History

High-Definition television was first developed by Nippon Hōsō Kyōkai, and was unveiled in 1969 ^[3].

Though the system did not become mainstream until the late 1990s.

In the early 2000s, a number of high-definition television standards were competing for the still-developing niche markets.

Three HDTV standards are currently defined by the International Telecommunication Union (ITU-R BT.709). They include 1080i (1,080 actively interlaced lines), 1080p (1,080 progressively scanned lines), and 720p (720 progressively scanned lines). All standards use a 16:9 aspect ratio, leading many consumers to the incorrect conclusion of equating widescreen television with HDTV. All current HDTV broadcasting standards are encompassed within the DVB specification.

HDTV is also capable of "theater -quality" audio because it uses the Dolby Digital (AC-3) format to support "5.1" surround sound. It should be noted that while HDTV is more like a theater in quality than conventional television, 35mm and 70mm film projectors used in theaters still have the highest resolution and best viewing quality on very large screens. Many HDTV programs are produced from movies on film as well as content shot in HD video.

The term "high-definition" can refer to the resolution specifications themselves, or more loosely to media capable of similar sharpness, such as photographic film. As of 2007, 24 million US households have HDTVs. However, only half are set up to actually receive HDTV programming^[4] as some consumers are not aware that they must get special receivers to get HDTV from cable, or use HDTV tuners to receive over-the-air broadcasts, and some are planning to use it in the future.

Advantages of HDTV expressed in non-engineering terms

High-definition television (HDTV) potentially offers a much better picture quality than standard television. HD's greater clarity means the picture on screen can be less blurred and less fuzzy. HD also brings other benefits such as smoother motion, richer and more natural colors, surround sound, and the ability to allow a variety of input devices to work together. However, there are a variety of reasons why the best HD quality is not usually achieved. The main problem is a lack of HD input. Many cable and satellite channels and even some "high definition" channels, are not broadcast in true HD. Also, image quality may be lost if the television is not properly connected to the input device or not properly configured for the input's optimal performance.

Almost all commercially available HD is digital, so the system cannot produce a snowy or washed out image from a weak signal, effects from signal interference, such as herringbone patterns, or vertical rolling. HD digital signals will either deliver an excellent picture, a picture with noticeable pixelation, a series of still pictures, or no picture at all. Any interference will render the signal unwatchable. As opposed to a lower-quality signal one gets from interference in an analogue television broadcast, interference in a digital television broadcast will freeze, skip, or display "garbage" information.

With HDTV the lack of imperfections in the television screen often seen on traditional television is another reason why many prefer high definition to analog. As mentioned, problems such as snow caused from a weak signal, double images from ghosting or multi-path and picture sparkles from impulse noise are a thing of the past. These problems often seen on a conventional television broadcast just do not occur on HDTV.

HD programming and films will be presented in 16:9 widescreen format (although films created in even wider ratios will still display "" bars on the top and bottom of even 16:9 sets.) Older films and programming that retain their 4:3 ratio display will be presented in a version of letterbox commonly called "pillar box," displaying bars on the right and left of 16:9 sets (rendering the term "fullscreen" a misnomer). While this is an advantage when it comes to playing 16:9 movies, it creates the same disadvantage when playing 4:3 television shows that standard televisions have playing 16:9 movies. A way to address this is to zoom the 4:3 image to fill the screen or re-frame its material to 14:9 aspect ratio, either during preproduction or manually in the TV set.

The colors will generally look more realistic, due to their greater bandwidth. The visual information is about 2-5 times more detailed overall. The gaps between scanning lines are smaller or invisible. Legacy TV content that was shot and preserved on 35 mm film can now be viewed at nearly the same resolution as that at which it was originally photographed. A good analogy for television quality is looking through a window. HDTV offers a degree of clarity that is much closer to this.

The "i" in these numbers stands for "interlaced" while the "p" stands for "progressive". With interlaced scan, the 1,080 lines are split into two, the first 540 being "painted" on a frame, followed by the second 540 painted on another frame. This method reduces the bandwidth and raises the frame rate to 50-60 per second. A progressive scan displays all 1,080 lines at the same time at 60 frames per second, using more bandwidth. (See: An explanation of HDTV numbers and layman's glossary)

Dolby Digital 5.1 surround sound is broadcast along with standard HDTV video signals, allowing full surround sound capabilities. (Standard broadcast television signals usually only include monophonic or stereophonic audio. Stereo broadcasts can be encoded with Dolby Surround, an early home video surround format.) Both designs make more efficient use of electricity than SDTV designs of equivalent size, which can mean lower operating costs. LCD is a leader in energy conservation.

The preceding information can be found at http://en.wikipedia.org/wiki/High-definition_television.