 |
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.)
While a number of high-definition television standards have been proposed or implemented on a limited basis, the current HDTV standards are defined in ITU-R BT.709 as 1080 active interlaced or progressive lines, or 720 progressive lines, using a 16:9 aspect ratio.
The term "high-definition" can refer to the resolution specifications themselves, or more loosely to media capable of similar sharpness, such as photographic film.
In the context of HDTV, the formats of the broadcasts are referred to using a notation describing:
- The number of lines in the vertical display resolution.
- Whether progressive frames (p) or interlaced fields (i) are used.
- The number of frames or fields per second.
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. The rate is then to be inferred from the context, in which case it can usually be assumed to be either 50 or 60.
It should be noted that the terminology described previously 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.
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. MPEG-2 is most commonly used as the compression codec for digital HDTV broadcasts.
|
Product Info
Widescreen Podcast
