Tivo settings and picture quality

Discussion in 'Cable TV & Virgin Media TV' started by ifb-online, Aug 4, 2012.

  1. ifb-online

    ifb-online
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    Just had a Virgin Tivo box installed and am loving the new user interface and facilities and features. But I don't know if it's just me but have been niggled by what I perceive as an issue with the refresh or frame rate compared to the Samsung V+ box (which has been relocated to another room).

    After doing a little research most of the advice I have seen recommends leaving the Tivo on 1080i output settings, which is what mine was on. It's connected to a 1080HD Samsung TV via HDMI, as the V+ box was, but if I recall correctly, the V+ box output 720p.

    So I have changed the Tivo output to 720p and I honestly feel the picture is more solid, with no frame rate flicker any more. Everything definitely looks smoother and more fluid than before.

    My understanding is that there is no 1080 resolution content being broadcast anyway although that may be out of date. But if that's true, what is the point of 1080i over 720p?

    Have I done the right thing?

    Ian
     
  2. Sick Boy

    Sick Boy
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    Just did the same thing on my new Tivo. My TV is only 1080i but my understanding is that 720p is more stable than 1080i, and like you say, there is no 1080p OUTPUT.
     
  3. carl.waring

    carl.waring
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    There is, AFAIK, 1080i output though :) I have my Tivo set to that and have not seen any such problems as you two describe. In fact, this is the first time anyone has mentioned it that I can remember.
     
  4. mike7

    mike7
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    Same here. Might be interesting to know which tivo box they have. Mine's a Samsung, but there is another manufacturer/supplier to VM. (Cisco?)
     
  5. mjbtin

    mjbtin
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    Just changed to a tivo box from Samsung V+ and seeing similar to the op slight picture flicker or maybe a better description a slight wobble in parts of picture that I didnt see with the V+ both outputting 1080i to Samsung plasma havent tried 720p yet:confused:

    Regards Martin
     
  6. dante01

    dante01
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    1080i is the HD standard for the UK and no broadcaster uses 720p.

    If broadcasters were to broadcast in 720p then the situation may differ and it would be superior to 1080i:




    But If using the box to output 720p in the UK then all HD broadcasts would need to be scaled to that resolution and deinterlaced by the box from 1080i. This is theoretically likely to cause deterioration to the resulting image. All PAL interlaced 1080i video flickers at the same frequency, maybe it is just a case of you perceiving it now due to closer scrutiny of the video in relation to your new TiVo?

    The V+ could and can output 1080i and was not limited to 720p as suggested. Progressive video is only advantageous when the video is natively progressive. Conversion up or down in resolution and in relation to interlacing causes degradation.
     
    Last edited: Aug 4, 2012
  7. ifb-online

    ifb-online
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    Thanks for all the feedback - much appreciated.

    I've checked my V+ box and it was set to 720 Wide. I have changed it to 1080 Wide but I have already noticed some loss in fluidity as if the frame rate has dropped, even on SD channels like BBC News channel. This is on a small 21 inch Samsung HD LCD TV in our back room. I'm not seeing any difference in sharpness or resolution.

    I will experiment with the 40 inch TV that is connected to the new Tivo box, but so far I am definitely feeling more comfortable with 720p output.

    I was told by a Virgin engineer a while back that Virgin only transmitted content in 720p while Sky transmitted 1080i. But I suppose some people might think they know more than they really do.

    Ian
     
  8. dante01

    dante01
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    He was categorically incorrect.

    No broadcaster uses 720p in the UK. 1080i is the HDTV standard in the UK. Although the BBC have run trials of 1080p via their Freeview HD service, no broadcaster broadcasts HD content at 720p via either Freeview HD, SKY satellite or Virgin Media cable and all UK HD channels use 1080i.
     
    Last edited: Aug 4, 2012
  9. ifb-online

    ifb-online
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    Maybe it's simply a case of being less comfortable with watching an interlaced display?

    Ian
     
  10. carl.waring

    carl.waring
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    Mine's the Cisco; the original one.

    What a pointless video.

    1. It's out of sync.
    2. It's not even in HD

    (Not blaming you, Dante, except maybe for linking to it in the first place ;))
     
    Last edited: Aug 5, 2012
  11. metalguru

    metalguru
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    Isn't it really whatever you think looks best for you;)
     
  12. dante01

    dante01
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    A bit like your post then?


    The quality of the video giving the explanation is of no importance. The point of the video was in order to explain the differences between 720p and 1080i so you are incorrect with your appraisal of it because it did have a point.
     
    Last edited: Aug 6, 2012
  13. bamber1981

    bamber1981
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    It is always worth looking at the display settings on your TV to see whether you can make any adjustments to improve the picture quality. All CRT TVs used to "overscan" meaning that the picture displayed on the TV was smaller than the picture broadcast, by having the edges cut off. Flat-screen TVs seem to come factory-set to do the same thing, so a broadcast picture is reduced to (say) 1900x1068 pixels and then has to be converted to be displayed on a 1920x1080 pixel screen. That must result in some loss of quality, as well as being wholly illogical.

    I don't know about other manufacturers, but my Sony TVs have a "full pixel" setting which displays the whole 1920x1080 frame as broadcast. To my eyes, it looks a lot better than the factory setting.
     
  14. dante01

    dante01
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    Why would overscan make any difference? The 720p image would be subject to the very same overscan as the 1080i image. The pixel mapping in relation to overscan would have no influence on what is being discussed. What is being discussed it that some people are determining 720p to be superior to a TiVo's 1080i output.

    Newer TVs sill overscan because older content was filmed and edited with overscan in mind and the edges of such content is less well refined. It is of little or no importance with new content, but if using 1:1 pixel mapping with older material then you notice the degradation around the edges of the images. These edges were never intended to be seen by a viewer. Some channels still persit in using the peripheries of a broadcasts image for inclusion of data streams, but this is less the case now that teletext is no longer with us (never really with us in Virgin's case).

    At a normal viewing distance, and using what would be considered an average size TV, there should be no perceivable difference in resolution between a 1080i or 720p broadcast, either with or without overscan, but you are correct in your assumption that pixels will not be remapped if using native 1:1 mapping. It is more important that you use the native mapping in conjunction with DVD and BD content than with TV broadcasts. You'd lose parts of the material around the edges that were intended to be seen if viewing such content with overscan applied.

    I'd suggest any difference being perceived due to the interlacing of the resolutions and not due to the resolutions themselves. Progressive is superior, but no UK broadcaster currently broadcasts HD content using a progessive format (apart from Freeview trials by the BBC).
     
    Last edited: Aug 8, 2012
  15. bamber1981

    bamber1981
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    It's the mathematics which makes overscan just as relevant to 720p. On a full pixel setting, 720 lines from the source are converted at a ratio of 1.5 to 1 for display on a 1080 screen, so every 2 lines from the source become 3 on the screen. Nice and neat. If the TV is overscanning, then the conversion can never be so neat and must affect picture quality.
     
  16. dante01

    dante01
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    Yes, but how is this relevant to the topic? You appear to be posting things that have no relevance. Overscan would still be aplied to a 1080i broadcast if not using 1:1 pixel mapping. Overscan is not exclusive to resolutions below 1080 and is applicable to all content regardless of resolution. Apart from this, it is the 720p output of the TiVo that some are saying is superior so why would using a 1:1 native mapping have any impact if you put what you've posted into practice?

    Again, what is the relevance?


    If just making a general comment then fair enough, yes, use 1:1 pixel mapping when possible, but the difference in PQ will not be drastic and you may experience some edge degradation in relation to older content that was purposely filmed with overscan in mind.
     
    Last edited: Aug 8, 2012
  17. dante01

    dante01
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    Last edited: Aug 8, 2012
  18. dante01

    dante01
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    Back on the topic of 720p vs 1080i

    The issue is further compounded by the fact that in order to get 720p from the native formats as broadcast by Virgin then deinterlacing has to take place within the STB.

    Deinterlacing is the process of converting interlaced video, such as 1080i signals to a non-interlaced form (progessive).

    The deinterlacing would need to be performed by a digital TV anyway in order for it to be able to display the image on its panel. CRT based displays were able to display interlaced video correctly due to their analogue nature. Newer displays are inherently digital in that the display comprises discrete pixels. Consequently the two interlaced fields need to be combined into a single frame (progressive), which leads to various visual defects which the deinterlacing process should try to minimise.

    Taking any natively interlaced video and deinterlacing it is detrimental to the PQ so it is even stranger to hear how some are seeing better PQ if employing the STB to output progressive 720 signals derived from native interlaced broadcasts.

    Whay maybe happening is that the deinterlacing capabilities of the STB are superior to those of the TV? This would explain why an already deinterlaced signal looks superior to a native interlaced signal deinterlaced by the TV?

    Basically, you've got duff and inferior TVs with poor deinterlacing capabilities. :D

    There's no set standard for deinterlacing and the algorithms used vary between video processor manufacturers so you'd expect some degree of varioation between different models and brands of TV.

    I don't think it an issue with the TiVo or the STB and think it more to do with the TVs being used? The TiVo is simply making a better job off deinterlacing the images than your TV is.
     
    Last edited: Aug 8, 2012
  19. bamber1981

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    More accurately, the original question was about an apparent deterioration in picture quality from the TiVo compared to the V+ box. I noticed the same thing when I had TiVo installed and switching between 720p and 1080i settings made no difference, but changing to the full pixel setting on my TV produced a marked improvement.

    Why criticise me, then, for posting something which helped me and may also help the OP? What harm could there be in trying?
     
  20. dante01

    dante01
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    For the sake of accuracy:



    Yes, thank you for your contribution in regards to pixel mapping :) , but pixel mapping has no bearing upon the OP's results in relation to 1080i or 720p. Why would it even have relevance to the topic as you've interpreted it? THe pixel mapping hasn't changed since the OP had a V+ STB???? I don't think Samsung TVs have fascility to invoke native pixel mapping on content flagged for overscan anyway, but I could be wrong about that?
     
    Last edited: Aug 8, 2012
  21. bamber1981

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    Well, eliminating other possible sources of picture degradation can only help the OP's comparison of 1080i and 720p.
     
  22. ifb-online

    ifb-online
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    Hi folks, I didn't realise there would be such a strong debate about this topic!

    Anyway as someone earlier here did point out, in the end it boils down to what you personally prefer. While I accept that on paper 1080i output is recommended, after several days of switching back and forth I prefer what I am seeing with the 720p output setting on both my old V+ box and the new Tivo box. I can't see any difference in resolution and sharpness at normal viewing distances and for me 720p doesn't give me the impression of a slower frame rate when a subject moves fast. It's more fluid and natural.

    The caveats are that both my TVs are relatively inexpensive and a few years old now and I wouldn't argue if anyone proposed that if I was using a newer and more expensive TV with some of the latest image enhancement features then 1080i could be the way to go.

    Anyway - thanks for all the insights! :)

    Ian
     
  23. Boostrail

    Boostrail
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    My opinion for what its worth!

    No modern LCD/PDP shows an interlaced display.

    All show a progressive display.

    If your TV appears better using the Tivo/VM box to de-interlace the incoming broadcast 1080i signal, only then for the box to downscale it to 720p and then for your TV to re-upscale it to 1080p ---- then my observation is that the de-interlacer of your TV must be abyssmal!
     

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