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Refresh rate vs reaction time vs frames/sec

Last response: in Graphics & Displays
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December 1, 2010 7:49:37 AM

Dear All

I'm having trouble understanding something. I look at a LCD Display (NEC MultiSync 2190UXp) that has a reaction time of 8ms (grey to grey). As soon as I connect it to my computer, I try to adjust the refresh rate to more than 60Hz, but I can't.
So, the reaction time is 8ms, but the refresh rate can't be higher than 60Hz.

And one other thing..... I read, that with a graphic card and some game, you would get up to 120 frames/sec (I don't remember the details).

So, how are those dots connected?! How can I get 120 frames/sec in a video game and have only a refresh rate of 60Hz? With a reaction time of 8ms, I would asume that the maximum refresh rate would be at 120Hz.

Is there an article you could recommend?

Thanks, I appreciate all help
Cheers,
Marco

Best solution

December 1, 2010 8:25:13 AM

I may be mistaken, but it seems like you are mixing two unrelated things together

Refresh rate is how often a monitor draws, or the amount of time the display 'refreshes' in a second

If it's 60Hz, then the monitor refreshes 60 times in a second.

Reaction time is how long the monitor takes to change a pixel's color, or the amount of time the display takes to 'react' to the new data it is receiving. This comes after Refresh rate.

If it's 8ms, it will take 8ms for the monitor to change from one color to another (in the case, grey to grey)

Reaction time is not a polling rate. It's not a constant thing, like Refresh rate. It only happens when it has to change colors.

To put this in prospective, let's play a video game.

If you have a good system, and you can render the game at around 120 frames per second, your monitor will have to throw away data every other second, because the refresh rate is only 60hz. This cases screen tearing, and is quite nasty.

However, if you have a slow response time (in my opinion, 8ms is pretty slow) you will experience a blurring or ghosting effect. This is when you can see a trail of the previous information along with the new information.

To explain that further, consider this. At 60hz, 60fps+ with triple buffering V-Sync, and a 2ms reaction time.. you're looking at the most ideal situation for a gamer. The motion is fluid and the picture is frame for frame displayed perfectly. If you had a higher reaction time, like 10, the motion would still be fluid.. but because of the slow reaction time, the previous information would stay on screen for 8ms longer, or four times as long as previously.

I hope this helps you understand :) 

Also, according to your math.. 8ms should have a maximum refresh rate of 125hz, not 120 :p 

FYI dipankar2007ind, while I sorta agree with you, human eyes do not work in the same terms as electronic computer monitors.
Sure, you could say that 120hz is really fast and is impossible to distinguish an individual frame between that and 60hz, but that doesn't mean our eyes see at 60hz, or any of that nonsense. If that was the case, then anything faster than 60fps would cause 'screen tearing' for our eyes, right? :p  Not to pick on you or anything, as you did only say that we can't tell the difference.. but just thought I'd clarify for the record
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December 1, 2010 8:42:16 AM

Quote:
Ghosting effect is overhyped.Most people will never notice it.MS is way too little time for our eyes to pick up.


Nowadays, yeah I tend to agree with you.

But man, back when LCD was fresh off the market.. I had horrible ghosting. I had to stick with my CRT for games.
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December 1, 2010 8:48:51 AM

Quote:
What are you trying to say?Do you want to say that we can distinguish the difference between 60 or 120fls?Screen tearing happens when a monitor displays more frames than its refresh rate.There are 60,75 and 120hz monitors.For a 75 hz monitor any gpu pumping more than 75 fls will cause tearing.Thats why we have vsync which caps the framerate according to the refresh rate.


Well, yes and no. Physically, I'm saying that no man could possible see a significant difference between 60 and 120hz

But, that doesn't mean we still can't see it. Our eyes, to my knowledge, do not have something similar to a refresh rate. If we did, then I would assume that there would be some sort of "tearing effect" equivalent when there was something going faster than what our eyes could see.

Just saying, I know you didn't say anything of the sort, you were merely saying that the consumer hype of 120hz isn't really needed (unless for 3D or perfect 24fps conversion) and you really can't tell a difference..
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December 1, 2010 10:52:10 AM

Daveid said:
I may be mistaken, but it seems like you are mixing two unrelated things together

Refresh rate is how often a monitor draws, or the amount of time the display 'refreshes' in a second

If it's 60Hz, then the monitor refreshes 60 times in a second.

Reaction time is how long the monitor takes to change a pixel's color, or the amount of time the display takes to 'react' to the new data it is receiving. This comes after Refresh rate.

If it's 8ms, it will take 8ms for the monitor to change from one color to another (in the case, grey to grey)

Reaction time is not a polling rate. It's not a constant thing, like Refresh rate. It only happens when it has to change colors.

To put this in prospective, let's play a video game.

If you have a good system, and you can render the game at around 120 frames per second, your monitor will have to throw away data every other second, because the refresh rate is only 60hz. This cases screen tearing, and is quite nasty.

However, if you have a slow response time (in my opinion, 8ms is pretty slow) you will experience a blurring or ghosting effect. This is when you can see a trail of the previous information along with the new information.

To explain that further, consider this. At 60hz, 60fps+ with triple buffering V-Sync, and a 2ms reaction time.. you're looking at the most ideal situation for a gamer. The motion is fluid and the picture is frame for frame displayed perfectly. If you had a higher reaction time, like 10, the motion would still be fluid.. but because of the slow reaction time, the previous information would stay on screen for 8ms longer, or four times as long as previously.

I hope this helps you understand :) 

Also, according to your math.. 8ms should have a maximum refresh rate of 125hz, not 120 :p 

FYI dipankar2007ind, while I sorta agree with you, human eyes do not work in the same terms as electronic computer monitors.
Sure, you could say that 120hz is really fast and is impossible to distinguish an individual frame between that and 60hz, but that doesn't mean our eyes see at 60hz, or any of that nonsense. If that was the case, then anything faster than 60fps would cause 'screen tearing' for our eyes, right? :p  Not to pick on you or anything, as you did only say that we can't tell the difference.. but just thought I'd clarify for the record


Thank you very much for your explanations, that helped very much. It seems that I mixed up a few things there :-)!
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a b U Graphics card
December 1, 2010 11:33:19 AM

Complicated, I know. I'm repeating a bit, but in a nutshell:

Refresh Rate: The maximum number of times a screen is capable of dsiplaying a single frame, per second. (IE: A 75Hz screen could display a maximum of 75 frames per second).

Response Time: The time period where individual pixels on a LCD screen take to change state, generally using a best-case Grey-to-Grey algorithm. (As such, actual real-world results are typically much worse). For instance, for a 16ms moniter:
.016ms * 60 = .96
60 / .96 = 62.5

In the above case, the moniter, using a best case GTG Response Time, is capable of displaying a maximum of 62.5 frames without ghosting. For a 8ms Response Time, the best case increases to 125 frames, and for 4ms, 250. (Note the maximum number of best case, ghosting free frame limit doubles as the Response Time is halved).

As a general rule, assume you need twice the necessary Response Time to be generally ghosting free. I'm not sure on the specifics, but depending on the color transition individual pixels need to undergo, actual results may vary significantly from the listed Reponse Time. Take the number listed as ONLY a best possible case.

It should also be noted, that for LCD crystals, there is NO Reponse Time if the pixel does not undergo a color change; the pixel in question simply retains its existing state.

Frames Per Second: The number of times a unique image is ready to be drawn to an output device (or more simply, how many unique frames are completed by the GPU per second). If this number is less then the moniters Refresh Rate, a few frames will be repeated. (IE: For a 30FPS output on a 60Hz moniter, every frame would be repeated twice). If the number is higher then the moniters Refresh Rate, the most recently completed image will be sent to the moniter, which CAN lead to some graphical tearing.

Vsync is an algorithm that ensures that no extra frames are drawn from a GPU. IE, if your moniter has a 60Hz Refresh Rate, no more then 60 frames will be created by the GPU, eliminating the tearing problem that occurs with high FPS numbers. It should be noted, in some shoddy implementations, using Vsync will effectivly half the maximum possible Frames Per Second rate (there is no reason why this should occur, but several games suffer from this).

As a final note, CRT's typically don't list a Response Time; the actual time it takes to draw an individual pixel is somewhere around .00001ms (give or take a few zeros), hence why CRT's NEVER suffer from ghosting.
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December 1, 2010 1:28:24 PM

Quote:
Well that's what i said.Difference between 60 and 120 is hard to notice.Then again there must be someone with special alien eyes evolved just to see the difference.And you will need a super powerful gpu to pump out 120 flps constantly with all setting tuned up.Or play a really old game.



The difference between 60hz and 120hz is like a slap in the face. It's noticeable from the desktop to ingame. Having a monitor that has a 120hz input makes a ridiculously MASSIVE difference.

Anyone who tells you other wise has never used a 120hz screen (not a TV, theres a difference), or is plain blind.
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a b U Graphics card
December 1, 2010 3:53:05 PM

Try a 240Hz CRT and tell me you cant see the difference. Trust me, its there, and its very, very, notable.
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December 13, 2010 5:29:44 AM

Best answer selected by mmz27.
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a c 273 U Graphics card
December 13, 2010 11:15:26 AM

This topic has been closed by Mousemonkey
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