1) What is the difference between CCD and CMOS cameras?

2) What is meant by resolution of Camera and how important it is in overall system?

3) How much area can a camera cover?

4) What kind of cabling is required for CCTV system?

5) Can a camera be watched on a TV or a Computer?

6) What is video loss and how can it be minimized?

7) About Illumination

8) About Cables for CCTV Systems

9) About Power Source for Cameras

10) What is CCD chip?

11) About IP Address

12) About Resolution of CCTV systems














1) What is the difference between CCD and CMOS cameras?


The very first and important element in a camera is the sensor that captures the image. As in photographic and film cameras the images are captured on film, in CCTV cameras the images are converted into electrical signals with a help of an image sensor which can be a CCD(Changed Coupled Device) or CMOS(Complementary MOSFET) . CCD cameras are more sensitive and produces higher resolution compared to the newly developed CMOS cameras. Ideally for CCTV application CCD cameras are only to be used. CMOS sensors have been long used for imaging in photocopy machines and other scanners. Now same have been experimented for CCTV cameras. However the resolution offered by CMOS cameras is very low and has a shorter life compared to CCD cameras. The only advantage is that they are cheaply priced.

2) What is meant by resolution of Camera and how important it is in overall system?

Reasolution is usally meant by Vertical resoluiton and it is determind by the number of vertical TV lines e.g. 380 TVL or 550 TVL. Horizontal resolution is seldom quoted is a function of frequency. Overall resolution is a function of vertical & horizontal resolutions. Overall resolution may be quantified by number of pixels or picture elements. For B/W camera normal resolution is is 350 - 400 TVLines and high resolution means 550 - 600 TVLines, whereas for a colour camera normal resolution means 250 - 300 TVLines and 450 - 480 TVLines means high resolution.
Note that the resolution of monitor is also important because afterall the resolution of the camera has to be produced on the monitor. So it is meaningless to have a monitor with a lesser resolution than that of the camera.

3) How much area can a camera cover?

The actual area covered by a camera is determined by the lens (focal length) and the format of the camera (i.e 1/3" or 1/2"). The following formulae can determine the distance covered by the camera:
Distance to camera from viewed screen = scene width x FL        or        scene height x FL
                                                                   FW                                       FH
where FL = Focal Length
FW = Format width (4.8mm for 1/3" and 6.4mm for 1/2")
FH = Format height (3.6mm for 1/3" and 4.8mm for 1/2")
Similarly depending on the scene width and height requirement , the focal length of the lens can be easily determined.
e.g Area of scene = 20 ft wide x 15 ft height
Distance to scene = 10 ft
Focal length = 10 x 4.8 =2.4mm
Thus a wide angle lens of F = 2.6mm is required to cover a area of 10 ft (L) x 20 ft (W) x 10 ft (H)

4) What kind of cabling is required for CCTV system ?

Co-axial cables were designed specifically to assist with the reduction of many forms of interface found in TV network. Co-axial are the more common, most well understood form of signal transmission and should always be a first consideration. Co-axial cable are graded using RG numbers which define the attenuation loss in decibels per meter. eg RG-59, RG-6, RG-11. They are also classified by their standardized per unit impedences. For CCTV application coaxial cable of 75 Ohm with single inner conductor and braided outter conductor is specified. CCTV signals may also be transmitted via following medium / link depending on distance and system used.

1) Twisted pair
2) Fibre optic
3) Wireless link
4) Telephone line

5) Can a camera be wached on a TV or a Computer ?

Normaly the CCTV monitor is specially designed to reproduce the CCTV camera images in terms of resolution and speed. However the output available from the camera is a composite video which can be hooked to any screen having facility of video input. It can be a domestic TV or a computer with TV/Video card or TFT LCD with video in. However the resolution of this is lesser and the quality of the image is poor than that on a CCTV monitor.

6) What is video loss and how can it be minimized ?

A video is a composite I Volt p-p signal. It is generated by the camera depending on its specifications. This has to reproduced in replica on the monitor. However there are certain losses which degrade the video signal & affects its resolution ( which is of prime cancern ). These can be cable loss and resolution loss. Cable losses can be taken care by using standerd recommended cable of good quality and can be compensated by using video amplifier. Resolution loss occures in each stage of video processing ( i.e. switching, multiplexing, recording, reproduction ). Which the use of digial equipments losses takes place at the stage of A-D conversion. If a normal resolution camera is recorded on TLVCR through a multiplexer then a final resolution of picture on playback is of 200 TVL . It is possible that such a picture may be of no use for the purpose for which the system was installed. So it is very important to check the resolution of all the video equipment when designing a system.

7) 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 color cameras need lights that contain all the colors 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; 0.01 LUX

A good B/W camera can see in full moon condition. But, a color camera will need an additional artificial light in full moon.

8) About Cables for CCTV Systems

Coaxial Cable
Coaxial cable has proper electrical features to transmit the video signals from the camera to the monitor. Among various coaxial cables, RG59/U is most common with a 75-ohm impedance and can be installed up to 450ft distance without loosing the video quality. This cable is usually connected by BNC connectors at both the ends.

Fiber-Optic Cable
Fiber-Optic Cable is not affected by electrical interference and has no problem even in contact with high-voltage power. It transmits video signals with extremely high efficiency and can run up to miles. The problem is that it is expensive and difficult to handle.

9) About Power Source for Cameras

12VDC
Most board cameras, mini cameras and about one third of the professional cameras work with 12VDC, 100mA to 200mA for B/W cameras and 150mA to 300mA for color ones. These cameras usually have DC jacks to accept DC power plugs. You should be careful about the polarity (positive and negative) for this power source. 12VDC power can be supplied by AC Adapter or battery pack. You may even use a "power cord" plugged to the cigarette lighter in a car.





10) 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 hy 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 color 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.

* A C-MOS (Complementary - Metal Oxide Semiconductor) chip, also a video image sensor, produces much lower quality picture than CCD chip.

11) About IP Address

IP, Internet Protocol, Address works as a website address on the Internet. When it is assigned to a Web Camera, you can open its video page with any web browser such as Microsoft Internet Explorer or Netscape by typing in the IP numbers. (Sample of an IP address: 65.104.93.35 - If you type these numbers in the "Address" box of any web browser, you will see a live video from web camera.)

Public IP Address and Private IP Address
Public IP Address is for the Internet like the above mentioned sample numbers. It's like a public phone number that you can call from any phones connected to the telephone service. Private IP Address, like an intercom numbers inside an organization, works only within a limited area such as LAN or WAN system. If you assign a private IP address to a Web Camera, you can see it in the LAN or WAN system, but not on the Internet. It is a Public IP Address that works on the Internet. There are two types in Public IP Address; Static and Dynamic.

Static IP Address and Dynamic IP Address
Static IP Address, like above-mentioned sample numbers, is an independent address that you can own yourself. Dynamic IP Address, or Floating IP Address is not an independent address and you have to share it with other subscribers. This also works on the Internet, but unlike Static IP Address, the address changes every time you log in. When you want to open the camera assigned with a Dynamic IP Address, you should go to the web site of the web camera's manufacturer where they have a list of all the web camera users who have Dynamic IP Address. Though it works, Dynamic address is not as convenient as Static IP Address. So, you'd better get a Static IP Address when you install a DSL for a web camera.

12) About Resolution of CCTV systems

The resolution of CCTV system is usually measured by TV lines in the field. The vertical TV line has maximum 350 TV lines in 525-line NTSC system and is not variable. But the horizontal TV lines, which are 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. Color 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 color 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.