A continuously varying action, or movement that takes
time to change from one position to another. Standard audio
and video signals are analog. An analog signal has an infinite
number of levels between its highest and lowest value. (Not
like digital, where changes are by steps.)
type of lens or adapter designed to produce a wide-screen
image from a condensed image on the film.
standard for measuring light output, used for comparing projectors.
relationship of the horizontal dimension to the vertical dimension
of a rectangle. In viewing screens, standard TV is 4:3, or
1.33:1; HDTV is 16:9, or 1.78:1. Sometimes the ':1' is implicit
making TV = 1.33 and HDTV = 1.78.
for J. M. E. Baudot, the inventor of the Baudot telegraph
code. The number of electrical oscillations per second, called
'baud rate'. Related to, but not the same as transfer rate
in bits per second, 'bps'.
Neill-Concelman. A cable connector used extensively in television
and named for its inventor. A cylindrical bayonet connector
operates with a twist-locking motion. To make the connection,
align the two curved grooves in the collar of the male connector
with the two projections on the outside of the female collar,
push and twist. This allows the connector to lock into place
without the need of tools.
refers to the amount or intensity of video light produced
on a screen without regard to colour. Sometimes called 'black
video display, this is a term to describe what happens when
an image has been displaying too long, resulting in a permanent
image being 'burned in' to the screen phosphor.
two-conductor wire in which one conductor completely wraps
the other with the two separated by insulation. Constant impedance
transmission cable. Example: 75 ohm, type RG-59u cable used
for video signals. Abbreviated as 'coax'.
colour quality, expressed in degrees Kelvin (K), of a light
source. The higher the colour temperature, the bluer the light.
The lower the temperature, the redder the light.
colour television system starts with three channels of information;
red, green, & blue (RGB). In the process of translating
these channels to a single composite video signal they are
often first converted to Y, R-Y, and B-Y. Both 3-channel systems,
RGB and Y, R-Y, B-Y are component video signals. They are
the components that eventually make up the composite video
signal. Higher quality program production is possible if the
elements are assembled in the component domain.
all-in-one video signal comprised of the luma (black and white),
chroma (colour), blanking pulses, sync pulses and colour burst.
range of light and dark values in a picture, or the ratio
between the maximum and the minimum brightness values. Low
contrast is shown mainly as shades of grey, while high contrast
is shown as blacks and whites with very little grey. It is
also the name of a TV monitor adjustment, which increases
or decreases the level of contrast of a displayed picture.
Also called 'white level'.
ratio of the high light output level divided by the low light
output level. Ideally, the contrast ratio of the projection
system should be at least 300:1. It is important to bear in
mind that projectors cannot project black so the blackest
black achievable is the base colour of the screen (usually
connector with rounded corners and angled ends, taking on
the shape of the letter 'D'. Commonly used in computers and
video, most D connectors have two rows of pins. If they have
more than two rows, they are usually called HD (high density)
The standard unit used to express gain or loss of power. It
indicates the logarithmic ratio of output power divided by
input power. A power loss of 3dB is an attenuation of half
of the original value. The term '3dB down' is used to describe
the 'half power point'. In audio work, 0dB is the threshold
of hearing. 120dB level is the threshold of pain. A change
of 3dB halves or doubles the apparent loudness.
fidelity with which a video picture is reproduced. The clearer
the picture, the higher the definition. Definition is influenced
system of data or image values in the form of discrete, non-continuous
codes, such as binary. When data is in a digital format, it
can be processed, stored (recorded) and reproduced easily
while maintaining its original integrity.
Digital video using separate colour components, such as Y'CbCr
or R'G'B'. See CCIR 601. It is sometimes incorrectly
referred to as D-1. (2) A digital representation of a component
analog signal set, most often Y, B-Y, R-Y. The encoding parameters
are specified by ITU-R BT.601-2 (CCIR 601). The parallel interface
is specified by ITU-R BT.656 (CCIR 656) and SMPTE 125M.
Digital video that is essentially the digitised waveform of
(M) NTSC or (B, D, G, H, I) PAL video signals, with specific
digital values assigned to the sync, blank, and white levels.
It is sometimes incorrectly referred to as D-2 or D-3. (2)
A digitally encoded video signal, such as NTSC or PAL video,
that includes horizontal and vertical synchronizing information.
Drive Image Light Amplifier. Developed by Hughes-JVC, D-ILA
uses digitally addressed ILA ® instead of CRT-addressed as
with earlier devices. See ILA. The D-ILA ? is a device
based on the Image Light Amplifier or ILA ® developed by Hughes-JVC
Technology Corporation. The new D-ILA technology is a reflective
liquid crystal modulator where electronic signals are addressed
directly to the device. The D-ILA device has an X-Y matrix
of pixels configured on a C-MOS single crystal silicon substrate
mounted behind the liquid crystal layer using a planar process
that is standard in IC technology.
acronym for Deutsche Industrie Norm. A round connector with
notches, or keys for alignment. They can be in several sizes:
4-pins, 5-pins, 8-pins, etc. A convenient way of combining
all of the signal lines in one connector, 4-pin DIN connectors
are often used for S-video.
A device that allows connection of one input source to multiple,
isolated (buffered) output destinations such as monitors or
light processing. See DMD.
micromirror device. In 1977, it was originally called 'Deformable
Mirror Device'. Texas Instruments has developed DMD microchips
used in DLP (digital light processing) projector subsystems
that hope to replace the 100-year old CRT technology. DMD
chips use an array of mirrors and memory cells. A digital
image is stored in the memory, and then projected when light
is reflected onto the mirrors.
Versatile Disc. An optical disc about the size of a CD-ROM,
but capable of storing an entire movie. The technology uses
MPEG-2 compression. Typical capacity for these discs is 4.5
GB, or about 133 minutes of digital video. Originally called
'Digital Video Disk'.
of Active Video. A digital code used with digital component
video signals, marking the end of a video line
data communication scheme used with digital camcorders, the
1394 FireWire manages the digitisation, compression and audio
synchronization processes while shooting. This puts broadcast
quality video footage directly into your computer or DV (Digital
Video) editing system.
front of a mirror. In mirrors intended for A/V applications,
the first surface is coated with a reflective material to
prevent double images (ghosting).
alternating change of light intensity, typically perceived
at a rate of a few Hertz to 60 Hz when viewing static images
such as text. Flicker can occur when the electron gun paints
the screen too slowly, giving the phosphors on the screen
time to fade before being refreshed. This may occur when the
refresh rate of the video is too low, or when the persistence
of the display device is too short. A fluorescent light fixture
may produce the same effect.
The distance between the centre of a lens and the point where
the image comes into focus. In projection, a shorter focal
length yields a larger image on the screen for any given projection
act of adjusting a lens to make the image appear sharp and
well defined. The best possible resolution of an image, showing
the image to be sharp and well defined.
thin, flat lens made by cutting concentric circular grooves
into its surface. The grooves act like prisms to bend and
focus light. A fresnel lens is a fraction of the size and
weight of a conventional lens, and the image is more distorted.
Because of its lower cost and compact weight and size, the
fresnel lens is often used for the condenser lens in overhead
projectors and in studio spotlights.
light-reflecting screen used when the image is projected from
a source in front of the screen. See Rear projection.
project an image from the audience's side of a light-reflecting
A general term for an increase in signal power or voltage
produced by an amplifier. The amount of gain is usually expressed
in decibels above a reference level. Opposite of attenuation.
(2) The amplification of a signal, unit or system. Expressed
in the unit of measurement appropriate to the signal or system,
or in a mathematical formulation (YxZ) for screens.
method of synchronizing video equipment by using a common,
external signal. This locks the sync generators of multiple
devices to a single source.
called ghosting, or 'reflections') A shadowy or weak duplication
of the original image. It can be the result of transmission
conditions where secondary signals are created and then displayed
earlier or later than the original signal. Ghosts can also
be the result of burning an image on a screen or by a mirror.
One billion cycles per second.
high-density 'D' connector having its pins arranged close
together, sometimes in three rows instead of two rows. Example:
a 15- pin VGA connector (HD) vs. a Mac connector (D).
definition television. Any one of a variety of video formats
offering higher resolution than the current NTSC, PAL and
SECAM broadcast standards. Current formats generally range
in resolution from 655 to 1,125 scan lines, with an aspect
ratio of 9 to 16, and bandwidth of 30 to 50 MHz.
The international term for cycles per second.
control. Hue is the parameter of colour that allows us to
distinguish between colours. The hue, or tint control adjusts
the amount of colour displayed.
light amplifier. Used in their large screen projectors, a
Hughes/JVC device that uses low-intensity images to modulate
high-intensity light through a liquid crystal layer.
reproduction or imitation of a person or thing displayed by
any type of visual media.
Light waves just outside the visible spectrum; that is, waves
slightly longer than those visible to the human eye. Infrared
light is sometimes filtered out to reduce heat on film or
slides. See Infrared control.
wireless medium of remote control, which sends signals to
a device via pulses, transmitted in the infrared light spectrum.
Its use is restricted to equipment within line-of-sight or
reflections off a wall or ceiling. This is sometimes called
source for data or a signal to be used by another device.
The physical connector or port for entering such a signal
or data is called the 'input'.
video problem in which stair step-like lines appear where
there should be straight-angled lines or smooth curves.
video problem in which the displayed image is unstable or
appears to shake.
Photographic Experts Group. A committee formed as a joint
effort between the International Standards Organization (ISO)
and CCITT that developed a standard for the still digital
image compression/decompression for use in computer systems.
The JPEG image size may be reduced by as much as 30:1 with
some loss of data. It does not work well with line art, text
or vector graphics. The file extension is '.jpg'.
distorted picture where one edge is not the same dimension
as the opposite edge, producing a tapered, or wedge shape.
Typically, this results when the image is projected to the
screen at an angle. In stone buildings, the tapered stone
at the top of an arch is the 'key' that prevents the arch
crystal display. A panel that utilizes two transparent sheets
of polarizing material with a liquid containing rod-shaped
crystals between. When a current is applied to specific pixel-like
areas, those crystals align to create dark images. The dark
areas are combined with light areas to create text and images
on the panel. LCD panels do not emit light but are often back-lit
or side-lit for better viewing.
device used to project video images through a liquid crystal
display and an overhead projector onto a large screen. The
panel is placed over the stage of an overhead projector, projecting
the computer display onto a screen.
the LCD technique, these projectors separate the red, green
and blue information to three different LCD panels. Since
LCD panels do not produce colour, the appropriate coloured
light is then passed through each panel and combined to exit
through the projector lens and onto a viewing screen.
means of moving a projector lens up, down and sometimes side
to side without distorting the image. Useful for fine picture
alignment and when stacking multiple projectors.
Increased Definition Television (IDTV) feature that doubles
the number of scan lines in a video picture. This fills the
space between the original lines, making them less noticeable
and increases the brightness of the picture. For example,
the NTSC video field of 262.5 lines is doubled to 525 non-interlaced
lines and the PAL field of 312.5 lines becomes 625.
A unit of measure for the amount of light emitted by a source.
0.98 Ft-c (foot-candles) of light covering a surface of 1
output on a projector providing a means of connecting a monitor.
Typically these are RGB (computer) only but on more advanced
models can accommodate video output on to a standard PC monitor
television standard for North America and parts of South America
having 525 lines/60 Hz (60 Hz refresh), two fields per frame
and 30 frames per second.
device that produces an image on a screen by transmitting
light through a transparent material placed on the stage of
alternate line. A television standard in which the phase of
the colour carrier is alternated from line to line. It takes
four full pictures for the colour to horizontal phase relationship
to return to the reference point. This alternation helps cancel
out phase errors. For this reason the hue control is not needed
on a PAL TV set. PAL, in many forms, is used in Australia,
England, Scandinavia, South Africa, and Western Europe. PAL
uses 625-line, 50-field composite colour transmission system.
plug most often used with line level audio signals. Also known
as an RCA plug.
illustration or table that names signals, voltages, etc. that
are on each pin of a connector or cable
in picture. Displaying a small picture within a larger picture
by scaling down one of the images to make it smaller. Each
picture requires a video source (camera, VCR, channel selector,
etc.). Consumer TV can use PIP for viewing two channels at
the same time or for viewing taped video and a channel, etc.
Videoconferencing uses PIP to display pictures from video
sources at each participating site onto each screen at the
same time. The large picture could be of the current speaker,
while pictures from the other sites display across the bottom
of the screen.
term used for video products that are compatible with the following
standards: NTSC 3.58, NTSC 4.43, SECAM, and PAL
extended graphics array. A graphics standard with 2048 x 1536
translucent screen with a special coating that allows an image
to be projected through the screen from the rear, instead
of from the front.
presentation method in which the image is projected through
a translucent screen toward the audience. The slide or film
must be reversed, or a mirror must be used to correct the
image for rear screen presentation. In some video or computer
projectors, the image can be reversed electronically.
device for controlling the function of a device at a distance.
May be wired or wireless.
density of lines or dots for a given area that make up an
image. Resolution determines the detail and quality in the
image. A measure of the ability of a camera or video system
to reproduce detail, or the amount of detail that can be seen
in an image. Resolution is often expressed as a number of
pixels, but more correctly it is the bandwidth. We say that
a sharp, clear picture has high resolution.
green and blue. The chroma information in a video signal.
The basic components of the colour television system. They
are also the primary colours of light in the "additive
form of colour video signal (red, green and blue) distinctly
different from the composite colour video used in standard
television sets. RGB can be displayed only on an RGB monitor
that has a separate electron gun for each of these primary
colours. Some colour television sets use only one gun. RGB
monitors are noted for their crisp, bright colours and high
resolution. RGB video can have four different forms: RGsB
(sync is on the green signal), RGBS (sync is separate from
the colours), RGBHV (sync is separate from the colours, and
the horizontal and vertical sync signals are separate) and
RsGsBs (sync on red, green and blue).
Electronic Industries Association (EIA) serial digital interface
standard specifying the characteristics of the communication
path between two devices using either DB-9 or DB-25 connectors.
This standard is used for relatively short-range communications
and does not specify balanced control lines. RS-232 is a serial
control standard with a set number of conductors, data rate,
word length and type of connector to be used. The standard
specifies component connection standards with regard to computer
interface. It is also called RS-232-C, which is the third
version of the RS-232 standard, and is functionally identical
to the CCITT V.24 standard.
called "video converter" or "TV converter",
a scan converter is a device that changes the scan rate of
a source video signal to fit the needs of a display device.
Examples: computer-video to NTSC (TV), or NTSC to computer-video.
European video-audio connector widely used in consumer equipment.
The scart connector has 21 pins, carrying 2 audio channels
- in and out, video channels - in and out, RGB signals, ground
and some additional control pins. Simplicity is an advantage,
however, the physical connection is quite weak and signal
leakage is quite high.
Couleur Avec Mémoire) Translated as 'sequential colour with
memory'. A composite colour transmission system that potentially
eliminates a need for both a colour and hue control on the
monitor. One of the colour difference signals is transmitted
on one line and the second is transmitted on the second line.
Memory is required to obtain both colour difference signals
for colour decoding. This system is used in France, Africa,
Asia, Russia, Saudi Arabia and many Eastern European countries.
It is similar to PAL, but produces colour signals in a different
manner. SECAM uses 625 horizontal scan lines, 50 fields per
input/output connection on the computer that allows it to
communicate with other devices in a serial fashion?data bits
flowing on a single pair of wires. The serial port is used
with RS-232 protocol.
occurs when signal strength is deteriorated by length of cable.
With low quality cable this will occur in relatively short
runs depending on signal type. It is possible to boost most
types of signals using line drivers but the economics may
suggest it is worth investing in higher quality cables to
Video Graphics Array. A term used to denote resolutions higher
than VGA (640 x 480). SVGA computer graphics cards have a
resolution of 800 x 600 (480,000 pixels) but may be able to
output resolutions of up to 1280 x 1024 and 16 million colours.
home system. A high band video recording process for VHS that
increases the picture quality and resolution capability. See
composite video signal is separated into the luma (Y, black
and white information) and the chroma (C, colour information).
A device which allows a selection between more than one source,
such as: video cameras, VCRs, etc. In audio/video, switchers
are a means of connecting an input source to an output device
or a system. (2) A term often used to describe a special effects
generator; a unit that allows the operator to switch between
video camera signals. Switchers are often used in industrial
or security applications to switch between video cameras that
view certain areas for display on a monitor, or system of
display devices. These kinds of switchers do not have sync
Extended Graphics Array. A graphics standard with a resolution
of 1280 x 1024 (1,310,720 pixels). This exceeds XGA (1024
x 768, at 786,432 pixels).
In video, sync is a means of controlling when things happen
with respect to other things. This is accomplished with timing
pulses to insure that each step in a process occurs at exactly
the right time. For example, horizontal sync determines exactly
when to begin each horizontal line (sweep) of the electron
beam. Vertical sync determines when to bring the electron
beam to the top left of the screen to start a new field. There
are many other types of sync in a video system. (Also called
'sync signal' or 'sync pulse'.)
stands for Thin-Film-Transistor. This new technology is mainly
used for manufacturing flat computer and video screens, which
are superior to classic LCD* screens. Color quality, fast response
and resolutions are excellent for video, and therefore, TFT
screens are replacing tube-based Wide Screen projectors* as
well. In the beginning there were some price and technical problems
with TFT screens. The price was high, mainly due to low yield
in the wafer production process, the brightness of the screen
was quite low and the resolution, although fine for composite
video, was not sufficient for high-resolution computer graphics.
As technology advanced, most of the problems were solved and
now, bright, high-resolution TFT screens are available at very
Pair. A system for transferring high frequency signals on a
twisted pair of wires instead of a coax cable. The TP system
is used in video and in the computer world as one of the network
interconnecting standards. The twisted pair system is essentially
a balanced* system, where antiphase signals are transmitted
on the two wires. Some sophisticated TP systems allow the transfer
of several signals simultaneously on the wires, such as video
and two audio channels.
Serial Bus. USB was developed by seven PC and telecom industry
leaders (Compaq, DEC, IBM, Intel, Microsoft, NEC and Northern
Telecom). The goal was easy plug-and-play expansion outside
the box, requiring no additional circuit cards. Up to 127
external computer devices may be added through a USB hub,
which may be conveniently located in a keyboard or monitor.
USB devices can be attached/detached without removing computer
power. The number of devices being designed for USB continues
to grow, from keyboards, mice, and printers to scanners, digital
cameras, ZIP drives, etc.
extended graphics array. A graphics standard resolution of
1600 x 1280 (2,048,000 pixels). This exceeds SXGA (1280 x
1024 = 1,310,720 pixels).
defined as video cassette recorder. In Europe, however, VCR
is a trademark for a particular video format developed by
Philips of The Netherlands.
Graphics Array. Introduced by IBM in 1987, VGA is an analog
signal with TTL level separate horizontal and vertical sync.
The video outputs to a 15-pin HD connector and has a horizontal
scan frequency of 31.5 kHz and vertical frequency of 70 Hz
(Mode 1, 2) and 60 Hz (Mode 3). The signal is non-interlaced
in modes 1, 2, 3 and interlaced when using the 8514/A card
(35.5 kHz, 86 Hz) in mode 4. It has a pixel by line resolution
of 640 x 480 with a colour palette of 16/256,000.
amplifier for strengthening the video signal so that it can
be supplied to a number of video monitors at the same time.
standard that supports a resolution of 1280 to 1366 horizontal
pixels by 720 to 800 vertical pixels. These are the most common
resolutions (ordered by number of pixels): 1280*720, 1280*768,
1280*800, 1360*768, and 1366*768. WXGA is commonly used by LCD
TV sets and computer monitors for widescreen presentation. The
136x by nnn resolutions commonly apply to LCD TVs while the
1280 by nnn resolutions are found mostly in notebooks/laptops.
Graphics Array Card. IBM?s graphics standard that includes
VGA and extended resolutions up to 1024 x 768 (interlaced
35 kHz) with 65k colours. This card uses a 15-pin HD VGA-style
video system which differs from standard Composite video in
several crucial ways. The bandwidth is considerably wider as
luminance* and chrominance are separated in the signal. This
format, named also Y/C, is widely used for production in semi-professional
as well as in many broadcast studios.
term used with cameras and video displays related to the ability
to change the view anywhere between near and far. Definitions
for near and far vary from one device to another.
lens with a variable focal length providing the ability to
adjust the size of the image on a screen by adjusting the
zoom lens, instead of having to move the projector closer