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By: Richard Del Cazzo
Web site: http://www.hdtv-hdtv.com
: Aspect ratio of traditional
NTSC TV screens, with 4 unit width by 3 unit height.
Aspect ratio of widescreen
DTV formats for all HDTV and some SDTV (Standard Definition)
content, 16 unit width by to 9 unit height.
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.
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.
Electronic device that
connects an analog television signal to a digital system.
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.
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.
the squeezing horizontally
of a 16:9 image into a full screen 4:3 display, resulting
in distortion of the image geometry.
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.
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).
"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.
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.
Unmodulated
analog video signal.
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).
A data modem that
provides an Internet connection over the TV cable network.
Video-on-demand or interactive services may require such a
connection.
Canadian Digital Television,
a not-for-profit, government-approved body, with members from
all sectors of the TV industry. CDTV is mandated to advise
its members, Industry Canada and the CRTC on the roll out
of DTV in Canada.
Consumer Electronics
Manufacturers Association. A U.S. industry group representing
manufacturers of consumer electronics products
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.
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.
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
An analog
video signal (NTSC, PAL or SECAM) that includes both luminance
(brightness) and chrominance (color) signals encoded together
to form a single signal.
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.
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.
Canadian Radio-television
and Telecommunications Commission, the federal regulatory
body for television programming and broadcasting in Canada.
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).
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.
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.
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.
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.
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.
Direct-to-Home satellite
delivery. May also be called DBS or Direct broadcast satellite.
In Canada, Bell ExpressVu and Star Choice provide DTH services
in both HDTV and SDTV.
"Digital television."
This comprises all the components of digital television, including
HDTV, SDTV, datacasting, and multicasting, falling under the
standards established by the ATSC.
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.
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.
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.
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.
Electronic program guide.
An on-screen display of channels and program data.
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.
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.
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.
TV
programming with interactive content and enhancements, blending
traditional TV viewing with the interactivity of a personal
computer.
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.
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.
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.
A method used
in some televisions to improve the visual quality of an NTSC
interlaced picture, making it comparable to a progressively
scanned picture.
Component of the
video signal that represents the brightness of the image.
Informational data
about the data, included in a signal's data stream.
Multichannel, Multipoint
Distribution System. A wireless cable system capable of being
encoded for pay-per-view and subscriber services.
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.
Term given to
the sharing of the digital television channel among 2, 3,
4 or more individual programs and/or data services
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.
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.
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.
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.
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.
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.
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.
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.
"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.
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.
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.
"Society of Motion
Picture and Television Engineers." A professional organization
that is responsible for the standards for film and television
production.
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.
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.
" 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.
A broadcast signal
transmitted "over the air" to an antenna.
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.
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.
" 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.
see 16:9
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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