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LCD refresh rates and ambiguity of measurement

Discussion in 'LCD & LED LCD TVs' started by ianh64, Oct 31, 2004.

  1. ianh64

    ianh64
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    I use to believe that, so long as a screen could support 16ms response rate for NTSC material and 20ms for PAL material, that faster refresh rates would make no difference.

    I stand corrected.

    Having read an article in Widescreen review, it looks like we are all being blinded with senseless numbers, much like we are blinded with contrast ratios.

    What is the refresh rate that the marketing people provide? 12ms, <14ms, 16ms, 25ms etc etc

    Well, it depends on how they measure it.

    My LCD display, a Loewe Xelos 32 SL, is rated at <14ms. The only time that I see motion blur is on some, fast moving horizonally scrolling credits, and I have seen the same with CRT's. This led me to believe that they were caused by digital blur rather than LCD response issues. However, reading the article in Widescreen Review, Nov04, now makes me believe that they could infact be LCD motion artifacts, even though the response time of the screen far exceeds the 20ms that would be required to produce optimal refresh.

    Being an American magazine, so its 60Hz NTSC signals with the 'test' screen also having a response time of 25ms, I would expect motion artifacts to be visible since the screen is not capable of refreshing at the 16.7ms required to support a NTSC signal. However, using fast still photography, mation artifacts could be seen as old as 67ms and 83ms (the timing range is due to the uncertainty of the point on the frame when shutter of the camera was activated). So basically, a screen with a 25ms quoted response rate can have a response rate much slower.

    How can this be?

    Well, like contrast ratios, there is some ambiguity of that is actually being measured. Normally, response times are quoted as measuring black to peak transitions, or vice versa. However, black to grey, or grey to white transitions take much longer, since the electrical forces moving the liquid crystal are much weaker. I think what is meant by grey here is not the physical colour, but a non peak transition within one of crystals governing an individual R, B or B colour. Some designs can speed up grey transitions by 'overdriving' them, but this tends to lead to flicker.

    So, 12ms, <14ms, 16ms, 25ms don't believe what you read. The only thing certain is that the 25ms will exhibit motion blur, but the faster ones may still, under some circumstances.

    -Ian
     
  2. Digitised

    Digitised
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    agreed.

    my 9986 has an amazing pitcure, but i have that eye...that eye that complains about every fault.

    The 9986 has a 12ms responce, in the world of tft monitors that 12ms would be regarded as the screens personal best, rather than a geniune average, or slowest responce.

    Since no companies state what is actually indacative by the measurement in ms... then we can only assume that it is the same as the tft monitors.
    Hence my tvs fastest result at moving colours is 12ms, which means the rest of the time it could easily be 25ms or slower.

    As i stated at the start of my post, i have found my tvs weakness.
    When i play games on the tv, i can see how changing the camera angles manually, noticably makes the onscreen colours run into each other darkening them.
    Its no big deal really, it is still perfectly playable, but i can see it is there.
    And that is really the only fault i can find with this amazing tvs picture.

    God knows how slower lcds play games on :S
     

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