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by Ziggydoom on November 25th, 2005

Ziggydoom

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Is an HDTV 1080i really an HDTV?

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  • by RedJohn on December 30th, 2005

    RedJohn

    As the other poster stated: yes.

    The ATSC (Advanced Television Systems Committee) has defined two high-definition (HD) broadcast standards: 720p and 1080i.

    The ATSC has also defined a 1080p standard, which is not used for broadcasting, but is available for use with video playback devices. 1080p requires twice the bandwidth of 1080i. Bandwidth is a 'rationed' commodity and stations would rather broadcast two 1080i channels instead of one 1080p channel, the quality of which would be appreciated by only a small number of viewers.

    Is 1080i any better than 720p? That all depends, as usual, on a host of things.

    Interlacing: 720p is a non-interlaced video system, while 1080i is interlaced. 1080i has the same problems with motion artifacts as do all NTSC 480i televisions (the broadcast system used in North America and a few other countries). A set that could convert 1080i to 1080p could reduce these problems.

    Native resolution: Even though a television supports the 1080i and 720p standards, its native resolution will be different (i.e., the physical number of pixels in the display). A set with a native resolution of 720 pixels has to downsample 1080i signals and deinterlace them. The quality of this process is dependent on the quality of the resampling / extrapolation algorithm used. Similarly, a 1080 pixel television has to upsample 720p signals and interlace them. Some cheap televisions have a native resolution of 480 pixels and, therefore, have to downsample both 720p and 1080i signals.

    What the broadcaster uses: The most recent information I have for North American markets is that NBC and CBS broadcast their HD programs in 1080i. Some PBS programs are also 1080i. Other broadcasters use 720p. Microsoft has been a significant promoter of 720 pixel broadcasting, as they hold the position that everything will eventually be seen on a computer screen. (This from the same outfit that purchased and then discarded HDCD, a CD format with real audible benefits.)

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  • by anguilla on December 16th, 2005

    anguilla

    Oh, yes! HDTV pictures are made up of either 720 horizontal lines or 1080 lines. The more lines, the more detail. Compare newspaper pictures to magazine pictures. Magazine pictures use more, smaller dots, so they have sharper pictures.

    So 1080i is good.

    Sort of.

    "1080i" means that the TV alternates displaying the odd-numbered lines of the picture (first, third, fifth, etc.) and the even-numbered lines. The "i" means "interlaced."

    Regular, non-HD TVs do this, too. They just use fewer lines, (525 in the U.S., 625 in other parts of the world) so the picture isn't as sharp as HD.

    There's also "720p" high-def TV. The "p" stands for "progressive." In 720p, all 720 lines that make up a picture are displayed at the same time. There's no alternating ("interlacing") of odd and even lines.

    So you could argue that since 1080i only shows you half its lines at any one moment (half of 1080 is 540), you aren't seeing as much detail at that moment as you would seen in a 720p picture, where ALL the lines are displayed together.

    If but then, there's "persistence of vision." That means your brain remembers the odd-numbered lines when they have disappeared and the even-numbered lines are being displayed. This works because the odds and evens switch every 60th of a second.

    So if your brain THINKS it's seeing all 1080 lines at the same time, that's just as good as REALLY seeing all 1080 lines at the same time. And 1080i will truly provide the sharper, more detailed picture.

    Some newer TVs even have electronics that "up-convert" 720p pictures to 1080 picture. That leads us off into a whole nother direction, which my fingers are too tired to type.

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