Page 168 - ITU Journal, ICT Discoveries, Volume 3, No. 1, June 2020 Special issue: The future of video and immersive media

ITU Journal: ICT Discoveries, Vol. 3(1), June 2020

The following represents an example for the use of this model: a Sender scans an original colour image
using a specific device-dependent colour space which may depend on the illuminant and/or filters of a
particular scanner system. The Sender converts the device-dependent colour data to the interchange colour
representation. The Sender then encodes the data using a coding algorithm such as ITU-T Rec. T.81 (JPEG).
The Receiver receives the encoded data. The data is decoded and converted to the colour space which is
device dependent. In order to define the colour representation, it is necessary to specify the white point,
illuminant and gamut range used in the interchange data representation.”

ITU-T T.563 [16] – though published – is practically not used and most likely has never been implemented.
Facsimile group 4 (including so called mixed mode terminals) existed only on paper and in the
Recommendation. The failure of facsimile group 4 had to do with: a) the different options in the network layers
(public switched telephone network (PSTN), packet switched data network (PSDN), circuit switched data
network (CSDN), ISDN – none of them too popular); b) damaging discussion on the incompatibility on ISDN
between facsimile groups 3 and 4. That was enough to kill the potential market.
4.1.3 Videotex: Annex F of ITU-T T.101 [18]

Actually, this application comes closest to what is today presented on web pages with photographic content.
Part of Annex F of ITU-T T.101 [18] reads,
“This annex defines a data syntax to be used for conveying photographic data in a Videotex environment.
The necessary tools are provided for the transfer of photographic data, typically from a Videotex Host to a
Videotex terminal. This data syntax is equally applicable to either storage or communication applications
and is independent of physical device or transmission media.
This annex does not deal with the visible appearance of the displayed pictures, however all the necessary
source image information is provided to make the proper physical adaptation at the receiving side. The
specification of post-processing techniques is left to the implementers and is, therefore, outside the scope
of this annex….
…. In particular, the …-Joint Photographic Experts Group (JPEG) compression algorithm, based on the
discrete cosine transform (DCT), the facsimile ITU-T Recommendation T.4 and CCITT Recommendation T.6
coding algorithms are used. In this annex the algorithms or compression techniques themselves are not
described, references are provided.”
ITU-T T.101 [18] was also adopted by the European Conference of Postal and Telecommunications
Administrations (CEPT) [19] and European Telecommunications Standards Institute (ETSI). About 5 000
terminals were built and put into operation in France alone. Today all videotex services worldwide have been
replaced by the web. Videotex was killed by: a) incompatibility of the major world regional standards; b) its
terminals were mostly dedicated (not PCs) and had no other functionality. Thus, it came one or two
generations too early.
Nevertheless, videotex is important from a historic point of view. Many concepts seen today on the web had
an early videotex variant, e.g. photo-videotex or tele-software (early and similar versions of web scripting
languages like ECMAScript and JavaScript.
4.1.4 Multimedia conferencing: ITU-T T.120 [13]; ITU-T T.126 [20]
ITU-T T.120 [13] (including ITU-T T.126 [20]) is one of the ITU-T Recommendations utilizing JPEG-1 and
implemented very often. The system architecture of ITU-T T.120 [13] is shown in Fig. 14. Screen sharing,
sharing of photographic images via internet and web-linked PC stations are classical uses. Thus, ITU-T T.120
[13] using JPEG-1 has been successful.

146 © International Telecommunication Union, 2020