Widescreen signaling
In television technology, widescreen signaling (WSS) is a digital stream embedded in the analog TV signal describing qualities of the broadcast, in particular the intended aspect ratio of the image. This can be used by a widescreen TV or other device to switch to the correct display mode.
PAL and SECAM Systems
For 625 scan line systems (PAL and SECAM), the signal is placed in line 23. It begins with a run-in code and start code followed by 14 bits of information.[1]
Group 1 (Aspect Ratio)
| b00 | b01 | b02 | b03 | Aspect ratio | Picture placement | Active lines |
|---|---|---|---|---|---|---|
| 0 | 0 | 0 | 1 | 4:3 | Full | 576 |
| 1 | 0 | 0 | 0 | 14:9 | Letterbox centre | 504 |
| 0 | 1 | 0 | 0 | 14:9 | Letterbox top | 504 |
| 1 | 1 | 0 | 1 | 16:9 | Letterbox centre | 432 |
| 0 | 0 | 1 | 0 | 16:9 | Letterbox top | 432 |
| 1 | 0 | 1 | 1 | >16:9 | Letterbox deeper than 16:9 | <432 |
| 0 | 1 | 1 | 1 | 14:9 | Full-height 4:3, framed to be "14:9-safe" | 576 |
| 1 | 1 | 1 | 0 | 16:9 | Full-height 16:9 (anamorphic) | 576 |
Group 2 (Enhanced Services)
| b04 | Mode |
|---|---|
| 0 | Camera Mode (interlaced) |
| 1 | Movie Mode (progressive scan) |
| b05 | Mode |
|---|---|
| 0 | PAL Standard |
| 1 | Colour Plus |
| b06 | Mode |
|---|---|
| 0 | No Vertical helper |
| 1 | Vertical helper present |
The above settings are related to PALplus.
| b07 | Ghost cancellation |
|---|
Group 3 (Subtitles)
| b08 | Mode |
|---|---|
| 0 | no subtitles |
| 1 | Teletext subtitles |
| b09 | b10 | Mode |
|---|---|---|
| 0 | 0 | No subtitles |
| 1 | 0 | Subtitles inside active image |
| 0 | 1 | Subtitles outside active image |
| 1 | 1 | Reserved |
Group 4 (Other)
| b11 | Mode |
|---|---|
| 0 | No surround sound information |
| 1 | Surround sound mode |
| b12 | Mode |
|---|---|
| 0 | No copyright asserted or status unknown |
| 1 | Copyright asserted |
| b13 | Mode |
|---|---|
| 0 | Copying not restricted |
| 1 | Copying restricted |
NTSC Systems
525 line systems made a provision using pulses for signalling wide screen and some other parameters in a similar manner to PAL and SECAM. However, no video player generates them and no NTSC compatible TV (including multiformat) recognises them. Accordingly, unless the wide screen is signalled via an alternate means (such as the wide screen discrete signal on SCART connection), the TV has to be manually switched between 4:3 and 16:9.
See also
References
- ETSI EN 300 294 "Television Systems: 625-Line Television Wide Screen Signaling (WSS)"
External links
- Renesas AN9716, Widescreen Signaling (WSS) covering 625 lines and 525 lines standard.