Reprinted from Wikipedia
High-definition television (HDTV) is a television broadcasting system with a significantly higher resolution than traditional formats (NTSC, SECAM, PAL) allow. Except for early analog formats in Europe and Japan, HDTV is broadcast digitally, and therefore its introduction sometimes coincides with the introduction of digital television (DTV): this technology was first introduced in the USA during the 1990s, by the Digital HDTV Grand Alliance (grouping together AT&T, General Instrument, MIT, Philips, Sarnoff, Thomson, and Zenith)[1].
While a number of high-definition television standards have been proposed or implemented on a limited basis, the current HDTV standards are defined as 1080 active interlaced or progressive lines, or 720 progressive lines, using a 16:9 aspect ratio in ITU-R BT.709. The term "high-definition" can refer to the resolution specifications themselves, or to media capable of similar sharpness such as movie film.
In the context of HDTV, the formats of the broadcasts are referred to using a notation describing:
For example, the format 720p60 is 1280 × 720 pixels, progressive encoding with 60 frames per second (60 hertz known as Hz). The format 1080i50 is 1920 × 1080 pixels, interlaced encoding with 50 fields (25 frames) per second. Often the frame or field rate is left out, indicating only the resolution and type of the frames or fields. Sometimes the rate is then to be inferred from the context, in which case it can usually be assumed to be either 50 or 60, except for 1080p which is often used to denote either 1080p24, 1080p25 or 1080p30 at present.
A frame or field rate can also be specified without a resolution. For example 24p means 24 progressive frames per second and 50i means 25 interlaced frames per second, consisting of 50 interlaced fields per second.
Most HDTV systems support some standard resolutions and frame or field rates. The most common are noted below.
It should be noted that the terminology described above was invented for digital systems in the 1990s. Before that, analog TV had no true "pixels" to measure horizontal resolution, and vertical scan-line count included off-screen scan lines with no picture information while the CRT beam returned to the top of the screen to begin another field. Thus NTSC was considered to have "525 lines" even though only 480 of them had a picture (625/576 for PAL). Similarly the Japanese MUSE system was called "1125 line", but is only 1035i by today's measuring standards. This change was made because digital systems have no need of blank retrace lines unless the signal was converted to analog to drive a CRT.
Note: This diagram lists only a few common video resolutions based on specification. For real life video resolutions, subject to interlace artifacts, please view the diagram at the end of this article or the display resolution article.
- NTSC is 720 x 480 non-square pixels
- PAL is 720 x 576 non-square pixels (Note that the PAL resolution given in the image above is for square pixels.)
NTSC uses pixels that are narrower than square (0.912), PAL uses pixels that are wider than square (1.094). This is referred to as the CCIR 601 standard for digital video.
- 23.976p (allow easy conversion to NTSC)
- 24p (cinematic film)
- 25p
- 30p
- 50p
- 60p
- 50i (PAL/SECAM)
- 60i (NTSC)
HDTV has at least twice the lineal resolution of standard-definition television (SDTV), thus allowing much more detail to be shown compared to analog television or regular DVD. In addition, the technical standards for broadcasting HDTV are also able to handle 16:9 aspect ratio pictures without using letterboxing, thus further increasing the effective resolution for such content.
HDTV at four times the areal resolution of SDTV.
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SDTV resolution.
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