- High Definition Television. A television display standard providing much
better picture quality than a standard (non-HD) television.
There are a number of different formats for high-definition, a TV which supports any one of these standards can claim to be high-definition (or HD Ready):
The number part specifies the number of vertical lines. 720p is 720 vertical lines (and 1280 lines horizontally). 1080i and 1080p are both 1080 vertical lines (and 1920 lines horizontally). HDTV are always widescreen, so having a horizontal to vertical ratio of 16:9
The letter "p" or "i" denotes "progressive" or "interlaced" respectively, which denotes how the picture is built up. With interlaced the image is built up in two passes, with every other line updated on each pass. With progressive scan a complete image is transmitted in each frame. What this means in practice is that progressive gives a smoother picture, especially where there is notion.
Occasionally the format may be expressed with an additional number after the "p" or "i". Where this is given this is the frame frame, i.e. the number of frames per second. Typically 720p is 60 frames per second (so 720p60 in full), and 1080i and 1080p are 50 frames per second.
For more information see: