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720p or 1080i?

Discussion in 'TVs' started by 00fjackson, Mar 20, 2005.

  1. 00fjackson

    00fjackson
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    To me this seems obvious. The higher resolution offered by 1080i will be a far more obvious improvement to the consumer than 720p. Many people do not even know what progressive scan is! Digital TV is currenty broadcast at about 575x1000 so 720p would not be that big a step forward. (In the US it has been a popular format because they had a much lower resolution before.) Plus, 100Hz scanning on interlaced DVD material is often seen as being better than the 50Hz progressive signal so would 720p be better than 1080i scanned 100Hz? With film source detection if we had 1080i we could get 1080p for movies! How good would that be! :thumbsup:
     
  2. mjcairney

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    I have a Panasonic S97 DVD player hooked up to my Pioneer PDP325FDE Plasma via HDMI and can get the DVD player to upgrade the output to either 720p or 1080i and, believe me, I cannot see any quality difference netween the two - no doubt, some of the experts would be able to tell me I'm wrong for whatever reason but, for the average punter like me, I think there is no real difference between the two.

    Don't know if this helps you - it's just my view.

    Cheers,

    Martin.
     
  3. Starburst

    Starburst
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    Perhaps I am stating the obvious but wouldn't the Plasma scale both resolutions to match it's native res and turn the interlaced signal into a progressive one anyway thus making any comparison invalid?
     
  4. Rimmer

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    The EBU argues that 720p is the best format for European consumers because it does not need to be de-interlaced, and because it thinks that sport - a major driver for HDTV take-up - looks better in 720p due to progressive scanning.

    However, this argument loses some ground when you listen to Americans who have access to both 720p and 1080i sources. They say that 1080i looks better for all types of programming, including sport, even when viewing on a display with 720p or 768p native resolution. Clearly there will be even more of a difference when comparing 720p to 1080i on a 1080p display.
     
  5. mjcairney

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    You may well be right - but you would need someone better qualified than me to give you the correct answer.

    Cheers,

    Martin.
     
  6. Gordon @ Convergent AV

    Gordon @ Convergent AV
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    The resolution of current broadcast in this country is 576interlaced lines....that's 288 lines per 50th of a second. If it's digital then it's 720x576i. 1280x720 Progressive is VASTLY superior in resolution.

    An upscaled DVD cannot be compared to a native HD signal of the same resolution. Video tapes and DVD's are both PAL, 576i....can you tell the difference in quality between the two? I hope so. It's the difference in what is encoded in the space you have that matters. There is much more info going to be in a 720P signal on HD. It's not a small difference.

    The ideal would be that all new material would be recorded progressively. Until we get 1080P capable recording and playback devices then I guess it'll be 720P recording. Film can be tele-cined to 1080i and good video processors can then do film detection (just like they do now with SD material) to re-create the 1080P frame. This would allow superior down or upscaling to the panels natve resolution as approriate. Yes starburst you are correct that a plasma display will have to either be fed its native resolution or rescale any signals to fit its pixel matrix

    While it might be hard to tell difference between 720P and 1080i on 480p and 768p panels you need to remember that soon there aren't going to be 480P panels and we'll be talking about 768P panels as being low resolution. The amount of pixels in a display is going to keep growing and we're going to want to have the best quality images being fed to these ultra-high resolution devices. I'm more concerned about how material is captured than played out right now....remember we want to capture progressively....then output in highest number possible....

    Gordon

    Just my thoughts
     
  7. 00fjackson

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    "There is much more info going to be in a 720P signal on HD. It's not a small difference."

    This is true, but I for one would prefer a more efficient use of that increased info as higher resolution- 1080i. Interlacing halves the data needed with little loss of picture quality. Interlaced video at a much higher resolution will be a more noticable improvement than full frame video at a barely increased resolution. This made please videophiles who like the idea of having a progressive image but it is of less benefit to the average consumer.

    "If it's digital then it's 720x576i"

    DTV is broadcast at true 16:9 576i, i.e. 576x1021 interlaced.
     
  8. Gordon @ Convergent AV

    Gordon @ Convergent AV
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  9. StooMonster

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    Because you obviously don't know what you are talking about! ;) "Digital TV is currenty broadcast at about 575x1000" err... no it isn't, and "DTV is broadcast at true 16:9 576i, i.e. 576x1021 interlaced." again this is completely inaccurate.

    European digital broadcast 625i/50 ("digital PAL")
    Resolution: 720x576 pixels
    Raster: interlaced
    Refresh: 50Hz
    Render: 10,368,000 pixels per second (720 x (576/2) x 50)
    * Anamorphic does not change resoluton.

    European digital broadcast 720p/50
    Resolution: 1280x720 pixels
    Raster: progressive
    Refresh: 50Hz
    Render: 46,080,000 pixels per second (1280 x 720 x 50)
    Ratio: 720p has 4.44:1 more picture information than digital PAL.

    European digital broadcast 1080i/50
    Resolution: 1920x1080 pixels
    Raster: interlaced
    Refresh: 50Hz
    Render: 51,840,000 pixels per second (1920 x (1080/2) x 50)
    Ratio: 1080i has 5:1 more picture information than digital PAL.

    One of the most common reasons for this is MPEG2 broadcasts are in 24-bit (8-bits per channel) colour, whereas many 728p displays are 30-bit (10-bits per channel) colour and unless some internal scaling is involved the picture remains 24-bit.

    Whereas providing a 1920x540@50Hz to a 1280x768@50Hz (or 1366x768@50Hz) requires more scaling and thus conversion from 24 to 30-bit, than 1280x720@50Hz to a 1280x768@50Hz (or 1366x768@50Hz) display.

    StooMonster
     
  10. StooMonster

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    And the ratio of 720p versus 1080i?

    46,080,000 pixels per second : 51,840,000 pixels per second

    1: 1.125 in favour of 1080i, i.e. 12.5% percent more picture information than 720p.

    However it's not as simple as more pixels per second equals better. 1080i is great for movies because with 2:2 pulldown the render is 1920x1080 pixels at 25fps; but less good for sport because the interlacing leads to combing of the 540 pixel vertical resolution, whereas 720p displays 50 entire progressive frames per seond.

    StooMonster
     
  11. 00fjackson

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    I agree but when would the 1080p 50 signal ever be used? (other than editing)
     
  12. Stephen Neal

    Stephen Neal
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    Don't mean to be picky - but can we stop using "PAL" when we mean digital component. I know that it is often used as short hand (DVD labelling is the biggest culprit) - but PAL implies analogue Phase Alternate Line subcarrier chroma encoding and all the composite/s-video nastiness that goes with it.

    Digital TV at 576/50i doesn't use any PAL subcarrier techniques - so to call it PAL is a bit disingenuous...
     
  13. Stephen Neal

    Stephen Neal
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    Come to that - 1080/50p is not actually that easy to produce "real" programmes in. Sure you can scan film at 1080/50p and record it on digital data formats, but real broadcast production kit, using HD-SDI interconnects, doesn't have the bandwith to carry uncompressed 1080/50p around a broadcast centre, unless you use two interconnects (which is impractical at the moment)

    HD-SDI maxes out at around 1.2Gbps - which is enough to carry 1080/50i, 1080/25p,720/50p etc. but not 1080/50p.

    All this talk of producing in 1080/50p ignores that it is currently not possible with the current broadcast technology available.
     
  14. stripe

    stripe
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    The BBC are planning on outputting 1080p late next year.
     
  15. Stephen Neal

    Stephen Neal
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    1. 576/50i DTV is not broadcast at 1000x576 - it is broadcast at either 544x576 or 720/704x576 - using non-square pixels (in both 4:3 and 16:9)
    2. You cannot compare the vertical resolutions of interlaced and progressive formats directly. Interlaced material is filtered vertically to reduce the amounts of interline twitter that would otherwise be present on interlaced display of vertical high frequency information.

    720x576/60i video contains almost no detail above the 400 line mark (still an improvement over the equivalent 288 line progressive format)

    However 720p has a full vertical resolution - as it is progressive - so 400 vs 720 is still pretty good.

    If you take a 1080/50i signal it doesn't have a full 1080 vertical resolution, it comes out at about 800ish, so 720 vs 800 is less massive a difference. Where 1080i usually wins is horizontal resolution - as 1920 vs 1280 vs 720 is a clear difference between all three standards. However 1440x1080 is also a common standard - and 1440 vs 1280 is also less marked, and both massively better than 720 or 544 (ITV1 is 544x576 on satellite for example...)

    As for 100Hz scanning of DVD material... Depends on whether the material is film (i.e. progressive) sourced or interlaced (i.e. video camera) sourced. 100Hz sets usually do a better job with material with no intra-frame motion (i.e. progressive/frame based stuff) - so film material (whether broadcast or from DVD) often looks better on 100Hz sets than interlaced video stuff (where the set has to interpolate fields to fields, rather than just repeat frames)

    Th argument for 100Hz interlaced over 60Hz progressive (i.e. why Europe has stayed interlaced for 100Hz and the US has gone progressive at 60Hz) - is more to do with 50Hz large area flicker being more noticable than 60Hz, and the US having the 3:2 pulldown issue (which progressive helps with)
     
  16. hornydragon

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  17. StooMonster

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    On which platform?

    StooMonster
     
  18. Gordon @ Convergent AV

    Gordon @ Convergent AV
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    I don't actually think I specified capturing at 1080p/50.....I said capture Progressively. I'd have thought for non sport you'd capture at 1080P/25....still it's out of our hands...

    Gordon
     
  19. StooMonster

    StooMonster
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    Guilty, but it's a common use short-hand isn't it? As you rightly point out even Region 2 DVDs say PAL on their cases, and Region 1s say NTSC too!

    I can almost guarantee that in the future global HDTV world, 60Hz stuff will still be called NTSC and 50Hz stuff will still be called PAL.

    StooMonster
     
  20. StooMonster

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    Stephen, you said that 576i video contains almost no detail above the 400 line mark, and 1080i contains no data above 800 lines -- to reduce the amounts of interline twitter in interlaced outputs by vertical filtering -- and I can see how that works.

    Your point is interesting, but I have a question:

    Is this vertical filtering is limited to video based material, and not film based materials? i.e. film being progressive 24/25fps.

    StooMonster
     
  21. Dutch

    Dutch
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    Aha! So that's why ITV always looks so sh!te on Sky Digital! :D Interesting stuff as always, Stephen. Thanks.

    Steve
     
  22. Stephen Neal

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    Films are usually vertically filtered in the telecine (film scanning) process.

    It IS possible to carry a 1080/25p video signal as a 1080/50i signal - and as long as you don't pass it through a DVE or similar device that employs vertical processing - then the 1080/25p signal won't suffer vertical resolution reduction.

    (Home and Away use a similar technique. They shoot 1080/25p, downconvert to 576/25p - edit in 576/50i (with the 25p full vertical resolution) - and then frame double the 576/25p to 576/50p for transmission - with more vertical resolution than a 576/50i signal)
     
  23. Stephen Neal

    Stephen Neal
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    However NTSC is not a description purely of the chroma standard - the NTSC standard also defines the 525/60 scanning parameters - so kind of is OK. PAL purely defines the chroma encoding standard - and doesn't include the line standard - so it is a bit of a case of "apples" and "oranges"...

    I too, am guilty of saying "PAL" or "NTSC" when I mean 625/50 or 625/50...
     
  24. Stephen Neal

    Stephen Neal
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    That - and the hideous levels of pre-filtering to soften the signal so that it doesn't block at the ludicrously high levels of compression employed. Too many services squeezed into too few transponders, with similar content so that statmuxing doesn't help...
     
  25. 00fjackson

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    Hey I totally agree. I always thought 50p was a waste for most subjects (i.e.non sport). The human eye only needs about 25fps for most things, they only came up with 50Hz because it was nesaserry to stop flicker on CRTs, but before the age of computers they couldn't double a progressive image in the studio or transmit 50p (too much bandwidth). It was also something to do with the 50Hz power supply.

    Of course the 1080p 25 image would have to be transmitted as interlaced 50 (for most TVs) and be reconstructed by film mode detection on high end models... :D
     
  26. Stephen Neal

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    Hmm - I really like the fluid nature of 50i/50p material - especially on entertainment and music shows. I personally find "the film look" - at 24 or 25fps - a bit juddery and jerky.

    Given that it isn't currently really feasible to run a mixed format "real world" network - I suspect 720/50p or 1080/50i are still the only likely broadcast formats.

    1080/25p makes sense for pre-recorded material (HD-DVD/BluRay etc.) though.
     
  27. NicolasB

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    Try saying that after six pints of beer....
    :beer: :beer: :beer: :beer: :beer: :beer:
     
  28. 00fjackson

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    I agree that for fast moving video, such as the music videos you stated, and sport it makes sense to use 1080 50/i but for the majority of drama etc. 50Hz is unnessasery and I would prefer a progressive 25Hz picture.

    I did say that it would be too late now to incorperate 1080 25/p into the HDTV broadcast/display standard (HD-Ready stickers are already being put on displays that cannot accept or display 1080 50/p or 25/p). However they can just send it as 1080 50/i and compatible TVs/decoders can deinterlace it and double the frame and it would still be compatible with all HDTVs.

    Don't know if you have seen my other thread discussing whether films will be stored as 1080 25/p or 50/i. Unless in the player spec they have to be able to interlace the progressive signal it will be stored as 50/i for compatibility with all HDTVs. Film mode detection will be able to make it progressive though.
     
  29. StooMonster

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    Don't see why not, regular DVD players have to be able to output interlace signal from progressive content, and add 3:2 pulldown for 60Hz material too.

    Annoyingly in all DVD players the MPEG2 chipsets output interlaced, even if content is progressive, and progressive-scan players then use deinterlacing chips sets to deinterlace the content before outputting it.

    Let's hope that 1080 formats keep progressive where applicable (i.e. in film based content) and allow it's output straight from the disc as 1080p.

    StooMonster
     
  30. 00fjackson

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    Didn't know that, so why don't we get DVDs ever with 25/p content? And why wasn't it compulsory for all DVD players to output a progressive signal (from progressive content)? Unless somthing changes e.g. progressive content doesn't automatically get interlaced anyway, we won't see 1080 25/p stored on HD-DVDs.
     

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