AGC
Automatic Gain Control. A circuit for
automatically controlling amplifier gain in order to maintain a constant
output voltage with a varying input voltage within a predetermined range
of input-to-output variation.
Aperture
In television optics, it is the
effective diameter of the lens that controls the amount of light
reaching the photoconductive or photo emitting image pickup sensor.
Aperture
Correction
Compensation for the loss in sharpness
of detail because of the finite dimensions of the image elements or the
dot-pitch of the monitor.
Aspect
Ratio
The ratio of width to height for the
frame of the televised picture. 4:3 for standard systems, 5:4 for 1K x
1K, and 16:9 for HDTV.
Attenuation
In general terms, a reduction in
signal strength.
Auto
Balance
A system for detecting errors in color
balance in white and black areas of the picture and automatically
adjusting the white and black levels of both the red and blue signals as
needed for correction.
Auto
Light Range
The range of light, e.g., sunlight to
moonlight, over which a TV camera is capable of automatically operating
at specified output.
Automatic Brightness Control
In display devices, the self-acting
mechanism which controls brightness of the device as a function of
ambient light.
Automatic Frequency
An arrangement whereby the frequency
of an oscillator is automatically maintained within specified limits.
Automatic Gain Control
A process by which gain is
automatically adjusted as a function of input or other specified
parameter.
Automatic Iris Lens
A lens that automatically adjusts the
amount of light reaching the imager.
Automatic Light Control
The process by which the illumination
incident upon the face of a pickup device is automatically adjusted as a
function of scene brightness.
Back Porch
That portion of the composite picture
signal which lies between the trailing edge of the horizontal sync pulse
and the trailing edge of the corresponding blanking pulse.
Bandwidth
The number of cycles per second
(Hertz) expressing the difference between the lower and upper limiting
frequencies of a frequency band; also, the width of a band of
frequencies.
Bar
Test Pattern
Special test pattern for adjusting
color TV receivers or color encoders. The upper portion consists of
vertical bars of saturated colors and white. The power horizontal bars
have black and white areas and I and Q signals.
Blooming
The defocusing of regions of the
picture where the brightness is at an excessive level, due to
enlargement of spot size and halation of the fluorescent screen of the
cathode-ray picture tube. In a camera, sensor element saturation and
excess which causes widening of the spatial representation of a spot
light source.
Bounce
Sudden variations in picture
presentation (brightness, size, etc.,) independent of scene
illumination.
Brightness
The attribute of visual perception in
accordance with which an area appear to emit more of less light.
(Luminance is the recommended name for the photo-electric quantity which
has also been called brightness.)
Broadband
In television system use, a device
having a band pass greater than the band of a single VHF television
channel.
Burned-In-Image
Also called burn. An image which
persists in a fixed position in the output signal of a camera tube after
the camera has been turned to a different scene or, on a monitor screen.
CCD
See Charge Coupled Device
C Mount
A television camera lens mount of the
16 mm format, 1 inch in diameter with 32 threads per inch.
CCTV
Common abbreviation for Closed-Circuit
Television.
Charge-Coupled Device
CCD. For imaging devices, a
self-scanning semiconductor array that utilizes MOS technology, surface
storage, and information transfer by shift register techniques.
Chroma
That quality of color which embraces
both hue and saturation. White, black, and grays have no chroma.
Chroma
Control
A control of color television receiver
that regulates the saturation (vividness) of colors in a color picture.
Chroma Detector
Detects the absence of chrominance
information in a color encoder input. The chroma detector automatically
deletes the color burst from the color encoder output when the absence
of chrominance is detected.
Chromatic Aberration
An optical defect of a lens which
causes different colors or wave lengths of light to be focused at
different distances from the lens. It is seen as color fringes or halos
along edges and around every point in the image.
Chromaticity
The color quality of light which is
defined by the wavelength (hue) and saturation. Chromaticity defines all
the qualities of color except its brightness.
Chrominance
A color term defining the hue and
saturation of a color. Does not refer to brightness.
Chrominance Signal
That portion of the NTSC color
television signal which contains the color information.
Clamp
A device which functions during the
horizontal blanking or synchronizing interval to fix the level of the
picture signal at some predetermined reference level at the beginning of
each scanning line.
Clamping
The process that established a fixed
level for the picture level at the beginning of each scanning line.
Clipping
The shearing off of the peaks of a
signal. For a picture signal. This effects the positive (white).
Coaxial
Cable
A particular type of cable capable of
passing a wide range of frequencies with very low signal loss. Such a
cable in its simplest form, consists of a hollow metallic shield with a
single wire accurately placed along the center of the shield and
isolated from the shield.
Color
Burst
That portion of the composite color
signal, comprising a few cycles of a sine wave of chrominance sub
carrier frequency, which is used to establish a reference for
demodulating the chrominance signal. Normally approximately 9 cycles of
3.579545 MHz.
Color
Edging
Extraneous colors appearing at the
edges of colored objects, and differing from the true colors in the
object.
Color
Encoder
A device which produces an NTSC color
signal from separate R, G, and B video inputs.
Color
Fringing
Spurious colors introduced into the
picture by the change in position of the televised object from field to
field.
Color
Purity
The degree to which a color is free of
white or any other color. In reference to the operation of a tri-color
picture tube it refers to the production of pure red, green or blue
illumination of the phosphor dot face plate.
Color Saturation
The degree to which a color is free of
white light.
Color Sync Signal
A signal used to establish and to
maintain the same color relationships that are transmitted.
Color Transmission
The transmission of a signal which
represents both the brightness values and the color values in a picture.
Composite Video Signal
The combined picture signal, including
vertical and horizontal blanking and synchronizing signals.
Compression
The reduction in gain at one level of
a picture signal with respect to the gain at another level of the same
signal.
Contrast
The range of light to dark values in a
picture or the ratio between the maximum and minimum brightness values.
Contrast Range
The ratio between the whitest and
blackest portions of television image.
Convergence
The crossover of the three electron
beams of a three-gun tri-color picture tube. This normally occurs at the
plane of the aperture mask.
Crosstalk
An undesired signal from a different
channel interfering with the desired signal.
dB
Basically, a measure of the power
ratio of two signals. In system use, a measure of the voltage ratio of
two signals, provided they are measured across a common impedance.
Decoder
The circuitry in a color TV receiver
which transforms the detected color signals into a form suitable to
operate the color tube.
Definition
The fidelity of a television system to
the original scene.
Depth
of Field
The in-focus range of a lens or
optical system. It is measured from the distance behind an object to the
distance in front of the object when the viewing lens shows the object
to be in focus.
Depth
of Focus
The range of sensor-to-lens distance
for which the image formed by the lens is clearly focused.
Digital Signal Processing
An algorithm within the camera that
digitizes data (the image). Examples include automatic compensate for
backlight interference, color balance variations and corrections related
to aging of electrical components or lighting. Functions such as
electronic pan and zoom, image annotation, compression of the video for
network transmission, feature extraction and motion compensation can be
easily and inexpensively added to the camera feature set.
Distortion
The deviation of the received signal
waveform from that of the original transmitted waveform.
Distribution Amplifier
A device that provides several
isolated outputs from one looping or bridging input, and has a
sufficiently high input impedance and input-to-output isolation to
prevent loading of the input source.
Dynamic
Range
The difference between the maximum
acceptable signal level and the minimum acceptable signal level.
EIA Sync
The signal used for the synchronizing
of scanning specified in EIA Standards RS-170, RS-330, RS-343, or
subsequent issues.
Equalizer
An electronic circuit that introduces
compensation for frequency discriminative effects of elements within the
television system, particularly long coaxial transmission systems.
Fiber
Optics
Also called optical fibers or optical
fiber bundles. An assemblage of transparent glass fibers all bundled
together parallel to one another. The length of each fiber is much
greater than its diameter. This bundle of fibers has the ability to
transmit a picture from one of its surfaces to the other around curves
and into otherwise inaccessible places with an extremely low loss of
definition and light, by a process of total reflection.
Field
One of the two equal but vertically
separated parts into which a television frame is divided in an
interlaced system of scanning. A period of 1/60 second separates each
field start time.
Field
of View
The maximum angle of view that can be
seen through a lens or optical instrument.
Focal
Length
Of a lens, the distance from the focal
point to the principal point of the lens.
Focal
Plane
A plane (through the focal point) at
right angles to the principal point of the lens.
Focal
Point
The point at which a lens or mirror
will focus parallel incident radiation.
Foot
candle
See lumen/ft 2.
Foot
lambert (FL)
A unit of luminance equal to 1/candela
per square foot or to the uniform luminance at a perfectly diffusing
surface emitting or reflecting light at the rate of one lumen per square
foot. A lumen per square foot is a unit of incident light and a foot
Lambert is a unit of emitted or reflected light. For a perfectly
reflecting and perfectly diffusing surface, the number of lumens per
square foot is equal to the number of foot lamberts.
Frame
The total area, occupied by the
television picture, which is scanned while the picture signal is not
blanked.
Frame
Frequency
The number of times per second that
the frame is scanned. The U.S. standard is 30 frames per second.
Frame
Transfer
A CCD imager where an entire matrix of
pixels is read into storage before being output from the camera. Differs
from Interline Transfer where lines of pixels are output
Frequency Interlace
The method by which color and black
and white sideband signals are interwoven within the same channel
bandwidth.
Frequency Response
The range of band of frequencies to
which a unit of electronic equipment will offer essentially the same
characteristics.
Front
Porch
The portion of a composite picture
signal which lies between the leading edge of the horizontal blanking
pulse and the leading edge of the corresponding sync pulse.
f/Stop
Also called F Number and F System.
Refers to the speed or ability of a lens to pass light. It is calculated
by dividing the focal length of the lens by its diameter.
Gain
An increase in voltage or power,
usually expressed in dB.
Gamma
A numerical value, or the degree of
contrast in a television picture, which is the exponent of that power
law which is used to approximate the curve of output magnitude versus
input magnitude over the region of interest.
Gamma Correction
To provide for a linear transfer
characteristic from input to output device.
Genlock
A device used to lock the frequency of
an internal sync generator to an external source.
Ghost
A spurious image resulting from an
echo.
Gray Scale
Variations in value from white,
through shades of gray, to black on a television screen. The gradations
approximate the tonal values of the original image picked up by the TV
camera.
Hue
Corresponds to colors such as red,
blue, etcetera.
Hum
Electrical disturbance at the power
supply frequency or harmonics thereof.
Image Intensifier
A device coupled by fiber optics to a
TV image pickup sensor to increase sensitivity. Can be single or multi
stage.
Image
Plane
The plane at right angles to the
optical axis at the image point.
Impedance (input or output)
The input or output characteristic of
a system component that determines the type of transmission cable to be
used. The cable used must have the same characteristic impedance as the
component. Expressed in ohms. Video distribution has standardized on
75-ohm coaxial and 124-ohm balanced cable.
Incident Light
The light that falls directly on an
object.
Insertion Loss
The signal strength loss when a piece
of equipment is inserted into a line.
Interference
Extraneous energy which tends to
interfere with the reception of the desired signals.
Interline Transfer
A technology of CCD design, where rows
of pixels are output from the camera. The sensor's active pixel area and
storage register are both contained within the active image area. This
differs from "frame transfer" cameras that move all active pixels to a
storage register outside of the active area.
Interlaced Scanning
A scanning process for reducing image
flicker in which the distance from center to center of successively
scanned lines is two or more times the nominal line width, and in which
the adjacent lines belong to different fields.
Iris
An adjustable aperture built into a
camera lens to permit control of the amount of light passing through the
lens.
Isolation Amplifier
An amplifier with input circuitry and
output circuitry designed to eliminate the effects of changes made at
either upon the other.
Jitter
Small, rapid variations in a waveform
due to mechanical disturbances or to changes in the characteristic of
components. Supply voltages, imperfect synchronizing signals, circuits,
etc.
Lens
A transparent optical component
consisting of one or more pieces of optical glass with surfaces so
curved (usually Spherical), that they serve to converge or diverge the
transmitted rays of an object, thus forming a real or virtual image of
that object.
Lens Preset Positioning
Follower Pots are installed on lens
that allows feedback to the controller information relevant to zoom and
focus positioning allowing the controller to quickly adjust to a
pre-selected scene and arrive in focus at the proper focal length
automatically.
Lens Speed
Refers to the ability of a lens to
transmit light, represented as the ratio of the focal length to the
diameter of the lens. A fast lens would be rated <f/1.4; a much slower
lens might be designated as> f/8. The larger the f number, the slower
the lens.
Light
Electromagnetic radiation detectable
by the eye, ranging in wavelength from about 400 to 750 nm.
Line
Amplifier
An amplifier for audio or video
signals that feeds a transmission line; also called program amplifier.
Loop
Through
Also called looping. The method of
feeding a series of high impedance circuits (such as multiple
monitor/displays in parallel) from a pulse or video source with a coax
transmission line in such a manner that the line is bridged (with
minimum length stubs) and that the last unit properly terminates the
line in its characteristic impedance. This minimizes discontinuities or
reflections on the transmission line.
Loss
A reduction in signal level or
strength, usually expressed in dB. Power dissipation serving no useful
purpose.
Low-Frequency Distortion
Distortion effects which occur at low
frequencies. In television, generally considered as any frequency below
the 15.75-kHz line frequency.
Lumen (LM)
The unit of luminous flux. It is equal
to the flux through a unit solid angle (steradian) from a uniform point
source of one candela or to the flux on a unit surface of which all
points are at a unit distance from a uniform point source of one
candela.
Lumen/FT2
A unit of incident light. It is the
illumination on a surface one square foot in area on which a flux of one
lumen is uniformly distributed, or the illumination at a surface all
points of which are at a distance of one foot from a uniform source of
one candela.
Luminance
Luminous intensity (photometric
brightness) of any surface in a given direction per unit of projected
area of the surface as viewed from that direction, measured in foot
lamberts (fl).
Luminance Signal
That portion of the NTSC color
television signal which contains the luminance or brightness
information.
Lux
International System (Sl) unit of
illumination in which the meter is the unit of length. One lux equals
one lumen per square meter.
Matrix Switcher
A combination or array of
electromechanical or electronic switches which route a number of signal
sources to one or more designations.
Modulation
The process, or results of the
process, whereby some characteristic of one signal is varied in
accordance with another signal. The modulated signal is called the
carrier. The carrier may be modulated in three fundamental ways: by
varying the amplitude, called amplitude modulation; by varying the
frequency, called frequency modulation; by varying the phase, called
phase modulation.
Monitor
A unit of equipment that displays on
the face of a picture tube the images detected and transmitted by a
television camera.
Monochrome
Black and white with all shades of
gray.
Monochrome Signal
In monochrome television, a signal
wave for controlling the brightness values in the picture. In color
television, that part of the signal wave which has major control of the
brightness values of the picture, whether displayed in color or in
monochrome.
Monochrome Transmission
The transmission of a signal wave
which represents the brightness values in the picture, but not the color
(chrominance) values.
ND Filter
A filter that attenuates light evenly
over the visible light spectrum. It reduces the light entering a lens,
thus forcing the iris to open to its maximum.
Noise
The word "noise" originated in audio
practice and refers to random spurts of electrical energy or
interference. In some cases, it will produce a "salt-and-pepper" pattern
over the televised picture. Heavy noise is sometimes referred to as
"snow".
Non-Composite Video
A video signal containing all
information except sync.
NTSC
Abbreviation for National Television
Systems Committee. A committee that worked with the FCC in formulating
standards for the present day United States color television system.
Output
The signal level at the output of an
amplifier or other device.
Pan and
Tilt
A device upon which a camera can be
mounted that allows movement in both the azimuth (pan) and in the
vertical plane (tilt).
Pan/Tilt Preset Positioning
Follower pots are installed on
pan/tilt unit to allow feedback to the controller and provides
information relevant to horizontal and vertical positioning, allowing
the controller to quickly adjust to a pre-selected scene automatically.
Patch
Panel
A panel where circuits are terminated
and facilities provided for interconnecting between circuits by means of
jacks and plugs.
Peak Pulse Amplitude
The maximum absolute peak value of a
pulse, excluding those portions considered to be unwanted, such as
spikes.
Peak-to-Peak
The amplitude (voltage) difference
between the most positive and the most negative excursions (peaks) of an
electrical signal. A full video signal measures one volt peak to peak.
Picture Element
See Pixel
Pixel
Short for Picture Element. A pixel is
the smallest area of a television picture capable of being delineated by
an electrical signal passed through the system of part thereof. The
number of picture elements (pixels) in a complete picture, and their
geometric characteristics of vertical height and horizontal width,
provide information on the total amount of detail which the raster can
display and on the sharpness of the detail, respectively.
Primary Colors
Three colors wherein no mixture of any
two can produce the third. In color television these are the additive
primary colors red, blue and green.
Resolution (horizontal)
The amount of resolvable detail in the
horizontal direction in a picture. It is usually expressed as the number
of distinct vertical lines, alternately black and white, which can be
seen in a distance equal to picture height.
Resolution, Limiting
The details that can be distinguished
on the television screen. Vertical resolution refers to the number of
horizontal black and white lines that can be resolved in the picture
height. Horizontal resolution refers to the black and white lines
resolved in a dimension equal to the vertical height and may be limited
by the video amplifier bandwidth.
Resolution (vertical)
The amount of resolvable detail in the
vertical direction in a picture. It is usually expressed as the number
of distinct horizontal lines, alternately black and white, which can
theoretically be seen in a picture.
Retained Image
Also called image burn. A change
produced in or on the target which remains for a large number of frames
after the removal of a previously stationary light image and which
yields a spurious electrical signal corresponding to that light image.
RF (Radio
Frequency)
A frequency at which coherent
electromagnetic radiation of energy is useful for communication
purposes. Also, the entire range of such frequencies.
Ripple
Amplitude variations in the output
voltage of a power supply caused by insufficient filtering.
Roll
A loss of vertical synchronization
which causes the picture to move up or down on a receiver or monitor.
Saturation
In color, the degree to which a color
is diluted with white light or is pure. The vividness of a color,
described by such terms as bright, deep, pastel, pale, etc. Saturation
is directly related to the amplitude of the chrominance signal.
Scanning
The process of moving the electron
beam of a pickup tube or a picture tube across the target or screen area
of a tube.
Sensitivity
In television, a factor expressing the
incident illumination upon a specified scene required to produce a
specified picture signal at the output terminals of a television camera.
Shutter
Ability to control the integration (of
light) time to the sensor to less than 1/60 second; e.g: stop motion of
moving traffic.
Signal-to-Noise Ratio
The ratio between useful television
signal and disturbing noise or snow.
Snow
Heavy random noise.
Spike
A transient of short duration,
comprising part of a pulse, during which the amplitude considerably
exceeds the average amplitude of the pulse.
Standard Minimum Signal
1000 micro-volts at 75 ohms (0dB mV)
in RF systems; 0.7-VPP non-composite, 1-VPP composite in video systems.
Sync
A contraction of "synchronous" or
"synchronize".
Sync
Generator
A device for generating a
synchronizing signal.
Sync Level
The level of the peaks of the
synchronizing signal.
Sync
Signal
The signal employed for the
synchronizing of scanning.
Synchronizing
Maintaining two or more scanning
processes in phase.
Tearing
A term used to describe a picture
condition in which groups of horizontal lines are displaced in an
irregular manner.
Test
Pattern
A chart especially prepared for
checking overall performance of a television system. It contains various
combinations of lines and geometric shapes. The camera is focused on the
chart, and the pattern is viewed at the monitor for fidelity.
Transients
Signals which exist for a brief period
of time prior to the attainment of a steady-state condition. These may
include overshoots, damped sinusoidal waves, etc.
Vertical Resolution
The number of horizontal lines that
can be seen in the reproduced image of a television pattern.
Video
Amplifier
A wideband amplifier used for passing
picture signals.
Video Band
The frequency band width utilized to
transmit a composite video signal.
Video Signal (Non-Composite)
The picture signal. A signal
containing visual information and horizontal and vertical blanking (see
also Composite Video Signal) but not sync.
Y Signal
A signal transmitted in color
television containing brightness information. This signal produces a
black and white picture on a standard monochrome receiver. In a color
picture it supplies fine detail and brightness information.
Zoom
To enlarge or reduce, on a
continuously variable basis, the size of a televised image primarily by
varying lens focal length.
Zoom Lens
An optical system of continuously
variable focal length, the focal plane remaining in a fixed position.
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