High-definition television
In practice, the best possible HD quality is not usually achieved. The main problem is that many operators do not follow HDTV specifications fully. They may use slower bitrates or lower resolution to pack more channels within the limited bandwidth, reducing video quality.[12] The operators may use a format that is different from the original programming, introducing generation loss artifacts in the process of re-encoding.[13] 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, which may be difficult because of customer confusion regarding connections.
Appropriate cabling must be used. In most cases, HDMI component cables are required. These are often more expensive. For instance, if composite or S-Video cables are used for connections from a cable box or satellite dish then only an SDTV quality picture will be seen. HDMI cables provide the best picture and sound but are also generally more expensive than component cables.
As high-definition video broadcasts are digital, the disadvantages of digital video broadcasting also apply. For example, digital video responds differently to analogue video when subject to interference. Unlike in analogue television broadcasting, in which interference causes only gradual image and sound degradation, interference in a digital television broadcast will freeze, skip, or display "garbage" information. This problem is particularly pronounced in the 8VSB modulation standard used for over-the-air transmission in the United States, which is highly sensitive to dynamic multipath interference that may be introduced by moving objects between the transmitting and receiving antennas. For instance, it is impossible to receive a 8VSB-modulated HDTV signal in a moving vehicle, and it may be difficult to maintain reception during high winds in locations where large trees are situated in the line between broadcasting antenna and receiver.
In order to view HDTV broadcasts, viewers may have to upgrade their TVs at some expense. Adding a new aspect ratio makes for consumer confusion if a display is capable of one or more ratios but must be switched to the correct one by the user. Traditional standard definition programs and feature films (mostly movies from before 1953) originally filmed in the standard 4:3 ratio, when displayed correctly on a 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 the appearance of being too wide or not tall enough. Alternatively, viewers may choose to zoom the image which removes content that was on the top and bottom of the original TV show.[14]
Broadcasters may demand, or cable-television operators may elect, to place HD signals in a premium band that requires higher cable fees. Some satellite companies may offer local HD channels as a service at additional cost (transmission comes from satellite). This leads some broadcasters to offer on-air broadcasts of local HD signals as 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 have to install an antenna to receive the digital broadcasts. Such issues entail economic and legal disputes more than technology.
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 for a period of time created confusion for consumers. This particular format war was recently "settled" with Blu-ray emerging as the victorious standard.
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Contemporary systems
1. HDTV Monitor
2. HD satellite receiver
3. Standard satellite dish
4. HDMI cable, DVI-D and audio cables, or audio and component video cables
Besides a HD-ready television set, other equipment is needed to view HD television. Cable-ready TV sets can display HD content without using an external box. They have a QAM tuner built-in and/or a card slot for inserting a CableCARD.[15].
High-definition image sources include terrestrial broadcast, direct broadcast satellite, digital cable, the high definition disc BD, internet downloads, and the PlayStation 3 and Xbox 360 game consoles.
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Recording and compression
HDTV can be recorded to D-VHS (Digital-VHS or 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, Dish Network's VIP 622 or VIP 722 high-definition Digital video recorder receivers, or TiVo's Series 3 or HD recorders), or a 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 who 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 TV companies have. As of July 2004, boxes are not included in the FCC mandate. This content is protected by encryption known as 5C.[16] This encryption can prevent duplication of content or simply limit the number of copies permitted, thus effectively denying most if not all fair use of the content.
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Table of terrestrial HDTV transmission systems
| Systems | ATSC | DVB-T | ISDB-T |
|---|---|---|---|
| Source coding | |||
| Video | Main Profile syntax of ISO/IEC 13818-2 (MPEG-2 – Video) | ||
| Audio | ATSC Standard A/52 (Dolby AC-3) | As defined in ETSI DVB TS 101 154 - as H.264 AVC and/or ISO/IEC 13818-2 (MPEG-2 – Layer II Audio) and/or Dolby AC-3 | ISO/IEC 13818-7 (MPEG-2 – AAC Audio) |
| Transmission system | |||
| Channel coding | |||
| Outer coding | R-S (207, 187, t = 10) | 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 code | Punctured convolution code(PCC): rate 1/2, 2/3, 3/4, 5/6, 7/8; constraint length = 7, Polynomials (octal) = 171, 133 | |
| Inner interleaver | 12 to 1 Trellis code | bit-wise, frequency, selectable time | |
| Data randomization | 16-bit PRBS | ||
| Modulation | 8VSB (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) |
COFDM QPSK, 16QAM and 64QAM 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 FFT |
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 |
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TV resolution
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See also
- 480p, 576p, 720p, 1080i, 1080p
- Advanced Television Systems Committee (ATSC)
- ATSC tuner
- Integrated Services Digital Broadcasting
- Digital Video Broadcasting
- Digital television
- HDTV input and colorspace (YPbPr/YCbCr).
- HD ready
- HDTV quality DVD Player
- SDTV (Standard Definition Television)
- Ultra-High Definition Video (UHDV)
- High-definition television in the United Kingdom
- Freesat
- High-definition television in the United States
- HDTV Blur
- Reed–Solomon error correction
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References
Cited references
- ^ HDTV in the Russian Federation: problems and prospects of implementation (in Russian).
- ^ Researchers Craft HDTV's Successor.
- ^ Digital TV Tech Notes, Issue #2.
- ^ Digital TV Tech Notes, Issue #41.
- ^ The Grand Alliance includes AT&T, General Instrument, MIT, Philips, Sarnoff, Thomson, and Zenith)
- ^ Carlo Basile et al. (1995). "The U.S. HDTV standard: the Grand Alliance". IEEE Spectrum (4): 36–45.
- ^ Digital TV Tech Notes, Issue #1.
- ^ Howstuffworks "How Digital Television Works"
- ^ Howstuffworks "How HD-DVD Works"
- ^ The HDTV Progressive Frame Rate Clarification Initiative.
- ^ 1366x768 resolution problems on HDTV, HD-Ready, and High Definition TV.
- ^ DirecTV HD Image Quality.
- ^ DirecTV's HD future is MPEG-4.
- ^ HDTV display modes: Information and Much More from Answers.com
- ^ HDTV information.
- ^ 5C Digital Transmission Content Protection White Paper (pdf) (1998-07-14).
General references
- Technology, Television, and Competition (New York: Cambridge University Press, 2004)
- Brazil begins HDTV transmissions with Japanese standard, from The Inquirer
- United States Federal Standard 1037C
- DTV channel protection ratios
- DVB HDTV standard
- Images formats for HDTV, article from the EBU Technical Review .
- High Definition for Europe - a progressive approach, article from the EBU Technical Review .
- High Definition (HD) Image Formats for Television Production, technical report from the EBU
- TV Azteca Plans HDTV Mexican Rollout_tcm
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External links
- US Government HDTV and DTV official site
- Advanced Television Systems Committee (ATSC)
- Canadian Radio-television and Telecommunications Commission
- http://whereishd.com
- http://www.dtv2009.gov/ US DoC Consumer DTV Converter Box Coupon Program
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