High-definition video
From Wikipedia, the free encyclopedia
High-definition (HD) video generally refers to any video system of higher resolution than standard-definition (SD), i.e. NTSC, PAL and SECAM. This article discusses the general concepts of high-definition video, as opposed to its specific applications in television broadcast (HDTV), professional acquisition (HDCAM, HDCAM-SR, DVCPRO-HD & D5-HD), consumer acquisition (HDV) and optical disc systems (Blu-ray and HD DVD).
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[edit] 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 25 fps and went on the air in 1964. SECAM (SÉquentiel Couleur Á Mémoire, French for "sequential colour with memory") was developed by France as the first European color television standard independent to the American NTSC standard, and soon competed by the West German PAL, also using 625 lines and 25 fps. SECAM was adopted during the Cold War by France and its colonial territories, as well as the Belgian colonies, and later adopted by countries rejecting the American standard, namely 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 30 fps, 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.
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, or so goes the most optimistic point-of-view. It remains to be seen if and when this can be achieved, due to the vast amounts of analog video equipment (TV stations and home TVs) which are currently installed. Upgrading to HDTV would require a great deal of financial capital, especially among large lower-income populations such as in China and India, where other financial priorities may take precedence.
[edit] 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 (sometimes traditionally quoted at 2.35:1). 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.
[edit] Close-up view
 HDTV at four times the resolution of SDTV. |
 SDTV resolution. |
[edit] 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 fields 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. (See also: Telecine) (Note: This is slightly more complicated because film is photographed at exactly 24.00 frames per second while NTSC digital video at 24p is recorded at 23.976 frames per second since color NTSC video is actually recorded at 59.97 fields per second (not 60.00) which is a difference of 1000/1001 from black and white NTSC video. Therefore, telecine from film to NTSC video also requires a slow down of the projection rate for both the picture and the audio by 0.1%.)
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.
[edit] HD in Filmmaking
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. Directors who have used HD to a large degree thus far are: George Lucas, Michael Mann, Robert Rodriguez, and independent producer/director Brian J. Terwilliger.
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:
- One Six Right: The Romance of Flying
- The Quiet
- Apocalypto
- Star Wars Episode II: Attack of the Clones
- Star Wars Episode III: Revenge of the Sith
- Spy Kids 2: The Island of Lost Dreams
- Spy Kids 3-D: Game Over
- Once Upon a Time in Mexico
- Sin City
- Sky Captain and the World of Tomorrow
- Russian Ark
- Scary Movie 4
- Collateral
- Miami Vice
- Superman Returns
- Voyeur Beach
- Find Me Guilty
- Wolf Creek
- Silent Hill (Darkness scenes)
- Dogville
- Flyboys
- Rocky Balboa (Boxing match scenes)
- My Name is Bruce
- My Scary Girl
[edit] Film to High Definition Transfer
Most movies are shot in 35 mm wide negative film. Film negative is a very high resolving medium. Resolution in film is measured in cycles/mm. One cycle is also called one line pair which consists of one black line and one white line. To make it simple one cycle is equivalent to 2 pixels, a black and a white. Film by itself can commonly resolve from 50 c/mm to 400 c/mm (100 pixels/mm to 800 pixels/mm) depending on emulsion stock. But since the image on film is formed by exposing it through a lens and this lens also has its own resolution limits, the final resolution on the photographed negative is always less than each component's resolution.
Depending on the year and format a movie was made in, the image can vary on 35 mm shot film from as big as 24 mm × 36 mm for VistaVision/Technirama 8 perforation cameras (same as 35 mm still photo film) going down through 18 mm × 24 mm for Silent Films or Full Frame 4 perforations cameras to as small as 9 mm × 21 mm in Academy Sound Aperture cameras modified for the Techniscope 2 perforation format. There are also a few films made with bigger than 35 mm cameras, like 70 mm films (22 mm × 48 mm) or the rarely used 55 mm and CINERAMA.
So far the four major formats dimensions that have been used in 35 mm by the pixels per millimeter gives approx: (mm dimensions have been rounded)
- Academy Sound (Sound movies before 1955): 15 mm × 21 mm (1.375) = 2160 × 2970
- Academy camera US Widescreen: 11 mm × 21 mm (1.85) = 1605 × 2970
- Current Anamorphic Panavision ('Scope"): 17.5 mm × 21 mm (2.39) = 2485 × 2970
- Super-35 for Anamorphic prints: 10 mm × 24 mm (2.39) = 1420 × 3390
In the process of making prints for exhibition this negative is copied onto other film (negative → interpositive → internegative → print) so the resolution gets decimated with each emulsion copying step and when the image passes through a lens (for example, on a projector) it's reduced once more. Sometimes the resolution is reduced down to 1/6th of the original negative's resolution, and that's with doing things correctly.
For 70 mm cameras the resolution can even go to further higher side.
Typical High Definition Home Video consists of following resolutions.
- 1280 × 720
- 1920 × 1080
Usually when studios master movies for home video release they use assets in high resolution as above and then master them to 1920 × 1080 and 1280 × 720. For standard definition applications(DVD, SDTV, etc.), they are also anamorphically compressed and mastered to 720 × 576(PAL) and 720 × 480(NTSC).
An Example of this is the work done by Digital Leisure in the high definition film transfer of dragon's lair to an hd format.
[edit] References
- 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
- Digital Terrestrial HDTV Broadcasting in Europe , technical report from the EBU
- TV Azteca Plans HDTV Mexican Rollout
[edit] See also
- Advanced Television Systems Committee (ATSC)
- ATSC tuner
- Integrated Services Digital Broadcasting
- DVB (Digital Video Broadcasting)
- Digital television
- HDTV input and colorspace (YPbPr/YCbCr).
- HD ready
- mariposaHD
- Ultra High Definition Video
[edit] External links
- ATSC
- CDTV Canadian Digital Television official website
- Home Theater Network What to look for in HDTVs.
- mariposaHD The world's first original HDTV show made for the Internet. Free 1080i and 720p videos, in WMV HD format, distributed with BitTorrent.
| Designation | Usage examples | Definition (lines) | Rate (Hz) | |
|---|---|---|---|---|
| Interlaced (fields) | Progressive (frames) | |||
| Low; MP@LL | LDTV, VCD | 240; 288 (SIF) | 24, 30; 25 | |
| Standard; MP@ML | SDTV, SVCD, DVD, DV | 480 (NTSC, PAL-M) | 60 | 24, 30 |
| 576 (PAL, SECAM) | 50 | 25 | ||
| Enhanced | EDTV | 480; 576 | 60; 50 | |
| High; MP@HL | HDTV, HD DVD, Blu-ray Disc, HDV | 720 | 24, 30, 60; 25, 50 | |
| 1080 | 50, 60 | 24, 30; 25 | ||
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| This table illustrates total horizontal and vertical pixel resolution via box size. It does not accurately reflect the screen shape (aspect ratio) of these formats, which is either 4:3 or 16:9. | ||||
