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
editFor 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]
| Bits (0 to 3) | Aspect ratio | Picture placement inside the broadcast area | Active lines |
|---|---|---|---|
| 0000 | - | - | - |
| 0001 | Full format 4:3 |  |
576 |
| 0010 | Letterbox 16:9 top |  |
432 |
| 0011 | - | - | - |
| 0100 | Letterbox 14:9 top |  |
504 |
| 0101 | - | - | - |
| 0110 | - | - | - |
| 0111 | Full format 14:9 centre shoot and protect 14:9 (see note) | |
576 |
| 1000 | Letterbox 14:9 centre |  |
504 |
| 1001 | - | - | - |
| 1010 | - | - | - |
| 1011 | Letterbox deeper than 16:9 centre |  |
undefined |
| 1100 | - | - | - |
| 1101 | Letterbox 16:9 centre |  |
432 |
| 1110 | Full format 16:9 anamorphic |  |
576 |
| 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.
| 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
edit525 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]
| Bit | Item |
|---|---|
| 1 | Reference signal |
| 2 | Reference signal |
| 3 | Aspect ratio (4:3 full format / 16:9 letterbox) |
| 4 | Even parity for B3 to B5 |
| 5 | Reserved |
| 6 | Field type (First field / Next field) |
| 7 | Frame type (Reference frame / Other frame) |
| 8 | Vertical temporal helper (no / yes) |
| 9 | Vertical high resolution helper (no / yes) |
| 10 | Horizontal helper (no / yes) |
| 11 | Horizontal helper pre-combing (no / yes) |
| 12 to 14 | For TV station use |
| 15 to 17 | Reserved |
| 18 to 23 | Error correction codes for B3 to B17 |
| 24 | Reference signal |
| 25 to 27 | Confirmation signal |
See also
editReferences
edit- ^ a b c APPLICATION NOTE 9716: Widescreen Signaling (WSS). Renesas. 1988.
- ^ 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.
- ^ a b c d e f RECOMMENDATION ITU-R BT.1119-2 - WIDE-SCREEN SIGNALLING FOR BROADCASTING (PDF). ITU. 1998.
- ^ "RECOMMENDATION ITU-R BT.1197-1 Enhanced wide-screen PAL TV transmission system (the PALplus system)" (PDF). itu.int.
- ^ FUKINUKI, Takahiko (March 1991). "EDTV".
- ^ Pollack, Andrew (September 15, 1994). "Japanese Taking to Wide-Screen TV" – via NYTimes.com.
- ^ ETSI EN 300 294 - Television systems; 625-line television Wide Screen Signalling (WSS) (PDF). ETSI. 2003.
- ^ 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) - ^ "All You Ever Wanted to Know About PALplus but were Afraid to Ask". Archived from the original on 3 March 2016.
- ^ "Fluke PM5420 Application Note PALplus" (PDF). assets.fluke.com. Archived from the original (PDF) on 3 March 2016. Retrieved 12 January 2022.
- ^ 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.
- ^ "The Journal of the Institute of Television Engineers of Japan". www.jstage.jst.go.jp.
- ^ AN9716: Widescreen Signaling (WSS). Renesas Electronics Corporation. 1998.
- ^ RECOMMENDATION ITU-R BT.1298 - Enhanced wide-screen NTSC TV transmission system (PDF). ITU. 1997.
- ^ Kageyama, Masahiro (2010). Thesis Research on high image quality and high functionality of television (PDF).
- ^ Jack, Keith; Tsatsoulin, Vladimir (2002-09-11). Dictionary of Video and Television Technology. Gulf Professional Publishing. ISBN 978-1-878707-99-4.
External links
edit- Renesas AN9716, Widescreen Signaling (WSS) covering 625 lines and 525 lines standard.