Glossary of Security Terms
Aberration: A term from optics that refers to anything affecting the fidelity of the image in regards to the original scene
AC: Alternating current
Activity detection: Refers to a method built into some multiplexers for detecting movement within the camera’s field of view (connected to the multiplexer), which is then used to improve camera recording update rate.
AC/DC: Alternating current / direct current
A/D (or AD): Refers to analog to digital conversion
ADC: Analog to digital conversion. This is usually the very first stage of an electronic device that processes signals into digital format. The signal can be video, audio, control output and similar.
AGC: Automatic gain control. A section in an electronic circuit that has feedback and regulated a certain voltage level to fall within predetermined margins.
ALC: Automatic light control. A part of the electronics of an automatic iris lens that has a function similar to backlight compensation in photography.
Aliasing: An occurrence of sampled date interference. This can occur in CCD image projection of high spatial frequencies and is also known as Moiré patterning. It can be minimized by a technique known as optical low pass filtering.
Alphanumeric video generator (also text inserter): A device for providing additional information, normally superimposed on the picture being displayed; this can range form one or two characters to full-screen alphanumeric text. Such generators us the incoming video signal sync pulses as a reference point for the text insertion position, which means if the video signal is of poor quality, the text stability will also be of poor quality.
Amplitude: The maximum value of a varying waveform.
Analog signal: Representation of data by continuously varying quantities. An analog electrical signal has a different value if volts or amperes for electrical representation of the original excitement (sound, light) within the dynamic range of the system.
ANSI: American National Standards Institute.
Anti-aliasing: A procedure employed to eliminate or reduce (by smoothing and filtering) the aliasing effects.
Aperture: The opening of a lens that 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 (F/1.4, F/1.8, F/2.8, etc.) less light is permitted to pass to the pickup device.
Apostilb: A photometric unit for measuring luminance where, instead of candelas, lumens are used to measure the luminous flux of a source.
Archive: Long-term off-line storage. In digital systems, pictures are generally archived onto some form of hard disk, magnetic tape, floppy disk or DAT cartridge.
Artifacts: Undesirable elements of defects in a video picture. These may occur naturally in the video process and must be eliminated in order to achieve a high-quality picture. The most common are cross-color and cross-luminance.
ASCII: American Standard Code for Information Interchange. A 128-character set that includes the uppercase and lowercase English alphabet, numerals, special symbols and 32 control codes. A 7-bit binary number represents each character. Therefore, one ASCII-encoded character can be stored in one byte of computer memory.
Aspect ratio: This is the ratio between the width and height of a television or cinema picture display. The present aspect ration of the television screen is 4:3, which means four units wide by three units high. Such aspect ratio was elected in the early days of television, when the majority of movies were of the same format. The new, high-definition television format proposes a 16:9 aspect ratio.
Aspherical lens: A lens that has an aspherical surface. It is harder and more expensive to manufacture, but it offers certain advantages over a normal spherical lens.
Astigmatism: The uneven foreground and background blue that is in an image.
Asynchronous: Lacking synchronization. In video, a signal is asynchronous when its timing differs from that of the system reference signal. A foreign video signal is asynchronous before a local frame synchronizer treats it.
ATM: Asynchronous transfer mode. A transporting and switching method in which information does not occur periodically with respect to some reference such as a frame pattern.
Attenuator: A circuit that provides reduction of the amplitude of an electrical signal without introducing appreciable phase or frequency distortion.
ATSC: Advanced Television System Committee (think of it as a modern NTSC.) An American committee involved in creating the high-definition television standards.
Attenuation: The decrease in magnitude of a wave, or a signal, as it travels through a medium or an electric system. It is measured in decibels (dB).
Auto iris (AI): An automatic method of varying the size of a lens aperture in response to changes in scene illumination
AWG: American wire gauge. A wire diameter specification based on the American Standard. The smaller the AWG number, the larger the wire diameter (see the reference table in the camera power supply section).
Back-focus: A procedure of adjusting the physical position of the CCD-chip/lens to achieve the correct focus for all focal length settings (especially critical with zoom lenses).
Back porch: 1. The portion of a video signal that occurs during blanking from the end of horizontal sync to the beginning of active video. 2. The blanking signal portion that lies between the trailing edge of a horizontal sync pulse and the trailing edge of the corresponding blanking pulse. Color burst is located on the back porch.
Balanced signal: In CCTV this refers to a type of video signal transmission through a twisted pair cable. It is called balanced because the signal travels through both wires, thus being equally exposed to the external interference, so by the time the signal gets to the receiving end, the noise will be cancelled out at the input of a differential buffer stage.
Balun: This is a device used to match or transform an unbalanced coaxial cable to a balanced twisted pair system.
Bandwidth: The complete range of frequencies over which a circuit or electronic system can function with minimal signal loss, usually measured to the point of less than 3 dB. In PAL systems the bandwidth limits the maximum visible frequency to 5.5 MHz, in NTSC to 4.2 MHz. The ITU 601 luminance channel sampling frequency of 13.5 MHz was chosen to permit faithful digital representation of the PAL and NTSC luminance bandwidths without aliasing.
Baseband: The frequency band occupied by the aggregate of the signals used to modulate a carrier before they combine with the carrier in the modulation process. In CCTV the majority of signals are in the baseband.
Baud: Date rate, named after Maurice Emile Baud, which generally is equal to 1 bit/s. Baud is equivalent to bits per second in cases where each signal event represents exactly 1 bit. Typically, the baud settings of two devices must match if the devices are to communicate with one another.
BER: Bit error rate. The ratio of received bits that are in error relative to the total number of bits received, used as a measure of noise induced distortion in a digital bit stream. BER is expressed as a power of 10. For example, a 1 bit error in 1 million bits is a BER of 10-6
Betamax: Sony’s domestic video recording format, a competitor of VHS.
Bias: Current or voltage applied to a circuit to set a reference operating level for proper circuit performance, such as the high-frequency bias current applied to an audio recording head to improve linear performance and reduce distortion.
Binary: A base 2 numbering system using the 2 digits 0 and 1 (as opposed to ten digits [0-9] in the decimal system). In computer systems, the binary digits are represented by 2 different voltages or currents, one corresponding to zero and another corresponding to one. All computer programs are executed in binary form.
Bipolar: A signal containing both positive-going and negative-going amplitude. May also contain a zero amplitude state.
B-ISDN: Broadband Integrated Services Digital Network. An improved ISDN, composed of an intelligent combination of more ISDN channels into one that can transmit more data per second.
Bit: A contraction of binary digit. Elementary digital information that can only be 0 or 1. The smallest part of information in a binary notation system. A bit is a single 1 or 0. A group of bits, such as 8 bits or 16 bits, compose a byte. The number of bits in a byte depends on the processing system being used. Typical byte sizes are 8, 16 and 32.
Bitmap (BMP): A pixel-by-pixel description of an image. Each pixel is a separate element. Also a computer file format.
Bit rate: Bps = Bytes per second, bps=bits per second. The digital equivalent if bandwidth, bit rate is measured in bits per second. It is used to express the rate at which the compressed bitstream is transmitted. The higher the bit rate, the more information that can be carried.
Blackburst (color-black): A composite color video signal. The signal has composite sync, reference burst and a black video signal, which is usually at a level of 7.5 IRE (50 mV) above the blanking level.
Black level: A part of the video signal, close to the sync level, but slightly above it (usually 20 mV – 50 mV) in order to be distinguished from the blanking level. It electronically represents the black part of an image, whereas the white part is equivalent to 0.7 V from the sync level.
Blanking level: The beginning of the video signal information in the signal’s waveform. It resides at a reference point taken as 0 V, which is 300 mV above the lowest part of the sync pulses. Also known as pedestal; the level of a video signal that separates the range that contains the picture information from the range that contains the synchronizing information.
Blooming: The defocusing of regions of a picture where brightness is excessive.
BNC: BNC stands for Bayonet-Neil-Concelman connector, and it is the most popular connector in CCTV and broadcast TV for transmitting a basic bandwidth video signal over a coaxial cable.
B-picture: Bidirectionally predictive coded picture; an MPEG term for a picture that is coded on CCTV broadcast TV for transmitting a basic bandwidth video signal over a coaxial cable.
Braid: A group of textile or metallic filaments interwoven to form a tubular structure that may be applied over one or more wires or flattened to form a strap.
Brightness: In NTSC and PAL video signals, the brightness information at any particular instant in a picture is conveyed by the corresponding instantaneous DC level of active video. Brightness control is an adjustment of setup (black level, black reference).
Burst (color burst): Seven to nine cycles (NTSC) or ten cycles (PAL) of sub-carrier placed near the end of horizontal blanking to serve as the phase (color) reference for the modulated color sub-carrier. Burst serves as the reference for establishing the picture color.
Bus: In computer architecture, a path over which information travels internally among various components of a system and is available to each of the components.
Byte: A digital word made of 8 bits (zeros and ones).
Cable equalization: The process of altering the frequency response of a video amplifier to compensate for high-frequency losses in coaxial cable.
CAD: Computer-aided design. This usually refers to a design of system that uses computer specialized software.
Candela [cd]. A unit for measuring luminous intensity. One candela is approximately equal to the amount of light energy generated by an ordinary candle. Since 1948 a more precise definition of a candela has become: “the luminous intensity of a black body heated up to a temperature at which platinum converges from a liquid state to a solid”.
CATV: Community antenna television.
C-band: A range of microwave frequencies, 3.7~4.2 GHz, commonly used for satellite communications.
CCD: Charge-coupled device. The new age imaging device, replacing the old tubes. When first invented in the 1970’s, it was initially intended to be used as a memory device. Most often used in cameras, but also in telecine, fax machines, scanners, etc.
CCD aperture: The proportion of the total area of a CCD chip that is photosensitive.
CCIR: Committee Consultatif International des Radiocommunique or, in English, Consultative Committee for International Radio, which is the European standardization body that has set the standards for television in Europe. It was initially monochrome; therefore, today the term CCIR is usually used to refer to monochrome cameras that are used in PAL countries.
CCIR 601: An international standard (renamed ITU 601) for component digital television that was derived from the SMPTE RP1 25 and EBU 3246E standards. ITU 601 defines the sampling systems, matrix values and filter characteristics for Y, Cr, Cb and RGB component digital television. It establishes a 4:2:2 sampling scheme at 13.5 MHz for the luminance channel and 6.75 MHz for the chrominance channels with eight-bit digitizing for each channel. These sample frequencies were chosen because they work for both 525-line 60 Hz and 625-line 50 Hz component video systems. The term 4:2:2 refers to the ration of the number of luminance channel samples to the number of chrominance channel samples; for every four luminance samples, the chrominance channels are each sampled twice. The D1 digital videotape format conforms to ITU 601.
CCIR656: The international standard (renamed ITU 601) defining the electrical and mechanical interfaces for digital television equipment operating according to the ITU 601 standard. ITU 656 defines both the parallel and serial connector pinouts, as well as the blanking, sync and multiplexing schemes used in both parallel and serial interfaces.
CCTV: Close circuit television. A television system intended for only a limited number of viewers, as opposed to broadcast TV.
CCTV camera: A unit containing an imaging device that produces a video signal in the basic bandwidth.
CCTV installation: A CCTV system, or an associated group of systems, together with all necessary hardware, auxiliary lighting, etc., located at the protected site.
CCTV system: An arrangement comprising of a camera and lens with all ancillary equipment required for the surveillance of a specific protected area.
CCVE: Stands for closed circuit video equipment. An alternative acronym from CCTV.
CD: Compact disc. A standard of media as proposed by Philips and Sony, where music and data are stored in digital format.
CD-ROM: Compact disc read only memory. The total capacity of a CD-ROM when storing data is 640 MB.
CDS: Correlated double sampling. A technique used in the design of some CCD cameras that reduces the video signal noise generated by the chip.
CFA: Color filter array. A set of optical pixel filters used in single-chip color CCD cameras to produce the color components of a video signal.
Chip: An integrated circuit in which all the components are micro-fabricated on a tiny piece of silicon or similar material.
Chroma crawl: An artifact of encoded video, also known as dot crawl or cross-luminance, occurs in the video picture around the edges of highly saturated colors as a continuous series of crawling dots and is a result of color information being confused as luminance information by the decoder circuits.
Chroma gain (chroma, color, saturation): In video, the gain of an amplifier as it pertains to the intensity if colors in the active picture.
Chroma key (color key): A video key effect in which one video signal is inserted in place of areas of a particular color in another video signal.
Chrominance: The color information of a color video signal.
Chrominance-to-luminance intermodulation (crosstalk, cross-modulation): An undesirable change in luminance amplitude caused by superimposition of some chrominance information on the luminance signal. Appears in a TV picture as unwarranted brightness variations caused by changes in color saturation levels.
CIE: Commission Internationale de l’Eclairage. This is the International Committee for Light, established in 1965. It defines and recommends light units.
Clamping (DC): The circuit or process that restores the DC component of a signal. A video clamp circuit, usually triggered by horizontal synchronizing pulses, re-establishes a fixed DC reference level for the video signal. A major benefit of a clamp is the removal of low-frequency interference, especially power line hum.
Cladding: The outer part of a fiber optics cable, which is also a fiber but with a smaller material density than the center core. It enables a total reflection effect so that the light transmitted through the internal core stays inside.
Clipping level: An electronic limit to avoid overdriving the video portion of the television signal.
C-mount: The first standard for CCTV lens screw mounting. It is defined with the thread if 1” (2.54mm) in diameter and 32 threads/inch, and the back flange-to-CCD distance of 17.526mm (0.69”). The C-mount description applies to both lenses and cameras. C-mount lenses can be put on both C-mount and CS-mount cameras; only in the latter case an adaptor is required.
CMYK: A color encoding system used by printers in which colors are expressed by the “subtractive primaries” (cyan, magenta and yellow) plus black (called K). The black layer is added to give increased contrast and range on printing presses.
Coaxial cable: The most common type of cable used for copper transmission of video signals. It has a coaxial cross-section, where the center core is the signal conductor, while the outer shield protects it from external electromagnetic interference.
CODEC: Code/Decode. An encoder plus a decoder is an electronic device that compresses and decompresses digital signals. CODECs usually perform A/D and D/A conversion.
Color bars: A pattern generated by a video test generator, consisting of eight equal width color bars. Colors are white (75%), black (7.5% setup level), 75% saturated pure colors red, green and blue, and 75% saturated hues of yellow, cyan and magenta (mixtures of 2 colors in 1:1 ratio without third color).
Color carrier: The sub-frequency in a color video signal (4.43 MHz for PAL) that is modulated with the color information. The color carrier frequency is chosen so its spectrum interleaves with the luminance spectrum with minimum interference.
Color difference signal: A video color signal created by subtracting luminance and/or color information from one of the primary color signals (red, green or blue). In the Beta cam color difference format, for example, the luminance (Y) and color difference components (R-Y and B-Y) are derived as follows:
Y = 0.3 Red + 0.59 Green + 0.11 Blue
R-Y = 0.7 Red – 0.59 Green – 0.11 Blue
B-Y = 0.89 Blue – 0.59 Green – 0.3 Red
The G-V color difference signal is not created because it can be reconstructed from the other three signals. Other color difference conventions include SMPTE, EBU-N1 0 and MII. Color difference signals should not be referred to as component video signals. That term is resaved for the RGB color components. In informal usage, the term “component video” is often used to mean color difference signals.
Color field: In the NTSC system, the color sub-carrier is phase-locked to the line so that on each consecutive line, sub-carrier phase is changed 180 degrees with respect to the sync pulses. In the PAL system, color sub carrier phase moves 90 degrees every frame. In NTSC this creates four different filed types, while in PAL there are eight. In order to make clean edits, alignment of color field sequences from different sources is crucial.
Color frame: In color television, four (NTSC) or eight (PAL) properly sequenced color fields compose one color frame.
Color phase: The timing relationship in a video signal that is measured in degrees and keeps the hue of a color signal correct.
Color sub-carrier: The 3.58 MHz signal that carries color information. This signal is superimposed on the luminance level. Amplitude of the color sub-carrier represents saturation and phase angle represents hue.
Color temperature: Indicates the hue of the color. It is derived from photography where the spectrum of colors is based upon a comparison of the hues produced when a black body (as in physics) is heated from red through yellow to blue, which is the hottest. Color temperature measurements are expressed in Kelvin.
Comb filter: An electrical filter circuit that passes a series of frequencies and rejects the frequencies in between, producing a frequency response similar to the teeth of a comb. Used on encoded video to select the chrominance signal and reject the luminance signal, thereby reducing cross-chrominance artifacts or conversely, to select the luminance signal and reject the chrominance signal, thereby reducing cross-luminance artifacts. Introduced in the S-VHS concept for a better luminance resolution.
Composite Sync: A signal consisting of horizontal sync pulses, vertical sync pulses and equalizing pulses only, with no-signal reference level.
Composite video signal: A signal in which the luminance and chrominance information has been combined using one of the coding standards NTSC, PAL, SECAM, etc.
Concave lens: A lens that has negative focal length; i.e., the focus is virtual and it reduces the objects.
Contrast: A common term used in reference to the video picture dynamic range, i.e., the difference between the darkest and the brightest parts of an image.
Convex lens: A convex lens has a positive focal length, i.e., the focus is real. It is usually called magnifying glass, since it magnifies the objects.
CPU: Central processing unit. A common term used in computers.
CRO. Cathode ray oscilloscope (see Oscilloscope)
Crosstalk: A type of interference of undesired transmission of signals from one circuit into another circuit in the same system. Usually caused by unintentional capacitance (AC coupling).
CS-Mount: A newer standard for lens mounting. It uses the same physical thread as the C-mount, but the back flange-to-CCD distance is reduced to 12.5mm in order to have the lenses made smaller, more compact and less expensive. CS-mount lenses can only be used on CS-mount cameras.
CS-to-C-mount adaptor: An adaptor used to convert a CS-mount camera to C-mount to accommodate a C-mount lens. It looks like a ring 5 mm thick, with a male tread on one side and a female on the other, with 1” diameter and 32 threads/inch. It usually comes packaged with the newer type (CS-mount) of cameras.
CVBS: Composite video bar signal in broadcast television this refers to the video signal, including the color information and syncs.
D/A (also DA): Opposite to A/D, i.e., digital to analog conversion.
Dark current: Leakage signal from a CCD sensor in the absence of incident light.
Dark noise: Noise caused by the random (quantum) nature of the dark current.
DAT (digital audio tape): A system developed initially for recording and playback of digitized audio signals, maintaining signal quality equal to that of a CD. Recent developments in hardware and software might lead to a similar inexpensive system for video archiving, recording and playback.
dB: Decibel. A logarithmic ratio in two signals or values usually refers to power, but also voltage and current. When power is calculated the logarithm is multiplied by 10, while for current and voltage by 20.
DBS: Direct broadcast satellite. Broadcasting from a satellite directly to a consumer user, usually using a small aperture antenna.
DC: Direct current. Current that flows in only one direction, as opposed to AC.
DCT: Discrete cosine transform. Mathematical algorithm used to generate frequency representations of a block of video pixels. The DCT is an invertible, discrete orthogonal transformation between time and frequency domain. It can be either forward discrete cosine transform (FDCT) or inverse discrete cosine transform (IDCT).
Decoder: A device used to recover the component signals from a composite (encoded) source.
Degauss: To demagnetize.
Delay line: An artificial or real transmission line or equivalent device designed to delay a wave or signal for a specific length of time.
Demodulator: A device that strips the video and audio signals from the carrier frequency.
Depth of field: The area in front of and behind the object in focus that appears sharp on the screen. The depth of filed increases with the decrease of the focal length, i.e., the shorter the focal length the wider the depth of field. The depth of field is always wider behind the objects in focus.
Dielectric: An insulating (nonconductive) material.
Differential gain: A change in sub-carrier amplitude of a video signal caused by a change in luminance level of the signal. The resulting TV picture will show a change in color saturation caused by a simultaneous change in picture brightness.
Differential phase: The change in the sub-carrier phase of a video signal caused by a change inn the luminance level of the signal. The hue of colors in a scene change with the brightness of the scene.
Digital disc recorder: A system that allows recording of video images on a digital disc.
Digital signal: An electronic signal where every different value from the real-life excitation (sound, light) has a different value of binary combinations (words) that represent the analog signal.
DIN: Deutsche Industrie-Normen. Germany’s standard.
Disk: A flat circular plate, coated with a magnetic material, on which data may be sorted by selective magnetization of portions of the surface. May be a flexible floppy disk or rigid hard disk. It could also be a plastic compact disc (CD) or digital video disk (DVD).
Distortion: Non- proportional representation of an original.
DMD: Digital micro-mirror device. A new video projection technology that uses chips with a large number of miniature mirrors, whose projection angle can be controlled with digital precision.
DOS: Disk operating system. A software package that makes a computer work with its hardware devise such as hard drive, floppy drive, screen, keyboard, etc.
Dot pitch: The distance in millimeters between individual dots on a monitor screen. The smaller the dot pitch the better, since it allows for more dots to be displayed and better resolution. The dot pitch defines the resolution of a monitor. A high-resolution CCTV or computer monitor would have a dot pitch of less than 0.3mm.
Drop-frame time code: SMPTE time code format that continuously counts 30 frames per second, but drops two frames from the count every minute except for every tenth minute (drops 108 frames every hour) to maintain synchronization of time code with clock time. This is necessary because the actual frame rate of NTSC video is 29.94 frames per second rather than an even 30 frames.
DSP: Digital signal processing. It usually refers to the electronic circuit section of a device capable of processing digital signals.
Dubbing: Transcribing from one recording medium to another.
Duplex: A communication system that carries information in both directions is called a duplex system. In CCTV, duplex is often used to describe the type of multiplexer that can perform two functions simultaneously, recording in multiplex mode and playback in multiplex mode. It can also refer to duplex communication between a matrix switcher and a PTZ site driver, for example.
DV-Mini: Mini digital video. A new format for audio and video recording on small camcorders, adopted by the majority of camcorder manufacturers. Video and sound are recorded in a digital format on a small cassette (66x48x12mm) superseding S-VHS and Hi 8 quality.
D-VHS: A new standard proposed by JVC for recording digital signals on a VHS video recorder.
Dynamic range: The difference between the smallest amount and the largest amount that a system can represent.
EBU: European Broadcasting Union.
EIA: Electronics Industry Association, which has recommended the television standard used in the U.S., Canada and Japan, based on 525 lines interlaced scanning. Formerly known as RMA or RETMA.
Encoder: A device that superimposes electronic signal information on other electronic signals.
Encryption: The rearrangement of the bit stream of a previously digitally encoded signal in a systematic fashion to make the information unrecognizable until restored on receipt of the necessary authorization key. This technique is used for securing information transmitted over a communication channel with the intent of excluding all other than authorized receivers from interpreting the message. Can be used for voice, video and other communications signals.
ENG camera: Electronic News Gathering camera. Refers to CCD cameras in the broadcast industry.
EPROM: Erasable and programmable read only memory. An electronic chip used in many different security products that stores software instructions for performing various operations.
Equalizer: Equipment designed to compensate for loss and delay frequency effects within a system. A component or circuit that allows for the adjustment of a signal across a given brand.
Ethernet: A local area network used for connecting computers. Printer, workstations, terminals, etc. within the same building. Ethernet operates over twisted wire and coaxial cable at speeds up to 10 Mbps. Ethernet specifies a CSMA/CD (carrier sense multiple access with collision detection). CSMA/CD is a technique of sharing a common medium (wire, coaxial cable) among several devices.
External synchronization: A means of ensuring that all equipment is synchronized to the one source.
FCC: Federal Communications Commission (U.S.)
FFT: Fast Fourier Transformation.
Fiber optics: A technology designed to transmit signals in the form of pulses of light. Fiber optic cable is noted for its properties of electric isolation and resistance of electrostatic and electromagnetic interference.
Field: Refers to one-half of the TV frame that is composed of either all odd or even lines. In CCIR systems each field is composed of 625/2 = 312.5 lines, in EIA systems 525/2 = 262.5 lines. There are 50 fields/second in CCIR/PAL, and 60 in the EIA/NTSC TV system.
Film recorder: A device for converting digital data into film output. Continuous tone recorders produce color photographs as transparencies, prints or negatives.
Fixed focal length lens: A lens with a predetermined fixed focal length, a focusing control and a choice of iris functions.
Flash memory: Nonvolatile, digital storage. Flash memory has slower access than SRAM or DRAM.
Flicker: An annoying picture distortion, mainly related to vertical syncs and video fields display. Some flicker normally exists due to interlacing; more apparent in 50 Hz systems (PAL). Flicker shows also when static images are displayed on screen such as computer-generated text transferred to video. Poor digital image treatment, found in low-quality system converts (going from PAL to NTSC and vice versa), creates an annoying flicker on the screen. There are several electronic methods to minimize flicker.
F-number: In lenses with adjustable irises, the maximum iris opening is expressed as a ratio (focal length of the lens) / (maximum diameter of aperture). This maximum iris will be engraved on the front ring of the lens.
Focal length: The distance between the optical center of a lens and the principal convergent focus point.
Focusing control: A means of adjusting the lens to allow objects at various distances from the cameras to be sharply defined.
Foot-candela: An illumination light unit used mostly in American CCTV terminology. It equals ten times (more precisely, 9.29) of the illumination value in luxes.
Fourier Transformation: Mathematical transformation of time domain functions into frequency domain.
Frame: (see also Field). Refers to a composition of lines that make one TV frame. In CCIR/ PAL TV system one frame is composed of 625 lines, while in EIA/NTSC TV system of 525 lines. There are 25 frames/second in the CCIR/PAL and 30 in the EIA/NTSC TV system.
Frame store: An electronic device that digitizes a TV frame (or TV files) of a video signal and stores it in memory. Multiplexers, fast scan transmitters, Quad compressors and even some of the latest color cameras have built-in framestores.
Frame switcher: Another name for a simple multiplexer, which can record multiple cameras on a single VCR (and play back any camera in full screen) but does not have a mosaic image display.
Frame synchronizer: A digital buffer that, by storage and comparison of sync information to a reference and timed release of video signals, can continuously adjust the signal for any timing errors.
Frame transfer (FT): Refers to one of the three principles of charge transfer in CCD chips. The other two are interline and frame-interline transfer.
Frame-interline transfer (FIT): Refers to one of the few principles of charge transfer in CCD chips. The other two are interline and frame transfer.
Frequency: The number of complete cycles of a periodic waveform that occur in a given length of time. Usually specified in cycles per second (Hertz).
Frequency modulation (FM): Modulation of sine wave or carrier by varying its frequency in accordance with amplitude variations of the modulating signal.
Front porch: The blanking signal portion that lies between the end of the active picture information and the leading edge of horizontal sync.
Gain: Any increase or decrease in strength of an electrical signal. Gain is measured in terms of decibels or number of times of magnification.
Gamma: A correction of the linear response of a camera in order to compensate for the monitor phosphor screen nonlinear response. It is measured with the exponential value of the curve describing the non-linearity. A typical monochrome monitor’s gamma is 2.2, and a camera needs to be set to the inverse value of 2.2 (which is 0.45) for the overall system to respond linearly (i.e., unity).
Gamut: The range of voltages allowed for a video signal, or a component of a video signal. Signal voltages outside of the range (i.e., exceeding the gamut) may lead to clipping, crosstalk or other distortions.
Gen-lock: A way o locking the video signal of a camera to an external generator of synchronization pulses.
GHz: GigaHertz. One billion cycles per second.
GB: Gigabyte. Unit of computer memory consisting of about one thousand million bytes (a thousand megabytes). Actual value is 1,073,741,824 bytes.
GND: Ground (electrical).
Gray scale: A series of tomes that range from true black to true white, usually expressed in 10 steps.
Ground loop: An unwanted interference in the copper electrical signal transmissions with shielded cable, which is a result of ground currents when the system has more than one ground. For example, in CCTV, when we have a different earthing resistance at the camera, and the switcher or monitor end. The induced electrical noise generated by the surrounding the electrical equipment (including mains) does not discharge equally through the two earthings (since they are different) and the induced noise shows up on the monitors as interference.
GUI: Graphical user interface.
HAD: Hole accumulated diode. A type of CCD sensor with a layer designed to accumulate holes (in the electronic sense), thus reducing noise level.
HDD: Hard disk drive. A magnetic medium for storing digital information on most computers and electronic equipment that process digital data.
HDTV: High definition digital television. The upcoming standard of broadcast television with extremely high resolution and aspect ratio of 16:9. It is an advancement from the analog high definition, already used experimentally in Japan and Europe. The picture resolution is nearly 2000 x 1000 pixels, and uses the MPEG-2 standard.
Headend: The electronic equipment located at the start of a cable television system, usually including antennas, earth stations, preamplifiers, frequency converters, demodulators, modulators and related equipment.
Helical scan: A method of recording video information on a tape, most commonly used in home and professional VCRs.
Horizontal drive (also Horizontal sync): This signal is derived by dividing sub-carrier by 227.5 and then doing some pulse shaping. The signal is used by monitors and cameras to determine the start of each horizontal line.
Horizontal resolution: Chrominance and luminance resolution (detail) expressed horizontally across a picture tube. This is usually expressed as a number of black to white transitions or lines that can be differentiated. Limited by the bandwidth of the video signal or equipment.
Herringbone: Patterning caused by driving a color-modulated composite video signal (PAL or NTSC) into a monochrome monitor.
Horizontal retrace: At the end of each horizontal line of video, a brief period when the scanning beam returns to the other side of the screen to star a new line.
Horizontal sync pulse: The synchronizing pulse at the end of each video line that determines the start of horizontal retrace.
Hertz: An unit that measures the number of certain oscillations per second.
Housings, environmental: Usually refers to cameras’ and lenses containers and associated accessories, such as heaters, washers and wipers, to meet specific environmental conditions.
HS: Horizontal sync.
Hue (tint, phase, chroma phase): One of the characteristics that distinguishes one color from another. Hue defines color on the basis of its position in the spectrum, i.e., whether red, blue, green or yellow, etc. Hue is one of the three characteristics of television color: see also Saturation and Luminance. In NTSC and PAL video signals, the hue information at any particular point in the picture is conveyed by the corresponding instantaneous phase of the active videosub-carrier.
Hum: A term used to describe an unwanted induction of mains frequency.
Hum bug: Another name for a ground loop corrector.
Hyper-HAD: An improved version of the CCD HAD technology, utilizing on-chip micro-lens technology to provide increased sensitivity without increasing the pixel size.