In
television
Television (TV) is a telecommunication medium for transmitting moving images and sound. Additionally, the term can refer to a physical television set rather than the medium of transmission. Television is a mass medium for advertising, ...
technology, Wide Screen Signaling (WSS)
is digital
metadata embedded in
invisible part of the
analog TV signal describing qualities of the broadcast, in particular the intended
aspect ratio of the image. This allows television broadcasters to enable both
4:3 and
16:9 television sets to optimally present pictures transmitted in either format, by displaying them in
full screen,
letterbox,
widescreen
Widescreen images are displayed within a set of aspect ratio (image), aspect ratios (relationship of image width to height) used in film, television and computer screens. In film, a widescreen film is any film image with a width-to-height aspect ...
,
pillar-box, zoomed
letterbox, etc.
This development is related to introduction of widescreen TVs and broadcasts,
with the
PALplus system in the
European Union
The European Union (EU) is a supranational union, supranational political union, political and economic union of Member state of the European Union, member states that are Geography of the European Union, located primarily in Europe. The u ...
(mid 1990s), the
Clear-Vision system in
Japan
Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...
(early 1990s), and the need to downscale
HD broadcasts to
SD in the US. The
bandwidth of the WSS signal is low enough to be recorded on
VHS (at the time a popular home video recording technology). It is standardized on Rec.
ITU-R BT.1119-2.
A modern digital equivalent would be the
Active Format Description, a standard set of codes that can be sent in a
MPEG video stream, with a similar set of aspect ratio possibilities.
625 line systems
For
625 line analog TV systems (like
PAL or
SECAM), the signal is placed in line 23.
It begins with a run-in code and starts code followed by 14
bits of information, divided into four groups, as shown on the tables below (based on Rec. ITU-R BT.1119-2) :
''
Note: The transmitted aspect ratio is 4:3. Within this area a 14:9 window is protected, containing all the relevant picture content to allow a wide-screen display on a 16:9 television set.''
525 line systems
525 line analog systems (like
NTSC or
PAL-M) made a provision for the use of pulses for signaling widescreen and other parameters, introduced with the development of
Clear-Vision (EDTV-II), a NTSC-compatible Japanese system allowing widescreen broadcasts. On these systems the signals are present in lines 22 and 285, as 27 data bits, as defined by
IEC 61880.
The following table shows the information present on the signal, based on Rec. ITU-R BT.1119-2 ("helper" signals are EDTV-II specific):
See also
*
PALplus
*
Clear-Vision
*
Active Format Description (AFD)
*
Teletext
References
External links
Renesas AN9716, ''Widescreen Signaling (WSS)''covering 625 lines and 525 lines standard.
{{Video formats
Television technology
de:Wide Screen Signalling