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Standard-definition television (SDTV; also standard definition or SD) 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]
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. [3] [4]
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. The audio encoding is the last to suffer a loss due to the lower bandwidth requirements.[ citation needed ]
Standards that support digital SDTV broadcast include DVB, ATSC, and ISDB. [5] 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.
The two SDTV signal types are 576i (with 576 interlaced lines of resolution, [6] derived from the European-developed PAL and SECAM systems), and 480i (with 480 interlaced lines of resolution, [3] 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.
In North America, digital SDTV is broadcast in the same 4:3 fullscreen aspect ratio as NTSC signals, with widescreen content often being center cut. [5]
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. Some broadcasters prefer to reduce the horizontal resolution by anamorphically scaling the video into a pillarbox.[ citation needed ]
| Video format | Display aspect ratio (DAR) | Resolution | Pixel aspect ratio (PAR) | After horizontal scaling |
|---|---|---|---|---|
| 480i | 4:3 | 704 × 480 (horizontal blanking cropped) | 10:11 | 640 × 480 |
| 720 × 480 (full frame) | 655 × 480 | |||
| 480i | 16:9 | 704 × 480 (horizontal blanking cropped) | 40:33 | 854 × 480 |
| 720 × 480 (full frame) | 873 × 480 | |||
| 576i | 4:3 | 704 × 576 (horizontal blanking cropped) | 12:11 | 768 × 576 |
| 720 × 576 (full frame) | 788 × 576 | |||
| 576i | 16:9 | 704 × 576 (horizontal blanking cropped) | 16:11 | 1024 × 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 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. 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.[ citation needed ] The display ratio for broadcast widescreen is commonly 16:9 (pixel aspect ratio of 40:33 for anamorphic); the display ratio for a traditional or letterboxed broadcast is 4:3 (pixel aspect ratio of 10:11).
An SDTV image outside the constraints of the SMPTE standards requires no non-proportional scaling with 640 pixels (defined by the adopted IBM VGA standard) 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.
Digital television (DTV) is the transmission of television signals using digital encoding, in contrast to the earlier analog television technology which used analog signals. At the time of its development it was considered an innovative advancement and represented the first significant evolution in television technology since color television in the 1950s. Modern digital television is transmitted in high-definition television (HDTV) with greater resolution than analog TV. It typically uses a widescreen aspect ratio in contrast to the narrower format (4:3) of analog TV. It makes more economical use of scarce radio spectrum space; it can transmit up to seven channels in the same bandwidth as a single analog channel, and provides many new features that analog television cannot. A transition from analog to digital broadcasting began around 2000. Different digital television broadcasting standards have been adopted in different parts of the world; below are the more widely used standards:
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.
Interlaced video is a technique for doubling the perceived frame rate of a video display without consuming extra bandwidth. The interlaced signal contains two fields of a video frame captured consecutively. This enhances motion perception to the viewer, and reduces flicker by taking advantage of the characteristics of the human visual system.
Advanced Television Systems Committee (ATSC) standards are an international set of standards for broadcast and 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 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.
The display resolution or display modes of a digital television, computer monitor, or other 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.
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.
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.
576i is a standard-definition digital video mode, originally used for digitizing 625 line 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.
Copy Generation Management System – Analog (CGMS-A) is a copy protection mechanism for analog television signals. It consists of a waveform inserted into the non-picture vertical blanking interval (VBI) of an analogue video signal. If a compatible recording device detects this waveform, it may block or restrict recording of the video content.
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.
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.
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.
Broadcast-safe video is a term used in the broadcast industry to define video and audio compliant with the technical or regulatory broadcast requirements of the target area or region the feed might be broadcasting to. In the United States, the Federal Communications Commission (FCC) is the regulatory authority; in most of Europe, standards are set by the European Broadcasting Union (EBU).
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 standard video format used in most broadcasts: terrestrial broadcast television, cable television, satellite television.
