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4:3: Aspect ratio of traditional NTSC TV screens, with 4
unit width by 3 unit height.
16:9: Aspect ratio of widescreen DTV formats
for all HDTV and some SDTV (Standard Definition) content,
16 unit width by to 9 unit height.
8-VSB: Acronym for the transmission
method used for over-the-air DTV broadcasting in Canada and
the USA. Eight discreet amplitude level, "vestigial side-band" broadcast
transmission technology. VSB is an analog modulation technique
used to reduce the amount of spectrum needed to transmit
information through cable TV, or terrestrial broadcasting.
AC-3: The 5.1-channel compressed
digital sound system specified for DTV broadcasting in Canada.
AC-3 delivers CD-quality digital audio and provides five
full-bandwidth channels for front left, front right, center,
surround left and surround right speakers, plus an LFE (low
frequency effect) subwoofer, for a total of 5.1 channels.
AC-3 is one member of a family of sound systems developed
by Dolby Labs.
A/D: Electronic device that connects an
analog television signal to a digital system.
Addressable Resolution: The highest
resolution signal that a display device (television or monitor)
can accept as input. Some display devices may not be capable
of displaying such signals and may downconvert them to a
lower resolution prior to display.
Analog Video: The conventional NTSC
television system in use today uses analog technology, in
which the image sound and the picture brightness and color
are represented by signals proportional to these values.
The values of these signals are vulnerable to interference
and noise. Digital television overcomes this vulnerability
and delivers signals that are totally clean.
Anamorphic: the squeezing horizontally
of a 16:9 image into a full screen 4:3 display, resulting
in distortion of the image geometry.
Artefacts: Unwanted visible effects
in the picture created by errors in the video processing
or noise/interference in analog circuits. Common artefacts
include 'edge crawl' or 'hanging dots' in analog pictures
or 'blockiness', noise or 'contouring' in digital pictures.
Aspect Ratio: the ratio of
image width to image height. The term may apply to the display
device configuration, or the shape of the content being displayed.
(See Letterboxing) HDTV uses an aspect ratio of 16 units
wide by 9 units high. Conventional television programming
and displays are at an aspect ratio of 4:3. Digital SDTV
programs may aspect ratios from 4:3 to 16:9, dependant on
content and its source (e.g. upconverted NTSC is likely to
be 4:3).
ATSC: "Advanced Television Systems
Committee." Formed to establish technical standards for U.S.
advanced television systems. ATSC is now used as the catch-all
nomenclature for DTV broadcast standards.
Bandwidth: The range of frequencies
used to transmit the television signal, including picture
and sound. Analog television signals have been allocated
at 6 Megahertz for each over-the-air channel. Digital channels
are allocated the same 6 Megahertz by Industry Canada. However,
by the use of digital compression, a combination of up to
5 SDTV programs and/or one HDTV program can be carried in
this 6 MHz digital channel.
Baseband Video: Unmodulated analog video signal.
Bit Rate: The rate at which
the data is transmitted, expressed as “bits per second” (bps).
The higher the bit rate, the more data that is transmitted,
generally resulting in better picture or sound quality. Video
data rates are usually expressed as Megabits per second (Mbps,
106) and audio data rates in kilobits per second (kbps, 103).
Cable Modem: A data modem that
provides an Internet connection over the TV cable network.
Video-on-demand or interactive services may require such
a connection.
Channel: A 6 MHz (bandwidth)
section of spectrum for over-the-air broadcast (channels
2 – 69) or in TV cable that carries one analog NTSC
program or one or more DTV programs.
Closed Captioning: A data stream
included in broadcast signal that provides text and/or narrative
description of dialogue, sounds, and other elements of the
picture for viewers with visual or auditory impairments.
Composite Video Connection:
A method to interconnect video devices (such as a DTV set-top
box and the analog television) by sending the signal over
a single cable. This method is suitable only for analog NTSC
signals
Composite Video: An analog video
signal (NTSC, PAL or SECAM) that includes both luminance
(brightness) and chrominance (color) signals encoded together
to form a single signal.
Compression: A method of
reducing the number of bits required to store or transmit
programs by the removal of redundant and/or non-critical
information in the digital picture and sound. The DTV broadcasting
standard for Canada, uses the MPEG-2 video and the AC-3 audio
compression coding. Compression allows the delivery of more
programs in a single channel.
CRT: An analog vacuum tube technology
that has been the mainstay of conventional TV displays for
many years, writing the picture on a phosphor coated screen
with an electron beam. It can produce bright pictures of
excellent resolution but the size and weight of a unit suitable
for the large, wide-screen displays needed for HDTV may be,
for some, a disadvantage.
Datacasting: The inclusion
of additional data in the broadcasting stream. Such data
may be related to the current program (e.g. sports statistics)
or may be completely independent (e.g. software downloading
or traffic advisories).
D/A: Conversion of digital signals
to analog signals. Most set-top boxes decode the digital
signals broadcast and then convert them to analog signal
for interconnection to the display device.
DLP (Digital Light Processing):
A technique in which the displayed image is produced by an
array of dynamic micro-mirrors formed on a chip, each reflecting
some of the light source to form a pixel on the screen. Each
micro-mirror controls the level of the light sent to the
screen for its pixel. Resolution is set by the size of the
mirror array and versions suitable for wide-screen HDTV are
now in production for uses in both front and rear projection
televisions.
Dolby Digital (Dolby AC-3):
The 5.1 channel audio standard for DTV and HDTV in Canada
and the USA. It includes six discreet audio channels: Left,
Center, Right, Left Surround (or side), Right Surround (or
side), and a subwoofer -- LFE, "low frequency effects" --
(considered the ".1" as it is limited in bandwidth). Many
televisions process these six channels into a two channel
stereo pair and do not provide the full 5.1 channel surround
sound.
Dot Pitch: The distance between
pixels (picture elements) in a display. In a CRT for HDTV,
the dot pitch is typically 0.25 – 0.3 mm. For full
resolution HDTV display approximately 1400 pixels are required
across the screen.
Downconvert: The process which
reduces the number of pixels in the scanning format used
to represent an image, so that it may be reproduced on a
display of lower resolution, such as a conventional television.
For example, an HDTV image may be downconverted to an SDTV
or NTSC image, but in the conversion significant detail information
may be lost.
DTV: "Digital television." This
comprises all the components of digital television, including
HDTV, SDTV, datacasting, and multicasting, falling under
the standards established by the ATSC.
DTS: Digital Theatre Sound System.
A Dolby proprietary discrete 5.1 channel surround system
similar to, but not the same as Dolby Digital AC-3, the DTV
standard. DTS is used in cinema presentations and in DVD’s.
DVD: Digital Versatile Disk. An
optical recording media similar to the familiar CD but having
seven times its capacity on a single side. In television
applications, DVD’s are capable of carrying full-length
commercial movies, plus additional material such as outtakes,
director's notes, movie trailers, etc.
EDTV: Enhanced Definition Television.
A term defining a television that displays the picture (either
from SDTV or HDTV) at a resolution of 480p lines in either
4:3 or 16:9 aspect ratio and which includes Dolby Digital
AC-3 multichannel sound.
Encryption: The process of coding
signals so that a specific code or key is required by the
viewer to recover the data so encrypted. Without this key,
the data is meaningless. Encryption is used to provide conditional
access for private television services.
EPG: Electronic program guide. An
on-screen display of channels and program data.
Fire Wire: A digital interface
originated by Apple Computer that can transport data at 100,
200, or 400 Mbps. It is widely used to interconnect digital
video devices, such as cameras and displays. Also referred
to as IEEE- 1394.
Fps: Frames per Second. To give
the illusion of motion, television actually transmits a series
of snapshot pictures referred to as frames. Increasing the
frame rate improves motion smoothness and may reduce flicker
in some displays. In Canada both analog and digital television
transmits 30 Fps.
HDTV: High
Definition Television:
HDTV is a TV system having approximately twice the vertical
and horizontal picture resolution of today's NTSC TV and
having a wide aspect ratio of 16:9. Two HDTV formats are
currently in use; (a) 1920 pixels per line and 1080i lines
per frame and (b) 1280 pixels per line and 720p lines per
frame. HDTV can be recognised by its spectacular picture
resolution, freedom from annoying artefacts and impressive
5.1 channel surround sound.
Interactive Television: TV programming
with interactive content and enhancements, blending traditional
TV viewing with the interactivity of a personal computer.
Interlaced Scanning: Some
HD televisions and most conventional televisions use the "interlace" method
of scanning, in which the picture is transmitted and painted
on the screen in two passes. In the first pass, every other
line is painted and in the second, the lines in between.
Some display types, such as LCD, plasma and DLP cannot display
directly images transmitted as interlaced signals and must
convert them to a progressive format prior to their display.
Letterbox: The full display of
a wide aspect ratio 16:9 picture on a display of aspect ratio
4:3 will result in black bars above and below the picture.
This arrangement is referred to as “Letterbox” and
is often seen during movies shown on television.
LCD. (Liquid Crystal Displays):
A flat panel technology, using thin-film crystal techniques,
widely used in laptop computers, other small portable displays
and more recently in televisions. Image brightness can be
very high and color performance can be good. For HDTV, wide-screen
displays of adequate resolution are available up to about
94 cm (37 in.) for direct viewing. LCD devices are also widely
used as the key element in many projection televisions, both
front and rear screen, up to very large sizes.
Line Doubling: A method used
in some televisions to improve the visual quality of an NTSC
interlaced picture, making it comparable to a progressively
scanned picture.
Luminance: Component of the video signal
that represents the brightness of the image.
Metadata: Informational data
about the data, included in a signal's data stream.
MMDS: Multichannel, Multipoint
Distribution System. A wireless cable system capable of being
encoded for pay-per-view and subscriber services.
MPEG-2: Compression standards
for moving images and for audio as set by Motion Pictures
Expert Group (MPEG). MPEG-2 video coding is the basis for
ATSC digital television transmission in the U.S and Canada.
Multicasting: Term given to
the sharing of the digital television channel among 2, 3,
4 or more individual programs and/or data services
NTSC: National Television Systems
Committee. The organisation that created the standards for
production and broadcasting of analog color television programming
in Canada and the United States. The term is widely used
to mean a composite analog television signal.
Over-the-air Broadcast (OTA): Also
called Terrestrial Broadcast. The delivery of TV and radio
signals, using UHF/VHF frequencies, directly to consumer
devices. Broadcasts may be either analog or digital.
Pixel: A picture element; a single
displayable video dot. HDTV requires from 1 to 2 million
pixels in the display for full resolution images to be shown.
Plasma Displays (PDP). A technique
that builds an image from a large number of pixels formed
in a glass panel. The pixels are individually controlled,
yielding a picture free of flicker and of high brightness.
Displays of excellent resolution and color are available
and the display approaches the "television picture on the
wall" ideal. PDP displays up to 160 cm (63in.) are available,
making them suitable for the home theatre.
Progressive Scanning: Some
HD televisions use the “progressive” method
of scanning, in which the whole picture is transmitted and
presented on the screen in one pass. The resulting image
is thus remarkably free of flicker and motion artefacts,
appearing more “life-like”. Some display types,
such as LCD, plasma and DLP are inherently of the progressive
scan type, while CRT’s may be scanned progressively
(as in computer monitors) or interlaced.
PSIP: Acronym for "Program and
system information protocol", an ATSC DTV specification that
enables a DTV receiver to identify the program information
and to create on-screen electronic program guides and content
advisories.
Resolution: A measure of the density
of lines and dots per line which make up a visual image.
Usually, the higher the numbers, the sharper and more detailed
the picture will be. In terms of DTV, maximum resolution
refers to the number of horizontal scanning lines multiplied
by the total number of pixels per line.
Reverse 3:2 Pull-Down: DTV material
originating on film at 24 fps is converted to the 30 fps
of DTV by repeating field or frames, resulting in some motion
artefacts. Some film presentations remove these repeated
images before transmission and send a signal to the television
causing it to process (termed Reverse 3:2 Pull-Down) this
material appropriately to make it suitable for display. In
this way, the displayed material closely matches the original
film quality, avoiding the motion artefacts.
SDTV: "Standard Definition Television." SDTV
are based on 480 lines of vertical resolution and may have
either 4:3 or 16:9 aspect ratios, and surround sound. Several
SDTV programs are sent together to form the simulcast bundle.
While SDTV pictures are of significantly better quality than
NTSC, they are not up to the standard of HDTV.
Set-top box (STB): A box, similar
to the familiar cable box, that is capable of receiving,
decoding and sending to the associated television the picture
and sound of the selected DTV broadcast. The use of an STB
would allow the use of conventional televisions to receive
DTB programs, but at reduced levels of resolution and with
imperfections due to aspect ratio differences, leading to
letterboxing or cropping of the sides of the picture.
Simulcast: The broadcast of the
same program simultaneously over two or more different systems
or channels, such as in HDTV and in NTSC. CRTC regulations
require today that broadcasters simulcast much of their schedules.
SMPTE: "Society of Motion Picture
and Television Engineers." A professional organization
that is responsible for the standards for film and television
production.
Stream: To send data on a network,
such as the Internet, in such a way as to provide or simulate
real-time delivery of video and/or audio.
S-Video Connection: A method
to interconnect video devices (such as a DVD player and the
analog television) by sending the two signals luminance (Y)
and an encoded color difference signal (C). The S-Video connection
is made using a cable terminated in a small 4-pin connector
(in some cases a 7 pin connector is used on computers to
allow inclusion of an NTSC composite signal). S-video can
greatly improve the picture when connecting SDTV or NTSC
displays to a high quality video source such as DVDs.
TCP/IP: " Transmission Control
Protocol/Internet Protocol." TCP/IP is the method most commonly
used in the Internet to transfer data, including streaming
video and audio, between computers.
Terrestrial: A broadcast signal
transmitted "over the air" to an antenna.
Upconvert: The process which
increases the number of pixels or frame rate used to represent
an image by creating new pixels at closer spacing. For instance
SDTV video having 720 x 480 pixels may be upconverted to
1280 x 720 pixels for use as HDTV. The upconversion process
does not increase the resolution of image.
Video-on-Demand (VOD): A programming
library service offering the individual viewer the choice
of the available content on demand. When the program is requested
and confirmed (by telephone or Internet) it is then delivered
to the viewer over an available channel in encrypted form.
VOD services are generally arranged on a “Pay per View” basis,
analogous to the cinema.
VSB: " Vestigial side band." VSB
is an analog modulation technique used to reduce the amount
of spectrum needed to transmit information through cable
TV, or over-the-air broadcasts.
Widescreen:
see 16:9
Y, PB, PR: A method for carrying the
video between HDTV or SDTV devices that retains the maximum
quality and is recommended for HD television. The video is
carried on three cables, respectively carrying luminance
(Y) and the two color difference signals (PB, PR).
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