is the difference between CCD and CMOS cameras?
is meant by resolution of Camera and how important it
is in overall system?
much area can a camera cover?
kind of cabling is required for CCTV system?
a camera be watched on a TV or a Computer?
is video loss and how can it be minimized?
Cables for CCTV Systems
Power Source for Cameras
is CCD chip?
About Resolution of
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
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
where FL = Focal Length
FW = Format width (4.8mm for 1/3" and 6.4mm for
FH = Format height (3.6mm for 1/3" and 4.8mm for
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)
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.
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 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 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.
Power Source for Cameras
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
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.
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: 188.8.131.52
- If you type these numbers in the "Address"
box of any web browser, you will see a live video from
Public IP Address and Private
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
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.
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.
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.
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.