1080i
Encyclopedia
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High-definition television
High-definition television is video that has resolution substantially higher than that of traditional television systems . HDTV has one or two million pixels per frame, roughly five times that of SD...
(high-definition video
High-definition video
High-definition video or HD video refers to any video system of higher resolution than standard-definition video, and most commonly involves display resolutions of 1,280×720 pixels or 1,920×1,080 pixels...
) mode. The i means interlaced video; 1080i differs from 1080p
1080p
1080p is the shorthand identification for a set of HDTV high-definition video modes that are characterized by 1080 horizontal lines of resolution and progressive scan, meaning the image is not interlaced as is the case with the 1080i display standard....
, in which the p stands for progressive scan
Progressive scan
Progressive scanning is a way of displaying, storing, or transmitting moving images in which all the lines of each frame are drawn in sequence...
. The term 1080i assumes a widescreen
Widescreen
Widescreen images are a variety of aspect ratios used in film, television and computer screens. In film, a widescreen film is any film image with a width-to-height aspect ratio greater than the standard 1.37:1 Academy aspect ratio provided by 35mm film....
aspect ratio
Aspect ratio (image)
The aspect ratio of an image is the ratio of the width of the image to its height, expressed as two numbers separated by a colon. That is, for an x:y aspect ratio, no matter how big or small the image is, if the width is divided into x units of equal length and the height is measured using this...
of 16:9, implying a frame size of 1920×1080 pixel
Pixel
In digital imaging, a pixel, or pel, is a single point in a raster image, or the smallest addressable screen element in a display device; it is the smallest unit of picture that can be represented or controlled....
s. Each frame of 1080i video consists of two fields of 1920×540 pixel
Pixel
In digital imaging, a pixel, or pel, is a single point in a raster image, or the smallest addressable screen element in a display device; it is the smallest unit of picture that can be represented or controlled....
s each.
The field rate
Field rate
The field rate of an interlaced video image is twice the effective frame rate, since interlacing draws only half of the image at a time. For example, a field rate of 60 Hertz will correspond to a 30 frames-per-second moving picture...
of 1080i is typically 60 Hz
Hertz
The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....
for countries that use or used System M
System M
System M, sometimes called 525 line, is the analog broadcast television system used in the United States since July 1, 1941, and also in most of the Americas and Caribbean, South Korea, and Taiwan. In addition, Japan uses System J, which is nearly identical to System M. The systems were given...
as analog broadcast television system
Broadcast television system
Broadcast television systems are encoding or formatting standards for the transmission and reception of terrestrial television signals. There are three main analog television systems in current use around the world: NTSC, PAL, and SECAM...
(such as United States, Canada, Japan, and Brazil) or 50 Hz for regions that traditionally used television systems with 25 frames/s rate (such as in Europe, Australia, much of Asia, and Africa). Both variants can be carried by both major digital television
Digital television
Digital television is the transmission of audio and video by digital signals, in contrast to the analog signals used by analog TV...
transmission formats: ATSC and DVB.
The frame rate can be implied by the context, while the field rate is generally specified after the letter i, such as "1080i60". In this case 1080i60 refers to 60 fields per second or 30 frames per second. The European Broadcasting Union
European Broadcasting Union
The European Broadcasting Union is a confederation of 74 broadcasting organisations from 56 countries, and 49 associate broadcasters from a further 25...
(EBU) prefers to use the resolution and frame rate (not field rate) separated by a slash
Slash (punctuation)
The slash is a sign used as a punctuation mark and for various other purposes. It is now often called a forward slash , and many other alternative names.-History:...
, as in 1080i/30 and 1080i/25, likewise 480i/30 and 576i/25. Resolutions of 1080i60 or 1080i50 often refers to 1080i/30 or 1080i/25 in EBU notation.
1080i is directly compatible with some CRT
Cathode ray tube
The cathode ray tube is a vacuum tube containing an electron gun and a fluorescent screen used to view images. It has a means to accelerate and deflect the electron beam onto the fluorescent screen to create the images. The image may represent electrical waveforms , pictures , radar targets and...
-based HDTV television set
Television set
A television set is a device that combines a tuner, display, and speakers for the purpose of viewing television. Television sets became a popular consumer product after the Second World War, using vacuum tubes and cathode ray tube displays...
s on which it can be displayed natively in interlaced form, but for display on modern progressive-scan
Progressive scan
Progressive scanning is a way of displaying, storing, or transmitting moving images in which all the lines of each frame are drawn in sequence...
LCD and plasma TV sets it must be deinterlaced and often scaled. Depending on the television's video processing capabilities, the resulting video quality may vary, but may not necessarily suffer. For example, film material at 25fps may be deinterlaced from 1080i50 to restore a full 1080p resolution at the original frame rate without any loss.
Most UK
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
HD channels on satellite, cable, and terrestrial platforms including BBC One HD and ITV1 HD broadcast in this format, while BBC HD
BBC HD
BBC HD is a high-definition television network provided by the BBC. The service was initially run as a trial from 15 May 2006 until becoming a full service on 1 December 2007...
broadcasts mostly in 1080p. In the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, 1080i is the preferred format for CBS
CBS
CBS Broadcasting Inc. is a major US commercial broadcasting television network, which started as a radio network. The name is derived from the initials of the network's former name, Columbia Broadcasting System. The network is sometimes referred to as the "Eye Network" in reference to the shape of...
, NBC
NBC
The National Broadcasting Company is an American commercial broadcasting television network and former radio network headquartered in the GE Building in New York City's Rockefeller Center with additional major offices near Los Angeles and in Chicago...
, and The CW, though some affiliates (especially those that broadcast two digital subchannel
Digital subchannel
In broadcasting, digital subchannels are a means to transmit more than one independent program at the same time from the same digital radio or digital television station on the same radio frequency channel. This is done by using data compression techniques to reduce the size of each individual...
s in HD) do broadcast in 720p
720p
720p is the shorthand name for 1280x720, a category of High-definition television video modes having a resolution of 1080 or 720p and a progressive scan...
. Fox
Fox Broadcasting Company
Fox Broadcasting Company, commonly referred to as Fox Network or simply Fox , is an American commercial broadcasting television network owned by Fox Entertainment Group, part of Rupert Murdoch's News Corporation. Launched on October 9, 1986, Fox was the highest-rated broadcast network in the...
and ABC
American Broadcasting Company
The American Broadcasting Company is an American commercial broadcasting television network. Created in 1943 from the former NBC Blue radio network, ABC is owned by The Walt Disney Company and is part of Disney-ABC Television Group. Its first broadcast on television was in 1948...
/ESPN
ESPN
Entertainment and Sports Programming Network, commonly known as ESPN, is an American global cable television network focusing on sports-related programming including live and pre-taped event telecasts, sports talk shows, and other original programming....
broadcast in 720p; many ABC affiliates owned by Hearst Television and Belo Corporation air their signals in 1080i and upscale ABC programming for master control and transmission purposes, as most syndicated programming is produced in 1080i and must be additionally downscaled to 720p.
Some cameras and broadcast systems that use 1080 vertical lines per frame do not actually use the full 1920 width of a nominal 1080i picture for image capture and encoding. Common subsampling ratios include 3/4 (resulting in 1440×1080i frame resolution) and 1/2 (resulting in 960×1080i frame resolution). Using half horizontal resolution and only one field of each frame (possibly with added anti-alias filtering or progressive capture) results in the format known as 540p, which has frame resolution 960×540 and 30 or 25 frames per second.
External links
- High Definition (HD) Image Formats for Television Production (EBUEuropean Broadcasting UnionThe European Broadcasting Union is a confederation of 74 broadcasting organisations from 56 countries, and 49 associate broadcasters from a further 25...
technical publication) - 720p vs. 1080p HDTV: The final word - CNET Review - December 5, 2007