High Definition Television

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celebrated having 100 HD channels on its Direct broadcast satellite service with a party in Hollywood; "HD" was spelled out by a large TV array.High-definition television (HDTV) is a digital television broadcasting system with a significantly higher Image resolution than traditional formats (NTSC, SECAM, PAL). While some early Analog high-definition television systems formats were broadcast in Europe and Japan, HDTV is usually broadcast digitally, because digital television (DTV) broadcasting requires much less bandwidth if it uses enough video compression. HDTV technology was first introduced in the US during the 1990s by a group of electronics companies called the Grand Alliance (HDTV).the Grand Alliance includes AT&T (1885-2005), General Instrument, MIT, Philips, David Sarnoff Research Center, Thomson SA, and Zenith Electronics)

History The first television system capable of 1125 lines was created in Soviet Union in 1958. The system was dubbed "Трансформатор" (in Russian) meaning "Transformer". The original purpose of the system was teleconferencing between high-ranked military command offices. This system was not intended for commercial use and was not implemented at the large scale.

Commercial High-Definition television was first developed by Nippon Hōsō Kyōkai, and was unveiled in 1969. However, the system did not become mainstream until the late 1990s.

In the early 2000s, a number of high-definition television standards were competing for the still-developing niche markets.

Three HDTV standards are currently defined by the International Telecommunication Union (ITU-R BT.709). They include 1080i (1,080 actively interlaced lines), 1080p (1,080 Progressive scan lines), and 720p (720 progressively scanned lines). All standards use a 16:9 aspect ratio (image), leading many consumers to the incorrect conclusion of equating widescreen television with HDTV. All current HDTV broadcasting standards are encompassed within the ATSC and DVB specifications. in a home theater, displaying a high-definition television image.HDTV is also capable of "movie theater-quality" audio because it uses the Dolby Digital (AC-3) format to support "5.1" surround sound. It should be noted that while HDTV is more like a theater in quality than conventional television, 35 mm and 70 mm film projectors used in theaters still have the highest resolution and best viewing quality on very large screens. Many HDTV programs are produced from movies on film as well as content shot in HD video.

The term "high-definition" can refer to the resolution specifications themselves, or more loosely to media capable of similar sharpness, such as photographic film and digital video. As of July 2007, HDTV saturation in the US has reached 30 percent – in other words, three out of every ten American households own at least one HDTV. However, only 44 percent of those that do own an HDTV are actually receiving HDTV programming, as many consumers are not aware that they must obtain special receivers to receive HDTV from cable or satellite, or use ATSC tuners to receive over-the-air broadcasts; others may not even know what HDTV is.

HDTV sources The rise in popularity of large screens and projectors has made the limitations of conventional Standard Definition TV (SDTV) increasingly evident. An HDTV compatible television set will not improve the quality of SDTV channels. To get a better picture HDTV televisions require a High Definition (HD) signal. Typical sources of HD signals are as follows:

Over the air with an antenna. Most cities in the US with major network affiliates broadcast over the air in HD. To receive this signal an HD tuner is required. Most newer HDTV televisions have an HD tuner built in. For HDTV televisions without a built in HD tuner, a separate set-top HD tuner box can be rented from a cable or satellite company or purchased.
Cable television companies often offer HDTV broadcasts as part of their digital broadcast service. This is usually done with a set-top box or CableCARD issued by the cable company. Alternatively one can usually get the network HDTV channels for free with basic cable by using a QAM tuner built into their HDTV or set-top box. Some cable carriers also offer HDTV Video on demand playback of movies and commonly viewed shows.
Satellite-based TV companies, such as Optimum, DirecTV, Sky Digital (UK & Ireland) (in the UK and Ireland), Bell ExpressVu and Dish Network, offer HDTV to customers as an upgrade. New satellite receiver boxes and a new satellite dish are often required to receive HD content.
Video game systems, such as the Xbox (NTSC only), Xbox 360, and Playstation 3, can output an HD signal. The Xbox Live Marketplace service offers HD movies, TV shows, movie trailers, and clips for download to Xbox 360 consoles.
Two optical disc standards, Blu-ray and HD DVD, can provide enough digital storage to store hours of HD video content.

Notation In the context of HDTV, the formats of the broadcasts are referred to using a notation describing:

The number of lines in the vertical display resolution.
Whether progressive scan (p) or interlace (i) are used. Progressive scan redraws all the lines (a frame) of a picture in each refresh. Interlaced scan redraws every second line (a field) in one refresh and the remaining lines in a second refresh. Interlaced scan increases picture resolution while saving bandwidth but at the expense of some flicker or other artifacts.
The number of frames or fields per second.

The format 720p60 is 1280 × 720 pixels, progressive encoding with 60 frames per second (60 hertz). The format 1080i50 is 1920 × 1080 pixels, interlaced encoding with 50 fields (25 frames) per second. Often the frame or field rate is left out, indicating only the resolution and type of the frames or fields, and leading to confusion. Sometimes the rate is to be inferred from the context, in which case it can usually be assumed to be either 50 or 60, except for 1080p which is often used to denote either 1080p24, 1080p25 or 1080p30 at present but will also denote 1080p50 and 1080p60 in the future.

A Frame rate or field rate can also be specified without a resolution. For example 24p means 24 progressive scan frames per second and 50i means 25 interlaced frames per second, consisting of 50 interlaced fields per second. Most HDTV systems support some standard resolutions and frame or field rates. The most common are noted below.

Changes in notation The terminology described above was invented for digital systems in the 1990s. A digital signal encodes the color of each pixel, or dot on the screen as a series of numbers. Before that, analog TV signals encoded values for one monochrome, or three-color signals as they scanned a screen continuously from line to line. By comparison, radio encodes an analog signal of the sound to be sent to an amplified speaker, typically up to 20 kHz, but video signals are in the MHz range, which is why they are much higher in the broadcast spectrum than audio radio. Analog video signals have no true "pixels" to measure horizontal resolution. The vertical scan-line count included off-screen scan lines with no picture information while the CRT beam returned to the top of the screen to begin another field. Thus NTSC was considered to have "525 lines" even though only 486 of them had a picture (625/576 for PAL). Similarly the Japanese Multiple sub-nyquist sampling Encoding system was called "1125 line", but is only 1035i by today's measuring standards. This change was made because digital systems have no need of blank retrace lines unless the signal was converted to analog to drive a CRT.

Standard resolutions

When resolution is considered, both the resolution of the transmitted signal and the (native) display resolution resolution of a TV set are taken into account. Digital NTSC- and PAL/SECAM-like signals (480i60 and 576i50 respectively) are transmitted at a horizontal resolution of 720 or 704 "pixels". However these transmitted DTV "pixels" are not square, and have to be stretched for correct viewing. PAL TV sets with an aspect ratio of 4:3 use a fixed pixel grid of 768 × 576 or 720 × 540; with an aspect ratio of 16:9 they use 1440 x 768, 1024 × 576 or PAL optimal; NTSC ones use VGA and WVGA or, seldom, 720 × 540.High Definition usually refers to one million pixels or more.

In Australia, the 576p50 format is also considered a HDTV format, as it has doubled temporal resolution though the use of progressive scanning. Thus, a number of Australian networks broadcast a 576p signal as their High-definition DVB-T signal, while others use the more conventional 720p and 1080i formats. Technically, however, the 576p format is defined as Enhanced-definition television.

Standard frame or field rates

23.977p (allow easy conversion to NTSC)
24p (cinematic film)
25p (PAL, SECAM DTV progressive material)
30p (NTSC DTV progressive material)
50p (PAL, SECAM DTV progressive material)
60p (NTSC DTV progressive material)
50i (PAL & SECAM)
60i (NTSC, PAL-M)

Comparison with SDTV {|class="wikitable" align="right"! colspan=2 | Close-up view|- align="center"| width=128 | | width=128 | |- valign="top"| HDTV resolution| SDTV resolution|}HDTV has at least twice the linear resolution of standard-definition television (SDTV), thus allowing much more detail to be shown compared with analog television or regular DVD. In addition, the technical standards for broadcasting HDTV are also able to handle 16:9 aspect ratio (image) pictures without using letterboxing or anamorphic stretching, thus further increasing the effective resolution for such content.

Format considerations The optimum formats for a broadcast depends on the type of media used for the recording and the characteristics of the content. The field and frame rate should match the source, as should the resolution. On the other hand, a very high resolution source may require more bandwidth than is available in order to be transmitted without loss of fidelity. The lossy compression that is used in all digital HDTV storage/transmission systems will then cause the received picture to appear distorted when compared to the uncompressed source.

Photographic film destined for the theater typically has a high resolution and is photographed at 24 frames per second. Depending on the available bandwidth and the amount of detail and movement in the picture, the optimum format for video transfer is thus either 720p24 or 1080p24. When shown on television in countries using PAL, film must be converted to 25 frames per second by speeding it up by 4.1 percent. In countries using the NTSC standard, 30 frames per second, a technique called 3:2 pulldown is used. One film frame is held for three video fields, (1/20 of a second) and then the next is held for two video fields (1/30 of a second) and then the process repeats, thus achieving the correct film rate with two film frames shown in 1/12 of a second.

Older (pre-HDTV) recordings on video tape such as Betacam SP are often either in the form 480i60 or 576i50. These may be upconverted to a higher resolution format (720i), but removing the interlace to match the common 720p format may distort the picture or require filtering which actually reduces the resolution of the final output.

Non-cinematic HDTV video recordings are recorded in either 720p or 1080i format. The format used depends on the broadcast company (if destined for television broadcast); however, in other scenarios the format choice will vary depending on a variety of factors. In general, 720p is more appropriate for fast action as it uses progressive scan frames, as opposed to 1080i which uses interlaced fields and thus can have a degradation of image quality with fast motion.

In addition, 720p is used more often with Internet distribution of HD video, as all computer monitors are progressive, and most graphics cards do a poor job of de-interlacing video in real time. 720p video also has lower storage and decoding requirements than 1080i or 1080p.

In North America, Fox Broadcasting Company, My Network TV (also owned by Fox Broadcasting Company), American Broadcasting Company, and ESPN (ABC and ESPN are both owned by The Walt Disney Company) currently broadcast 720p content. NBC, Universal HD (both owned by General Electric), CBS, PBS, The CW, HBO, Showtime, Starz!, MOJO HD, HDNet ,Turner Network Television, and Discovery HD Theater currently broadcast 1080i content.

In the United Kingdom on Sky Digital (UK & Ireland), there are BBC HD, Sky One HD, Sky Arts HD, Sky Movies HD1 & 2, Sky Sports HD1,2 & X, Discovery HD, National Geographic Channel HD, The History Channel HD & Sky Box Office HD1 & 2. With MTV HD, FX HD, Living (channel) HD Rush HD, Ultra HD & Eurosport HD to come in the near future. BBC HD is also available on Virgin Media. The BBC Trust has given provisional approval for a BBC HD channel, which would be broadcast satellite, cable and DTT.

Public consultation on the Trust's provisional conclusions on the proposed BBC HD service is open until 23 October 2007.

Technical details tuner cards.MPEG-2 is most commonly used as the compression codec for digital HDTV broadcasts. Although MPEG-2 supports up to 4:2:2 YCbCr chroma subsampling and 10-bit quantization, HD broadcasts use 4:2:0 and 8-bit quantization to save bandwidth. Some broadcasters also plan to use H.264/MPEG-4 AVC, such as the BBC which is trialing such a system via satellite broadcast, which will save considerable bandwidth compared to MPEG-2 systems. Some German broadcasters already use MPEG-4 AVC together with DVB-S2 (Pro 7, Sat.1 and Premiere (pay television network)). Although MPEG-2 is more widely used at present, it seems likely that in the future all European HDTV may be MPEG-4 AVC, and Ireland and Norway, which have not yet begun any digital television broadcasts, are considering MPEG-4 AVC for SD Digital as well as HDTV on terrestrial broadcasts.

HDTV is capable of "movie theater-quality" audio because it uses the Dolby Digital (AC-3) format to support "5.1" surround sound. The pixel aspect ratio of native HD signals is a "square" 1.0, in which each pixel's height equals its width. New HD compression and recording formats such as HDV use rectangular pixels to save bandwidth and to open HDTV acquisition for the consumer market. For more technical details see the articles on HDV, ATSC Standards, DVB, and ISDB.

Television studios as well as production and distribution facilities, use HD-SDI SMPTE 292M interconnect standard (a nominally 1.485 Gbit/s, 75-ohm Serial communications digital interface) to route uncompressed HDTV signals. The native bitrate of HDTV formats cannot be supported by 6-8 MHz standard-definition television channels for over-the-air broadcast and consumer distribution media, hence the widespread use of compression in consumer applications. SMPTE 292M interconnects are generally unavailable in consumer equipment, partially due to the expense involved in supporting this format, and partially because consumer electronics manufacturers are required (typically by licensing agreements) to provide encrypted digital outputs on consumer video equipment, for fear that this would aggravate the issue of copyright infringement.

Newer dual-link HD-SDI signals are needed for the latest 4:4:4 camera systems (Sony HDC-F950 & Thomson Viper), where one link/coax cable contains the 4:2:2 YCbCr info and the other link/coax cable contains the additional 0:2:2 CbCr information.

Advantages of HDTV expressed in non-engineering terms High-definition television (HDTV) potentially offers a much better picture quality than standard television. HD's greater clarity means the picture on screen can be less blurred and less fuzzy. HD also brings other benefits such as smoother motion, richer and more natural colors, and the ability to allow a variety of input devices to work together.

Almost all commercially available HD is digital, so the system cannot produce a snowy or washed out image from a weak signal, effects from signal interference, such as Bond (masonry)#Herringbone bond patterns, or vertical rolling.

With HDTV the lack of imperfections in the television screen often seen on traditional television is another reason why many prefer high definition to analog. As mentioned, problems such as snow caused from a weak signal, double images from ghosting (television) or multi-path and picture sparkles from electromagnetic interference do not occur with HDTV digital broadcasts.

The colors will generally look more realistic, due to greater bandwidth. The visual information is about 2-5 times more detailed overall. The gaps between scanning lines are smaller or invisible. Legacy TV content that was shot and preserved on 35 mm film can now be viewed at nearly the same resolution at which it was originally photographed. A good analogy for television quality is looking through a window. HDTV offers a degree of clarity that is much closer to this.

The "i" in these numbers stands for "interlaced" while the "p" stands for "progressive". With interlaced scan, the 1,080 lines are split into two, the first 540 being painted on a frame, followed by the second 540 painted on another frame. This method reduces the bandwidth and raises the frame rate to 50-60 frames per second. A progressive scan displays all 1,080 lines at the same time at 60 frames per second, using more bandwidth. (See: An explanation of HDTV numbersand laymen's glossary)

Dolby Digital 5.1 surround sound is broadcast along with standard HDTV video signals, allowing full surround sound capabilities. (Standard broadcast television signals usually only include monophonic or stereophonic audio. Stereo broadcasts can be encoded with Dolby Surround, an early home video surround format.) Both designs make more efficient use of electricity than SDTV designs of equivalent size, which can mean lower operating costs. LCD is a leader in energy conservation.

Disadvantages of HDTV expressed in non-engineering terms However, there are a variety of reasons why the best HD quality is not usually achieved. The main problem is a lack of HD input. Many cable and satellite channels and even some "high definition" channels are not broadcast in true HD. Also, image quality may be lost if the television is not properly connected to the input device or not properly configured for the input's optimal performance.HD digital signals will either deliver an excellent picture, a picture with noticeable pixelation, a series of still pictures, or no picture at all. Any interference will render the signal unwatchable. As opposed to a lower-quality signal one gets from interference in an analogue television broadcast, interference in a digital television broadcast will freeze, skip, or display "garbage" information.

HDTV is the answer to a question few consumers were asking.http://spamontoast.blogspot.com/2007_04_01_archive.html Viewers will have to upgrade their TVs in order to see HDTV broadcasts, incurring household expense in the process. Adding a new Aspect_ratio_%28image%29#Criticism makes for consumer confusion if their display is capable of one or more ratios but must be switched to the correct one by the user. Traditional Standard-definition television TV shows and feature films (mostly movies from before 1953) originally filmed in the standard 4:3 ratio, when displayed correctly on an HDTV monitor, will have empty display areas to the left and right of the image. Many consumers aren't satisfied with this unused display area and choose instead to distort their standard definition shows by stretching them horizontally to fill the screen, giving everything a too-wide or not-tall-enough appearance. Alternately, they'll choose to zoom the image which removes content that was on the top and bottom of the original TV show.http://www.answers.com/topic/hdtv-display-modes?cat=technology

As of 2007, broadcasters may demand, or cable-television operators may elect, to place HD signals in a premium band that requires higher cable fees. That some satellite companies offer the local HD channels as a service at additional cost (transmission comes from satellite) suggests to some broadcasters that on-air broadcasts of local HD signals must be a premium service to subscribers. Viewers may be denied some television channels that they expected, be allowed only access to the non-digital, and obviously sub-standard non-digital signal, or to install an antenna to receive the digital broadcasts. Such issues more entail economic and legal disputes than they entail technology.

Some viewers of HDTV will notice a type of distortion during faster scene movement or total scene change. This "pixelation" or "blockiness" distortion is caused by aggressive video compression in the source material. Technically this is not a fault of HDTV, which is generally just displaying what is provided by the tuner or source (like a cable tv or satellite tv decoder box). The higher the compression used on the video, the more pronounced the pixelation. Since each content provider can choose bitrate (hence, the amount of bandwidth) used for the video, providers who devote more bandwidth will have higher video quality HDTV content and less distortion. This type of pixelation did not occur using traditional, broadcast, analog TV.

Another disadvantage of HDTV compared to traditional television has been consumer confusion stemming from the different standards and resolutions, such as 1080i, 1080p, and 720p. Complicating the matter have been the changes in television connections from component video, to DVI, then to HDMI. Finally, the HD-DVD vs. Blu-ray Disc high definition storage format war engenders even more animosity for consumers. The confusion has led to slower uptake of the technology as many people wait to see what becomes the "ultimate" de-facto standard.

Early systems The term "high definition" was used to describe the electronic television systems of the late 1930s and 1940s beginning with the former British 405-line black-and-white system, introduced in 1936; however, this and the subsequent 525-line U.S. NTSC system, established in 1941, were high definition only in comparison with previous mechanical and electronic television systems, and NTSC, along with the later European 625-line PAL and SECAMs, is described as SDTV today.

On the other hand, the 819-line French black-and-white television system introduced after World War II arguably was high definition in the modern sense, as it had a line count and theoretical maximum resolution considerably higher than those of the 625-line systems introduced across most of postwar Europe. However, it required far more bandwidth than other systems, and was switched off in 1986, a year after the final British 405-line broadcasts.

Japan was the only country where commercial analog HDTV was launched and had some success. In other places, such as Europe, analog (HD-MAC) HDTV failed. Finally, although the United States experimented with analog HDTV (there were about 10 proposed formats), it soon moved towards a digital approach.

Contemporary systems In addition to an HD Ready television, other equipment is often needed for the home user to view High Definition Television. Cable Ready TV sets can display HD content without the use of an external box. They provide a card slot that accepts a CableCARD. There are several sources of high definition content and the equipment used to control each of these must be HD compatible.

High Definition picture sources include terrestrial broadcast, direct broadcast satellite, digital cable, high definition discs (Blu-ray Disc and HD DVD), internet downloads and the latest generation of games consoles. The availability of television pictures broadcast in the HD format varies by region and country.

Recording and compression HDTV can be recorded to D-VHS (Data-VHS), W-VHS (analog only), to a HDTV-capable digital video recorder (for example DirecTV's high-definition Digital video recorder, Sky HD's set-top box, or TiVo's Series 3 or HD recorders), or an HDTV-ready HTPC. Some cable boxes are capable of receiving or recording two broadcasts at a time in HDTV format, and HDTV programming, some free, some for a fee, can be played back with the cable company's on-demand feature. The massive amount of data storage required to archive uncompressed streams make it unlikely that an uncompressed storage option will appear in the consumer market soon. Realtime MPEG-2 compression of an uncompressed digital HDTV signal is also prohibitively expensive for the consumer market at this time, but should become inexpensive within several years (although this is more relevant for consumer HD camcorders than recording HDTV). Analog tape recorders with bandwidth capable of recording analog HD signals such as W-VHS recorders are no longer produced for the consumer market and are both expensive and scarce in the secondary market.

In the United States, as part of the FCC's "plug and play" agreement, cable companies are required to provide customers that rent HD set-top boxes with a set-top box with "functional" Firewire (IEEE 1394) upon request. None of the direct broadcast satellite providers have offered this feature on any of their supported boxes, but some cable television companies have. As of 2004, boxes are not included in the FCC mandate. This content is protected by encryption known as 5C. This encryption can prevent duplication of content or simply limit the number of copies permitted, thus effectively denying most if not any fair use of the content.

Table of terrestrial HDTV transmission systems {| class="wikitable"|+ Main characteristics of three DTTV systems! Systems! ATSC Standards !! DVB-T !! ISDB-T – Video)|-! Audio| ATSC Standard A/52 ([Dolby AC-3) ]) and Dolby AC-3 || ISO/IEC 13818-7 (MPEG-2 – Advanced Audio Coding Audio)|-!colspan="4" align="left"| Transmission system|-! Channel coding|colspan="3"||-! Outer coding| R-S (207, 187, t = 10) ||colspan="2"| R-S (204, 188, t = 8)|-! Outer interleaver| 52 R-S block ||convolutional (I=12, M=17, J=1) ||12 R-S block|-! Inner coding| rate 2/3 Trellis modulation code ||colspan="2"| Punctured convolution code: rate 1/2, 2/3, 3/4, 5/6, 7/8; constraint length = 7, Polynomials (octal) = 171, 133|-! Inner interleaver| 12 to 1 Trellis modulation code ||colspan="2"| bit-wise, frequency, selectable time|-! Data randomization|colspan="3"| 16-bit PRBS (Only used for over the air transmission)
[16VSB (Designed for cable, but rejected by the cable industry, cable TV uses 64QAM or 256QAM modulation as a de facto standard)]
QPSK, Quadrature amplitude modulation and Quadrature amplitude modulation
Hierarchical modulation: multi-resolution constellation (16QAM and 64QAM)
Guard interval: 1/32, 1/16, 1/8 & 1/4 of OFDM symbol
Two modes: 2k and 8k Fast Fourier Transform| BST-COFDM with 13 frequency segments
DQPSK, QPSK, 16QAM and 64QAM
Hierarchical modulation: choice of three different modulations on each segment
Guard interval: 1/32, 1/16, 1/8 & 1/4 of OFDM symbol
Three modes: 2k, 4k and 8k FFT|}

TV resolution References Cited referencesGeneral references

Federal Standard 1037C
DTV channel protection ratios
DVB HDTV standard
Images formats for HDTV, article from the European Broadcasting Union Technical Review .
High Definition for Europe - a progressive approach, article from the European Broadcasting Union Technical Review .
High Definition (HD) Image Formats for Television Production, technical report from the European Broadcasting Union
TV Azteca Plans HDTV Mexican Rollout_tcm