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upscale or downscale?

Discussion in 'TVs' started by Edame, Aug 3, 2005.

  1. Edame

    Edame
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    Like a lot of people I'm a bit confused about HDTV. I'm looking at buying either an LCD or rear-projection TV later in the year but I can't get my head around resolutions. I'm looking at using it mostly for HD-DVD and xbox360 but can't figure out whether a native 720p or 1080i resolution would be optimal.

    From what I've read here, the LCDs have to display at their native resolution, so if they're 720p, then a 1080i signal has to be downscaled to that. If I had a 1080i native resolution, then a 720p signal has to be upscaled to 1080i.

    Am I correct in thinking that upscaling may show larger pixels or artifacts, but that downscaling might lose detail? I think 720p seems to be the signal I would be using most, but for films I would like to try 1080i. If I had a 720p screen would that basically mean that I'm not really seeing the extra detail from 1080i as it's being downscaled? Am I imagining upscaling to be worse than it is?

    I can't quite grok it.
     
  2. Starburst

    Starburst
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    At this time there are few 1920*1080 panels on sale and for a while that won't change at least not at a price point that is viable for the avergae consumer.
    So you will probably be looking at a HD Ready panel that has minimum vertical resolution of 720.

    Any panel can only show images at it's native resolution, source material that isn't at the native resolution will be scaled (up or down) as required. In this respect a 1080i source on a 720p panel will be scaled down to the resolution of the panel (1280*720 or 1366*768). On a 1080i panel then a 720p source will be upscaled although I suppose if the manufacturer decides it's useful the 720 image could be displayed at native resolution leaving blank areas around the screen (same as 4:3 on a 16:9 display).

    Upscaling adds information based on complex equations that the scaler uses to "guess" what is required while down scaling removes picture info.
    The results of both processess is totally dependent upon the source material and the power/flexibility of the scaling engine which is why many people buy standalone scalers/de-interlacers rather than letting the panel do the job.

    Hmmmm, started off simple and started to get a bit convoluted at the end:)
     
  3. Gordon @ Convergent AV

    Gordon @ Convergent AV
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    Most displays that are 1280 X 720 or 1366 X 768 will actually upscale the 1080i lines as each field only has 540...so the 540 will be scaled to 720 or 768 lines per 50th/60th of a second......The Horizontal resolution or vertical columns will be downscaled....it's crazy complicated this game....

    The thing to remember is that there are no 1080i panels and that a 1080P panel would not be the same as a 1080i panel, if such existed....this is a whole can of worms though....

    Gordon
     
  4. AML

    AML
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    Would you say that even the Sharp 45" LCD that is suppsed to be 1920X1080 actually isnt?
     
  5. Gordon @ Convergent AV

    Gordon @ Convergent AV
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    It's a 1080P display not 1080i .

    1080i displays work in an interlaced fashion......only examples I can think of would be CRT tv's designed for HD.
    1080P displays are progressive.
     
  6. pjskel

    pjskel
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    Thing is, the Sharp 45"er can't accept a 1080p signal - unless there's a firmware mod able to be done down the line sometime, when 1080p is perhaps more relevant then. It's certainly not now, nor will likely be for at least 3 years, perhaps 5.
     
  7. Edame

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    Now I'm even more confused :)

    I guess what I'm wondering is if there's really any point watching something in 1080i on say, a 720p screen if the image is being scaled up/down anyway?

    Would a scaled 1080i/p signal look any different than a 720p one if the set is 720p native? Would you see more detail from a higher res signal scaled down than you would from a normal 720p signal? I'm under the impression that 1080i/p will have a 'better' picture, but is this wasted on a lower res screen?
     
  8. pjskel

    pjskel
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    A 1080i when deinterlaced effectively has a resolution of about 800 lines (vertically), so there's not a whole lot of difference. 720p native transmission is supposedly better for fast action, 1080i gives a more cinematic feel to the image.
    I've not seen this for myself yet, but it's what others have written on the forums, who seem to know their onions.

    1080p, if/when that becomes an accepted resolution or an adopted standard for broadcasting or pre-recorded playback media would be another level again over 720p, but it's easily 5+ years off yet. It'll only be looked at seriously, once HD has really started to become commonplace, so don't worry about it.
     
  9. Stephen Neal

    Stephen Neal
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    You have to be careful when talking about 1080p - to some people it means 1080/24-30p (which is an unused part of the US ATSC broadcast spec - and 1080/24p is the main US drama shooting format), whereas in this case I think you mean 1080/50p or 1080/60p - i.e. the progressive equivalent of 1080/50i or 60i (with the same motion quality), or 720/50p or 60p...
     
  10. pjskel

    pjskel
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    Ah, forgot about the US using 24/30p recording. Yes, spot on about the equivalent of 720p - which is 50 or 60 frames.
     
  11. Stephen Neal

    Stephen Neal
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    Yep - and we're using 1080/25p for HD drama (and some rock concerts) in Europe.
     
  12. pjskel

    pjskel
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    Oh Christ! Blinkin minefield this malarky.
     
  13. Stephen Neal

    Stephen Neal
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    Oh yes...

    Basically 1080/24/25/30p are direct equivalents to 16mm or 35mm film production. In the US they traditionally shot at 24 fps for their TV film production (same as feature films) - but to transfer this to 60i or 60p they have to use a 3:2 system.

    In Europe we shoot TV film at 25fps, which means we can use 2:2 to transfer to 50p or 50i standards. (Though this costs more with film as we shoot an extra frame a second...)

    If 24fps material is shown in Europe it is usually played a bit faster at 25fps (as 3:2 60i to 2:2 50i conversion looks bad).

    If 25fps stuff is shown in the US then it can either be converted from 2:2 50i to 60i using a converter, or slowed down to 24fps and then 3:2 converted, there is less of a problem with a 50i to 60i conversion as there are no 3:2 issues to mess it up.)
     

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