A teletext control codes encoding suggestion

Kent Karlsson kent.b.karlsson at bahnhof.se
Tue Jan 4 07:11:26 CST 2022

1) These ”controls” are not ligatures in any way whatsoever.
2) These ”controls” are very much geared towards a particular codepage architecture that is specific to Teletext. Thus making them completely unsuitable for everything else.
3) You are right that they are spacing graphic characters, but usually rendered as SPACE (but in some circumstances as a ”mosaic” character).

While it is not the worst suggestion in relation to how to handle these (far from), it is still not an appropriate approach in a Unicode context (why? see the three points above).

And… It is strange that you refer (only) to a specification from 1976. The most recent specifications are:

Enhanced Teletext specification, ETSI EN 300 706 V1.2.1, https://www.etsi.org/ <https://www.etsi.org/>deliver/etsi_en/300700_300799/300706/01.02.01_60/en_300706v010201p.pdf, 2003.
Digital Video Broadcasting (DVB); Specification for conveying ITU-R System B Teletext in DVB bitstreams, ETSI EN 300 472 V1.4.1, https://www.etsi.org/deliver/etsi_en/300400_300499/300472/01.04.01_60/en_300472v010401p.pdf <https://www.etsi.org/deliver/etsi_en/300400_300499/300472/01.04.01_60/en_300472v010401p.pdf>, 2017.

These are the standards for Teletext implemented in all currently produced, and all produced for several years (decades) back, TV sets and TV ”boxes”. The specifications go through hoops to be backwards compatible with the original Teletext, only providing ”enhancements” (and having several ”presentation levels”). The enhancements include: more colours and support for bold, italic and proportional font (via non-spacing out-of-line attributes).

It is true that using Teletext for news services is rapidly declining (though not quite dead yet). But it is still used for optional subtitling for accessibility reasons (subtitling is using the Box start and Box end controls for the subtitle lines, plus different colours for participants in a dialogue), despite that DVB provides another way of doing optional subtitles (image based, so that any fonts used need only be on the broadcaster side, not in the TV set).

/Kent K

> 3 jan. 2022 kl. 17:28 skrev William_J_G Overington via Unicode <unicode at corp.unicode.org>:
> http://www.users.globalnet.co.uk/~ngo/a_teletext_control_codes_encoding_suggestion.pdf
> William Overington
> Monday 3 January 2022

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