Is 720 res good enough for HD?

Discussion in 'Satellite TV, Sky TV & FreeSat' started by nevtra, Dec 24, 2006.

  1. nevtra

    nevtra
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    Hi
    I own a Sagem HD telly and have just ordered HD from sky.

    My question is this, is there a marked difference between the HD picture on a 1080 res screen and a 720 res screen. I'd be greatful if anyone could let me know what they think of the images produced on a 720, ideally a Sagem.
     
  2. jet_andy

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    Not a lot - don't forget it's 720p as oppossed to 1080i.

    I have my Sky HD output fixed at 720p (into a Panny 42") as I prefer it, but there's not a lot of difference to 1080i.
     
  3. remlap

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    I have a Sagem DLP 50" Model set the SKY Box to Auto and I think it looks fantastic.
     
  4. sanderton

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    A 1080 panel is definitely preferable, but 720 gives a great hi-def picture, massively better than SD.

    A lot will depend on how far away you view the screen - beyond a certain point there is no discernable differerence between 720 and 1080 displays. Where that point is depens on the size of the screen and the individual concerned.
     
  5. Mighty Gaz

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    the number isnt the important part here. the letter is. the progresive scan is far superior to the interlaced scan. far far superior.
     
  6. Bachstrad

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    Eh? I might be taking in 1080i, but I'm watching in 1080p! ;) :cool:

    ATB

    Max
     
  7. Mighty Gaz

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    unlikely. there are very few tv's that can actually deinterlace a 1080i source and provide a real 1080p output. its not just as simple as setting it to 1080p you know....
     
  8. Bachstrad

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    All LCD panels display the final image progressively.

    ATB

    Max
     
  9. Mighty Gaz

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    lol no. they dont. you also need to bear in mind that even if you have one that that does, its probable that it is not doing a full deinterlace. many which do this use cheap workarounds and you do not get any real quality increase in what it claims is a 1080p picture. even if it does have a good deinterlacer built in, the signals from skyhd are compressed, and even the best deinterlacers are not gonna improve it any. if you want true 1080p, you either need 1080p source, or an uncompressed interlaced source.

    3:2 pulldown reversal uses a lot of processing power to do it on the fly, and to do it well. and more than a few sets generate enough artifacting that they just shouldnt have bothered. bluray and hddvd can be deinterlaced fine in this manner, but compressed TV feeds are another matter entirely. many moan about picture quality as is, you try and deinterlace these poor quality images and at best you'll see no change. though it could well get worse.
     
  10. starfire

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    Yes, they do. All new LCD, Plasma and projector displays are inherently progressive display devices, NOT interlaced.
     
  11. mjw1999

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    1080i = 540p as far as the video processor in some displays is concerned.
    In other words your losing out on res.
     
  12. 7hil

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    Common sense dictates that 1080i cannot be turned into a True 1080p picture. You are merely upconverting to 1080p.

    It's like saying that a 720p signal from an upconverting DVD player is True 720p HD. It isnt.
     
  13. Bachstrad

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    Final image is a progressive one ... That's what I said, nothing more, nothing less. 1080i in and 1080p is viewed by me on my 1920 x 1080 panel.

    ATB

    Max
     
  14. Mighty Gaz

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    there is some very poor knowledge of the display technology being displayed here. any device that can display progressively can display an interlaced picture and will do so when presented with it as a source. to claim anything else is just wrong. when i have time i will post a full explanation of why.
     
  15. Bachstrad

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    All modern panels display their final images progressively. I have never claimed anything else. I look forward to when you have the time to explain why this isn't so. I'm always ready to be re-educated.

    As far as my 'poor knowledge goes', a 1080i input into my panel is de-interlaced and then displayed progressively, so I'm viewing a 1080p image. This is totally different to upscaling, where the missing information is 'added' to the image. A panel not capable of displaying a full 1080 image will downscale the source, but will also still be displaying a final progressive image.

    My panel will also accept a 720p source and display that upscaled at 1080p too. There are no broadcast 1080p signals at this time and it's very unlikely that there will be, due to bandwidth issues. Sky HD is broadcast at 1080i which is the native resolution of my panel, i.e. 1920 x 1080 after de-interlacing.

    Interestingly, although my Toshiba panel displays it's final image as 1080p, it cannot accept and display a 1080p input. It takes a 1080i input, de-interlaces it and displays a 1080 progressive image (1080p). No upscaling is taking place at all


    ATB

    Max
     
  16. Ian_S

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    I think people are getting confused over film and video sources. Other than the amount of compression and the codec used, there is little difference to receiving a film in 1080i from HD-DVD, Blu-ray or SkyHD. Each half frame sent can (if correctly de-interlaced) be pieced back together to make a full progressive frame. This is quite straightforward and most half decent HD ready sets ought to be able to do this now reasonably well.

    Video is a completely different ball game however as each half frame sent in 1080i mode is part of a different frame unlike films. Therefore, you only ever have half the frame of each image. This doesn't matter so much when the image is static as usually the camera records alternate scan lines for each field and on a static image if simply pieced together they do actually form a detailed full image. However as soon as stuff moves, processing has to kick in to try and get rid of jaggies etc, make up what's missing based on what might have moved where, and the perceived resolution drops. This is why when the camera pans on HD football coverage people complain that it gets blurry and often wrongly blame LCD response times. It's actually IMO the poor processing you get in most TV's. Performing full motion adaptive per pixel deinterlacing processing on an HD feed requires a lot of power and is what VP's are built for.

    This is also why HD demo discs have lots of slow moving or still footage as it doesn't show up display deficiencies like fast moving football does. Football for most people would probably have looked better if Sky had stuck with 720p for sports as then people's de-interlacing processing would not have mattered. But Sky chose 1080i...
     
  17. Ian_S

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    The best thing to do is use your own eyes... Try both on the same footage and see which you think gives the better picture.

    What it boils down to is which is better at de-interlacing TV pictures, your Sagem or the SkyHD box. If it's the Sky HD box 720p will look better. If it's your TV, 1080i will look better. Don't worry if you think 720p looks better, either way on a non 1080 set, you throw info away. Whether it's your screen or the SkyHD box that ultimately does that doesn't matter. What does is which one you think looks better.
     
  18. andykn

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    One of the technical team on the Freeview HD trial posted this:

    "Many of the drama and natural history programmes are in fact 1080p. They are 1080p25 (at 25Hz similar to films at 24Hz) carried within 1080i which we call "Progressive Segmented Frame" or PSF. The 1080p term is being misued a lot at the moment. There is currently no production or delivery of programmes possible in 1080p50. High Definition DVD formats will be carrying some films using 1080p24 but not 50Hz of 60Hz content which is needed for television programmes such as sport and music."

    What I don't know is how many 1080 screens can decode PSF properly.
     
  19. Pecker

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    http://www.avsforum.com/avs-vb/showthread.php?t=767929

    Blind test. 1080 lined projector v 720.

    35 A/V experts with the highest possible standards.

    Only 1 out of 35 thought 1080 was noticeably better on a 103" screen at less than 1.5 screen widths viewing distance.

    Steve W
     
  20. uno

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    What is the best setting to have your Sky HD box set on 720p or 1080i ?
     
  21. Smurkenstein

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    Thats really interesting. But its really good kit. My question..consider kit that doesnt deinterlace so well. With 1080, the "comb" effect or "jaggies" caused by a poor/incomplete deinterlace will be 25% more compressed in both X and Y axis...therefore less easily noticeable...?

    My other thought. I have a 40 inch screen...to really appreciate nice HD (watching Galapagos, as I type), to REALLY appreciate the detail...with my eyes (20/20) I have to sit 1 1/2 to 2 meters from the panel. Normal viewing 3-6 metres HD is clearly better over SD...but I dont get the extreme detail. At 3-6 metres I am pretty sure there will be no discernable different in 720 -vs- 1080.
     
  22. choddo2006

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    1080i. Unless somehow you've managed to get your hands on a TV that can do a worse deinterlacing job than the SkyHD box.
     
  23. choddo2006

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    I look forward to it. Since it's patent nonsense. All LCDs and nearly all plasmas can ONLY display a progressive image. The other stuff you said about having to deinterlace etc is precisely because of this.
     
  24. andykn

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    I agree. I think that Sky transmit all their HD in 1080i, so if you have the box set to output 1080i it will not process the signal and leave it to your screen to sort out.

    If you put it to 720p then the Sky box converts from 1080i to 720p and then your screen may have to convert again to 768.

    Although you could try both and stick with whatever looks best.
     
  25. nevtra

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    Things have drifted a little from my original question but it's very interesting.

    thanks
     
  26. Mighty Gaz

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    ok, heres the thing. people seem to be confusiong the fact that these tv's are designed to display a progressive scan pic with them only being able to display a progressive scan pic. which is just not true. tv's will deinterlace an image, the HD box WILL NOT! any conversion is done by the TV. not the box. where you all got this idea is anyones guess.

    only the most expensive TV's can properly deinterlace a 1080i source to a 1080p output with no issues, and even then from a compressed 1080i source you are never gonna get any better a final image than the 1080i source. if you have an uncompressed source, like a bluray or HD-DVD then yes, some screens will produce a better 1080p result than a 1080i source, but these are only the very top of the range sets.
     
  27. RenaultSport

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    If you set the set top box output to 720p does it not have to deinterlace and downscale the 1080i image?
     
  28. Mighty Gaz

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    yes. sorry. poor wording on may part. it will downscale and deinterlace from 1080i to 720p. however this is far easier than deinterlacing from 1080i to 1080p. the final output has way less information contained in it. yet still is not as good as a native 720p image due to this conversion process.

    if a HD box was capable of deinterlacing a 1080i source to 1080p, then it would have a setting to output that.
     
  29. Billy Hunt

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    I'll second that. :thumbsup:
     
  30. Bachstrad

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    Who said anything about the HD box? I still stand by the fact that all LCD's show a progressive image finally.

    I take a 1080i feed from my Sky HD box, my panel de-interlaces it and displays a 1080p image, you haven't said anything to convince me otherwise.

    ATB

    Max
     

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