World System Teletext (WST) is the name of a standard for encoding and displaying

teletext Teletext, or broadcast teletext, is a standard for displaying text and rudimentary graphics on suitably equipped television sets. Teletext sends data in the broadcast signal, hidden in the invisible vertical blanking interval area at the to ...

information, which is used as the standard for teletext throughout

Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...

today. It was adopted into the international standard CCIR 653 (now

ITU-R The ITU Radiocommunication Sector (ITU-R) is one of the three sectors (divisions or units) of the International Telecommunication Union (ITU) and is responsible for radio communications. Its role is to manage the international radio-frequenc ...

BT.653) of 1986 as CCIR Teletext System B.

Development

WST originally stems from the UK standard developed by the

BBC The British Broadcasting Corporation (BBC) is a British public service broadcaster headquartered at Broadcasting House in London, England. Originally established in 1922 as the British Broadcasting Company, it evolved into its current sta ...

and the UK

Independent Broadcasting Authority The Independent Broadcasting Authority (IBA) was the regulatory body in the United Kingdom for commercial television ( ITV and Channel 4 and limited satellite television regulation – cable television was the responsibility of the Cable Author ...

in 1974 for teletext transmission, extended in 1976 as the Broadcast Teletext Specification. With some tweaks to allow for alternative national character sets, and adaptations to the

NTSC NTSC (from National Television System Committee) is the first American standard for analog television, published and adopted in 1941. In 1961, it was assigned the designation System M. It is also known as EIA standard 170. In 1953, a second ...

525-line system as necessary, this was then promoted internationally as "World System Teletext". It was accepted by CCIR in 1986 under international standard CCIR 653 (now

BT.653) as one of four recognised standards for teletext worldwide (most commonly referred to as CCIR Teletext System B).

WST in Europe

Almost all television sets sold in Europe since the early '80s have built-in WST-standard teletext decoders as a feature. WST is used for all teletext services in Europe & Scandinavia, including '' Ceefax'' from the

and services from ''Teletext'' on ITV in the

United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Northwestern Europe, off the coast of European mainland, the continental mainland. It comprises England, Scotlan ...

, ''ZDFtext'' from

ZDF ZDF (), short for (; ), is a German public-service television broadcaster based in Mainz, Rhineland-Palatinate. Launched on 1 April 1963, it is run as an independent nonprofit institution, and was founded by all federal states of Germany ( ...

and ''ARDText'' from ARD in

Germany Germany, officially the Federal Republic of Germany, is a country in Central Europe. It lies between the Baltic Sea and the North Sea to the north and the Alps to the south. Its sixteen States of Germany, constituent states have a total popu ...

, and ''Tekst-TV'' from NRK in

Norway Norway, officially the Kingdom of Norway, is a Nordic countries, Nordic country located on the Scandinavian Peninsula in Northern Europe. The remote Arctic island of Jan Mayen and the archipelago of Svalbard also form part of the Kingdom of ...

, among many other teletext services offered by other television networks throughout the European continent.

WST in the United States

WST saw some use in the

United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

in the 1980s, for the ''Electra'' service, which was carried on SuperStation WTBS (now TBS). It was also used for other teletext services on other television stations and networks in the US.

Zenith The zenith (, ) is the imaginary point on the celestial sphere directly "above" a particular location. "Above" means in the vertical direction (Vertical and horizontal, plumb line) opposite to the gravity direction at that location (nadir). The z ...

in the US also included built-in WST teletext decoders in their higher-end models of TV sets, such as their line throughout the 1980s. Also, Dick Smith Electronics offered through their American distributors a WST teletext decoder in the form of a set-top box, which was sold as a kit. This was all in competition to another teletext standard developed exclusively in North America, NABTS (North American Broadcast Teletext Standard). It was developed in Canada by Norpak, and was used by CBS for their '' ExtraVision'' service and for a very short time by

NBC The National Broadcasting Company (NBC) is an American commercial broadcast television and radio network serving as the flagship property of the NBC Entertainment division of NBCUniversal, a subsidiary of Comcast. It is one of NBCUniversal's ...

for their NBC Teletext service in the mid-1980s. However, NABTS never became as successful as WST in the American continent, since NABTS was a more advanced technology, which required a much more complicated and expensive decoder (even though it had improved graphics capability over WST).

Levels

In the early 1980s a number of higher extension levels were envisaged for the specification, based on ideas then being promoted for worldwide

videotex Videotex (or interactive videotex) was one of the earliest implementations of an end-user information system. From the late 1970s to early 2010s, it was used to deliver information (usually pages of text) to a user in computer-like format, typi ...

standards (telephone dial-up services offering a similar mix of text and graphics). The proposed higher content levels included geometrically-specified graphics (Level 4), and higher-resolution photographic-type images (Level 5), to be conveyed using the same underlying mechanism at the transport layer. No TV sets currently implement the two most sophisticated levels.

Level 1 (1976)

The initial Broadcast Teletext Specification set out by the BBC, IBA, BREMA in September 1976: * ''Alpha-mosaic characters'' (drawn using a 2×3 block matrix) characters (similar to some characters of the TRS-80 character set): * spacing attributes * fixed colour palette (red, green, yellow, blue, magenta, cyan, white over a black background) * support for double height or flash effect * 40 columns × 24 rows character grid (Level 1 was replaced by level 1.5)

Level 1.5 (1981)

An extended version of level 1, with support for 13 extended

character sets Character encoding is the process of assigning numbers to graphical character (computing), characters, especially the written characters of human language, allowing them to be stored, transmitted, and transformed using computers. The numerical v ...

and other

ASCII ASCII ( ), an acronym for American Standard Code for Information Interchange, is a character encoding standard for representing a particular set of 95 (English language focused) printable character, printable and 33 control character, control c ...

-like characters. *Croatian, Serbian and Slovenian *Czech and Slovak *Danish, Swedish and Finnish *English *Estonian *French *German *Italian *Lettish and Lithuanian *Polish *Portuguese and Spanish *Romanian *Turkish This is the most common system and still used by most TV channels as of 2021.

Level 2 (1988)

World System Teletext Level 2 was introduced in 1988. New features were: * Multi-language support * 32 colour mode. * Non-spacing attributes * Allows re-definable characters (Level 2 was replaced by level 2.5)

Level 2.5 / Hi-Text (1995)

Level 2.5 or ''HiText''. was first broadcast in 1994 by the bilingual French-German channel

ARTE Arte (, , ; ' ('), sometimes stylised in lowercase or uppercase in its logo) is a European Union, European public service Television channel, channel dedicated to culture. It is made up of three separate companies: the Strasbourg-based Europea ...

. With Level 2.5 it is possible to set a background colour and have higher resolution text and images. The system was adopted initially by ARTE, ARD, ZDF, Bayern 3 and SwissTXT. New features of Level 2.5 teletext: * Multi-language support * Non-spacing attributes * Allows re-definable characters * Wider colour palette with re-definable colours (4,016 colour palette) * Provides side panels for additional text or graphics in 16:9 TVs * nexTView EPG The system has not been widely implemented, with only a handful of European state broadcasters supporting it. Television stations which are known to transmit Level 2.5 teletext in the late 2010s include: * Netherlands: public broadcaster NOS (background colour on all pages, and a test page with hi-res graphics), * France:

France 3 France 3 () is a French free-to-air Public broadcasting, public television network. The second flagship network of France Télévisions, it broadcasts a wide range of general and specialized programming. France 3 is structured as a Region ...

* Germany: **

(some pages), **

3sat 3sat (, ''Dreisat'') is a free-to-air German-language public service television channel. It is a generalist channel with a cultural focus and is jointly operated by public broadcasters from Germany ( ZDF, ARD), Austria ( ORF) and Switzerlan ...

(some pages) **

Bayerisches Fernsehen (; "Bavarian Broadcasting"), shortened to BR (), is a public broadcasting, public-service radio and television broadcaster, based in Munich, capital city of the Bavaria, Free State of Bavaria in Germany. BR is a member organization of the ARD (b ...

(and formerly also now-renamed BR-alpha) (in the past on almost all pages, now only on some pages), ** phoenix (on some pages), ** Bürgerfernsehen Gera (background-colour on all pages, test pages 460 to 485) and ** SWR Fernsehen (included completely backwards-compatible Level 2.5 teletext, with higher quality text and graphics on nearly all pages). By late 2021, SWR Fernsehen stopped using the system, but ZDF, 3sat, Bayerisches Fernsehen and Phoenix has at least some Level 2.5 enhanced pages. One of the problems with Level 2.5 is that it often takes several transmission cycles before the higher resolution items show on the screen. In order to watch Level 2.5 teletext, a rather recent television set with a special decoder chip is required. If not, Level 1.5 text will be shown.

Level 3

New features: * Dynamically Redefined Character Set (DRCS) allowing the display of non- Roman characters (e.g. Arabic and Chinese) * Pictorial graphic characters can also be defined (Level 3 was replaced by level 3.5)

Level 3.5 (1997)

Level 3.5 extends the number of re-definable characters and their complexity and introduces different font styles and proportional spacing. New features: * Dynamically Redefined Character Set (DRCS) allowing the display of non-Roman characters (e.g. Arabic and Chinese) * Pictorial graphic characters can also be defined * Different font styles * Proportional spacing.

Level 4 (1981)

Level 4 was proposed in 1981 and tested by IBA. No TV set implements this level. *

Vector graphics Vector graphics are a form of computer graphics in which visual images are created directly from geometric shapes defined on a Cartesian plane, such as points, lines, curves and polygons. The associated mechanisms may include vector displ ...

in resolutions of 320×256 * Needs computing power to generate the display from a sequence of drawing instructions * 250,000 colours palette

Level 5

Level 5 allows full-definition still pictures with better quality than video cameras. No TV set implements this level. *

Modulated Signal modulation is the process of varying one or more properties of a periodic waveform in electronics and telecommunication for the purpose of transmitting information. The process encodes information in form of the modulation or message ...

onto a carrier * No noise added to the picture during transmission *

Image compression Image compression is a type of data compression applied to digital images, to reduce their cost for computer data storage, storage or data transmission, transmission. Algorithms may take advantage of visual perception and the statistical properti ...

used

References

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