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LCD Response Times

Discussion in 'LCD & LED LCD TVs' started by NNOMANN, Nov 4, 2004.

  1. NNOMANN

    NNOMANN
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    Hello!
    Does anyone have any opinions on the significance of pixel response times? On these forums they are mentioned a great deal, but it also seems apparent that manufacturers do not use a standard benchmark test to arrive at their figures.

    I ask because I am currently caught in a dilemma. I cannot decide which is the better buy - the Sharp LC-26GA3E or the Toshiba 26WL46. The Sharp is lighter (about 50%!), has detatchable speakers, picture in picture and DVI input. The Toshiba is £100 cheaper and has a quoted response time of 8ms as opposed to the Sharp's 16ms.

    Are the Sharp's benefits worth giving up for what appears to be double the response time?

    Cheers,
    NOMAN
     
  2. daveb975

    daveb975
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    The lower the response time, the less smearing that you should see when displaying fast moving images.

    In practice, they are not that reliable as different manufacturers use different measures.

    I have the 26WL46 and have not noticed any image smearing, even on console games.

    Probably worth checking out the Sharp to see if you can notice any difference, especially if those extra features are important to you.
     
  3. alfie786

    alfie786
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    I have the tosh 32wl48 no smearing or blurring etc. I hear everyone in the gaming and tft for pc's world say that 16ms or lower is required for no ghosting blurry images. That says that 16ms should be fine! Above 16ms and at 25ms u will notice small amounts, and over25ms def see ghosting.

    Hope that helps as gamers require 16ms or lower tft screens. I would too look at the sharp as they excellent contrast ratios and of course take off their speakers.
     
  4. ianh64

    ianh64
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    Im going to open this one up for debate!

    Before anyone speed reads, ignores my comments but looks at the attachments and sees ghosting on one of them, I would expect to see this.

    These are digital photos taken from my Loewe Xelos SL 32 HD diaplay whilst playing the Extron Electronics sequence from opening titles from the PAL version of Digital Video Essentials (DVE). Input resolution is 720p@50 Hz via HDMI->DVI. The response time of the panel is <14ms.

    On my display, the only time I witness ghosting is on some fast moving titles, which includes this particular one. Having posted an earlier topic on response times, I decided to investigate further. I must admit, if my maths is correct and my assumptions are valid, I cannot explain why I see ghosting on this particular sequence. I am glad to be proven wrong in my assumptions so please give your own views.

    The first attachment is taken at 1/100th of a second exposure. No ghosting is seen. By my maths, 1/100th second is 10ms, so it represents part of a single field of PAL video (20ms). My conclusion from this is that the panel response time is not causing glosting, infact I would recon that the response time is <10ms. If it was not, and there was ghosting from a previous frame, you would see it in the photo.

    The second attachment is taken at 1/15th second exposure. By my maths, about 66ms, or between 2 and 3 fields, or just over a frame worth of video - I cannot be sure at what point during a frame that the shutter was fired. As one would expect, ghosting can be seen since you are seeing more than one frame of video.

    I am at a loss why I can see 'ghosting' on this sequence, unless physically my eyes cannot respond as quick as the frame rate.

    -Ian
     

    Attached Files:

  5. jimg

    jimg
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    ianh64

    I am still waiting for my copy of DVE to arrive, nobody seems to have one!
    When it does arrive I shall use it to calibrate my Sharp Aquos LC-37GA4E.
    Tell me, did you find it made a big difference to the final Picture Quality?
    I am quite pleased with the results so far, by just trial and plenty of error!
    If it does, then I am looking forward to a brilliant picture :smashin:
     
  6. jgrg

    jgrg
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    Hi Ian,

    I'm puzzled too! You're calculations are correct.

    Have you eliminated the possibility that the ghosting is actually on the source material? You could check this by pausing and stepping through frame by frame.

    I have the same DVD, so I'll check to see if I can see the same effect on my interlaced CRT TV!

    Do you see the same problems on the motion test sequences in DVE?

    James
     
  7. hwharton

    hwharton
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    Yo Guys

    AFAIK the camera will only pick up the refresh rate on the screen, 60 hz for NTSC and 50 hz for PAL.

    What the responce rate measures is how fast a pixel can change colour, this is usually measured in terms of Black - White - Black, or Grey - White - Grey. A 25ms screen couldn't change colour fast enough to keep up with fast moving action resulting in the smearing.

    I think Grey White Grey is the better bench mark as it is harder for a pixel to zero in on grey that to just turn the pixel off on off.

    Hope this helps and if i'm wrong i'm sure someone will let me know.

    H
     
  8. ianh64

    ianh64
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    The biggest problem that I find with DVE, other than the dire navigation, is its bias towards CRT type displays. Some of the calibration techniques for that are not valid for digital or non CRT type displays. Whilst alternative methods are mentioned, its only lip service with techno mumbo jumbo being blurted out rather than the careful instructions for CRT relevant methods. The reference material however is invaluable.

    I have only played the disc a handful of times as it does not make for great Sunday evening viewing, however I do have a great tip ~
    Use the index sheet to find the relevant sections and use direct title selection to go straight to the section. For example, most of the video calibration patterns are in Title 12. Calibration instructions are title 7. You probably want to thorougherly understand the troubleshooting pages as these give alternatives relevant to LCD type displays. Don't bother using the first calibration technique for contrast. In the end, I used one of the other patterns.

    As for the quality of calibration. My impression is that, short of entring the service menu of the display, it will give an improvement, but nothing that a great deal of experimentation with contrast, brightness and colour could offer. Infact, my 'by eye' calibration was only slightly out from that determined by using the disc. But it does give a feeling of correctness that you are never quite sure about when doing it by eye.

    When all my kit is together and interconnects final, I may consider splashing out £250 to get the display properly calibrated. But if I feel that im 90% of the way there, I probably won't bother.

    -Ian
     
  9. jimg

    jimg
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    Ian,
    Thanks for that I agree at the end of the day it is about what looks right for you.

    Jim
     
  10. jgrg

    jgrg
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    Hi Ian,

    I don't see any ghosting. Maybe your DVD player is not correctly de-interlacing this short sequence?

    The "Extron Electronics" text that scrolls in horizontally does serve as an excellent example of interlaced display combing artifacts on motion!

    I agree with you about the awful navigation in DVE. I had to learn how to navigate straight to a particular title and chapter with my DVD player. As far as I can see, you can only get to some of the test patterns with direct navigation. But I don't know of any alternatives.

    James
     
  11. ianh64

    ianh64
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    My DVD player is fine, it looked OK on my old CRT and its a pretty decent player anyhow. Im stumped. If the refresh rate was >16ms I would understand or if the 100th/s photo showed a ghost image, but how things stand, I can't fathom it. The photo evidence certainly backs up a quoted refresh rate of <14ms but im still seeing the ghosting on fast scrolling text. The other thing is that with the DVI input, as far as I am aware, especially in 'original' (ie dot-for-dot mode) format, very little, if any, additional processing is being performed by the display. Also, some TV programs with extremely fast horizontal cause it - infact, it is where I first spotted the 'problem'.

    I did a few shots of a PS2 game, F1 2002 with the map of the circuit spinning around and that motion is smooth and backed up again but photo evidence.

    -Ian
     
  12. NNOMANN

    NNOMANN
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    hwharton: it's interesting what you say about the different ways of measuring response times (Black - White - Black, or Grey - White - Grey). Have you any idea which manufacturers use which method?

    Is it possible that the Toshiba, quoted at 8ms, and the Sharp, quoted at 16ms, are actually closer than the figures would suggest?

    NOMAN
     
  13. jgrg

    jgrg
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    Hi Ian,

    I've been thinking more about this. The text that moves vertically into the Ektron Electronics logo moves quite fast, such that in the new frame it is in "free space" - ie: doesn't overlap the position of the text in the previous frame. The screen has 1/25th of a second to draw each frame. There must be a point in time, during the 16ms transition, where the new frame is partially drawn, and the old frame is not yet completely faded. So each film frame will spend 16ms fading in to view, and 24ms being displayed. I would therefore predict that if you try enough photos as 1/100s you will catch it in the act of ghosting. You might also want to try a higher shutter speed.

    When you are looking at computer graphics, the PC is sending a completely fresh frame every 1/60th of a second. The chances are greater, therefore, that a moving object will partially overlap its previous position on the screen, and disguise any ghosting. Motion will also look smoother, especially close to the screen.

    James
     
  14. hwharton

    hwharton
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    Sorry NOMAN i don't know who uses which benchmark, sometimes if you look at the technical spec of the tvs off the official website (usually in PDF format) then it tells you the one they've used but not always.

    H
     
  15. ianh64

    ianh64
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    James

    I went back and realised that I suffered brain fade - took PAL at NTSC calculations. I have edited my original post, and also updated based upon my understanding for timings for frame and field rates. I don't know what I was thinking first time around. Anyhow, everything makes a bit more sense and corresponds to the photo's better.

    I think you are right, at some point, with enough shots at faster then field rate exposure, I would imagine that I would see ghosting of the previous field on some of the shots. Based upon a 14ms refresh rate, I would expect at some point to see the first 7ms worth of the frame as a ghost image (since refresh rate is measured as a on-off-on [or vice versa] transition). In this case, being a partial transition, ie not full on to full off, it may even be slower depending on how Loewe have measured their response rate.

    I would be interested to see how other LCD screens respond with the 'Extron Electronics' test screen.

    -Ian
     

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