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Frame Rates And Judder

Discussion in 'Plasma TVs' started by Oblomov, Dec 16, 2004.

  1. Oblomov

    Oblomov
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    As a novice, could somebody explain the correlation between frame rate and judder. I have been following the various threads about the Panasonic HDMi scandal and the FRC tests that Gordon did with the Pioneer and I am a little confused.

    If a plasma, such as the MXE1, is capable of a 50hz refresh rate why does it FRC all such signals to 100 hz. Is it purely to reduce judder and if so, why is it the opposite effect to a CRT where the 100 hz models have a lot more judder on fast motion? Also, why does FRC from 50 or 60 to 75hz induce so much more judder?

    With regard to PAL 50hz signals is it better to use premium video processing equipment on a HCPC to FRC and output a 60hz signal to the DVI input on the plasma where no FRC would take place, or would less judder result from outputting a 50hz, unmodified signal from the PC and allow the plasma to FRC to 100 hz?

    A big thank you to anyone who takes the time to educate me on these matters.
     
  2. Oblomov

    Oblomov
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    Please, please, one of you technical guys, help me out here. It's giving me a headache........
     
  3. grahamtriggs

    grahamtriggs
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    Forget about the 100hz issue - it's all about removing the interlace / flicker that you see on an old 50hz CRT set. But plasmas are a bit different, as is the deinterlacing, and it's all just more of a headache than you need to worry about. Plasmas (generally) are progressive display devices, require a de-interlaced signal, and the de-interlacers used generally do a pretty good job - you don't really need to know much more.

    For 50/60/75hz conversion, it's quite hard to avoid judder. The frame rate is the number of images that you are displayed per second - 50 images on PAL, 60 images on NTSC. Whilst you see fluid motion thanks to the speed at which they pass, the images are 'snapshots' of time - all at equally spaced intervals.

    If the 50hz images were shown at 60hz - such that one image/frame from the 50hz signal is only used as one frame at 60hz - then the motion would be perfectly smooth, but 20% too quick. Obviously, that isn't much use, so you need to generate additional frames for the 60hz signal. The simplest way is to take 20% of the frames, and display them twice. So you get a sequence like:

    1-2-3-4-5-5-6-7-8-9-10-10-11-12-13-14-15-15-etc.

    When frames 5, 10, 15, 20, 25, etc. are being displayed for twice as long as the other frames - yet were initially meant to be shown at equal intervals - hence the judder.

    It is better not to do FRC between rates that are not whole multiples of each other. ie. 50->100hz is OK, 50->60hz should be avoided.
     
  4. Oblomov

    Oblomov
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    Graham,

    Thanks a lot for that, I appreciate it. Much more effective than Nurofen.

    I think it is bad news. It means that I cannot get a decent TV picture via a HCPC and DVI on a Panasonic. I suppose that I could use VGA but with all the other complications regarding the lack of Panasonic/Sky HD compatibility it looks like I am in for a long wait before I can sensibly purchase a plasma. The MXE1 is no good because there is no HDMi and the DVI input is not HDCP complaint, and the 435 FRCs everything to 75hz or thereabouts. Besides, I don't like Pioneer blacks, or rather the lack of them.

    Thanks again for your help.

    A frustrated Oblomov
     
  5. astirling

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    Isn't this only in the purecinema - advanced mode?
     

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