1080i vs. 1080p vs. 720p - What does it mean?

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You've been looking for a new high definition TV (HDTV), and have come head to head with lots of new terminology.  The biggest buzzwords you'll see when choosing a new flat screen, plasma TV or DVD player include 1080i and 720p, as well as 1080p.

Your main concern when choosing a high definition screen is the "structure" of the screen, which refers to the pixels on its digital display.  This would be the equivalent of scan lines on the older tube type TV screens.  The more pixels (or lines), the less obvious they are, and the better your image looks.

There are two main flavors of high definition TV, 1080i (the i is for interlaced) and 720p (p for progressive).  1080i offers the most pixels, with a matrix of 1920x1080 pixels, while 720p has fewer pixels at 1280x720 pixels.  However, the difference is made up with the frame rate, which is only 30 frames per second with 1080i, but is double that with 720p, at 60 frames per second.  The total pixels displayed per second is actually very similar, with 720p offering 55 million pixels per second, while 1080 is slightly higher at 62 million pixels per second.

What does all that mean?  It all depends on the type of TV you watch.  720p is better at showing pictures with plenty of motion, since the higher frame rate helps smooth any quick motion on the screen - this is better for sports or action movies.  1080i offers more detail, which is for movies with lots of images or panoramas.

The best of all is the 1080p option.  It offers the best of both world, 60 frames per second at 1920 x 1080 pixels.  The toal bandwidth is 124 million pixels per second, double that of 1080i.  It can display any HDTV signal without any downconverting.  720p signals are upconverted, while 1080i signals only require some gently "de-interlacing" to work properly.  1080p is the perferred option is possible - its backwards compatible with all old formats, and is ready for upcoming high definition discs.

Some terms you'll need to be aware of:

EDTV (Enhanced-Definition Television - 480p)
A TV that can display signal in 480-line progressive (480p) mode, as well as  480p signals from video sources such as progressive-scan DVD players. You will find that 480p picture quality is superior to standard analog TV (also known as 480i), but not quite as sharp as true HDTV (1080i or 720p). You can find EDTVs in lower end plasma or flat-panel LCD models.

HDTV (High-Definition Television - 1080i or 720p)
HDTV refers to the highest-resolution formats of the 18 different DTV formats. Although not clearly defined by the industry,  HDTV is generally considered to be 1,080-line interlaced (1080i) or 720-line progressive (720p).

Vertical resolution:
The number of horizontal lines (or pixels) that can be resolved from the top of an image to the bottom. (Think of hundreds of horizontal lines or dots stacked on top of one another.) The vertical resolution of the analog NTSC TV standard is 525 lines. But, some lines are used to carry other data like closed-captioning text, test signals, etc., so we end up with about 480 lines in the final image, regardless of the source. So, all of the typical NTSC sources — VHS VCRs, cable and over-the-air broadcast TV (analog), non-HD digital satellite TV, DVD players, camcorders, etc. — have vertical resolution of 480 lines. DTV (Digital Television) signals have vertical resolution that ranges from 480 lines for SDTV, to 720 or 1080 lines for true HDTV.

Horizontal resolution:
The number of vertical lines (or pixels) that can be resolved from one side of an image to the other. Horizontal resolution is a trickier concept, because while the vertical resolution of all analog (NTSC) video sources is the same (480 lines), the horizontal resolution varies according to the source. Some examples for typical sources: VHS VCRs (240 lines), analog TV broadcasts (330 lines), non-HDTV digital satellite TV (up to 380 lines), and DVD players (540 lines). DTV signals have horizontal resolution that ranges from 640 lines for SDTV, to 1280 lines (for 720p HDTV) or 1920 lines (for 1080i HDTV).

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