Widescreen signaling

Summary

In television technology, widescreen signaling (WSS) is a 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 letterbox, widescreen, pillar-box, zoomed letterbox, etc.[1][2]

This development is related to introduction of widescreen TVs and broadcasts[2] and with the PALplus system in Europe (mid 1990s) and the need to downscale HD broadcasts to SD in the US. The bandwidth of the WSS bits is low enough to be recorded on VHS (at the time a popular home video recording technology).

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 scan line systems (like PAL or SECAM), the signal is placed in line 23.[2] It begins with a run-in code and start code followed by 14 bits of information, divided into groups as shown on the tables below:[3][4]

Group 1 (aspect ratio)

b00 b01 b02 b03 Aspect ratio Picture placement Active lines
0 0 0 0 - - -
0 0 0 1 4:3 Full
4 3 full.jpg
576
0 0 1 0 16:9 Letterbox top
16 9 lb t.jpg
432
0 0 1 1 - - -
0 1 0 0 14:9 Letterbox top
14 9 lb t.jpg
504
0 1 0 1 - - -
0 1 1 0 - - -
0 1 1 1 14:9 Full-height 4:3, framed to be "14:9-safe"
4 3 full.jpg
576
1 0 0 0 14:9 Letterbox centre
14 9 lb.jpg
504
1 0 0 1 - - -
1 0 1 0 - - -
1 0 1 1 >16:9 Letterbox deeper than 16:9
+16 9 lb.jpg
<432
1 1 0 0 - - -
1 1 0 1 16:9 Letterbox centre
16 9 lb.jpg
432
1 1 1 0 16:9 Full-height 16:9 (anamorphic)
16 9 full.jpg
576
1 1 1 1 - - -

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

525 line systems

525 line systems (like NTSC or PAL-M) made a provision using pulses for signaling widescreen and some other parameters in a similar manner to PAL and SECAM. Players output them and NTSC compatible TVs (including multiformat) recognize them. On these systems the signals are present in lines 22 and 285.[2]

The following table shows the information present on the signal:[2]

Bit Item
B1 Reference signal
B2 Reference signal
B3 Aspect ratio (4:3, 16:9)
B4 Even parity for B3 ~ B5
B5 Reserved
B6 Field type (first, next)
B7 Reference frame (reference, other)
B8 Vertical temporal helper (no, yes)
B9 Vertical high resolution helper (no, yes)
B10 Horizontal helper (no, yes)
B11 Horizontal helper pre-combing (no, yes)
B12~14 for TV station use
B15~17 Reserved
B18~23 Error correction codes for B3-B17
B24 Reference signal
B25~27 Confirmation signal

See also

References

  1. ^ 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.
  2. ^ a b c d e https://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.1119-2-199802-I!!PDF-E.pdf
  3. ^ http://www.divitec.se/sites/default/files/microvideo_wss-dec.pdf
  4. ^ https://www.dmi.unict.it/~battiato/download/IISFAMemberbook2011.pdf
  • 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.