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What is High Definition?
So what do we mean when we say HD, High Resolution or resolution? A television is made up of a vertical and horizontal resolution.

high definitionA standard CRT (Cathode Ray Tube) TV displays 576 vertical lines (these lines are counted from the top down or down up). This is called the Vertical Resolution. High Definition televisions either display 720 or 1080 vertical lines, hence the reason for the extra detail that can be seen on a HD set. The vertical resolution is the most important resolution because it is the most noticeable to the human eye.

The Horizontal Resolution will vary depending on the source of the video. The horizontal resolution is not as critical as vertical resolution because the human eye can't see it as well during normal viewing.

Within the High Definition sets, there are various resolutions:

720p: 1,280x720 pixel resolution. High Definition picture that is displayed progressively. Each line is displayed on the screen simultaneously, therefore it is smoother than an interlaced picture.

1080i: 1,920x1,080 pixel resolution. High Definition picture that is displayed interlaced. Each odd line of the picture is displayed, followed by each even line, and the resulting image is not as smooth as a progressive feed. 1080i is therefore a more detailed picture suited to documentaries and wildlife footage, but less suitable for action-oriented material such as sports and movies.

1080p: 1,920x1,080 pixel resolution. High Definition picture that is displayed progressively. Each line is displayed on the screen simultaneously, therefore it is smoother than an interlaced picture. This is the ultimate high definition standard -- the most detailed picture, displayed progressively.

There are two main formats for HDTV, namely 720p (i.e. a 720 line picture progressively scanned 50 times a second) and 1080i (1080 lines interlaced at 50 cycles per second). The picture resolution of a high definition digital TV is about 4 times greater than a typical 576 line TV picture.

Plant TiftNet's HD digital boxes currently support 720p and 1080i. As 1080p is somewhat a new standard, it is not currently supported. As it becomes common, box manufacturers will add this capability.

[We would like to credit the text of this write-up to the following website where most of the information was available: http://www.hdtvorg.co.uk/focus/resolution.htm]