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|Home >> CCTV Glossary of Terms|
|CCTV Glossary of Terms|
Camera Superstore CCTV glossary of terms. To help you speak the language, here are the most commonly used terms and acronyms.|
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Access Card: A coded employee card, usually the size of a credit card,
recognizable to the access control system and read by a reader to
allow access. It can be used for photo identification of the cardholder
and for other data collection purposes. Card technologies include
magnetic strips, Wiegand-effect, proximity (active/passive), barium fer-rite,
and smart/intelligent cards.
Access Code: Any system or method which automatically
controls the passage of people and vehicles into or out of an area or
Access Level: The door or combination of doors and/or barriers an
individual is authorized to pass through.
Access Mask: Electronic alarm masking suppresses the annunciation
of an alarm condition that would have been reported in the secure
mode of operation. Masking does not block the reporting ability of tam-per
or fault conditions that may not be seen when alarm shunting is
Access Point: Each means of entry into a controlled security area,
consisting of a card reader, monitor switches and/or latches. Access
points are wired to an access control panel.
Access Relay: An electrically operated switch that is activated when
access is granted to unlock a door.
Access Time: The period of time during which an access point is
unlocked. (Also see shunt time).
Activity Detection: A feature used in multiplexers that uses video motion
detection techniques to improve the camera update times. It can also give a relay
Alarming: The ability of CCTV equipment to respond to an input signal, normally
a simple contact closure. The response varies depending on equipment type.
Angle of view: The angular range that can be focused within the image size. Small
focal lengths give a wide angle of view, and large focal lengths give a narrow field of
Annunciator: An audible and/or visual signaling device.
Anti-Passback (Anti-Tailgating): This feature protects against more
than one person using the same card or number. It defines each sys-tem
card reader and card I.D. number as IN, OUT, or Other. Once a
card is granted access to and IN reader, it must be presented to an OUT
reader before another IN reader access is granted. Cards will continue
to have access to all authorized OTHER readers.
Aperture: The opening of a lens which controls the amount of light reaching the
surface of the pickup device. The size of the aperture is controlled by the iris
adjustment. By increasing the f stop number (f1.4, f1.8, f2.8, etc.) less light is
permitted to pass to the pickup device.
Aspect ratio: The ratio of the picture frame width to the picture frame height
in standard TV systems. It is 4 units horizontal over 3 units vertical.
Aspherical Lens: A lens designed with a non spherical shape so that it refracts
the light passing through it to either lower the lens aperture so that it passes more
light or decrease barrel distortion on wide angle lenses.
Attenuation: A decrease or loss in a signal.
Audit Trail: A listing created which may be created in real time which
may be used to monitor the progress of a person through protected
Automatic frequency control (AFC): An electronic circuit used whereby the frequency of an oscillator is automatically maintained within specified limits.
Automatic gain control (AGC): An electronic circuit used by which the gain of a signal is automatically adjusted as a function of its input or other specified parameter.
Automatic iris lens: A lens in which the aperture automatically opens or closes
to maintain proper light levels on the faceplate of the camera pickup device.
Automatic Level Control (A.L.C.): A feature on Auto iris lenses (also known as the peak/average control). Adjusting this control allows the auto iris circuitry to either take bright spots more into consideration (peak), bringing out detail in bright areas, or less into consideration (average) bringing out detail in shadows.
Auto-terminating: A feature where the equipment (ex. Monitor) automatically selects the correct termination depending on whether the video output BNC is connected.
Auto White Balance: A feature on color camera that constantly monitors the light and adjusts its color to maintain white areas.
BNC:Bayonet Neill-Concelman. The connector was named after its bayonet mount locking mechanism and its two inventors, Paul Neill of Bell Labs (inventor of the N Connector ) and Amphenol engineer Carl Concelman (inventor of the C connector )
Back focal distance: The distance from the rear most portion of the lens to the
Back Light Compensation (B.L.C.): A feature on newer CCD cameras which
electronically compensates for high background lighting to give detail which would
normally be silhouetted.
Badge: To use a card key in a reader to gain access to
protected areas; a card key itself, especially one with a photo I.D.
Bandwidth: A measure of the carrying capacity of information over a network. Video , for example, takes more bandwidth to transmit over a network than text. Bandwidth is an important issue for Network Administrators.
Biometrics: Refers to readers that identify human attributes such as
fingerprint, hand geometry, voice recognition or retinal analysis.
Black level: The level of the video signal that corresponds to the maximum
limits of the black areas of the picture.
Blanking: The process of cutting off the electron beam in a camera pickup
device or picture tube during the retrace period. It is a signal that is composed of
recurrent pulses at line and field frequencies. It is intended primarily to make the
retrace on a pickup device or picture tube invisible.
Blooming: The halation and defocusing effect that occurs around the bright
areas of the picture (highlight) whenever there is an increase in the brightness
Bridging: A term indicating that a high impedance video line is paralleled,
usually through a switch, to a source of video
Buffer Capacity: Refers to the amount of information the system can
store, this may include the users, time of day and specific door.
"C" mount/"CS" mount: CCTV lenses are available in two
different lens mounts. "C-mount" lenses have a flange back distance of 17.5mm
vs. 12.5mm for "CS-mount" lenses. Many of today's cameras can accept either type
of lens, but it is important to make sure that camera and lens are compatible and set up
properly. C-mount lenses can be used on CS-mount cameras by utilizing a 5mm adapter or
adjusting the camera for C-mount lenses. Because of the shorter back focal distance,
CS-mount lenses can only be used on CS-mount cameras. Your picture will be out of focus if
you use a CS-mount lens on a C-mount camera.
CCD. (Charged Coupled Device): A CCD. chip that is the pick up devise on a
camera, performing a similar function as a camera tube.
CCTV: The common abbreviation for Closed Circuit Television.
Candlepower: The unit measure of an incident light.
Coatings: Light is lost by reflection from optical surfaces that are intended
to be refractors only. This loss is effectively reduced by very thin coatings on the lens
surfaces. This can be seen as a blue or violet hue on the lens surface.
COAXIAL CABLE: A type of cable capable of passing a range of frequencies with
low loss. It consists of a hollow metallic shield in which one or more center conductors
are put in place and isolated from one another and from the shield.
Coercivity: The property of a magnetic material, as on a magnetic
stripe keys, which is a measure of the coercive force. It is used when
describing the strength of magnetic saturation when discussing magnetic
stripe card keys.
Color burst: The portion of a composite video signal that comprises a few
cycles of a sine wave of chrominance subcarrier frequency used to establish a reference
for demodulating the chrominance signal.
Composite video The combined video signal that includes the picture signal,
the vertical and horizontal blanking and synchronizing pulses.
Conditional Refresh: A technique used in slow and fast scan transmission
equipment, where only small screen changes are transmitted. Up to a certain percentage of
the on-screen picture can be updated before a full picture is required.
Crosstalk: An undesired signal that interferes with the desired signal.
Database: A collection of data used and produced by a computer pro-gram.
The files created at the host of the access control system forms
db (Decibel): A measure of the power ratio of two signals. It is equal to ten
times the logarithm of the ratio of the two signals.
DC TYPE lens: An auto-iris lens with internal circuit which receives voltage
and a video signal from the camera to adjust the iris.
Default Gateway The IP Address of the Router, needed to send information or video from one network to another.
Depth of field: The front to back zone in a field of view which is in focus in
the televised scene. With a greater depth of field, more of the scene, near to far, is in
focus. Increasing the f-stop number increases the depth of field of the lens. Therefore,
the lens aperture should be set at the highest f-stop number usable with the available
lighting. The better the lighting, the greater the depth of field possible. In other
words, the depth of field is the area in front of the camera which remains in focus. The
larger the f-number the greater is the depth of field.
Device Address: Value set on an access control device to determine
its unique identity
Digital: A signal that levels are represented by binary numbers.
Distribution Amplifier: A device that accepts a (video) signal and sends it out
to a number of independent outputs.
Distributed Intelligent Devices: Access control devices that make
their own access decisions uploading event messages periodically to
the central processing unit for storage
Door Open Time: The time allowed for a controlled door to remain
open after a valid entry. At the expiration of this time, the system
records a transaction which may be defined as an alarm. If the alarm
bypass relay is used, it would also de-energize at the end of this time.
Duplex (multiplexer): A multiplexer that allows the user to look at
multi-screen images while performing time multiplex recording.
Dwell Time: The length of time a switcher holds on a camera before moving on to
the next in sequence.
E.I. (Electronic Iris): Automatically changes a CCD camerašs shutter to mimic
Auto Iris control, allowing fixed or manual iris lenses to be used in a range of areas
that used to require an auto iris lens.
E.I.A. (Electronic Industry Association): US TV standard 525 lines 60 fields.
Electronic shuttering: Electronic shuttering is the ability of the camera to
compensate for moderate light changes in indoor applications without the use of auto iris
Equalization: The process of correcting losses of certain components in a
Ethernet: A type of LAN that is recognized as an industry standard.
Extension tube: Kit consisting of various size spacers that are used between
the lens and the camera to reduce the lens M.O.D. Generally used for very close-up
applications. Not recommended for zoom lenses due to loss of tracking.
f-number: The f-number indicates the brightness of the image formed by the
lens, controlled by the iris. A smaller f-number means a brighter image.
f-stop: A term used to indicate the speed of a lens. The smaller the f-number,
the greater is the amount of light passing through the lens.
Fiber optics: - Flexible glass fibers used to conduct energy. It is valuable in
the coupling of multi-stage image intensifiers.
Field: One half of a frame, consisting of either the odd or the even numbered
lines, 60 fields are transmitted every second.
Flange back: The distance from the flange of the lens (beginning of the lens
mount) to the focal plane. C-mount lenses have a flange back distance of 17.526mm vs.
12.5mm for CS-mount.
Focal length: The distance from the center of the lens to a plane at which
point a sharp image of an object viewed at an infinite distance from the camera is
produced. The focal length determines the size of the image and the angle of the field of
view seen by the camera through the lens. That is the distance from the center of the lens
to the pickup device.
Foot-candle: It is the light intensity (illumination) of a surface one foot
distant from a source of one candela. It is equal to one lumen per square foot. (1FC = 1
lm ft2). The foot-candle is the unit used to measure incident light.
Frame: The total area of the picture which is scanned while the picture signal
is not blanked.
Front porch: The portion of the composite video signal which lies between the
leading edge of the horizontal blanking pulse and the leading edge of the corresponding
Full Duplex: Simultaneous data transmission in both directions.
Gen-lock A method used to synchronize one or more cameras by external means
such as: composite video, composite sync, horizontal or vertical sync.
Ghost: A shadowy or weak image in the received picture, offset either to the
right or to the left of the primary image. It is the result of transmission conditions
where secondary signals are created and received earlier or later than the primary signal.
Ground: An electrical connection point that is common to either a metal
chassis, a terminal, or a ground bus.
Ground Loop: Caused by different earth potentials in a system. Effects video
pictures in the form of a black shadow bar across the screen or as a tearing in the top
corner of a picture.
Hi-Z (Unterminated): Video input of a piece of CCTV equipment, wired so as to
allow the video signal to be fed to further equipment. Does not necessarily include extra
sockets for the extra coaxial cables.
Horizontal blanking: The blanking signal that is produced at the end of each
Horizontal (hum) bars: Horizontal bars, alternately black and white, which
extend over the entire picture. They are known as venetian-blinds. They may be stationary
or move up or down. They are often caused by approximately 60 Hertz interfering frequency
or its harmonic frequencies.
Horizontal resolution: The maximum number of individual picture elements that
can be distinguished in a single scanning line.
HUB: A device on a network that connects multiple computers together to form a LAN. There are two types of hubs - standard and switching.
- standard hub shares bandwidth across all ports. For example, if you have an eight-port 100 Mps standard hub, then all eight ports share the 100 Mps of bandwidth.
- switching hub each port gets a dedicated amount of bandwidth. For example, if you have an eight-port 100 Mps switching hub, then each port gets a full 100 Mps of bandwidth.
IP Address (Static and DHCP):
Identifies a particular computer on a network to other computers. An IP address is similar to your home address. In a neighborhood, each house has a unique address; on a network each computer must have a unique address. There are two types of IP Addresses - static and DHCP.
static address is where someone physically connects to a computer and defines the IP address for that computer. A static address does not change unless someone physically changes it.
- DHCP (Dynamic Host Configuration Protocol) address is dynamically assigned from a server that contains a pool of addresses. The server leases the computer one of the available addresses for a specified amount of time. Once the specified time has expired, the computer renews the lease or requests a new IP address.
I.S.D.N. (Integrated Services Digital Network): Digital phone lines that allow
transmission of video signals via fast scan at speeds of 128Kb/second; used with terminal
Image size: Reference to the size of an image formed by the lens onto the
camera pickup device. The current standards are: 1", 2/3", 1/2" and
1/3" measured diagonally.
Impedance: The opposition which a circuit or component offers to the flow of
electric current. It is expressed in ohms and is equal to the ratio of the effective value
of the voltage applied to the circuit to the resulting current flow. In A.C. circuits, the
impedance is a complex quantity that includes both resistance and reactance. In D.C.
circuits, it is purely resistive.
Incident light: The light that is falling directly over an object.
Insertion loss: The signal strength loss that occurs when a piece of equipment
is inserted into a line.
Interlace: A scanning process where every other horizontal line is scanned in
one field while the alternate lines are scanned in the next field to produce a complete
Interleaving: A method used in alarms or activity detection which allows extra
frames of video from alarmed cameras to be added to a time multiplexed sequence whilst a
state of alarm exists.
Internet: A public network of computers and people sharing information. Anyone can access the Internet through an Internet service provider
Intranet A private network of computers using web-based technology that lets people within a company share information. Typically this information is confidential to the company and Intranets are not accessible by the general public.
Lag: The image retention of an object after the object has been scanned.
Sometimes, it causes smearing effect.
LAN: Local Area Network; multiple computers connected together to share information. Shared information could be e-mail, files, and printers.
Level control: Main iris control. Used to set the auto-iris circuit to a video
level desired by the user. After set-up, the circuit will adjust the iris to maintain this
video level in changing lighting conditions. Turning the control towards High will open
the iris, towards Low will close the iris.
Line Lock: To synchronize the field sync pulses, of an AC powered camera, to
the frequency of the voltage input (line voltage). looping - A term indicating that a high
impedance device has been permanently connected in a parallel to a video source.
Looping: A term indicating that a high impedance device has been permanently
connected in a parallel to a video source.
Lux: A unit of measuring the intensity of light. (1 FC = 10 lux).
Manual iris lens: A lens with a manual adjustment to set the iris opening (F
stop) in a fixed position. Generally used for fixed lighting applications.
Matrix Switcher: A switcher able to route any of its (camera) inputs to any of
its (monitor) outputs, they often includes telemetry control.
Mechanical Focus (back-focus): The mechanical aligning of the imaging device
with the focal point of the lens; it is most important on zoom lenses to be sure the image
stays in focus throughout the zoom range.
Minimum object distance (MOD): The closest distance a given lens will be
able to focus upon an object. This is measured from the vertex (front) of the lens to the
object. Wide angle lenses generally have a smaller MOD than large focal length lenses.
Modulate: To change or vary some parameter such as varying the amplitude of a
signal for amplitude modulation or the frequency of a signal for frequency modulation. The
circuit which modulates the signal is called a modulator.
Monochrome: Having only one color. In television it is black and white.
Monochrome signal: In monochrome television, a signal for controlling the
brightness values in the picture. In color television, the signal which control the
brightness of the picture, whether the picture is displayed in color or in monochrome.
N/D (Neutral Density) Filter: A filter that attenuates light equally over the
whole visible spectrum.
Network: Computers connected together to share information. Think of a network as a city and the computers as houses within the city. Two types of networks are LAN and WAN.
- LAN: Local Area Network; multiple computers connected together to share information. Shared information could be e-mail, files, and printers. Think of a LAN as a neighborhood.
- WAN: Wide Area Network; multiple LANs connected together, usually over a great distance, to share information. Think of a WAN as all neighborhoods in a city.
Noise: Random spurts of electrical energy or interference.
NTSC: NTSC (National Television System Committee) is an organization that formulated the standards for the current United States color television system. This system is used in most countries of the Americas, as well as other parts of the world. It was designed to be compatible with the existing monochrome TV sets, so that they would not become obsolete and color televisions would also be able to receive monochrome transmissions. NTSC employs 525 lines per frame, 29.97 frames per second and 59.94 fields per second.
Passive: A non powered element of a system.
PAL: PAL (Phase Alternation Line) is a European color TV system featuring 625 lines per frame, 25 frames per second and 50 fields per second. PAL is used mainly in Europe, China, Malaysia, Australia, New Zealand, the Middle East, and parts of Africa.
PCMCIA Card: Personal Computer Memory Card International Association card. PCMCIA cards are about the size of a credit card and these PC Cards have been developed to be a standard for hardware capability expanding devices. Cards used in digital cameras offer removable storage and an easy way to transfer photos from the camera to a notebook or desktop PC.
Peak-to-peak: The amplitude difference between the most positive and the most
negative excursions of a signal.
Pinhole lens: Lens used for applications where the camera/lens must be hidden.
Front of lens has a small opening to allow the lens to view an entire room through a small
hole in a wall.
Pixel: Short for picture element, Pixels are the tiny dots of information that make up a digital image. The more pixels there are on the camera's image sensor (CCD or CMOS), the higher the image resolution will be. The higher the resolution, the clearer an enlarged print can be.
Power: The rate at which electrical energy is applied to or taken from a
device. It is expressed in terms of watts, milliwatts or microwatts.
Pre-position lenses: Zoom lenses which utilize a variable-resistor
(potentiometer) to indicate zoom/focus position to the lens controller. After initial
set-up, this allows the operator to view different pre-set areas quickly without having to
re-adjust the zoom and focus each time.
Random interlace: A scanning technique commonly used in CCTV systems in which
there is no external control over the scanning process. That is, there is no fixed
relationship between adjacent lines and successive fields.
Range finder: Used to determine the focal length needed and what the picture
will look like on the monitor. The user looks through the device and adjusts the range
finder to the desired picture. Numbers on the outside of the range finder indicate the
focal length needed.
Raster: The rectangular pattern of scanning lines upon which the picture is
produced. The illuminated face of the TV monitor without the video information present.
Reflected light: The scene brightness or the light being reflected from a
scene. Usually it represents 5 to 95 percent of the incident light, and it is expressed in
Resolution: A measure of the ability of a camera or television system to
reproduce detail. That is the number of picture elements that can be reproduced with good
definition. It is a factor of the pickup device or the TV CRT characteristics and the
video signal bandwidth.
Retained image: (image burn) A change produced in or on the target of the
pickup device which remains for a large number of frames after the removal of a previously
stationary light image and which yields a spurious electrical signal that corresponds to
that light image.
Radio Frequency (RF): Signals with a repetition rate above audible range, but
below the frequencies associated with heat and light.
Roll: A loss of vertical sync which causes the picture to move up or down on
the TV screen.
Router A router is a device that connects two networks. The router reads the destination address of information sent over a network and then sends the information to the next step in its route.
RS232: A commonly used computer serial interface.
Saturation (color): - The vividness of a color. It is directly related to the
amplitude of the chrominance signal.
Scanning: The rapid movement of the election beam in a pickup device of a
camera or in the CRT of a television receiver. It is formatted in a line-for-line manner
across the photo sensitive surface which produces or reproduces the video picture. When
referred to a video surveillance field, it is the panning or the horizontal camera motion.
Sensitivity: (pickup device) The amount of current developed per unit of
incident light. It can be measured in watts with the projection of an unfiltered
incandescent source of light at 2870 K degrees to the pickup device surface area. It can
be then expressed in foot-candles.
Server: A computer and its software that provides some service for other computers connected to it through a network.
Signal to noise ratio: The ratio between a useful video signal and unwanted
Simplex (multiplexer): A multiplexer that allows the user to look at
multi-screen images or perform time multiplex recording. It cannot record multiplexer
pictures while showing multi-screen pictures.
Spot filter: A small insert used in a lens to increase the f-stop range of the
S/N (Signal to noise) Ratio: Measure of noise levels of a video signal: the
higher the number the better.
Super V.H.S. (Super Video Home System): A new format of high resolution VHS
video recorders, capable of giving greatly improved picture if all features and special
tapes are used. VHS compatible.
Sync: Electronic pulses that are inserted in the video signal for the purpose
of assembling the picture information in the correct position.
Tearing: A picture condition in which horizontal lines are displaced in an
Termination: A non-inductive resistor that has the same resistance as the
characteristic of the cable being used.
Time Base Corrector (T.B.C.): An electronic circuit that aligns unsynchronized
video signals before signal processing. Used in multiplexers and quad splatters.
Tracking: A zoom lens' ability to remain in focus during the entire zoom range
from wide angle to telephoto position.
Vertical interval: The time of vertical retrace.
Vertical retrace: The return of the electron beam to the top of a television
picture tube screen or a camera pickup device target at the completion of the field scan.
Video Motion Detection: A system that uses the video signal from a camera to
determine if there is any movement in the picture and set of an alarm.
Video type lens: An auto-iris lens without an internal circuit to control the
iris. All iris control voltages come from a circuit located within the camera.
Vidicon: A common type of camera pickup tube. It translates the effect of light
striking its photo-sensitive surface into electrical impulses.
WAN: Wide Area Network; multiple LANs connected together, usually over a great distance, to share information.
Zoom lens: A lens system that may be effectively used as a wide angle, standard
or telephoto lens by varying the focal length of the lens.
Zoom ratio: The ratio of the starting focal length (wide position) to the
ending focal length (telephoto position) of a zoom lens. A lens with a 10X zoom ratio will
magnify the image at the wide angle end by 10 times.