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.
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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.
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CCTV Components
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.
- Fixed focus lenses are the simplest type of
Lens. The preset focal length means a precise calculation is required to
select the lens most suitable for the location, based on the desired size
of viewing area and its distance from the camera. Typical Lens sizes offer
either 30 degree view - narrow to allow more detail at distance - or 60
degree, which offers a much wider angle of view.
- Varifocal lenses offer more flexibility,
allowing the field of view to be adjusted manually to get the view
required rather than the limited by the constraints of the fixed Lens.
- Zoom lenses are the most complex type,
offering the widest choice of associated features and technologies. Zoom
lenses can be remotely adjusted to allow variation of the focal length.
This means that a single lens can be used to view a wide area until an
intruder is detected whereupon it can be zoomed into capture facial
details. Generally Zoom lenses incorporate an Auto Iris mechanism to
permit 24-hour usage.
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:.
- Ability to view and control the system from
computers around the world.
- Interconnectivity to Computer networks.
- Motion Detection for setting alarm events and
immediate retrieval.
- Ability to go direct to a time or incident without
the need to search through hours of videotape.
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 Domes
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:
- Coaxial Cable- A coaxial cable is one that
provides a continuous physical connection - or closed circuit - between
the camera and the monitor. The cable is shielded to minimize interference
from any nearby electronic devices or electrical wires. Copper braided
coaxial cable is recommended to maximize conductivity and minimize
potential interference. For traditional CCTV systems, as well as many
applications today, this is the most common economical method of signal
transmission over relatively short distances (few hundred feet).
- Fiber Optics- Fiber optic technology
changes an electronic video signal into pulsed or laser light and injects
(transmits) it into one end of a glass rod (the fiber optic cable). At the
other end, a receiver translates the pulsed light back into an electronic
signal capable of being displayed on a monitor. The transmission is
unaffected by any kind of interference, water in conduit or high voltage
being run in the same conduit. Fiber optic capable have a large signal
capacity (bandwidth) and no possibility of a spark from a broken fiber.
Hence, there is no fire hazard to a facility even in the most flammable
environment. Fiber optics offers a cost-effective method of sending large
transmissions over long distances.
- Telephone line- A telephone line is a
standard twisted pair of wires that can transmit the image for distances
up to one kilometer without signal boosting. The dedicated line connects
the transmitter (camera end) with a receiver (monitor end). Through the
use of specialized transmission and receiver equipment, it is possible to
use standard telephone lines for video signal transmission (RSM).
- Microwave- If already in place, microwave
can be a very efficient and cost-effective method of delivering black and
white or color video. Microwave turns the video and data signals into high
radio frequency signals and transmits them from one point to another via
free air and space. A receiver then converts the transmission back into
the video and data signals and displays the scene on a monitor. Good
quality transmission can be achieved over a line of sight path. Microwave
technology offers a large bandwidth to carry video, however it can be
affected by environmental conditions. It is a practical option when a wire
path between the camera and the monitor locations cannot be established or
is prohibitively expensive. Microwave transmissions are regulated by the
FCC and a license is required.
- Radio Frequency- Radio frequency (RF) is a
reliable, but short distance, line of sight video transmission technology.
It is becoming increasingly popular where hardwiring methods are easier
impossible or impractical, and has been used successfully to reduce
cabling costs even within large buildings. Environment conditions or other
RF in the area can affect it.
- Network/IP Cameras- Cameras can be
connected Ethernet IP networks with a built-in 10Base-T/100Base-TX
Ethernet connection to allow you to monitor and control the units via an
IP-protocol network from a networked PC. The cameras can operate on
multiple protocols, including TCP/IP, HTTP, FTP, SMTP, DHCP, and others,
depending on model. This flexibility allows you to utilize existing LANs,
WANs, or Virtual Private Networks - and even the public Internet - to
monitor remote locations without installing standalone video networks.
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.
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Automatic Cameras
Continuous still cameras, also known as automatic
cameras, take pictures at preset intervals and may be turned on and off by a
timing mechanism during certain hours.
Sequence cameras take photos only when activated. A
push button, connection with a holdup system or connection to a motion
sensor or alarm may be used to activate the camera.
Both types of cameras usually use film cartridges
which are removed to be developed after the camera is activated.
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How to Choose a CCTV Camera?
Choosing the correct CCTV Camera for your
surveillance system is very important. The CCTV Camera, together with a CCTV
Lens, uses a CCD (Charge Coupled Device) sensor that captures the image and
turns it into an electric signal which can be sent to a monitor or
surveillance system.
You need to decide the following when choosing a CCTV
camera & lens:
- The environment the camera will be in i.e. Will
the camera be situated:
Indoors / Outdoors
- The amount of light or variable light conditions
for the camera i.e. Will the camera have to record in low-light
conditions?
- The Field of View required for the camera. How
wide or narrow an angle you require. The distance within which objects in
a picture are in focus.
- The Focal Length- How far away objects you wish to
record will be from the camera
- Your budget
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How Do I Find a Qualified CCTV Installer?
The New York Department of Public Safety Private
Security Board (PSB) requires that CCTV businesses and installers of CCTV
equipment be licensed. Ask for a license number when evaluating potential
companies.
LIAA members are here for you to answer your
questions and respond to your needs. Remember, it is important to be a smart
consumer, but you do not need to be a security expert that is what we are
here for! To find a LIAA
company in your area click here.
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