In television technology, Wide Screen Signaling (WSS)[1] 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, pillar-box, zoomed letterbox, etc.[2][3]

This development is related to introduction of widescreen TVs and broadcasts,[3] with the PALplus[4] system in the European Union (mid 1990s), the Clear-Vision[5][6] system in Japan (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.[3]

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.[3] 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) :[7][8][9][10][1]

Group 1 - Aspect ratio
Bits (0 to 3)Aspect ratioPicture placement inside the broadcast areaActive lines
0000---
0001Full format 4:3576
0010Letterbox 16:9 top430
0011---
0100Letterbox 14:9 top504
0101---
0110---
0111Full format 14:9 centre shoot and protect 14:9 (see note)576
1000Letterbox 14:9 centre504
1001---
1010---
1011Letterbox deeper than 16:9 centreundefined
1100---
1101Letterbox 16:9 centre430
1110Full format 16:9 anamorphic576
1111---

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.

Group 2 to 4
Bit Item Group
4 Camera Mode (interlaced) / PALplus Film Mode (progressive scan) 2 - Enhanced Services
5 Conventional PAL / PALplus Motion Adaptative Colour Plus encoding
6 No Vertical helper / PALplus Vertical helper present
7 Reserved / Ghost cancellation
8 No subtitles / subtitles within teletext 3 - Subtitles
9 No open subtitles / Subtitles in active image area
10 Subtitles out of active image area / Reserved
11 No surround sound / Surround sound mode 4 - Reserved
12 No copyright asserted or status unknown / Copyright asserted
13 Copying not restricted / Copying restricted

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.[11][12] On these systems the signals are present in lines 22 and 285, as 27 data bits, as defined by IEC 61880.[3][13][14][15][1][16]

The following table shows the information present on the signal, based on Rec. ITU-R BT.1119-2 ("helper" signals are EDTV-II specific):[3]

BitItem
1Reference signal
2Reference signal
3Aspect ratio (4:3 full format / 16:9 letterbox)
4Even parity for B3 to B5
5Reserved
6Field type (First field / Next field)
7Frame type (Reference frame / Other frame)
8Vertical temporal helper (no / yes)
9Vertical high resolution helper (no / yes)
10Horizontal helper (no / yes)
11Horizontal helper pre-combing (no / yes)
12 to 14For TV station use
15 to 17Reserved
18 to 23Error correction codes for B3 to B17
24Reference signal
25 to 27Confirmation signal

See also

References

  1. 1 2 3 APPLICATION NOTE 9716: Widescreen Signaling (WSS). Renesas. 1988.
  2. ↑ Loncaric, Matej; Tralic, Dijana; Brzica, Maja; Petrovic, Juraj; Grgic, Sonja (September 17, 2009). "Managing mixed HD and SD broadcasting". pp. 79–82 – via IEEE Xplore.
  3. 1 2 3 4 5 6 RECOMMENDATION ITU-R BT.1119-2 - WIDE-SCREEN SIGNALLING FOR BROADCASTING (PDF). ITU. 1998.
  4. ↑ "RECOMMENDATION ITU-R BT.1197-1 Enhanced wide-screen PAL TV transmission system (the PALplus system)" (PDF). itu.int.
  5. ↑ FUKINUKI, Takahiko. "EDTV".
  6. ↑ Pollack, Andrew (September 15, 1994). "Japanese Taking to Wide-Screen TV" – via NYTimes.com.
  7. ↑ ETSI EN 300 294 - Television systems; 625-line television Wide Screen Signalling (WSS) (PDF). ETSI. 2003.
  8. ↑ Battiato, Farinella, Puglisi (2011). IISFA Member book 2011 - Image/Video Forensics: Casi di Studio (PDF). IISFA. p. 8.{{cite book}}: CS1 maint: multiple names: authors list (link)
  9. ↑ "All You Ever Wanted to Know About PALplus but were Afraid to Ask". Archived from the original on 3 March 2016.
  10. ↑ "Fluke PM5420 Application Note PALplus" (PDF). assets.fluke.com. Archived from the original (PDF) on 3 March 2016. Retrieved 12 January 2022.
  11. ↑ Nakayama, K.; Kojima, T.; Miyaguchi, H.; Sawaragi, T.; Yaguchi, Y. (August 5, 1995). "EDTV-II decoder by SVP2 (the 2nd generation of scan-line video processor)". IEEE Transactions on Consumer Electronics. 41 (3): 634–642. doi:10.1109/30.468089 – via IEEE Xplore.
  12. ↑ "The Journal of the Institute of Television Engineers of Japan". www.jstage.jst.go.jp.
  13. ↑ AN9716: Widescreen Signaling (WSS). Renesas Electronics Corporation. 1998.
  14. ↑ RECOMMENDATION ITU-R BT.1298 - Enhanced wide-screen NTSC TV transmission system (PDF). ITU. 1997.
  15. ↑ Kageyama, Masahiro (2010). Thesis Research on high image quality and high functionality of television (PDF).
  16. ↑ Jack, Keith; Tsatsoulin, Vladimir (2002-09-11). Dictionary of Video and Television Technology. Gulf Professional Publishing. ISBN 978-1-878707-99-4.
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