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What would look better 720p or 1080i?

Discussion in 'LCD & LED LCD TVs' started by Rob20, Oct 23, 2004.

  1. Rob20

    Rob20
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    Just wondering. Have a Toshiba 26" WL46 which displays 768 lines but supports 720p and 1080i. If Sky's hi-def service offered a choice of either which would give the better picture on my lcd?

    How do you fit a picture with 1080i lines onto a 768 line tv? :confused:
     
  2. ianh64

    ianh64
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    I've tried both 720p and 1080i on my 32" Loewe Xelos (1366x768) via a HDMI->DVI input. I much prefer the 720p scaled up over 1080i scaled down.

    -Ian
     
  3. hornydragon

    hornydragon
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    720p is handled better by most screens fro SD plasma to LCD....
     
  4. Rob20

    Rob20
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    Cheers. What sources were you using? also, what format do you think Sky will use?
     
  5. Forest Fan

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    Hi guys,

    From what I understand 1080i is actually 540i. It only has shows half the picture at any one time, when refreshed it shows the other half (Interlacing). Wheras 720p shows the whole image. So 720p in my opinion is better and has more lines.

    1080i isn't actually scaled down it's de-interlaced, if thats the right word and then scaled up.

    Now 1080p is the ultimate and would be scaled down on a 1377x768 screen.
     
  6. ianh64

    ianh64
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    1080i is definately 1080 lines per frame. It is split into two fields, which are interlaced, so the field rate is twice the frame rate. One field contains all the odd lines, and the other contains the even lines.
     
  7. jgrg

    jgrg
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    720p actually has almost the same data rate as 1080i. In Europe HDTV displays repaint the screen 50 times per second. But because 1080i is interlaced, this is 50 half resolution fields per second. The rates in pixels per second are:

    720p = 720 x 1280 x 50 = 46,080,000 pixels per second
    1080i = 1080 x 1920 x 25 = 51,840,000 pixels per second

    This comparisson is a bit unfair, because it assumes that you have 50 frames of "new" information in 720p. If you are displaying a film, then it will show each frame twice in a row. But there are high speed 720p cameras in use in the USA that deliver 60 frames per second for showing sports on their HTDV service. Imagine how smooth motion on that system looks!

    The trouble with interlacing is that it introduces artifacts, such as combing, on moving objects and only really works on a CRT display. LCD and other flat panels are progressive displays, so need to de-interlace signals, which can be difficult to do correctly.

    If your display can show the full 1080i resolution, and there isn't movement between frames, then 1080i will look better. But if there is movement, then 720p will look better.

    It would be better if we didn't have the 1080i standard, but had 1080p at 25 frames per second. 25 frames per second on a CRT would flicker very badly, but on a LCD it doesn't matter, because the LCD doesn't flicker. Or how about 1080p at 24 frames a second - that would match the cinema frame rate exactly.

    So my answer is that 720p will look better on your monitor, especially if it comes from true 720p source material.

    James
     
  8. Forest Fan

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    I'd previosly read this link from another thread :-

    http://alvyray.com/DigitalTV/default.htm

    If 1080i was 1080 lines per frame then wouldn't you need a display with a resolution of 1920x1080 not 1280x720?
     
  9. hornydragon

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    yes but there is only one of those on the market at the moment the 45" Sharp LCD...... but 1080i downscaled to 1366x768 is very good.....
     
  10. Forest Fan

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    So what your saying is, 1366x768 LCD TV's downscales 1080i signals.
    I'm not saying your wrong but it doesn't make sense to me. Especially since these LCD tv's don't accept 1080p. If LCD displays actually downscale signals themselves, surely downscaling 1080p would be easier than 1080i.
     
  11. ianh64

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    The 1080i will be deinterlaced (to 1080p) within the set and down scaled. Much the same way that 480i/576i is delinterlaced and upscaled.
     
  12. Forest Fan

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    Ok, didn't realise they did that. The reason I found it confusing was that the displays that I've looked at wont accept a 1080p signal. So I find it bizarre that they would downscale a 1080i but not a 1080p when progressive is the preffered method of an LCD display.

    Cheers
     

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