Standard-definition television

Last updated

SDTV resolution by nation; due to historical reasons, different countries use either 480i or 576i as the standard-definition picture format. TV-line-count-world.svg
SDTV resolution by nation; due to historical reasons, different countries use either 480i or 576i as the standard-definition picture format.

Standard-definition television (SDTV, SD, often shortened to standard definition) is a television system that uses a resolution that is not considered to be either high or enhanced definition. [1] Standard refers to offering a similar resolution to the analog broadcast systems used when it was introduced. [1] [2]

Contents

The two SDTV signal types are 576i (with 576 interlaced lines of resolution, [3] derived from the European-developed PAL and SECAM systems), and 480i (with 480 interlaced lines of resolution, [4] based on the American NTSC system). SDTV refresh rates are 25, 29.97 and 30 frames per second, again based on the analog systems mentioned.

SDTV originated from the need for a standard to digitize analog TV (defined in BT.601) and is now used for digital TV broadcasts and home appliances such as game consoles and DVD disc players. [4] [5]

Standards that support digital SDTV broadcast include DVB, ATSC, and ISDB. [6] The last two were originally developed for HDTV, but are also used for their ability to deliver multiple SD video and audio streams via multiplexing.

Digital SDTV broadcast eliminates the ghosting and noisy images associated with analog systems. However, if the reception has interference or is poor, where the error correction cannot compensate one will encounter various other artifacts such as image freezing, stuttering, or dropouts from missing intra-frames or blockiness from missing macroblocks. [lower-alpha 1]

In North America, digital SDTV is broadcast in the same 4:3 aspect ratio as NTSC signals, with widescreen content often being center cut. [6]

In other parts of the world that used the PAL or SECAM color systems, digital standard-definition television is now usually shown with a 16:9 aspect ratio, with the transition occurring between the mid-1990s and late-2000s depending on the region. Older programs with a 4:3 aspect ratio are broadcast with a flag that switches the display to 4:3. [lower-alpha 2]

Pixel aspect ratio

The table below summarizes pixel aspect ratios for the scaling of various kinds of SDTV video lines.

Video formatDisplay aspect ratio (DAR)ResolutionPixel aspect ratio (PAR)After horizontal scaling
480i 4:3704 × 480 (horizontal blanking cropped)10:11640 × 480
720 × 480 (full frame)655 × 480
480i 16:9704 × 480 (horizontal blanking cropped)40:33854 × 480
720 × 480 (full frame)873 × 480
576i 4:3704 × 576 (horizontal blanking cropped)12:11768 × 576
720 × 576 (full frame)788 × 576
576i 16:9704 × 576 (horizontal blanking cropped)16:111024 × 576
720 × 576 (full frame)1050 × 576

The pixel aspect ratio is the same for 720- and 704-pixel resolutions because the visible image (be it 4:3 or 16:9) is contained in the center 704 horizontal pixels of the digital frame. In the case of a digital video line having 720 horizontal pixels (including horizontal blanking), only the center 704 pixels contain the actual 4:3 or 16:9 image, and the 8-pixel-wide stripes on either side are called nominal analog blanking or horizontal blanking and should be discarded when displaying the image. Nominal analog blanking should not be confused with overscan, as overscan areas are part of the actual 4:3 or 16:9 image.

For SMPTE 259M-C compliance, an SDTV broadcast image is scaled to 720 pixels wide [lower-alpha 3] for every 480 NTSC (or 576 PAL) lines of the image with the amount of non-proportional line scaling dependent on either the display or pixel aspect ratio. The display ratio for broadcast widescreen is commonly 16:9, [lower-alpha 4] the display ratio for a traditional or letterboxed broadcast is 4:3. [lower-alpha 5]

An SDTV image outside the constraints of the SMPTE standards requires no non-proportional scaling with 640 pixels [lower-alpha 6] for every line of the image. The display and pixel aspect ratio is generally not required with the line height defining the aspect. For widescreen 16:9, 360 lines define a widescreen image and for traditional 4:3, 480 lines define an image.

See also

Notes

  1. The audio encoding is the last to suffer a loss due to the lower bandwidth requirements.
  2. Some broadcasters prefer to reduce the horizontal resolution by anamorphically scaling the video into a pillarbox.
  3. Only 704 center pixels contain the actual image and 16 pixels are reserved for horizontal blanking though a number of broadcasters fill the whole 720 frames.
  4. Pixel aspect ratio of 40:33 for anamorphic
  5. Pixel aspect ratio of 10:11
  6. Defined by the adopted IBM VGA standard

Related Research Articles

<span class="mw-page-title-main">Video</span> Electronic moving image

Video is an electronic medium for the recording, copying, playback, broadcasting, and display of moving visual media. Video was first developed for mechanical television systems, which were quickly replaced by cathode-ray tube (CRT) systems, which, in turn, were replaced by flat-panel displays of several types.

<span class="mw-page-title-main">ATSC standards</span> Standards for digital television in the US

Advanced Television Systems Committee (ATSC) standards are an American set of standards for digital television transmission over terrestrial, cable and satellite networks. It is largely a replacement for the analog NTSC standard and, like that standard, is used mostly in the United States, Mexico, Canada, South Korea and Trinidad & Tobago. Several former NTSC users, such as Japan, have not used ATSC during their digital television transition, because they adopted other systems such as ISDB developed by Japan, and DVB developed in Europe, for example.

Enhanced-definition television, or extended-definition television (EDTV) is a Consumer Electronics Association (CEA) marketing shorthand term for certain digital television (DTV) formats and devices. Specifically, this term defines an extension of the standard-definition television (SDTV) format that enables a clearer picture during high-motion scenes compared to previous iterations of SDTV, but not producing images as detailed as high-definition television (HDTV).

Anamorphic widescreen is a process by which a comparatively wide widescreen image is horizontally compressed to fit into a storage medium with a narrower aspect ratio, reducing the horizontal resolution of the image while keeping its full original vertical resolution. Compatible play-back equipment can then expand the horizontal dimension to show the original widescreen image. This is typically used to allow one to store widescreen images on a medium that was originally intended for a narrower ratio, while using as much of the frame – and therefore recording as much detail – as possible.

<span class="mw-page-title-main">Display resolution</span> Number of distinct pixels in each dimension that can be displayed

The display resolution or display modes of a digital television, computer monitor or display device is the number of distinct pixels in each dimension that can be displayed. It can be an ambiguous term especially as the displayed resolution is controlled by different factors in cathode ray tube (CRT) displays, flat-panel displays and projection displays using fixed picture-element (pixel) arrays.

480p is the shorthand name for a family of video display resolutions. The p stands for progressive scan, i.e. non-interlaced. The 480 denotes a vertical resolution of 480 pixels, usually with a horizontal resolution of 640 pixels and 4:3 aspect ratio or a horizontal resolution of 854 pixels for an approximate 16:9 aspect ratio. Since a pixel count must be a whole number, in Wide VGA displays it is generally rounded up to 854 to ensure inclusion of the entire image. The frames are displayed progressively as opposed to interlaced. 480p was used for many early plasma televisions. Standard definition has always been a 4:3 aspect ratio with a pixel resolution of 720 × 480 at 60 Hz for NTSC regions, and 720 or 768 × 576 for PAL regions. However, standard definition defines a 15.7k Hz horizontal scanrate, which means that interlacing has to be used for those resolution modes. The lowercase letter "p" in 480p stands for progressive, so the two must not be confused.

<span class="mw-page-title-main">720p</span> Video resolution

720p is a progressive HD signal format with 720 horizontal lines/1280 columns and an aspect ratio (AR) of 16:9, normally known as widescreen HD (1.78:1). All major HD broadcasting standards include a 720p format, which has a resolution of 1280×720p.

1080i is a combination of frame resolution and scan type. 1080i is used in high-definition television (HDTV) and high-definition video. The number "1080" refers to the number of horizontal lines on the screen. The "i" is an abbreviation for "interlaced"; this indicates that only the even lines of each frame, then only the odd lines, are drawn alternately, so that only half the number of lines are ever updated at once. A related display resolution is 1080p, which also has 1080 lines of resolution; the "p" refers to progressive scan, which indicates that each full frame appears on the screen in sequence.

<span class="mw-page-title-main">480i</span> Standard-definition video mode

480i is the video mode used for standard-definition digital video in the Caribbean, Japan, South Korea, Taiwan, Philippines, Myanmar, Western Sahara, and most of the Americas. The other common standard definition digital standard, used in the rest of the world, is 576i.

<span class="mw-page-title-main">576i</span> Standard-definition video mode

576i is a standard-definition digital video mode, originally used for digitizing analogue television in most countries of the world where the utility frequency for electric power distribution is 50 Hz. Because of its close association with the legacy colour encoding systems, it is often referred to as PAL, PAL/SECAM or SECAM when compared to its 60 Hz NTSC-colour-encoded counterpart, 480i.

576p is the shorthand name for a video display resolution. The p stands for progressive scan, i.e. non-interlaced, the 576 for a vertical resolution of 576 pixels. Usually it corresponds to a digital video mode with a 4:3 anamorphic resolution of 720x576 and a frame rate of 25 frames per second (576p25), and thus using the same bandwidth and carrying the same amount of pixel data as 576i, but other resolutions and frame rates are possible.

Overscan is a behaviour in certain television sets, in which part of the input picture is cut off by the visible bounds of the screen. It exists because cathode-ray tube (CRT) television sets from the 1930s to the early 2000s were highly variable in how the video image was positioned within the borders of the screen. It then became common practice to have video signals with black edges around the picture, which the television was meant to discard in this way.

<span class="mw-page-title-main">Pillarbox</span> Black bars on the sides of an image

The pillarbox effect occurs in widescreen video displays when black bars are placed on the sides of the image. It becomes necessary when film or video that was not originally designed for widescreen is shown on a widescreen display, or a narrower widescreen image is displayed within a wider aspect ratio, such as a 16:9 image in a 2.39:1 frame. The original material is shrunk and placed in the middle of the widescreen frame.

Nominal analogue blanking is the outermost part of the overscan of a standard definition digital television image. It consists of a gap of black pixels at the left and right sides, which correspond to the end and start of the horizontal blanking interval: the front porch at the right side, and the back porch at the left side. Digital television ordinarily contains 720 pixels per line, but only 702 (PAL) to 704 (NTSC) of them contain picture content. The location is variable, since analogue equipment may shift the picture sideways in an unexpected amount or direction.

<span class="mw-page-title-main">Pixel aspect ratio</span> Proportion between the width and the height of a pixel

A Pixel aspect ratio is a mathematical ratio that describes how the width of a pixel in a digital image compared to the height of that pixel.

<span class="mw-page-title-main">Technology of television</span> Telecommunications, sound and video

The technology of television has evolved since its early days using a mechanical system invented by Paul Gottlieb Nipkow in 1884. Every television system works on the scanning principle first implemented in the rotating disk scanner of Nipkow. This turns a two-dimensional image into a time series of signals that represent the brightness and color of each resolvable element of the picture. By repeating a two-dimensional image quickly enough, the impression of motion can be transmitted as well. For the receiving apparatus to reconstruct the image, synchronization information is included in the signal to allow proper placement of each line within the image and to identify when a complete image has been transmitted and a new image is to follow.

High-definition television (HDTV) describes a television or video system which provides a substantially higher image resolution than the previous generation of technologies. The term has been used since at least 1933; in more recent times, it refers to the generation following standard-definition television (SDTV). It is the current de facto standard video format used in most broadcasts: terrestrial broadcast television, cable television, satellite television.

The aspect ratio of an image is the ratio of its width to its height, and is expressed with two numbers separated by a colon, such as 16:9, sixteen-to-nine. For the x:y aspect ratio, the image is x units wide and y units high. Common aspect ratios are 1.85:1 and 2.39:1 in cinematography, 4:3 and 16:9 in television photography, and 3:2 in still photography.

<span class="mw-page-title-main">Ultrawide formats</span> Photo and video display formats

Ultrawide formats refers to photos, videos, and displays with aspect ratios greater than 2. There were multiple moves in history towards wider formats, including one by Disney, with some of them being more successful than others.

References

  1. 1 2 "standard definition television (SDTV)". ATSC : NextGen TV. Retrieved 2023-06-18.
  2. "HDTV". siliconimaging.com. Retrieved 2023-06-18.
  3. "What means 576i?". Afterdawn.com.
  4. 1 2 "What means 480i? – AfterDawn". afterdawn.com.
  5. "BT.601: Studio encoding parameters of digital television for standard 4:3 and wide screen 16:9 aspect ratios". ITU.
  6. 1 2 "All-Digital Television Is Coming (And Sooner Than You Think!)". Federal Communications Commission. Archived from the original on Sep 29, 2008.