1. Join Now

    AVForums.com uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

What is an "on/off" response time?

Discussion in 'LCD & LED LCD TVs' started by JackFlash, Mar 9, 2005.

  1. JackFlash

    JackFlash
    Guest

    Products Owned:
    0
    Products Wanted:
    0
    Ratings:
    +0
    I've noticed that most LCD TV manufacturers measure a "gray to gray" response time (whatever that is). However I've come across one manufacturer who've measured there's as an "on/off" response time rather than "gray-to-gray". Does anyone know the difference?
     
  2. ianh64

    ianh64
    Active Member

    Joined:
    Aug 7, 2004
    Messages:
    2,233
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    51
    Location:
    SW London/Surrey borders
    Ratings:
    +63
    A 'grey' to 'grey' transition is potentially the slowest transition that a LCD display needs to do - the difference in voltage is often not enough to get the lazy little pixels to move responsively. The black to white transition require must mre power, the the lazy pixels are kicked into action so the transition is much quicker.

    There are some ways around the problem, one of which is to briefly over drive the panel but it can introduce flicker. This is probably what the Sharp quick shot is doing and Philips are touting as the next best thing for their panel.

    Unfortunately at present, panel response times are difficult to compare since different manufacturers use different methods of measuring response times.
     
  3. jon2099

    jon2099
    Active Member

    Joined:
    Jun 4, 2003
    Messages:
    183
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    18
    Location:
    Hampshire
    Ratings:
    +4
    AFAIK the current accepted definition of 'reponse time' is the time it takes for a pixel to change from black to white and back to black again. This is faster than black to grey and grey to grey times so it gives the smallest number and gives the impression of a faster panel.

    Note that the pixel rise time (Tr) isn't always the same as the fall time (Tf), that's only true for IPS and MVA/PVA panels. The cheaper TN+Film panels have a larger Tr than Tf. MVA/PVA panels are also known to have the largest Tr for black-to-grey transitions (and hence exhibit smearing in dark videos), sometimes 40ms or more even for a panel with a 16ms black-to-white-black response time. IPS panels are the opposite, with TN+Film somewhere in the middle. That's why it's possible for a 'slower' 20ms IPS panel to look less smeary than a 'faster' 16ms TN+Film panel as the black-to-grey transition is faster on the former.

    From what I've seen, quoting a grey-to-grey response time seems to be a recent phenomenon, possibly to convince people that the panel is fast on that type of transition as well.
     
  4. LcdGuru

    LcdGuru
    Guest

    Products Owned:
    0
    Products Wanted:
    0
    Ratings:
    +0
    There's no way my Sharp GA4 could get from black to white and back to black in 16ms.

    The Sharp quickshoot system works by overdriving transitions for one field period - so you get to the new greylevel faster. By definition this must mean the un-overdriven response takes longer than 16ms - otherwise you'd overshoot all the transitions.

    Also, you can't overdrive black to white (since there's no headroom in the drive voltage) so you're struck with the uncorrected response time.

    One point though. Quickshoot doesn't introduce 'flicker' as mentioned above. In the worst case, if the signal is noisy, quickshoot will tend to enhance the noise (kind of the opposite of the DNR control). Also, it may tend to bring out the interlace line flicker on regular interlaced video - but this is actually a good thing since it will increase the vertical resolution.
     
  5. jon2099

    jon2099
    Active Member

    Joined:
    Jun 4, 2003
    Messages:
    183
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    18
    Location:
    Hampshire
    Ratings:
    +4
    I'm basing my comments mostly on this article:

    http://www.xbitlabs.com/articles/other/display/lcd-guide.html

    (You may want to click on 'print article' on the left column as it is 27 pages long)

    In the section on pixel response times the black-to-white-to-black definition of response times is mentioned in the 3rd paragraph.

    Look at the graphs for the pixel rise times of the various types of panels. In nearly all cases, the black-to-white transition is fastest. The one case where it isn't (for the panels they've tested) the rise time to a grey level of 200 (out of 255) was about 1-2ms faster than black-to-white.
     

Share This Page

Loading...