What is HDTV?

High-Definition Television (HDTV) is a television broadcasting system with a significantly higher resolution than traditional formats (NTSC, SECAM, PAL) allow.
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 interlace or progressive scan lines, or 720 progressive scan 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.

Comparing HDTV to SDTV

HDTV has at least twice the linear resolution of standard-definition television (SDTV), thus allowing much more detail to be shown compared with 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 or anamorphic stretching, thus further increasing the effective resolution for such content.

HDTV resolution compared to PAL and NTSC (normal television) resolution. XGA is the average resolution of a PC monitor.

Advantages of HDTV

• High-definition television (HDTV) offers a much better picture quality than standard television. HD's greater clarity means the picture on screen is less blurred and less fuzzy. HD also brings other benefits - smoother motion, richer and more natural colors, surround sound and the chance for different equipment to work better together.
• All commercial HD is digital, so the signal will either deliver an excellent picture, a picture with noticeable pixelation, a series of still pictures, or no picture at all. 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. This is also a disadvantage, because 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.
• HD programming and films will be presented in 16:9 widescreen format (although films created in even wider ratios will still display "letterbox" 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. 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 reframe it 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.
• Two new pre-recorded disc formats support HDTV resolutions, namely HD DVD (supporting 720p, 1080i and 1080p) and Blu-ray (supporting up to 1080p). Most players for both systems are backward-compatible with DVDs. However, the two formats are not currently compatible with each other.
• The increased clarity and detail make larger screen sizes more comfortable and pleasing to watch.
• 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 stereo audio.)
• 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.

Contemporary systems

In addition to an HD Ready television, other equipment is often needed for the home user to view High Definition Television. There are several sources of high definition content and the equipment used to control each of these must be HD compatible.
High Definition picture sources include terrestrial broadcast, direct broadcast satellite, digital cable, high definition discs (Blu-ray and HD DVD), internet downloads and the latest generation of games consoles.
The availability of television pictures broadcast in the HD format varies by region and country.

Further reading

hd-streams.de

Web-cross-guide