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World System Teletext
Teletext standard
Teletext standard
| Field | Value |
|---|---|
| name | World System Teletext encodings |
| image | WST-Latin-infobox2.svg |
| caption | Examples of WST Latin G0 sets: reference version (US-ASCII) and United Kingdom version (BS_viewdata). National codes in red. |
| standard | ETS 300 706, ITU-R (CCIR) BT.653 |
| otherrelated | ISO 646, ISO 2022, ISO 6937 |
Development
WST originally stems from the UK standard developed by the BBC and the UK Independent Broadcasting Authority 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 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 ITU-R 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 BBC and services from Teletext on ITV in the United Kingdom, ZDFtext from ZDF and ARDText from ARD in Germany, and Tekst-TV from NRK in Norway, 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 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 in the US also included built-in WST teletext decoders in their higher-end models of TV sets, such as their Digital System 3 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 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 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.
{{anchor|Alpha-mosaic character}}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):
| 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | A | B | C | D | E | F | 2 | 3 | 6 | 7 | ||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| [[File:TRS-80 character 0x80.png | NBSP]] | [[File:TRS-80 character 0x81.png | 🬀]] | [[File:TRS-80 character 0x82.png | 🬁]] | [[File:TRS-80 character 0x83.png | 🬂]] | [[File:TRS-80 character 0x84.png | 🬃]] | [[File:TRS-80 character 0x85.png | 🬄]] | [[File:TRS-80 character 0x86.png | 🬅]] | [[File:TRS-80 character 0x87.png | 🬆]] | [[File:TRS-80 character 0x88.png | 🬇]] | [[File:TRS-80 character 0x89.png | 🬈]] | [[File:TRS-80 character 0x8A.png | 🬉]] | [[File:TRS-80 character 0x8B.png | 🬊]] | [[File:TRS-80 character 0x8C.png | 🬋]] | [[File:TRS-80 character 0x8D.png | 🬌]] | [[File:TRS-80 character 0x8E.png | 🬍]] | [[File:TRS-80 character 0x8F.png | 🬎]] | ||||
| [[File:TRS-80 character 0x90.png | 🬏]] | [[File:TRS-80 character 0x91.png | 🬐]] | [[File:TRS-80 character 0x92.png | 🬑]] | [[File:TRS-80 character 0x93.png | 🬒]] | [[File:TRS-80 character 0x94.png | 🬓]] | [[File:TRS-80 character 0x95.png | ▌]] | [[File:TRS-80 character 0x96.png | 🬔]] | [[File:TRS-80 character 0x97.png | 🬕]] | [[File:TRS-80 character 0x98.png | 🬖]] | [[File:TRS-80 character 0x99.png | 🬗]] | [[File:TRS-80 character 0x9A.png | 🬘]] | [[File:TRS-80 character 0x9B.png | 🬙]] | [[File:TRS-80 character 0x9C.png | 🬚]] | [[File:TRS-80 character 0x9D.png | 🬛]] | [[File:TRS-80 character 0x9E.png | 🬜]] | [[File:TRS-80 character 0x9F.png | 🬝]] | ||||
| [[File:TRS-80 character 0xA0.png | 🬞]] | [[File:TRS-80 character 0xA1.png | 🬟]] | [[File:TRS-80 character 0xA2.png | 🬠]] | [[File:TRS-80 character 0xA3.png | 🬡]] | [[File:TRS-80 character 0xA4.png | 🬢]] | [[File:TRS-80 character 0xA5.png | 🬣]] | [[File:TRS-80 character 0xA6.png | 🬤]] | [[File:TRS-80 character 0xA7.png | 🬥]] | [[File:TRS-80 character 0xA8.png | 🬦]] | [[File:TRS-80 character 0xA9.png | 🬧]] | [[File:TRS-80 character 0xAA.png | ▐]] | [[File:TRS-80 character 0xAB.png | 🬨]] | [[File:TRS-80 character 0xAC.png | 🬩]] | [[File:TRS-80 character 0xAD.png | 🬪]] | [[File:TRS-80 character 0xAE.png | 🬫]] | [[File:TRS-80 character 0xAF.png | 🬬]] | ||||
| [[File:TRS-80 character 0xB0.png | 🬭]] | [[File:TRS-80 character 0xB1.png | 🬮]] | [[File:TRS-80 character 0xB2.png | 🬯]] | [[File:TRS-80 character 0xB3.png | 🬰]] | [[File:TRS-80 character 0xB4.png | 🬱]] | [[File:TRS-80 character 0xB5.png | 🬲]] | [[File:TRS-80 character 0xB6.png | 🬳]] | [[File:TRS-80 character 0xB7.png | 🬴]] | [[File:TRS-80 character 0xB8.png | 🬵]] | [[File:TRS-80 character 0xB9.png | 🬶]] | [[File:TRS-80 character 0xBA.png | 🬷]] | [[File:TRS-80 character 0xBB.png | 🬸]] | [[File:TRS-80 character 0xBC.png | 🬹]] | [[File:TRS-80 character 0xBD.png | 🬺]] | [[File:TRS-80 character 0xBE.png | 🬻]] | [[File:TRS-80 character 0xBF.png | █]] |
- 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 and other ASCII-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 redefinable 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. 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 redefinable characters
- Wider colour palette with redefinable 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
- Germany:
- ZDF (some pages),
- 3sat (some pages)
- Bayerisches Fernsehen (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 redefinable 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 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 onto a carrier
- No noise added to the picture during transmission
- Image compression used
References
References
- "Recommendation ITU-R BT.653-3 (02/1998) Teletext systems".
- (1993). "Teletext Transmission". ExamPointer.
- Graziplene, Leonard R.. (2000). "Teletext: its promise and demise". Lehigh University Press.
- (1997). "Enhanced Teletext specification". ETSI.
- [https://www.etsi.org/deliver/etsi_i_ets/300700_300799/300706/01_60/ets_300706e01p.pdf#page=126 Graphics Character Sets] etsi.org
- Wiels. "TeleText - Het Protocol".
- de Kogel, Marcel. "P2000 Architecture".
- "Teletext Gallery: BBC Ceefax".
- Kramer, D.. "Higher-level teletext in action". EBU Technical Review.
- (2002). "ETSI EN 300 706 - Enhanced Teletext specification". EBU.
- Tozer, E.P.J.. (2013). "Broadcast Engineer's Reference Book". Focus.
- Lewis, Geoff. (1994). "Communications Technology Handbook". Newnes.
This article was imported from Wikipedia and is available under the Creative Commons Attribution-ShareAlike 4.0 License. Content has been adapted to SurfDoc format. Original contributors can be found on the article history page.
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