Alternating Current Adapter; when plugged to AC Power (usually 117VAC/60Hz in the United States) it produces 12VDC, 24VAC or others. "UL Listed" and "Regulated" recommended. It is also called Power Transformer.

<More details>
12VDC
Most board cameras, mini cameras and about one third of the professional cameras work with 12V DC 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. 12V DC power can be supplied with AC Adapter or battery pack. You may even use a "power cord" plugged to the cigarette lighter in a car.
24VAC
About two thirds of the professional cameras work with 24VAC, 20VA to 40VA. The cameras usually have screw type connections and you don't need to worry about the polarity. This power is usually supplied with AC Adapter and you need to prepare separate power cable for the connection. Unlike 12VDC, this power can be transmitted to a long distance up to 450ft and is proper for the cameras that are to be installed out-door or when you don't have the power outlet near the camera.
< DIN Cable >
When a camera is connected to a monitor by DIN cable like in most "observation system*", the power (usually 12VDC) is supplied from the monitor so that you don't need to worry about the power for the camera.(* The "observation system" means the monitor has a built-in quad splitter or switcher and has usually 4 DIN jacks. But, some observation systems which are packaged by dealers or retailers may have a monitor without DIN jack and the power for the camera should be supplied separately.)

Alternating Current Power. In the United States, the standard AC Power is single-phase 117VAC/60Hz and is provided from power outlets in the house. 24V AC power can be produced from an AC Adapter.

The video signal is amplified at low light levels by an automatic gain control circuit. Unfortunately noise is also amplified. In some cameras the gain level can be controlled manually. (MGC = manual gain control).

Continuously variable numerical values such as voltage, current, etc.(The CCD camera produces analogue video signals.)

< What is a CCD? >
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 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.

The scene angle that a video camera lens can show on the monitor, like Diagonal Angle, Horizontal Angle and Vertical Angle, usually described in degree

<More details>
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.

Automatically adjusts the lens focus from surrounding scene and keeps a moving object in focus.

A diaphragm device in the lens that adjusts to light level changes. The iris diaphragm opens or closes the aperture to control the amount of lights coming through the lens.

A balun is a device that joins a balanced line (one that has two conductors, with equal currents in opposite directions, such as a twisted pair cable) to an unbalanced line (one that has just one conductor and a ground, such as a coaxial cable). A balun is a type of transformer: it's used to convert an unbalanced signal to a balanced one or vice versa. Baluns isolate a transmission line and provide a balanced output. A typical use for a balun is in a television antenna. The term is derived by combining balanced and unbalanced.

In a balun, one pair of terminals is balanced, that is, the currents are equal in magnitude and opposite in phase. The other pair of terminals is unbalanced; one side is connected to electrical ground and the other carries the signal.
Balun transformers can be used between various parts of a wireless or cable communications system.?
Some baluns provide impedance transformation in addition to conversion between balanced and unbalanced signal modes; others provide no impedance transformation. For 1:1 baluns (no impedance transformation), the input and output are usually both 50 ohms or 75 ohms. The most common impedance-transformation ratio is 1:4 (alternatively 4:1). Some baluns provide other impedance-transformation ratios, such as 1:9 (and 9:1), 1:10 (and 10:1), or 1:16 (and 16:1). Impedance-transformer baluns having a 1:4 ratio are used between systems with impedances of 50 or 75 ohms (unbalanced) and 200 or 300 ohms (balanced). Most television and FM broadcast receivers are designed for 300-ohm balanced systems, while coaxial cables have characteristic impedances of 50 or 75 ohms. Impedance-transformer baluns with larger ratios are used to match high-impedance balanced antennas to low-impedance unbalanced wireless receivers, transmitters, or transceivers.
In order to function at optimum efficiency, a balun must be used with loads whose impedances present little or no reactance. Such impedances are called "purely resistive."  As a general rule, well-designed communications antennas present purely resistive loads of 50, 75, or 300 ohms, although a few antennas have higher resistive impedances.

The number of hertz (cycles per second) showing the difference between the lower and upper frequencies of a frequency band Video uses higher frequency than audio, thus requires a wider bandwidth.

A lens system that has two different focal length lenses and images two identical or different scenes onto a single camera sensor. The two captured scenes appear as a split image on the monitor.

Bayonet Neil-Concelman or British Naval Connector. A connector widely used in the CCTV industry, usually for coaxial cable. Easy to install and reliable with little video signal loss

The manual bias control on a cathode ray tube or other display device that controls the average brightness and also the contrast of a picture

An application program that provides a way to look at and interact with all the information on the World Wide Web Netscape and Microsoft Internet Explorer are the two browsers that vast majority uses.

Abbreviated with capital "B". A unit of data that is eight bits long and is used by most computers to represent a character such as a letter, number or symbol

An industry standard for lens mounting
C-Mount is 1inch diameter with 32 threads per inch. A C-Mount lens needs C-ring when it is mounted at a CS-Mount camera.

<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 1inch diameter with 32 TPI (threads per inch).

Complementary - Metal Oxide Semiconductor A video image sensor chip that produces much lower quality picture than CCD chip

Video image sensor
CCD or C-MOS chip

<More details>
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 color cameras, is 4mm (diagonal), 3.2mm (horizontal) and 2.4mm (vertical).

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

Charge Coupled Device. A video image sensor chip
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 color cameras, is 4mm (diagonal), 3.2mm (horizontal) and 2.4mm (vertical).

International Radio Consultative Committee; has made the technical recommendation for the European 625 line standard for video signals.

Closed Circuit Television
It does not broadcast TV signals but transmits them over a closed circuit through electrically conducting cable or wireless transmitter and receiver.

<More details>
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 that uses the Internet for remote surveillance

A part of the CCTV system that receives the video pictures from a CCTV camera and displays them.

<More details>
B/W Monitor and Color Monitor
In the past, 9 to 12 inch (diagonal) B/W monitors were widely used in the field. These days, many people are looking for 14 inches for color monitor and 17 inches for B/W. As the color monitor needs 3 different color dots to produce one pixel of information on the monitor, it usually has lower resolution than B/W monitor.

Single Monitor, Quad Monitor and 4-Ch. Monitor
Single Monitor is usually professional monitor with one video input of BNC jack. Quad splitter, video switcher or multiplexer can be connected to single monitor to combine multiple cameras. Quad monitor has built-in quad splitter and usually has 4 DIN jacks for video inputs. 4-Ch. Monitor has built-in 4 channel video switcher and usually has 4 DIN jacks for video inputs. Quad Monitor or 4-Ch. Monitor is usually a part of packaged observation system and is not compatible with other manufacturer's camera or cable.

A cable that can carry a wide range of frequencies with very low signal loss It consists of a metallic shield with a single wire placed along the center of a shield and isolated from the shield by an insulator.

A combined signals in a television transmission. The picture signal, blanking signal, and vertical/horizontal synchronizing signals are all combined.

An industry standard for lens mounting
CS-Mount is 1inch diameter with 32 threads per inch. A C-Mount lens needs C-ring when it is mounted at a CS-Mount camera.

< More details>
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.)

Installed between a CCTV camera and a monitor, it generates the information of Date, Time and camera ID.

Direct Current Power; can be derived from an AC adapter or from a battery. Among DC voltages of 6, 9, 12, 24, 28, 12VDC is most common in the CCTV industry.
<12VDC>
Most board cameras, mini cameras and about one third of the professional cameras work with 12V DC, 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. 12V DC power can be supplied with AC Adapter or battery pack. You may even use a "power cord" plugged to the cigarette lighter in a car.

Dynamic Host Configuration Protocol; lets network administrators manage centrally and automate the assignment of IP addresses in an organization's network.

Multi-wire cable with DIN connectors at both ends that usually has 5 or 6 inner wires. Different diameter and configuration from maker to maker
<DIN Cable>
Most observation systems that are pre-assembled at the factory have DIN cables with DIN connectors at both ends. DIN cables have 5 or 6 wires inside the configuration of which is, for example; wire 1 is for video, wire 2 is for audio, wire 3 is for power (12VDC, positive), wire 4 and 5 are for speaker (positive and negative), wire 6 is for ground. Mini DIN cable, which is used for mini camera package, comes with 4 wires inside. DIN cable, large or mini, can run up to 250 ft distance without loosing the video quality.

Digital Subscriber Line
A technology for bringing higher-bandwidth information to homes and businesses over ordinary copper telephone lines

<More details>
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 with 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)

Digital Video Recorder records video pictures digitally. DVR, Digital Video Recorder, records video pictures digitally on a hard disk drive(HDD). This HDD, usually built-in, has capacity of 20 Gb, 30 Gb or 60Gb to store the records. You can program the picture resolution and recording time according to the application; real-time or time-lapse recording also available. Overwriting the oldest pictures is programmable. Event alarm recording that 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.

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.

The most widely installed Local Area Network (LAN) technology. Specified in a standard IEEE802.3.10/100 BASE-T, the most commonly installed Ethernet system provides transmission speed up to 100 megabits per second.

A private network
It uses the Internet Protocol to securely share part of the business information with suppliers, vendors or others

Federal Communications Commission; controls also wireless camera system as one of the commercial broadcasting systems.

One of the video transmit way used for a long distance transmission up to miles

<More details>
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.

One video frame is composed of two fields; one field consists of the odd numbered lines in the frame and the other field consists of the even numbered lines.

FOV. The width, height or diameter of a scene to be monitored
Usually determined by the focal length of a lens, the sensor format and the distance to the objects.

Focal Length. The distance from the center of a lens (or, the secondary principal point, if it has) to the focal point (sensor)
The longer the focal length, the narrower is the angle of view.

<More details>
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

It is the distance from the flange surface (contact point between camera and lens) and the focal length and is always fixed, depending on mount type.

Or flash RAM (Random Access Memory). A type of constantly powered nonvolatile memory that can be erased and reprogrammed in units of memory called blocks.

Optical or lens speed. Smaller f-number means faster lens.

<More details>
Optical Speed is about how fast a lens collects lights and is defined by the f-number like f/1.2, f/2.0, etc. This speed is determined by the Focal Length (FL) and the Diameter (D) of a lens; f-number = FL/D.

Larger FL, if the Diameter is same, makes higher f-number (like f/4 or f/8) lens that collects less lights to the camera sensor and results a slower lens. Lower f-number (like f/1.2 or f/1.4) lenses pass more lights to the camera sensor. Larger Diameter, if the FL is given, will make a lower f-number lens which can operate in lower light level.

In conclusion, the lower the f-number, the more lights reaching the camera sensor and the better the video picture. The f-numbers are usually marked at the iris rings of lenses.

FL. The distance from the center of a lens (or, the secondary principal point, if it has) to the focal point (sensor)
The longer the focal length, the narrower is the angle of view.

<More details>
Focal Length. The distance from the center of a lens (or, the secondary principal point, if it has) to the focal point (sensor)
The longer the focal length, the narrower is the angle of view.
<More details>
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.

Field of View
The width, height or diameter of a scene to be monitored
Usually determined by the focal length of a lens, the sensor format and the distance to the objects.

A whole video image; is composed of two interlaced fields. A CCD chip produces 30 frames per second at NTSC system and 25 frames at PAL.

It is a corrective value to take in account the fact that picture display re-produced by monitor is not linear. Generally it is set at 0.45; however with some industrial applications it is preferably set to 1. By changing gamma value the contrast of image is also changed.

As a network product, a hub may include a group of modem cards for dial-in users, a gateway card for connections to a Local Area Network (LAN), and a connection to a line.

Electrical characteristic of a system or component, expressed in ohms. CCTV industry has standardized 75-ohm impedance. In order to operate correctly, a monitor (when being the terminal element of the system) must have the same impedance value as the camera and the transmission cable, i.e. 75 ohm. However when other monitor are connected together and the video signal is looped in the next monitor, only the terminating monitor must have a 75 ohm impedance, while the intermediate monitors must have a high impedance to avoid picture distortions. A switch allows impedance setting between the two values.

Internet Protocol. A set of rules to send and receive messages at the Internet address level

<More details>
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.

An adjustable opto-mechanical aperture built into a camera that controls the amount of lights coming through the lens.

Joint Photographic Experts Group. A graphic image file or a image compression algorithm.

<More details>
Video Image Compression Technology is the core of web cameras because the compressed video file size should be small enough to run fast through a network line of the Internet or LAN. Another main factor to decide the speed of a web camera is the speed (bandwidth) of the network line itself.

How to Compute the Speed

a) " The speed of a network line " divided by 8 is numerator. Please note that 8 bits is 1 Byte. For example,
if you use 192 Kbps DSL line, the numerator is 24 KBps (192 divided by 8)
if you use 384 Kbps DSL line, the numerator is 48 KBps (384 divided by 8)
if you use 1.1 Mbps DSL line, the numerator is 137 KBps (1,100 divided by 8)

b) " The size of the compressed file of a video picture " is denominator. It depends on the format a web camera uses to compress the video picture. For now, Wavelet is the best format for this function. Following table compares the Wavelet and other formats.

Local Area Network
A group of computers and associated devices that share a common communications line

<More details>
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.

The area where a lens is mounted
There are two types; C- or CS-Mount.

<More details>
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 1inch diameter with 32 TPI (threads per inch).

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.

Optical speed, expressed by f-number
Smaller f-number means faster lens.

<More details>
Linux Optical Speed is about how fast a lens collects lights and is defined by the f-number like f/1.2, f/2.0, etc. This speed is determined by the Focal Length (FL) and the Diameter (D) of a lens; f-number = FL/D.

Larger FL, if the Diameter is same, makes higher f-number (like f/4 or f/8) lens that collects less lights to the camera sensor and results a slower lens. Lower f-number (like f/1.2 or f/1.4) lenses pass more lights to the camera sensor. Larger Diameter, if the FL is given, will make a lower f-number lens that can operate in lower light level.

In conclusion, the lower the f-number, the more lights reaching the camera sensor and the better the video picture. The f-numbers are usually marked at the iris rings of lenses.

Scanning is not linear at edges and corners of monitor screen and horizontal and vertical lines appear to be bent. Linearity value shown in monitor specifications is the percentage of this distortion. The smaller is the percentage value shown, the less the picture will be distorted by non linearity and the better thus is the monitor.

Lumens per Square Meter
Unit of illumination amount

<More details>
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 1meter 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 color camera will need an additional artificial light in full moon.

Metal-oxide Semiconductor. One of video image chips like CCD, but it produces lower quality video.

A camera lens equipped with small electric motor that enables focusing lens, opening or closing the iris diaphragm, or changing the focal length.

Moving Picture Experts Group.
A standard for a digital video & audio compression

<More details>
Video Image Compression Technology is the core of web cameras because the compressed video file size should be small enough to run fast through a network line of the Internet or LAN. Another main factor to decide the speed of a web camera is the speed (bandwidth) of the network line itself.

How to Compute the Speed

a) " The speed of a network line " divided by 8 is numerator. Please note that 8 bits is 1 Byte. For example,
if you use 192 Kbps DSL line, the numerator is 24 KBps (192 divided by 8)
if you use 384 Kbps DSL line, the numerator is 48 KBps (384 divided by 8)
if you use 1.1 Mbps DSL line, the numerator is 137 KBps (1,100 divided by 8)

b) " The size of the compressed file of a video picture " is denominator. It depends on the format a web camera uses to compress the video picture. For now, Wavelet is the best format for this function. Following table compares the Wavelet and other formats.

Now, if you send video pictures of 360 by 243 resolution over 384Kbps DSL line, the speed is ;
(Wavelet Format) 48 KBps divided by 3 KBpf = 16 fps (frame per second)
(Other Formats) 48 KBps divided by 15 KBpf = 3.2 fps,

if you send a picture of 720 by 486 resolution over 1.1Mbps DSL line, the speed is ;
(Wavelet Format) 137 KBps divided by 50 KBpf = 2.7 fps
(Other Formats) 137 KBps divided by 250 KBpf = 0.5 fps

< * Above speeds are maximum. Actual speed may be lower depending on the traffic and other conditions. >

Combines two or more video/audio signals into one channel. Usually accepts 10 or 16 video inputs and displays them in various formats.

National Television System Committee; formulates standards for American color television system. NTSC system has 525 horizontal scan lines and 30 frames per second.

Lens speed, expressed by f-number. Smaller f-number means faster lens.

<More details>
Optical Speed is about how fast a lens collects lights and is defined by the f-number like f/1.2, f/2.0, etc. This speed is determined by the Focal Length (FL) and the Diameter (D) of a lens; f-number = FL/D.

Larger FL, if the Diameter is same, makes higher f-number (like f/4 or f/8) lens that collects less lights to the camera sensor and results a slower lens. Lower f-number (like f/1.2 or f/1.4) lenses pass more lights to the camera sensor. Larger Diameter, if the FL is given, will make a lower f-number lens which can operate in lower light level.

In conclusion, the lower the f-number, the more lights reaching the camera sensor and the better the video picture. The f-numbers are usually marked at the iris rings of lenses.

Phase Alternating Line system.
A color television system used in Europe, Australia, parts of Africa and the Middle East
It has 625 horizontal scan lines and 25 frames per second.

Photo Sensor site in the image sensor like CCD chip; converts the input light image to an electronic signal.

<More details>
These are the individual photo-diodes that form the sensor matrix. Their number varies according to sensor type and is strictly related to camera resolution. The number of pixels is usually given in two different forms:

a) Total pixels
It is the total number of pixels on the CCD faceplate; however some of them are not usable.

b) Active pixels
It is the actual number of active pixels; this value is always a lower figure than total pixel, but is the only reliable value.

Picture Element. Photo Sensor site in the image sensor like CCD chip; converts the input light image to an electronic signal.

Combines up to 4 video inputs into one channel and displays them on one monitor screen split into 4.

<More details>
Quad Splitter is a combiner to combine up to 4 cameras and to show them on a monitor screen split into 4 at the same time. Usually, it also has built-in switcher that can display the pictures one by one. Some models have BNC jacks for video inputs and others RCA jacks. You may choose one according to your camera's video connection type. But, if the video input jack is different with your camera's connection, you can get a BNC/RCA converter easily at any electronic parts shop like Radio Shack or Best Buy, etc. B/W splitter works with B/W cameras and color splitter with color cameras. A quad splitter is to be connected to a CCTV monitor, TV or VCR.

Random Access Memory
The place in a computer where the operating system, application programs, and data in current use are kept temporarily so that they can be quickly reached by the computer's processor.

The Radio Corporation of America; conveniently used to describe phono jack and plug, one of the audio/video connectors.

Expressed by TV lines or pixels, it indicates the quality level of video images.

<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.

The Restriction of Hazardous Substances Directive (RoHS) 2002/95/EC was adopted in February 2003 by the European Union. The RoHS directive took effect on July 1, 2006, but is not a law; it is simply a directive. This directive restricts the use of six hazardous materials in the manufacture of various types of electronic and electrical equipment. It is closely linked with the Waste Electrical and Electronic Equipment Directive (WEEE) 2002/96/EC which sets collection, recycling and recovery targets for electrical goods and is part of a legislative initiative to solve the problem of huge amounts of toxic e-waste.

A device on the Internet that determines the next network point to which a data should be forwarded.

Sequential Couleur A'Memorie, a color television system used in France, Russia and other countries that do not use either the NTSC or PAL system. It has 625 horizontal scan lines and 25 frames per second.

Sensitivity can be quoted in two different ways.
a) Usable picture
Sometimes this is called minimum illumination. This gives merely an indication of minimum light level at which the camera start providing an output video signal.
b) Full video
This is the real value to be taken into consideration as it gives the lowest light value at which camera supplies a full output video signal "1V peak to peak". This value is important for the whole CCTV system because many devices need a full signal to operate properly.

Sensitivity can be measured:
a) At the faceplate
In this way, it measures the camera performance when all light falls directly on the sensor faceplate. Although this is a technically correct figure, it never actually happens, because to get a real picture you need a lens, which reduces in some ways the light amount falling on the faceplate.
b) At the lens
This is a more effective value of the actual sensitivity of the camera + lens system. Obviously the lower is the F-No the better result you get

<For instance>
A camera having a value of 0.1Lux (full video) with f1.4 lens has a higher sensitivity than a camera showing the same value of 0.1Lux with f1.2 lens. By using f1.2 lens with the 1st camera its sensitivity would be possibly around 0.08Lux. Another value to be taken into consideration is the scene reflectance (which is the light amount, in percentage, reflected by the scene).
The higher is the reflectance value, the higher is the light amount available to the camera faceplate. Usually the reflectance is something between 65% and 90%.

<For Instance>
A camera having a sensitivity of 0.1Lux (full video) with a f1.2 lens with a reflectance value of 70% is more sensitive than a camera having the same sensitivity (full video) with the same lens but at 90%.
The sensitivity value is normally specified in ‘Lux’. However some American manufacturers give this value in foot-candle. 1Lux = 10fc.

Video Switcher. A device that allows the video signals from multiple cameras to be displayed on a monitor, or recorded on a VCR one at a time in sequence.

<More details>
Video Switcher is a combiner to combine multiple cameras and to show them on a monitor screen one by one, manually or automatically. When it works on automatic sequential mode, you can program the dwelling time on each camera, usually from 1 second to 30 or 60 seconds. Most video switchers have BNC jacks for video input so that if your cameras have RCA connections, you will need BNC/RCA adapters. This adapter may be provided by the equipment supplier or can be found easily at any electronic parts shop like Radio Shack or Best Buy, etc. Most commercialized video switchers are for 4 channels or 8 channels, which can be connected by up to 4 or 8 cameras. Video Switcher works for both B/W and color cameras and is to be connected to a CCTV monitor, TV or VCR.

A computer program that provides services to other computer programs in the same or other computers or, the computer that a server program runs

It is a measure showing the amount of interference caused by noise. Its value is important especially at low light values. The higher its value, the better will be the picture quality at low light levels. It is usually measured with AGC switched on ‘on’ position.

Sequential Switcher or Video Switcher. A device that allows the video signals from multiple cameras to be displayed on a monitor, or recorded on a VCR one at a time in sequence.

<More details>
Video Switcher is a combiner to combine multiple cameras and to show them on a monitor screen one by one, manually or automatically. When it works on automatic sequential mode, you can program the dwelling time on each camera, usually from 1 second to 30 or 60 seconds. Most video switchers have BNC jacks for video input so that if your cameras have RCA connections, you will need BNC/RCA adapters. This adapter may be provided by the equipment supplier or can be found easily at any electronic parts shop like Radio Shack or Best Buy, etc. Most commercialized video switchers are for 4 channels or 8 channels, which can be connected by up to 4 or 8 cameras. Video Switcher works for both B/W and color cameras and is to be connected to a CCTV monitor, TV or VCR.

Transmits luminance and color portions separately, using multiple wires, thus avoiding the color encoding process and its inevitable loss of picture quality.

Most cameras have an internal sync generator that generates both the sync pulse for CCD sensor scanning and the synchronization pulses used by monitor to scan the displayed image. However the internal sync generator is not enough, when the system includes more than one camera. It is thus necessary to have an external synchronization.
There are two ways, nowadays, to have an external synchronization:
a) Gen-lock
A number of cameras is synchronized by an external sync signal. Often the video output signal of one camera is used to synchronize the other cameras, because, being a composite signal, it has the sync pulses.
b) Line-lock
In this case, the power supply frequency is used to lock the camera sync and phase lock must be set. This method cannot be used if camera is DC powered.

Installed between a CCTV camera and a monitor, it generates the information of Date, Time and camera ID.

A video recorder that can be set to record continuously over long period of time
This can be anything from two hours to 960 hours.

<More details>
Time Lapse VCR records up to 24 hours or 960 hours continuously on a standard T-120 VHS tape. For example, if you program to record one picture per every 0.4 seconds the VCR will record for 48 hours on a T-120 VHS tape. This video will show you 2 and half pictures every second. Audio can be recorded only up to 18 hours recording mode on a T-120 VHS tape or 24 hours on a T-160 VHS tape. You can also program a time zone to record daily or weekly. Usually auto-repeat recording is available. When motion detection sensor is connected, it will record for a predetermined length of time when the alarm is triggered. (Home VCRs are not designed for long time recording and is not durable enough to operate continuously for security application.)

Short for unshielded twisted pair, a popular type of cable that consists of two unshielded wires twisted around each other. Due to its low cost, UTP cabling is used extensively for local-area-network(LANs) and telephone connections. UTP cabling does not offer as high bandwidth or as good protection from interference as coaxial or fiber optics cable, but it is less expensive and easier to work with.
UTP cables are not shielded. This lack of shielding results in a high degree of flexibility as well as rugged durability. UTP cables are found in many ethernet networks and telephone systems.

A device that accepts signals from a video camera/microphone and records video/audio on magnetic tape in a cassette
The VCR can play back recorded video/audio on a television set or CCTV monitor.

Switcher or Sequential Switcher
A device that allows the video signals from multiple cameras to be displayed on a monitor, or recorded on a VCR one at a time in sequence.

<More details>
Video Switcher is a combiner to combine multiple cameras and to show them on a monitor screen one by one, manually or automatically. When it works on automatic sequential mode, you can program the dwelling time on each camera, usually from 1 second to 30 or 60 seconds. Most video switchers have BNC jacks for video input so that if your cameras have RCA connections, you will need BNC/RCA adapters. This adapter may be provided by the equipment supplier or can be found easily at any electronic parts shop like Radio Shack or Best Buy, etc. Most commercialized video switchers are for 4 channels or 8 channels, which can be connected by up to 4 or 8 cameras. Video Switcher works for both B/W and color cameras and is to be connected to a CCTV monitor, TV or VCR.

A mathematical function useful in digital signal processing and image compression
In the Internet communications, wavelet has been used to compress images to a greater extent than is generally possible with other methods such as JPEG or MPEG.

<More details>
Video Image Compression Technology is the core of web cameras because the compressed video file size should be small enough to run fast through a network line of the Internet or LAN. Another main factor to decide the speed of a web camera is the speed (bandwidth) of the network line itself.

How to Compute the Speed

a) " The speed of a network line " divided by 8 is numerator. Please note that 8 bits is 1 Byte. For example,
if you use 192 Kbps DSL line, the numerator is 24 KBps (192 divided by 8)
if you use 384 Kbps DSL line, the numerator is 48 KBps (384 divided by 8)
if you use 1.1 Mbps DSL line, the numerator is 137 KBps (1,100 divided by 8)

b) " The size of the compressed file of a video picture " is denominator. It depends on the format a web camera uses to compress the video picture. For now, Wavelet is the best format for this function. Following table compares the Wavelet and other formats.

Now, if you send video pictures of 360 by 243 resolution over 384Kbps DSL line, the speed is ;
(Wavelet Format) 48 KBps divided by 3 KBpf = 16 fps (frame per second)
(Other Formats) 48 KBps divided by 15 KBpf = 3.2 fps,

if you send a picture of 720 by 486 resolution over 1.1Mbps DSL line, the speed is ;
(Wavelet Format) 137 KBps divided by 50 KBpf = 2.7 fps
(Other Formats) 137 KBps divided by 250 KBpf = 0.5 fps

< * Above speeds are maximum. Actual speed may be lower depending on the traffic and other conditions. >

A CCTV Camera with built-in web server computer.

<More details>
Web Camera (or Web Camera Server) is a CCTV Camera with built-in computer server so that you can connect it to a network line such as DSL or T-1 for the Internet or LAN. When you assign an IP address to the camera, you can see the camera's video at any place where an Internet browser (Microsoft Internet Explorer or Netscape) is available because the IP address works as a website address.

The most important thing you have to know about the web camera is the speed. That is, a web camera should have a good image compression technology that can compress the video images to a size small enough to go through the network line with fast speed. For now, the Wavelet is the best compression algorithm with compression rate 30% to 300% higher than other technology such as JPEG or MPEG.

Another excellent feature of web camera is that you can program it to send you an email with up to 5 pictures when the movement is detected with the camera. And it usually has enough flash memory for you to customize your own Internet homepage.