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720p HD signal scaled up to 1366x768 is good?

Discussion in 'LCD & LED LCD TVs' started by ranguyen, Aug 23, 2005.

  1. ranguyen

    ranguyen
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    I've always read that LCD's look best when shown in there native resolution. And that any scaling degrades clarity.

    So if your source is a 720p or 1080i HD signal, wouldn't that look best on a LCD or Plasma TV that has a native resolution of either 1280x720 or 1920x1080?

    Then why is it that all of the larger Plasma's and LCD's TV's have funny native resolutions like 1366x768 or 1280x768? Doesn't this mean when they are displaying a HD signal of 720p, it's getting scaled up to 768 and losing clarity?

    Furthermore, these native resolutions of 1366x768 or 1280x768 are not even 16:9 ratios.

    What am I missing here?
     
  2. ianh64

    ianh64
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    You are absolutely right. But in reality it is not a problem if the scaler on the TV is of sufficient quality. Also, even if the display was 1280x720 and was being fed 720p, it is likely that the picture would be scaled anyway as this is a TV rather than a PC monitor so would be having to deal with overscan.

    1366x768 is 16:9
    1280x768 is 15:9
    1280x720 is 16:9

    -Ian
     
  3. daxie

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    1366x768 is 16:9...

    It all has to do with economics... It's for some reason easier and more economical to build panels with 1366x768 resolution...

    The larger 1920x1080 panels will come in the near future, but will be pretty pricey in the beginning...
     
  4. danvitale

    danvitale
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    The 1920x1080 panels are already here (Sharp 45G1DE).. and yes theyre pretty pricey ;)
     
  5. bishman

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    And they'll still have to scale 720P images. Fixed pixel displays will always be compromised by scaling with one of the standard HD signals.
     
  6. Gordon @ Convergent AV

    Gordon @ Convergent AV
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    You may also want to note that you can have 16:9 panels (plasma) that have pixel resolutions that do not appear 16:9 but as the pixels are not square....they are rectangular, the image is 16:9.

    Also 1080P panels will be required to process 1080i material....each 1080i field is 540 lines......not 1080.

    Gordon
     
  7. RockySpieler

    RockySpieler
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    One common answer, expressed elsewhere on the forums, as to why panels are W-XGA (1366x768) when they serve to reproduce 720p images is "overscan".

    However my question is this, why have 1080p panels, with native 1920x1080 why are they not larger to accomodate overscan. If the same % increase used on 720p to 768p is used on 1080p panels they would be 2048x1152.

    Is overscan an analogue OTA "thing", and will digital HD sources with DVI/HDMI (such as Sky HD) not produce it?

    What about Xbox360 with its internal scaler 720p or 1080i analogue output over component, will this have overscan?

    Any ideas/comments?
     
  8. Gordon @ Convergent AV

    Gordon @ Convergent AV
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    Well we already have a digital transmission medium and different channels on Sky require less or more overscan to remove unwanted non-picture information from the borders. I imagine that this "safe" area broadcasting will continue when we move to HD.

    If you have a display with a native or 1:1 aspect then you will be able to choose whether you see or don;t see the rubbish on the edges.

    Gordon
     
  9. andrewfee

    andrewfee
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    I had initially thought it might've been overscan, but it doesn't seem to be the case.

    My theory is that, because it's LCD, it makes more sense to use x768 because you can then feed the display 1024x768 from a PC for 1:1 mapping in a 4:3 ratio. That way doesn't require any extra configuration to get 1:1 mapping, as some people have a lot of trouble getting their system to output 1280x720, 1280x768, 1360x768 etc. (I had no trouble at all, but that's not the point)

    Newer systems / displays seem to be able to detect the resolution automatically, but many don't.
     
  10. psotfx

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    This is my belief too ... the industry has lots of existing plant which I imagine (not being an expert on LCD production) was built to knock out 768 line resolution panels for as noted the PC monitor industry. That market is fast drying up with average LCD monitor sizes now sitting at 17" and a 1280 * 1024 resolution. So I imagine (again with provisos that I have no first hand knowledge of the manufacturing process) that it's a lot cheaper to use that (increasingly redundant but expensive) existing plant to knock out TV panels than retool (which again I imagine is necessary) for 720 line.

    Why therefore are there native 1080 line plant? Well again my guess would be that the next step up PC monitor wise is 1024 lines which of course is under native 1080 resolution and thus pointless. So new plant is being built to produce those panels ... And guess what resolution Sharp's "PAL Optimised" displays are ... 540 lines. Coincidence that these are exactly 1/4 a 1080 line panel? Don't think so, economy of scale I think (no matter what their blurb may suggest).

    IOW I think the vertical res of all these panels is down to economics rather than "technical reason". I'm sure as 768 line plant is shut down we'll see either 1080 line panels across the board or new 720 line plant come onstream. Assuming some other technology hasn't replaced LCD by then of course!
     
  11. Rob1698

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    You may have misunderstood the "overscan" issue.
    The true SMPT standards for 720p and 1080i specify that a border of 16 pixels all around is reserved for scanning tolerances (on CRT screens) and should normally not be displayed. So the actual visible area is less than 1280x720 or 1920x1080.
    A pixel-based screen does not need this overscan for its technical operation, but it should crop off this area and scale the remainder to the panel size. So even when your panel is 1280x720 there would still be scaling.
    (in practice there also are displays that ignore this overscan. however, when you are using such a screen you might sometimes see trash at the extreme borders of the screen, as certain content producers only watch the offical area of the screen and leave artifacts in the overscan area)

    Having a screen resolution better than the content resolution allows (requires) the TV to do "upscaling", i.e. inventing extra pixels that were not there in the original material. This is something different from overscan.
    Upscaling can improve the picture, because advanced processing algorithms can extract and process information that is not visible to the eye when you are just displaying pixels 1:1.
    Examples of this are transient improvement and staircase elimination.
     
  12. RockySpieler

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    Thanks for the reply I think I understand a bit more.

    Is overscan on the source HD material, or is it introduced when transmitted, does it affect DVD's for example, or Video games consoles?

    Will SkyHD via DVI have overscan, or only via HD component?

    Does a PC via DVI have overscan?

    If it is 720 lines including overscan does it mean my 32" LCD scaler is stretching 688 lines (720-32) to 768 in the worst case?

    If the overscan varies between channels as suggested by Gordon, how does a LCD TV's scaler know which bit is overscan, and which rows are the actual picture?

    So many questions, so little time ;) !
     

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