PALplus

PALplus (or PAL+) is an extension of the PAL analogue broadcasting system for transmitting 16:9 programs without sacrificing vertical resolution.[1] It followed experiences with the HD-MAC and D2-MAC, standards that were incompatible with existing receivers but featured a 16:9 aspect ratio. It was developed in Germany University of Dortmund in cooperation with German terrestrial broadcasters and European and Japanese manufacturers.

History

In the late 1980s a new broadcasting standard was created, HD-MAC, that was HDTV and 16:9 capable (up to 2048×1152 picture resolution), twice the number of available lines in PAL. As a transitional standard, D2-MAC was established. Like HD-MAC, it is 16:9-ready, but with the same number of lines that PAL uses. When D2-MAC failed due to being an incompatible system with existing sets, the PALplus norm was introduced as an attempt to create a compatible widescreen EDTV transmission format.

Initially, PALplus was the name of a strategy group founded in 1989 in order to develop an enhanced system for terrestrial transmission compatible with standard-PAL. In the beginning, the group consisted of the public broadcasting corporations of Germany (ARD and ZDF), Austria (ORF), Switzerland (SRG) and the United Kingdom (BBC and UKIB, United Kingdom Independent Broadcasters) together with the consumer electronics manufacturers Grundig, Nokia, Philips and Thomson. Sony as well as the Spanish and Portuguese broadcasters joined the group later on.

At the 1993 International Consumer Electronics Exhibition in Berlin, the first experimental PALplus broadcasts began. At the same year, the European Union approved a plan to support the production and broadcast of 16:9 programs.[2]

In 1994 broadcasts began adopting the format and Nokia launched the first PALplus TV set in Germany.

In 1995 one of the four big Korean electronics manufacturers, Samsung, joined the PALplus consortium.

On January 1996, the PALplus board published the specifications of the standard in order to support the further dissemination of this standard for wide-screen transmissions. After German broadcasters started to broadcast some of their programmes in PAL+, the PALplus board ended its work at the end of that same year.

At the beginning of 1998, PALplus programmes were broadcast on a regular basis in nine European countries, which made PALplus the mostly used standard for 16:9 transmissions in Europe.

Criticism

The decoding of a 16:9 picture in PALplus is technically complex and requires the use of the two fields of the full picture. Because of this, only the high end TVs of the time (such as 100 Hz TV sets) could decode the 16:9 mode of PALplus.

For all this, the takeup of PALplus was marginal, with the standard eventually being replaced by digital television broadcasting (DVB) in widescreen format.

Operation

A standard PAL receiver will display the 16:9 image in letterbox format with 432 active lines. This reproduces noticeably less detail than the 576 lines used for 4:3 broadcasts. A PALplus receiver can use extra information hidden in the black bars above and below the image to fully recover the 576 lines of vertical resolution.[3]

For compatibility reasons, the horizontal bandwidth remains at 5.0 MHz. This means that a PALplus signal provides no extra horizontal resolution to compensate for the image being stretched across a wider screen. The result is a horizontal resolution that is 73% of the vertical resolution, or 51% when the Kell factor is ignored.

A special signal tells the receiver when PALplus is in use, and also whether the original content was interlaced ("Camera mode" 576i50) or progressive scanned ("Film mode" 576p25). An additional signal can enable a "Ghost Cancellation" feature.

A separate feature related to PALplus is ColourPlus, which improves colour decoding performance.[3]

Extensions

The PALplus standard comprises three extensions to standard PAL:[1]

Vertical helper

A broadcaster creates a PALplus signal by scaling an anamorphic 16:9 picture with 576 lines down to 432 lines, so that the picture appears letterboxed on a regular PAL TV set. For luminance, the scaling is done using a pair of matching low-pass and high-pass filters, with the low-pass result appearing in the broadcast. One out of every 4 lines of the high-pass result is then hidden in the remaining 144 black lines at the top and bottom of the picture, using the U colour subcarrier. The filtering is such that this is enough to restore the complete 576 line resolution. The use of the colour subcarrier means the signals sometimes appear as blue and yellow patterns on a regular PAL TV set. The 16:9 PAL-plus receiver combines 432 visible lines plus 144 helper lines into 576 new visible lines.

In Film mode (progressive scan), the operation is performed on a per-frame basis, while in Camera mode (interlaced) the operation is performed per-field.

Colour-plus (or Clean PAL)

The PAL colour carrier is modulated making use of correlation between 2 fields, in order to give a cleaner Y/C separation in the PAL-plus receiver. It is used with signals with high horizontal luminance frequencies (3 MHz) that share the spectrum with the chrominance signals. Colour pictures on both standard and PAL Plus receivers are enhanced.

For progressive "Film mode" material, "Fixed" Colour-Plus is used, as there is no motion between the image fields. For camera based images, "Motion Adaptive Color-Plus" (MACP) is used based on movement.

Signaling bits

A special WSS signal tells the receiver whether 4:3/16:9/PALplus is in use, and also whether the original content was interlaced ("Camera mode") or progressive scanned ("Film mode"). An additional signal can enable a "Ghost Cancellation" feature. The bandwidth of these bits is low enough to be recorded on VHS and allow the receiver to switch to the proper format.

PAL-plus compatible sets

The standard permits using the mark "PAL-plus" if just the vertical helper reconstruction implemented, with Colour-plus being optional.

Some PALPlus compatible sets:[1]

Most widescreen sets without any PAL-plus processing will switch the display format automatically between 4:3 and 16:9, based on the signaling bits. These sets will display only the centre 432 lines of the 4:3 image, to fill all of the 16:9 frame.

Availability

PALplus was used in the following European countries:

Belgium

In Belgium, the Flemish public broadcasting service VRT has a policy that all of its self-created TV programmes are broadcast in PALplus. For example, the news is broadcast daily in PALPlus, as are almost all of the weekly scheduled shows. VRT does however always respect the original ratio of the footage. So new films and series are usually broadcast in PALplus. The commercial TV station VTM also broadcasts a lot in PALplus. The VTM news for example is also broadcast in PALplus. So are the commercials. Special shows and films are always broadcast in PALplus too. VTM tends to change 4:3 footage to 16:9 too. Even the third broadcasting organisation SBS Belgium with its stations VT4 and VijfTV broadcast in PALplus for all of their new productions and they also broadcast the news and the commercials in P+. The Walloon public broadcasting service RTBF broadcasts bought 16:9 programmes in PALplus, like films, but chooses to create their own programmes in 4:3. Walloon commercial TV station RTL-TVi now broadcasts almost all its shows in PALPlus and tends to convert its old shows to 16:9 too.

Germany

In Germany all public broadcasters (ARD, ZDF, etc) comply with this standard. However, private broadcasters (RTL, Pro Sieben, etc) have shown no interest in either this standard or in the 16:9 format. Pay-per-view channels such as those on Sky often broadcast in 16:9, but use a different standard that requires another kind of decoder.

Netherlands

In the Netherlands the public broadcasters used PALplus until 2005 but have stopped using it because they preferred digital television (anamorphic widescreen) over PALplus. The public broadcasters and all the major commercial stations have a policy of broadcasting their own and new shows in widescreen, this isn't converted to PALplus on the analogue signal of the cable operators. As cable is the most widespread form of receiving television in the Netherlands the system isn't used anymore. Terrestrial analogue signals stopped in November 2006 in this country.

Portugal

In Portugal, the private broadcaster TVI began broadcasting movies in PALplus in 1994, but some years after it left the standard behind.

The public broadcaster RTP started using the format in December 5, 1997.[4] The system was used to broadcast selected programs (about five programs each day) and some widescreen movies on analog terrestrial broadcasts. Cable distributors occasionally strip the signal of the WSS bits, rendering the system inoperative. Also, when Digital Terrestrial Television broadcasts started, there was no dedicated anamorphic simulcast for the digital channels. Therefore, PALPlus over terrestrial analog PAL broadcasts remained the only source of 576 lines widescreen TV in Portugal for many years.

Since the middle of 2010 PALPlus was dropped in favor of regular 16:9 letterbox, because the system caused considerable image degradation (with an effective horizontal resolution of only about ~400px compared to 720px of a digital SDTV image) when used on digital transmissions. After that, with the end of analog broadcasts by 2012, the system became officially obsolete.

Finland

In Finland, the commercial broadcaster MTV3 started broadcasting the youth music program Jyrki in PALplus format on 1997-08-18, but the experiment ended when the program ended some four years later. Now both MTV and the public broadcaster YLE have switched to digital TV technology.

Greece

In Greece, there used to be sporadic PALplus broadcasts, on the national television (E.R.T. - Hellenic Radio Television). Through the '90s there were few attempts from commercial broadcasters to adopt the system, but they all failed to gain popularity.

Because of the nature of ERT's broadcasting equipment, events and documentaries shot by ERT in PALPlus used to be broadcast as such, as they left control room to be distributed. However, PALplus reaching audiences is a different story. PALplus is not preserved when content is distributed via NOVA, due to heavy MPEG encoding since WSS signaling and additional information embedded in PALplus are seriously degraded to the extent that renders them no longer decodable. As some of the repeaters of ERT's channels are fed via OTE (Greek public telecom provider) in uncompressed form over terrestrial links, and others are fed via NOVA (Greece's only satellite platform) it depends on each repeater's feed source whether the content terrestrially broadcast (VHF - UHF) is PALplus or not.

Spain

In Spain, the Catalan public television, TV3, trialed the PALplus format in the late 1990s, with a weekly broadcast of a film in this format. Other public regional stations (like Galicia's TVG) tested the format too, but after these trials the technology was dropped and 16:9 digital broadcasts were not introduced until 2007.

United Kingdom

In the United Kingdom, Channel 4 broadcast selected films as PALplus during the late 1990s. Some programmes, including Fifteen to One and the omnibus edition of Brookside were also broadcast this way. All of the six main broadcasters, BBC, ITV, Channel 4, Five, Sky and Virgin Media, now all broadcast in anamorphic widescreen on digital.

See also

References

  1. 1 2 3 PALplus
  2. ↑ EUR-Lex - 31993D0424 - EN
  3. 1 2 http://assets.fluke.com/appnotes/it_products/B0291A-16U9509_NL_EN.pdf
  4. ↑ Porquê 16:9?

External links

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