HDTVs, Direct-View

High-definition television (HDTV) means broadcast of television signals with a higher resolution than traditional formats (NTSC, SÉCAM, PAL) allow. more...

Except for early analog formats in Europe and Japan, HDTV is broadcasted digitally, and therefore its introduction sometimes coincides with the introduction of digital television (DTV).

Historically, the term high-definition television was also used to refer to television standards developed in the 1930s to replace the early experimental systems, although, not so long afterwards, Philo T. Farnsworth, John Logie Baird and Vladimir Zworykin had each developed competing TV systems but resolution was not the issue that separated their substantially different technologies. It was patent interference lawsuits and deployment issues given the tumultuous financial climate of the late '20s and '30s. Most patents were expiring by the end of World War II leaving the market wide open and no worldwide standard for television agreed upon. The world used analog PAL, NTSC, SÉCAM and other standards for over half a century.

HDTV is defined as 1080 active lines, 16 x 9 aspect ratio in ITU-R BT.709.

Notation

In the context of HDTV, the formats of the broadcasts are referred to using a notation describing:

• The number of lines in the display resolution.
• Progressive frames (p) or interlaced fields (i).
• 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. It can then usually be assumed to be either 50 or 60, although some displays claim to support 1080p, but only support 1080p/30. Consumer displays are available that allow 1080p/60 input and render it at full temporal and spatial resolution.

Read more at Wikipedia.org