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High-definition video

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This article is about high-definition video technology. For television systems, see HDTV, for the tape format HDV and High-definition pre-recorded media and compression for compression and prerecorded media


High Definition Video generally refers to any video system of higher resolution than standard-definition (SD), i.e. NTSC, PAL and SECAM. It is important to note the difference between general purpose high-definition video as discussed in this article, and its specific applications in television (HDTV), professional acquisition(HDCAM, HDCAM-SR, DVCPRO-HD & D5-HD), consumer acquisition(HDV) and optical disc systems (HDDVD and Blu-ray).

History

Original HD specifications date back to the early 1980s, when Japan developed an 1125-line TV standard operating at 30 frames per second (fps). Japan presented their standard at an international meeting of television engineers in Algiers in 1981 and Japan's NHK presented its analog HDTV system at Swiss conference in 1983. The NHK system was standardized in the United States as SMPTE (Society of Motion Picture and Television Engineers) standard #240M in the early 1990s.

Historically, the term high-definition television was used to refer to television standards developed in the late 1930s to replace the early experimental mechanically-scanned systems that ranged from 15 lines to about 220 lines of resolution. John Logie Baird of the UK was a major proponent of these early mechanically scanned systems, but they were quickly replaced by all-electronic systems developed by engineers such as Philo T. Farnsworth, Vladimir Zworykin and the EMI team including Alan Blumlein under Isaac Shoenberg.

The United Kingdom was the first to start regular broadcast television - the BBC Television Service - in 1936 from Alexandra Palace, initially with a 240-line, 25 frames-per-second (fps) mechanically-scanned system by Baird Television Limited alternating with a 405-line Marconi-EMI interlaced system at 50 fields per second (each frame consisting of two fields). The Baird system was dropped after the end of 1936. This was referred to as the world's first scheduled 'high definition' television service, and thus the term must be regarded as originally identifying systems offering 240-line resolution or better. The Marconi-EMI specification went on to be adopted across Europe as CCIR System A.

In the United States, the National Television System Committee (for which the NTSC standard is named) standardized on 525 lines at 30 fps in 1940, with regular broadcasts starting on July 1, 1941. The NTSC standard was updated to include first a non-compatible 441-line color standard in 1950, which was then replaced by a compatible 525-line, 29.97fps color standard approved in 1953 and used to this day. PAL (Phase Alternating Line) was developed in the late 1950s with 625 lines at 25fps and went on the air in 1964. SECAM (SEquential Colour Avec Memoir) was developed by the French as a competitor to PAL, also using 625 lines and 25fps. SECAM was adopted by France and its colonial territories, as well as the Soviet Union, the Peoples' Republic of China, and their satellite communist governments.

The current high definition video standards were developed during the course of the advanced television process initiated by the Federal Communications Commission in 1987 at the request of American broadcasters. The FCC process, led by the Advanced Television Systems Committee (ATSC) adopted a range of standards from interlaced 1080 line video (a technical descendant of the original analog NHK 1125/30fps system) with a maximum frame rate of 30fps, and 720 line video, progressively scanned, with a maximum frame rate of 60 fps. The FCC officially adopted the ATSC transmission standard (which included both HD and SD video standards) in 1996, with the first broadcasts on October 28, 1998.

Details

High-definition signals require a high-definition television or computer monitor in order to be viewed. High-definition video has an aspect ratio of 16:9 (1.78:1). The aspect ratio of regular widescreen film shot today is typically 1.85:1 or 2.40:1. Standard-definition television (SDTV) has a 4:3 (1.33:1) aspect ratio.

High-definition television (HDTV) resolution is 1080 or 720 lines. In contrast, regular digital television (DTV) is 486 lines (upon which NTSC is based) or 576 lines (upon which PAL/SECAM are based). However, since HD is broadcast digitally, its introduction sometimes coincides with the introduction of DTV. Additionally, current DVD quality is not high-definition, although the high-definition disc systems HD-DVD and Blu-ray are.

The world has transmitted analog PAL, NTSC, SECAM for over 60 years. However, with the advent of digital broadcasting including HD formats, analog transmissions will cease in the coming years and NTSC, PAL and SECAM will pass into history.

Close-up view

  • HDTV at four times the resolution of SDTV.
    HDTV at four times the resolution of SDTV.
  • SDTV resolution.
    SDTV resolution.

Format considerations

The optimum format 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 may require more bandwidth than is available. The lossy compression that is used in all digital HDTV systems will then cause the picture to be distorted.

Photographic film destined for the theater typically has a high resolution and is photographed at 24 frame/s. 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%. In countries using the NTSC standard, (60 fps) 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. (See also: Telecine)

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. (See also: Deinterlacing)

Non-cinematic HDTV video recordings are recorded in either 720p or 1080i format. The format 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 fields, 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 sub-optimal job of de-interlacing video in real time. 720p Video also has lower storage and decoding requirements than 1080i or 1080p, and few people possess displays capable of displaying the 1920x1080 resolution without scaling. 720p appears at full resolution on a common 1280x1024 LCD, which can be found for under $250. An LCD capable of native 1080i resolution still costs over a thousand US dollars.

In North America, Fox, ABC, and ESPN (ABC and ESPN are both owned by Disney) currently broadcast 720p content. PBS, NBC, Universal-HD (both owned by General Electric), CBS, UPN, Showtime, INHD, HDNet and Time-Warner-owned HBO-HD, the WB and TNT currently broadcast 1080i content.

Movies that have been shot in HD

Film as a medium has inherent limitations, such as difficulty of viewing footage whilst recording, and suffers other problems, caused by poor film development/processing, or poor monitoring systems. Given that there is increasing use of computer-generated or computer-altered imagery in movies, and that editing picture sequences is often done digitally, some directors have shot their movies using the HD format via high-end digital video cameras. Whilst the quality of HD video is very high compared to SD video, and offers improved signal/noise ratios against comparable sensitivity film, film remains able to resolve more image detail than current HD video formats. In addition some film has a wider dynamic range (ability to resolve extremes of dark and light areas in a scene) than even the best HD cameras. Thus the most persuasive arguments for the use of HD are currently cost savings on film stock and the ease of transfer to editing systems for special effects. Two directors who have used HD are George Lucas and Robert Rodriguez.

Many television shows with science fiction themes and special effects — such as Star Trek: Enterprise and Stargate — have also begun to use digital cameras.

Movies that have been shot on HD digital video include:

References

See also

Wikiquote has quotations related to High-definition video.
Look up HDTV in Wiktionary, the free dictionary.
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