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LCD tvs and Interlacing

Discussion in 'LCD & LED LCD TVs' started by Bluestraw, Apr 22, 2005.

  1. Bluestraw

    Bluestraw
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    I wonder if someone could possibly explain the way that LCD TVs handle interlaced displays properly? I'm guessing they must do, otherwise the pictures would look bad.

    For example, when watching a NTSC DVD via a PC monitor, there are often clear 'interlacing artefacts' (i.e. combing) introduced as the PC is showing a progressive picture made up of 2 non-consistent fields. This can be undone by good inverse telecine, but I was wondering how the TV would handle it?

    I'm sure I must be missing something obvious, otherwise there would be a lot more people shouting about the benefits of 720p versus 1080i especially for LCDs!
     
  2. SeanT

    SeanT
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    720p is a hell of a lot better than 1080i for cheaper LCDs, as the LCD contains a deinterlacer and scaler to produce it's image.
    More expensive LCDs tend to have better built in deint/scaling, which is why I now have a cheap external deinterlacer for my Sonix :smashin:
     
  3. NicolasB

    NicolasB
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    Most LCD TVs have resolutions like 1280x768, so there's relatively little advantage to having a 1920x1080 source image (1080i) rather than a 1280x720 source image (720p). On something like the Sharp LC45GD1E, which is actually 1920x1080, 1080i should look amazing.
     
  4. MikeK

    MikeK
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    Bluestraw

    It depends on the nature of the signal as to how you deinterlace it, and then it depends on the quality of the deinterlacer as to how good the results will be.
    The quality of the deinterlacer will also determine how good it is at deciding which deinterlacing mode to use.

    Combing is the result of wrongly applying film mode deinterlacing (ie assuming that the source signal was originally progressive in nature) to independant field video material (which was never progressive to start with).

    Cheap deinterlacers may not have a film mode at all, in which case every field is deinterlaced in video mode, which means each half resolution field has it's missing lines interpolated (or guessed at) by the deinterlacer. The fact they are cheap in nature, usually means the more advanced methods of doing this are not present (such as per pixel motion adaptive) - without these methods, the resultant picture can look "soft", as it can essentially be missing up to half it's vertical resolution. The more advanced video mode deinterlacing methods can be pretty good, depending on the type of images being deinterlaced.
    Some deinterlacers even with a film mode, can't reliably recreate original progressive images properly, such as a movie (for a variety of reasons), and these can result in a very annoying intermittent slight softening of the picture - caused by the deinterlacer continually switching between film and video mode.

    All in all it's a bit of a minefield - personally I wish we could leave interlacing/deinterlacing behind now, but sadly it seems it's here to stay for the forseeable future at least.
     
  5. Bluestraw

    Bluestraw
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    Mike,

    Thank you - very detailed explanation!

    So am I right in thinking that, say, the 9986 would have a deinterlacer that is pretty good and should be able to cope well with, say, IVTC?
     
  6. MikeK

    MikeK
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    Sorry, couldn't tell you that!

    Even if I'd seen one, you'd really need to form such an opinion either by living with it for a while, or purposely testing it with known difficult material to see if it slips up!
     
  7. Bluestraw

    Bluestraw
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    Fair point! Maybe a 9986 owner could help - how well does the set cope with deinterlacing film-based interlaced material?
     
  8. ianh64

    ianh64
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    Just a guess, but probably just adequate due to comments that people make on how good a progressive feed is. If it was top notch, the difference between progressive component and interlaced RGB would not be so noticable.
     
  9. Bluestraw

    Bluestraw
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    Has anyone tried feeding 1080i content (via a HTPC), and if so what's the quality like from that?
     
  10. Rob1698

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    With 1080i there is lineflicker (visible when you display a static image like a PC desktop), so apparently it does not attempt to de-interlace a 1080i picture but just dumps the frames on the screen and leaves the de-interlacing to your eyes. Like a CRT TV does.
     
  11. LcdGuru

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    Sounds like you're running in 'film mode'. Try selecting 'video mode' or 'deinterlace'. Can't see the difference between 1080i and 720p on my Sharp GA4 since I only have 768 rows. But I'm sure 1080i would look better if I had the res - particularly when viewing deinterlaced movie material - since then you would get the full 1920 x 1080 pixel res at the film frame rate of 25fps.
     

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