HDTV information resource - HD TV plasma television

In order to understand the specifics of how HDTV works, its best to start off with a discussion of the current technical specs of traditional Analog TV.

In a typical analog TV, a 6 MHZ analog signal carries intensity and color information for each scan line of the picture. In the U.S., an analog TV signal has 525 scan lines (Europe has 625) for the image, and each image is refreshed every 30th of a second. The horizontal resolution is equivalent to approx 500 dots for a color set.

Analog signals are transmitted through a process similar to radio transmission. The signal is susceptible to "ghosting" or snow depending on the distance between the tower emitting the signals and the location of the TV the signal is being received from. The further away your TV is, the poorer the reception might be. There is also the matter of "bandwidth" (the amount of data that can be passed along a communication channel) assigned to a particular TV channel, which might further interfere with the resolution and overall level of quality of the image.

In comparison, digital signal transmission is either "on" or "off"-eliminating any gradual signal loss or "ghosting." Your TV is either able to receive the signal or not, there is no in between. DTV signals are made up of "bits" which take up much less space than traditional analog signals. Thus, the current bandwidth sizes which accommodate analog signals allow DTV broadcasters to provide extra features such as surround sound, text services, multiple language audio etc. There are currently 18 approved DTV formats (HDTV is one of those formats). The ability to broadcast in true widescreen format (16 x 9) is also a major plus with DTV transmission, transforming the TV viewing experience into something much more akin to watching a movie in a theater.

HDTV,or High Definition TV represents the highest level of quality available in the class of digital televsion. All HDTV's are digital, however, not all digital TV's are HD.

HDTV has either 720 or 1080 scan lines of resolution (in comparison to the 525 scan lines available in analog TV sets). Each additional scan line translates into a much sharper picture, resulting in film-like quality. 720p (the "p" stands for progressively which refers to how the lines are scanned) is currently considered the HDTV "standard" and has been adopted by Fox and ABC as their minimum HDTV broadcasting standards.

1080i (1080 lines of resolution scanned in alternate lines of 540 each) is the most commonly used HDTV format and has already been adopted by NBC, CBS, PBS and HBO as their HDTV standard. In order to fully appreciate the quality of 1080i, it should be viewed on a TV larger than 36". The drawback to this format is that the signal is displayed in an "interlaced" manner, meaning that lines are scanned alternately rather than progressively. However, this broadcast format is thought to display the most detailed images, of all of the 18 approved DTV formats.

HDTV requires special production and transmission equipment, as well as an HDTV equipped television in order to view it properly.