720p native screens?

Discussion in 'Plasma TVs Forum' started by drpatterson, Aug 22, 2006.

  1. drpatterson

    drpatterson
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    I'm thinking of switching my ageing Sony Wega CRT for a 42" plasma. One thing that concerns me is that most displays seem to be something x 768 pixels, my DVD player will output 720p so obviously some scaling is going to be done by the display.

    In my head this means a loss of quality, even if I move to hi-def sources 768 is not a native HD resolution so there will always be scaling involved. Have I missed something?
     
  2. NonPayingMember

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    What you might have missed is that fact that even if it was 720p your DVD player is STILL scaling??? For plasma screens I advise turning OFF upscaling in most cases!!! No point trying to find a screen with a video resolution as something is always scaled somewhere. e.g. 720p display must downscale 1080 HD and upscale 480 and 576 DVD/SDTV. 1080 display has to upscale everything non-1080. Better to find a screen (or dedicated processor) that has a good scaler to start with then it doesn't matter LOL!
     
  3. drpatterson

    drpatterson
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    Thanks for the quick answer but I think I'm still missing something. The HDMI can carry at 720/1080 and the display can show at 768. This means that there must be scaling for every signal. The player goes from 576 to 720, the display from 720 to 768. Why not just make a display that meets the resolution of the interface? All panels seem to be based around PC resolutions rather than HDTV ones which doesn;t make sense to me.
     
  4. NonPayingMember

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    My point is that there is more than one resolution in terms of source:

    VCRs are 240 lines
    DVDs and Sky TV is 576 Lines
    US DVDs are 480 lines
    HDTV is 720 or 1080 lines

    Since a fixed pixel display can only be one fixed pixel resolution, something somewhere is always going to be scaled.

    Agreed 720p res might seem to make a bit more sense for the home market, but it would only stop one of the incoming signals (720p) from being scaled. And that would be 720p which nobody uses. All HD seems to be 1080i (HDTV) or 1080p (HD-DVD/Blu-Ray, eventually). 720p outputs from these players are downscaled from 1080 on disk. 720p outputs from normal DVD players are upscaled from 576/480 on disk. So it's still scaled somewhere whether in the plasma or in the source.

    PC resolutions did come from a more IT nature to the product (most plasmas in existence today are public display running XGA....). But to change it all over to 720p, especially given my point above, has just never been worth doing. We're already all looking at 1920x1080 screens now...
     
  5. Jet_Set_Jim

    Jet_Set_Jim
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    Also - even with a genuine 720p source, most displays will over-scan. This means that of the 720 lines information, only say 700 are visible, and these will then be scaled up over the 720 lines.

    So there will always be processing occuring unless you're using video processor 1-1 pixel mapping voodoo... the key is to avoid multiple scaling as much as possible.
     
  6. JTHM

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    I believe it was down to production technologies and computers were originally the only kit that could feed large screens at high resolutions so panels were made for them. I mean, why design a production technology for a panel with a resolution that doesn't yet exist? That said, my Panny 37" is a 720 but the 42" and 50" in the same range are both 768s. An upscaled 42" 768 will look marginally better than a 42" 720 because the pixels will be smaller and the upscaler will interpolate between the pixels rather than simply enlarge each pixel.

    I expect that eventually smaller plasma panels and cheaper LCDs will stay at 720 and larger plasma panels and quality LCD panels will all come in a native resolution of 1080 (we're starting to see them now but they're rare beasties indeed and darn expensive).

    Bascially we're still in a transition driven by HD broadcasting in the US and JP. If you want to buy an HD telly now you have to accept that there will be scaling in one direction or another.

    I might venture to adjust what Liam @ Prog AV said when he writes "..720p which nobody uses" by adding "..nobody 'in Europe' uses". Actually ABC, ESPN and Fox broadcasters in the US do broadcast in native 720p due to their sports coverage (720p is better than 1080i for fast action) and there was surprise when Sky decided to go against the EBUs (European Broadcasting Union) recommendation to broadcast in 720p by going for 1080i, and not least because the crux of their HD programming is sport based. That said, every other HD broadcaster in Europe has gone against this recommendation and also broadcast in 1080i.
     
  7. keith symonds

    keith symonds
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    hi please can you explain why the broadcast is 1080i when the new panels are 1080p or cant the broadcasting be done progressive, sorry if this is a daft question
     
  8. JTHM

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    I'm no expert - I just know what I read, however, I believe the answer is mainly bandwidth. A progressive (i.e. 1080p) transmission carries all lines per frame, or 1080 lines. An interlaced (i.e. 1080i) transmission carries alternate lines per frame (i.e. 1st frame carries lines 1, 3, 5, 7, 9, etc. and the 2nd frame carries lines 2, 4, 6, 8, etc.). Your eyes (or a deinterlacing processor) then merge the two images to make a whole.

    Thus a single 1080p frame carries 2,073,600 pixels of data (1920 across x 1080 down) and a single 1080i frame carries 1,036,800 pixels (1920 across x 540 down). Thatwithstanding, a single 720p frame carries just 737280 pixels (1024 across x 720 down) of data which is less obviously than a single 1080i frame.

    Now, a static 1080i image can show more detail than a static 720p image however in faster moving shots and due to the deinterlacing that your eyes must do the 1080i image starts to degrade due to the old frame still being visible on the screen together with the newer 'translated' frame. Obviously a progressive image does not suffer with this as no part of the old frame is displayed at the same time as the new frame (except in laggy LCDs of course! ;) ) This is why a 720p transmission is better suited to sport.
     
  9. Jonstone

    Jonstone
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    The only problem with this arguement is that sky are using 1080i for their football coverage.
     
  10. Joe Fernand

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    Hello keith symonds

    In simple terms a 1080i or 1080p broadcast ought to look identical on a 1920x1080 pixel array; assuming the Display has a decent video processing engine.

    Assuming the above to be correct then the bandwidth and technology the broadcasters require is very different (read a LOT less expensive) for 1080i compared with 1080p.

    Best regards

    Joe
     
  11. JTHM

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    I'm not arguing with that! :rotfl:
     
  12. JTHM

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    Joe

    I can understand this if a static or relatively slow moving image is displayed, yes, but not a fast moving action or sport scene (even cricket at times! :D - ideal for crown green bowls! :thumbsup: ).

    Your post reads as though a 1080i broadcast is actually better than a 1080p broadcast because it gives the same results at a much cheaper price. How can this be the case when you're loosing the half the frame rate for each of the interlaced frames? A degree of blurring or interlaced artefact display will always be present on a fast moving HD interlaced display. Ok, people won't be able to pick this out in a retail environment so standing in front of two identical displays side-by-side in a shop, one interlaced and one progressive, they will likely look identical but if you were in a position to do the same at home there will surely be a noticable clarity increase with the progressive broadcast.
     
  13. RonCH

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    You could buy one of the new Denon DVD players which can upscale to 768 lines. According to the DVD-2930 manual the Denon player can scale to 480/576i, 480/576P, 720P, 1080i, 1080P and 640 x 480 (60 Hz), 1024 x 768 (60 Hz), 1280 x 768 (60 Hz), 1280 x 1024 (60 Hz).
     
  14. keith symonds

    keith symonds
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    OK So as always comes down to cost, I was just trying to get my head round all the scaling and deinterlacing, as stoomonster had said about managing to get 576i out of the sky hd, but if they (sky) are broardcasting in 1080i to my mind it seems that there would be less scaling if this was used as the output from the sky hd ? or is this totally wrong?
     
  15. NonPayingMember

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    HD channels are 1080i, SD channels are 576i. So whatever resolution your display, one (or both) of them is being rescaled.

    Denon 768p upscalers (same as Arcam DV137) are to 1366x768. Your display must accept that natively without rescaling (Panasonic 50" but not Fuji as Fuji is 1360...). So not that useful for 42" (1024x768). Many displays actually accept their native resolution, and still rescale!

    1080i is comparable to 1080p as we know it (25fps) since as yet the average consumer TV hasn't seen a 50frame progressive 1080p feed. It's such a high bandwidth it's only really seen in professional digital cinemas that implement it and in recording studio etc. IIRC it take two HD-SDI feeds running in-sync to get all the bandwidth from the server to the digital camera! (it might even be two twin HD-SDI! It's something astronomic anyway). But agreed 1080p50 would be pheneomenal. And this is what the football argument, the entire Internet let out a sigh of disapointment when Sky announced 1080i football coverage as we would rather lose pixel resolution (720 instead of 1080) than temporal resolution (25 frames instead of 50 frames progressive).
     

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