel responds to light falling on it by storing a tiny charge of electricity. The pixels are arranged on a precise grid, with vertical and horizontal transfer registers carrying the signals to the camera's video processing circuitry. This transfer of signals occurs sixty times per second.
The 1/3" CCD chip is the most widely used sensor format these days; its size is 5.5mm (diagonal), 4.4mm (horizontal) and 3.3mm (vertical). The 1/4" sensor format, recently being used in colour cameras, is 4mm (diagonal), 3.2mm (horizontal) and 2.4mm (vertical).
The CCD chip's Electronic Shutter plays a major role in making a fantastic and reliable picture.
* CCD (charge coupled device) and CMOS (complementary metal oxide semiconductor) image sensors are two different technologies for capturing images digitally. Each has unique strengths and weaknesses giving advantages in different applications.
What is Electronic Shutter?
Electronic Shutter, one of the major features of CCD camera, is not really a moving shutter, but a clever piece of signal processing. Under low light conditions, the CCD is allowed to gather signal at the electronic shutter speed of full 1/60th of a second. Under brighter lighting conditions, the video processing chip automatically responds by reading the CCD and then immediately "early purging" it, resulting in precise control over the video level. Even at a shutter speed of 1/100,000th of a second, the CCD camera is still delivering 60 images per second, but each image is gathered over a much shorter period of time. It doesn't end with the CCD...the image is constantly monitored and optimized by advanced on board signal processing circuitry. The end result is a fantastic picture, with no fiddling, no adjustments, and best of all, unbelievable reliability.
About Lens Mount
C-Mount Lens
The flange back (distance from the surface where the lens comes in contact with the camera to the focal point) of C-Mount lens is 17.526mm(0.69 inch). This is the only difference between the C-Mount lens and CS-Mount lens. C-Mount lens, as well as CS-Mount, is 1 inch diameter with 32 TPI (threads per inch). A C-Ring (5mm spacer ring) is required when a C-Mount lens is to be mounted to a CS-Mount camera unless the camera has built-in Flange-back Adjusting Ring.
CS-Mount Lens
The flange back of CS-Mount lens is 12.5mm(0.492 inch). This is 5mm shorter than the C-Mount lens and you need a 5mm spacer ring (or, C-ring) when you mount a C-Mount lens to a CS-Mount camera. (So, CS-Mount camera is always compatible with C- or CS-Mount lens. But, C-Mount camera is not compatible with CS-Mount lens. Most professional cameras are CS-Mount cameras and include a C-ring.)
Fixed Mount Lens
While C- or CS-Mount lens can be changed according to your application, the fixed mount lens, usually found on board cameras and mini cameras does not have standard mount size and can not be changed as easily as C- or CS-Mount lens.
Focal Length and Angle of View
Focal Length(FL) is the distance from the center of a lens to the focal point (CCD sensor chip). FL, as well as the CCD chip's format, is the major factor to determine the angle of view of a lens. For example, a 6.0mm FL lens on 1/3" sensor format has 56.8 degree of diagonal angle of view and a 5.0mm FL lens on 1/3" sensor format has 66.9 degree. But, the same 6.0mm FL lens can see 75.5 degree on 1/2" sensor format. The angle of view also varies a little depending on the manufacturer of the lens.
For 1/3" CCD chip camera, the following formula is a simple way to determine the focal length of a lens needed.
(Distance to subject / Width of subject) x 4.5mm = Focal Length.
For example, if you want to watch a subject of 5.5ft width at 10ft distance with a 1/3" CCD camera, you will need a 8.0mm FL lens. That is, 10ft / 5.5ft x 4.5mm = 8.18mm. A 8.0mm FL lens mounted on 1/3" CCD camera will cover the subject you want to watch.
About Illumination
To see properly, a video surveillance camera requires a certain amount of lights produced by natural or artificial illumination. B/W cameras work with any type of light sources, but colour cameras need lights that contain all the colours in the visible spectrum.
The amount of lights is defined by LUX(Lumens per Square Meter). One LUX is a candle light volume at one meter distance. Followings are some examples of natural lights expressed in LUX.
Full daylight: 10,000 LUX
Very dark day: 100 LUX
Twilight: 10 LUX
Deep twilight: 1 LUX
Full moon: 0.1 LUX
Quarter moon: 0.01LUX
A good B/W camera can see in full moon condition. But, a colour camera will need an additional artificial light in full moon.
The technology in this field enables us to use the Internet or intranet line as a video transmission method. DSL and T-1 are for the Internet connection and LAN (or WAN) is for intranet.
DSL
DSL, Digital Subscriber Line, is commercialized with the speeds from 144 Kbps to 1.1 Mbps. (More than 1.5 Mbps speed is called T-1). To connect a web camera to a DSL, you need a router with RJ45 jack. The router is usually provided by DSL supplier. If you need to connect multiple web cameras, you should have a hub which has multiple RJ45 jacks and which is to be connected to the router. You will have static and public IP address(es) (provided by the DSL supplier) to assign to the web camera(s). This IP address will work as a web site address on the Internet.
At the site of web camera, business grade SDSL(Symmetric DSL) is recommended. SDSL has same upstream and downstream bandwidth, while other DSL (IDSL or ADSL) has larger downstream bandwidth than upstream. As web camera's video data should be uploaded to the Internet, a SDSL is much better for the web camera. But to see the pictures from the camera, that is to download it, a residential DSL or even Cable TV line will work fine. (See more details about the bandwidth and the speed of a web camera)
LAN
LAN, Local Area Network or WAN, Wide Area Network has intranet network in a limited area or organization and has a lot of computers connected to the network. Web camera servers, as like other computers, can be connected to LAN or WAN so that other computers can share the video data. Web camera servers can be connected to LAN or WAN through RJ45 jacks.
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The difference between CCD cameras and CMOS Cameras
Note: The camera styles shown below are just for demonstration purposes. It doesn't matter what the cameras look like. For example the manufacturer of the camera shown below sells this camera both in a CCD model and a CMOS model. From the outside you can't tell the difference but when you look at the image that they produce that's where you see the big difference.. The camera on the Left has a CCD and the one on the Right has a CMOS image sensor.
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CCD VS CMOS
CCD cameras produce a higher quality picture mainly because the image sensor is used strictly for collecting the image and all of the other necessary processing that it takes to deliver the image to the video output of the camera are handled by other components on the camera board.
With a CMOS camera the image senor is not only used to collect the image but it’s also used to process the image. This means several things. One being that that camera is slower at doing what cameras do “Collect light and convert it to a usable image”. The same chip that is used to collect the light is also used to do the necessary processing that it takes to deliver the image to the video output. This means that the process is slower and the image that is products is of lesser quality.
CMOS cameras do have the advantage when it come to power consumption. Because there are less components in the camera board it draws less power meaning that it will run longer if used on a battery.
CCD cameras on the other hand have more components but produce a much higher quality image and draw more powder.
This is why most cell phones use CMOS because it doesn’t put such a heavy load on the phone battery. Then phones that do actually have CCD camera will give a better picture but the battery won’t last nearly as long.
Anyway, the basic concept is that you will get a much better image from a CCD camera then you will from a CMOS camera. The other difference is that sellers out there can get just about the same price for a camera that has a CMOS image sensor as they can for a CCD camera but the catch is that it cost sellers a lot less (Up to 50%) to buy the CMOS cameras. If you’re a seller that relies on the ignorance of your client base rather then making sure that your delivering a quality product then it’s real money making proposition. We prefer to deliver high quality products ensuring that the customer will be happy with what they get rather then how much we can make on the product.
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