Introduction
According
to oxford dictionary teletext means computerised service providing information
on television screens experimental television broadcasting started in the 1920s
in the United states of America. Teletext is a one-way, or non-interactive,
system for transmission of text and graphics via broadcasting or cable for
display on a television set. A decoder or microchip resident in the TV set is
needed to extract the teletext information[1]. The information
is organised in 'pages' using alphanumeric characters and block graphics. Pages
are transmitted in a continuous cycle. Pages are accessed by keying a
three-digit number on a remote- control keypad and waiting for the selected
page to arrive
Teletext is free, simple and up-to-date (well, mostly). It consists of a
variety of numbered frames that you can access via a suitably equipped
television or computer[2]. These frames contain
up-to-date news, TV guides, chat, advertising, and other things that the
broadcaster thinks may be of use to you. Teletext is
aimed mainly at the domestic user, though some of the information has
commercial importance. People are able to obtain information at any time the TV
station is transmitting. People can see the news, for example, without waiting
for certain times of day and they can choose for themselves how long to spend
on any particular item. Teletext information is frequently updated and urgent
newsflashes can be made to appear on the screen as scan as the information is
available. People whose hearing is not very good can use teletext subtitles to
follow the main TV programme. Not all programmes are subtitled but the service
covers news reviews, documentaries, films and other entertainments.
Who
provides Teletext[3]
Teletext
in Britain is transmitted by the BBC as CEEFAX on BBC 1 and BBC 2 and also by
Independent Television on Channel 3 and 4 as ORACLE. The name 'CEEFAX' is
obviously a play on the words 'SEE' and' FACTS'. The word 'ORACLE' means one
who speaks knowledge or wisdom and also stands for 'Optional Reception of
Announcements by Coded Line Electronics'.
Types and information services through Teletext
ü News
and current affairs
ü Travel
information, Road, Rail. Sea and Air
ü Weather
forecasts
ü Sports
fixtures and results
ü TV
Programme information (listings and background)
ü Subtitles
for programme being shown
ü Financial
information, personal and business; Market prices
ü Amusement,
puzzles, quizzes and competitions;
ü Holidays
ü Shopping
ü Advertisement
Advantage
of Teletext[4]
ü Up to
the minute Information can to provided.
ü Information
can be changed as new situations develop.
ü Teletext
provides subtitles for hearing-impaired viewers.
ü Viewdata
user can communicate in the system to order goods
ü Data
can be stored from Viewdata or teletext on personal computers.
ü Teletext
is free whereas newspaper and magazines have to be paid for.
Limitations
of teletext[5]
The
main limitations of CEEFAX and ORACLE are
ü The
types, range and depth of information available; some other countries make
much more extensive use of teletext.
ü The
display method used in teketext and viewdata; 24 rows of 40 columns,
limited character set with very low
resolution (block) graphics and very limited animation.
ü The
number of pages available; a few hundred pages on each channel.
ü The
access time or delay waiting for a page to 'arrive'.
The
number of pages available is limited by the rate of data transmission and the
average length of time users are willing to wait for the page to 'arrive'.
Increasing the number of pages would mean that the cycle-time would be
increased unless the capacity of the transmission system was also increased or
example by using more lines of the transmuted TV signal for teletext.
Bibliography
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