The High definition television reference article from the English Wikipedia on 24-Apr-2004
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High definition television

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High Definition Television (HDTV) means broadcast of television signals with a higher resolution than traditional formats (NTSC, SECAM, PAL) allow. Its introduction coincides with that of digital television (DTV).

Table of contents
1 Technical Details
2 History outside the US
3 Adoption
4 Recording and Prerecorded Media
5 References
6 External links

Technical Details

The HDTV screen uses a 16:9 aspect ratio. The high resolution images (1920 pixels × 1080 lines or 1280 pixels × 720 lines) allow much more detail to be shown. MPEG-2 is used as the compression codec. The images are expected to be at least 6 times as sharp as standard definition television or analog television. Like NTSC and PAL, most 1920 × 1080 broadcasts use interlacing to reduce bandwidth demands. Alternating scan lines are broadcast 60 times a second, similar to NTSC's 60 Hz interlacing. This format is entitled 1080i, or 1080i60. In areas traditionally using PAL 50 Hz (1080i50) is also used. A progressive scan format is available, but usually with reduced number of frames per second of 24 (1080p24 for movies) or 30 (1080p30), although 25, 50 and 60 was also possible. The 1280 × 720 format in practice is always progressive scan (with the entire frame refreshed each time) and is thus termed 720p.

The US digital television system also allows lower, non HD resolutions to be encoded, such as Enhanced Digital Television (EDTV), which is a standard size of 720 × 480 (PAL: 720 × 576) TV picture, only in progressive format, allowing 60 (PAL: 50) full frames per second. Also included is a system for broadcasting Standard Definition Television (SDTV) with the interlacing.

Dolby Digital AC-3 is used as the audio codec, allowing the transport of up to 5 channels of sound with a 6th channel for low frequency effects (the so-called "5.1" configuration). Japanese HDTV broadcasts use MPEG's Advanced Audio Coding (AAC) as the audio codec, which also allows 5.1 audio output. DVB allows both.

Digital HDTV transmission is designed to occupy the same 6 MHz terrestrial band now used in the US for analog NTSC broadcasts. A single NTSC 6 MHz channel can carry 19.2 Mbit/s of information using ATSC's standard 8-VSB (8-level Vestigial Side Band) modulation method. This is sufficient to carry up to 6 standard definition TV channels, or a single HDTV channel. As a side note, the standard for HD signal transmission over digital cable television systems in the US is now fixed as QAM 256 (Quadrature Amplitude Modulation), which is technically part of the DVB standard (but not ATSC) and is a de facto cable industry standard. This method has higher bandwidth than 8-VSB, allowing two 19.2 Mbit/s channels in a 6 MHz bandwidth, due to its lower tolerance for errors which are generally less of a concern in a wired environment. The ATSC standards included a provision for 16-VSB transmission over cable at 38.4 Mbit/s, but the encoding never gained wide acceptance.

Due to technical reasons having to do with the video equipment, recording technologies, and the 19.2 Mbit/s-limited ATSC channel, some HDTV signals will not reach their nominal resolution. Most notably, 1080i60 is impossible to broadcast without artifacts at this bandwidth using ATSC. Most 1080i broadcast signals actually are filtered to 1440 horizontal samples to allow adequate compression, and most current consumer HDTVs based on CRTs cannot resolve even 1440 horizontal samples (most rear-projection CRTs will resolve 1200-1300 at best, unless based on 9" guns). Despite this, HDTV viewed even on existing sets is still far superior to PAL or NTSC in resolution, and future sets are likely to offer superior resolution at the same or lower prices.

History outside the US

It has been technically possible to create higher-resolution televisions for many years—for instance, computer monitors have been able to display high-resolution images with superior color and refresh rates since the 1980s. Theoretically, one need only spend the money to scale up the relatively feeble light output of computer monitors to that of a consumer TV and one has the physical basis for an HDTV.

Japan

Japan had the earliest working HDTV system, with design efforts going back to 1979. Japan began broadcasting analog HDTV signals in the early 1990s using an interlaced resolution of 1035 lines (1035i). The Japanese MUSE system employed filtering tricks to reduce the original source signal to decrease bandwidth utilization. For example, three successive picture elements on a line were actually derived from three separate scans. Whole camera pans would result in a loss of 50% of horizontal resolution.

Europe, HD-MAC, DVB

The EEC (later, the EU) established a European standard for HDTV in a 1986 directive (MAC). The standard didn't prove to be popular along broadcasters. It was required that all high powered satellite broadcasters used MAC from that year. However, the advance of technology and the launch of middle powered satellite provider Astra allowed broadcaster to avoid using MAC at all. It was used in transcontinental satellite transmissions, though.

Another reason for HD-MAC's failure was that it was not realistic to use 36àMHz for a high definiton signal in terrestrial broadcasting (SDTV uses 6, 7 (VHF) or 8àMHz (UHF) ). That way, HD-MAC could only be used by cable and satellite providers, were there was a wider bandwidth. Thus, HDTV could not replace conventional analog television (terrestrial) PAL/SECAM , making HD-MAC sets unnatractive to potential consumers.

The HD-MAC standard was abandoned in 1993, and since then all EU and EBU efforts have focused on the DVB system (Digital Video Broadcasting), which allows both SDTV and HDTV.

One must notice that although HDTV is still possible with DVB-T, most EU countries are taking the "more channels on a single multiplex" aproach than the "one single channel in HDTV" followed in the USA, Canada, Japan and Australia. Some European goverments aim to switch to digital in order free the VHF spectrum for other uses. HDTV is thus left to satellite (DVB-S) and cable (DVB-C) distribution for the moment.

A single HDTV channel would take up to four SDTV channels from any of the 3 to 8 multiplexes, so HDTV doesn't seem suitable for terrestrial broadcasting in Europe. Also, many broadcasters and producers assume that the average European consumer does not demand HDTV at the moment, nor will he benefit from HDTV with current TV sets.

Adoption

United States

One of the current reasons for the US government's push for digital transmission is the desire to auction off part of the UHF spectrum, channels #52 through #69, for other two way and one way fixed and mobile services. This could include digital mobile TV broadcasting. However, this is not the only reason historically. HDTV had been in development for some years in the US. In the 1980's there was a fear among many in the US that Japanese advances in HDTV would contribute to the further erosion of US leadership in electronics and other high-tech industries, not to mention the defense industry implications of having a high resolution television system. (Japan has since all but abandoned its old MUSE system and has introduced a digital system.) The Federal Communications Commission (FCC) began soliciting proposals for a new television standard for the US in the late 1980s and later decided to pick a digital standard in 1993. HDTV sets became available in the US in 1998 and broadcasts began around November 1998.

Because HDTV requires more broadcast spectrum for the transition period, it has been the topic of great political controversy in the United States. Stations currently receive a free channel, generally in the UHF range, over which they are to broadcast their digital signal, while still providing analog service. According to FCC rules, all television broadcasting in the United States by current full power broadcasters on channels 2-51 will by the beginning of 2007 be digital, with an escape clause that 85% of the serviced area must be "capable" of receiving digital signals. At the time of analog shutoff, one channel would then be returned to the government for transfer to the new private owner, while the other would have only the digital signal. Current analog TV sets would still work with cable or satellite service or with a converter box that would convert digital OTA signals to analog. Current (Jan. 2004) indications from industry and FCC officials including its chairman are that the cutoff date for digital-only broadcasts will not meet the intended 2007 and the actual timeline for analog shutoff in the US will realistically be in the 2010-2015 timeframe.

Of importance is that the FCC has not mandated HDTV signals; it has only mandated that digital TV signals be broadcast. The prevailing expectation, however, is that HDTV during primetime will be the rule. It is not clear whether broadcasting HDTV or multiple standard definition channels during non primetime hours will become common.

At this time (early 2004), most HDTV sets in the US have the capability to display HDTV signals but not to decode the broadcast. Generally only the more expensive TVs will have an 8-VSB (and often QAM) tuner built-in. Because a large percentage of people in the US receive their television through cable or satellite (particularly those who have the money to spend on an HDTV), and because different cable and satellite systems use different encoding standards, most HDTVs only include standard-definition tuners. This allows the user to purchase or rent a separate tuner to receive HDTV signals. An ATSC receiver can currently be purchased for around $350 in the US, although this is expected to drop sharply as demand increases. Alternately, in the US one can purchase a satellite tuner to receive satellite HD signals, or rent a cable HD tuner to receive cable signals. The situation is similar to UHF tuners, which initially were an aftermarket accessory in the early days when NTSC was initially broadcast only in the VHF range.

To expedite the availability of HD reception, the FCC has ruled that 50% of TV sets with screens of at least 36 inches must have 8-VSB tuners by July 2004, with complete tuner coverage in that size class by July 2005, while the requirement for smaller sets and digital VCRs would be phased in from 2005 to 2007. It is anticipated that the price of tuner hardware will fall as the market enlarges. It should be noted that the FCC also mandated the inclusion of UHF tuners in all NTSC TVs which eventually lead to their being integrated at no marginal cost.

The transition to HDTV in the US has not yet reached critical mass but there is increasing availability of premium as well as freely available terrestrial broadcast HD content. As equipment for HDTV production becomes cheaper and more widespread, this will only accelerate. For example, the US President's State-of-the-Union speech in January 2004 was broadcast using a mixture of HD and a few SD camera signals, which was the first major US news event to see any significant use of HD. On the equipment side, TVs capable of displaying HDTV signals are available as of January 2004 for under $1000 USD in the direct view CRT market. Standard resolution CRT TV sets are completely extinct in the larger rear-projection CRT units.

Satellite television companies in the USA, such as Dish Network, started to carry HD programming in 2002. Some cable television companies, such as Comcast, started to do the same in 2003. As of July 2003, HD programming is carried by all major television networks (except Fox which plans to go HD in mid 2004) including ABC, CBS, NBC, PBS and The WB as well as other cable/satellite channels including Discovery HD Theater, HBO, HDNet, Showtime HDTV and INHD. Cable and satellite providers typically also offer HDTV pay-per-view movies. The production of HDTV programming is very time consuming. According to PBS, it took 1000 hours to produce a three hour program. PBS only produces about 10 hours of HD programming per month (as of July 2003). As of July 2003, ABC provides the most hours of HD programming per day among other non-cable networks.

Canada

In Canada, on November 22 2003, CBC had their first broadcast in HD. Bell ExpressVu, a Canadian satellite company has TSN HD and Discovery HD (Canadian Edition). The Canadian Discovery HD Channel has commercials and is sponsored By Franklin Templeton Investments. Other networks are continuing to announce availability of HD signals.

Elsewhere

Many countries show limited interest in HDTV. Most of Europe has instead gone to widescreen EDTV using the DVB standard for now, though satellite delivery of HD started in Europe January 1st 2004.

Australia seems to be the only true believer in HDTV. It is the only country that has mandated HD and the amount of content that broadcasters are obligated to broadcast.

Recording and Prerecorded Media

HDTV can be recorded to D-VHS (Digital-VHS) or to an HDTV capable Digital Video Recorder.

D-VHS recording is done in the US utilizing a digital transport such as Firewire (IEEE 1394) to carry the MPEG-2 Transport Stream from the tuning device to the recorder. Analog tape recorders with bandwidth capable of recording HD signals such as W-VHS recorders are no longer produced for the consumer market and are neither widely available nor inexpensive.

The only widely available prerecorded HD media, aside from scarce Japanese analog MUSE-encoded laserdiscs, is D-Theater, a format available on D-VHS. D-Theater is an encrypted format and only D-Theater capable D-VHS players can play back these tapes. D-Theater utilizes a 28 Mbit/s MPEG2 stream at 720p or 1080i. This format is superior to broadcast HDTV due to its higher bandwidth and, of course, the ability to do non-realtime optimization of the encoding which is not possible with broadcast HDTV. This format is currently a niche market even in the HDTV US consumer market and its overall future is not certain.

It is possible to record HD media to optical disc using a Sony Blu-ray DVD player, currently available only in Japan with a Japanese satellite tuner. This uses a blue-laser optical disc system with MPEG2 as the codec.

In an attempt to provide a bitrate-compatible high-definition format for high-definition video on standard DVDs, Microsoft introduced into their Windows Media 9 Series codec the ability to compress a high-definition bitstream into the same space as a conventional NTSC bitstream (approximately 5 to 9 megabits per second). It remains to be seen if the codec will be adopted for widespread use, if only as a Wi-Fi industry standard. As of November, 2003, this format required a significant amount of processing power to encode and decode and the only commercially available movie that used the codec was the : Extreme Edition DVD. Since then, more titles have become available in this format. 1

Other similar codecs are in contention such as AVC and VP6 from ON2. VP6 has been chosen by China for both digital TV and DVD production. This is as a result of China's desire to avoid royalties on WM9 or AVC. As an advantage, VP6 requires only a per-device royalty of $2 and no royalties on recorded media. As China starts to dominate manufacturing of TV and DVD units, the country's choice of standards becomes more central for everyone. VP6 is considered to be a superior codec by many people. It is likely this codec will appear quickly in low-end US players, given their dependence on low-cost Asian chipsets. However, given the general contempt of the Asian markets for intellectual property rights, no major US studio will commit to this format. It is unlikely one will do so, once the codec becomes available in the US without additional provisions for copy-protection.

Recently, the DVD-Forum and the Blu-ray group failed to agree on standards for high definition 12 cm discs. A format war is now very likely between between Sony's HD-DVD (formerly Advanced Optical Disc) standard and the Blu-ray disc standard. To complicate things further, Sony also makes movies via its Columbia-Tristar subsidiary. As a result, this will likely lead to certain films becoming available only on one format. Both sides of the HD disc camp are likely to leverage studio partners against each other through exclusive arrangements. A possible outcome of a messy format war could be the emergence of combo players, as the physical disc sizes are identical.

There are now some DVD players that will output enhanced or high-definition signals from standard-definition DVDs. These players, however, are not considered to be true HD-DVD players since they only include an integrated scaler to upconvert the standard-definition DVD video to high-definition video. This upconversion process generally can improve the percieved picture quality of standard-definition video.

References

External links