Response Time

G

Guest

Guest
I've been looking over previous posts, and I'm curious about flat panel response times. I do do vision research, so delays are rarely acceptable, unless the delay is constant. CRTs are annoying since you have to sync with the refresh, but the delay is consistant. My questions regarding the response time are:
1. Does the image appear gradually over this 20ms or is it 'instant' on but with a delay?
2. is the delay consistant? does 20ms delay mean 20ms every time? Is there some place I can track down the Variance?
3. Is the delay caused by the monitor itself, or in the communication (is it improved by going true DVI)
3. Does drawing happen every 20ms on a cycle (T+0, T+20, T+40) or does it draw 20ms after a program tells it to. If its a cycle, will a draw command at T+15 appear at the T+20 'cycle', and can you detect the start of a cycle.
If its a delay, what would happen if the priogram tried to draw at T+15 and T+20, would they appear at T+35 and T+40? Would only one be likely to appear?
I'm thinking its the latter, since the refresh frequency of these monitors rarely seem to jive with the response times.
A lot of questions, I know. :) I'd settle for a good article/book/web site on the topic if no-one has the time to answer.
Joe
 

flamethrower205

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Jun 26, 2001
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Response time is composed of rise and fall time. What rise time means is how long it takes the crystal to change states so that it allows light to pass through (in other words the crystal "lights"). Fall is how long it takes it to change states so that light isn't allowed to pass through (in other words the crystal "darkens"). The total reponse time is only when the crystal "lights" and then "darkens". This blockage and allowing of light to pass through are what makes the colors. So what would happen is, say your LCD has rise time of 5ms and fall of 15ms, and you are moving your mouse across the screen. It will take 5ms for the mouse to "move" one pixel, and 15ms for the back end of it to disappear. You can notice this if you have TV-Out, and move the mouse across the screen. You will notice a blurry trail behind it. That is what happens, except on an LCD w/ good response time to a lesser extent.

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G

Guest

Guest
That sounds better than I had hoped. I usually need a small onset for static images as apposed to moving images. Do you know if this rise time is consistant? across pixels and between draws? Do maufacturers specify how their Response times break down?
 

flamethrower205

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When you start an LCD, it needs time to warm up; some LCD's take as much as 15,mins before they acheive their spec response time. In addition, if you kepp and LCD at a low temperature area (10 degrees farenheit or less), it's response time increases. Assuming those requirements are met, response time can only be better- sometimes a pixel may only need to swith from say bright green to white. In that case, it will "rise" faster.

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GoSharks

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Feb 9, 2001
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Switching from bright green to white will not increase the pixel response time. A pixel on an LCD monitor is made up of three individual sub-pixels, one red, one green and one blue. If the green sub pixel is on (Bright green) the blue and red sub pixels are (off). They will take the typical pixel response (rise) time to turn on to create white.

Jim Witkowski
Chief Hardware Engineer
Cornerstone / Monitorsdirect.com

Jim at http://www.monitorsdirect.com
 

flamethrower205

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Jun 26, 2001
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However, in most cases it isn't so unless you have colors switching to darker/lighter shades. In certain cases though, it won't apply since to get dark green, red and blue are also used, hence to go to bright green, red and blu must shut off.

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