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Is a refresh rate higher than 100 Hz still noticeable for the human eye?

Tv manufacturers are still taking these refresh rates to new heights, but is there really a noticeable difference between a refresh rate of 100 Hz and 200 Hz, Let alone 400 Hz?

Are there any applications when a refresh rate should be as high as possible?

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6 Answers 6

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No, there is no practical limit that we know of yet to what would be best, there is however a practical limit to what we can capture and display.

In tests with airforce pilots, subjects were able to identify a plane from being shown a frame for only 1/220th of a second.1 They eye is able to pull information out of extremely short periods of time, but unfortunately our eyes are also very good at concealing lack of information (which is actually why video works in the first place), so it is extremely hard (possibly impossible) to determine the actual point at which we wouldn't benefit from more information.

Either way, it is almost certainly upward of the current 1/600 mark and often theorized to be beyond the 1/1000 mark. The problem comes not from how much information we present, but that we don't have enough information to present.

Generally videos are normally not played back faster than 48 frames per second at the fastest and video games normally don't go beyond actually displaying 120 or so. This is due to a lack of being able to store sufficient data and stream it in an efficient enough manner to display in an affordable manner.

Instead, to make things appear more smoothly, the TV interpolates additional frames to fill the gaps. It looks at where one frame is and where the next frame will be and generates frames in-between to smooth it out. The problem is, not all motion is perfectly smooth and interpolation isn't a perfect process. The result is that unnatural artifacts appear in the video which we can detect and end up being unsettling and eventually start causing more harm to the persistence of vision than the extra frames help.

This is why, when you move in to higher refresh rates it is sometimes better to use a lower setting without the interpolation. Video is about simulating reality for your eyes. In reality, there is no refresh rate, any time your eyes chose to process, they get whatever is there at the time. Thus, higher and higher frame rates will more closely emulate reality as long as the information is actually based around reality rather than something invented by electronics on the fly.

Eventually, we may exceed the "refresh rate" of the eye, but as of yet, we don't definitively know what that is and are pretty certain we haven't hit it yet.

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I'm trying to find another reference for the frame interpolation issues. I've read good things on it in the past, but am having trouble finding references atm. If anyone knows a good one, please feel free to post it and I'll add it to the answer (or just add it as a reference yourself.) –  AJ Henderson Jul 10 at 14:13
    
If the airforce pilot could recognize a frame for 1/220th of a second, i'm assuming that the frames before and after were drastically different from that 1 frame. If tv's with a higher refresh rate than the frame rate of the source create 'in-between' frames calculated on the previous and next frame, those differences would be much smaller, no? So to distinguish those would be even harder than the pilot test, if my assumption is correct. (reference would indeed be nice) –  jan Jul 10 at 14:36
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@jan - yes, the point is that we know that the eye can sample an image well enough to identify it in under that time. Adding frames to video playback is beneficial in better emulating reality until we can have it fast enough that a new frame is displayed every time the eye can capture a frame. Until that point, increasing frame rate still makes it closer to reality. I think with the air force test, they were flashing the image on blackness. The point was to figure out the minimum amount of time for eyes to sample with enough detail to identify. –  AJ Henderson Jul 10 at 15:01

The reason why modern TVs have been pushing higher framerates is not because people can see much beyond 30-60Hz, but because if the source framerate and the display framerate doesn't match exactly, then the display has to either drop frames, or add frames. This mismatch is visible, particularly during panning scenes, for instance.

It used to be that made-for-TV was captured at 30 interlaced frames per second. Movies are shown at 24 frames per second. When you want to show a 24 frame per second video on a 30 frame per second TV, what do you do? Well, they performed what's called a 3:2 pulldown, which converted the 24 frames per second into a reasonably acceptable 30 interlaced frames per second. This isn't perfect, though - there are still artifacts and visible differences between watching a film at 24 frames per second, and watching it on a TV with 3:2 pulldown.

So TV manufacturers starting increasing the refresh rate so that each frame could be shown onscreen the same amount of time as every other frame, leading to the ideal viewing given the capture frame rate.

The minimum frame rate this is possible for both TV (30 and 60 frames per second) and movies (24 frames per second) is 120Hz. This display will show each 30fps frame four times, each 60fps frame twice, and each 24fps frame 5 times.

Newer displays support 240Hz frame rate. This is necessary for a seamless 3D experience when using active shutter type glasses. It will allow the display to show 60fps, 120fps, and 48fps 3D images without any timing problems.

There's little point to advertising anything lower than 120Hz, because what you're essentially saying is that you can't display either 30Hz or 24Hz material exactly as it was captured - there's no single framerate below 120Hz that is good for both. However, some display devices meant for serious gamers do advertise lower rates, such as 60Hz, because as gamers they simply want the highest content framerate, and aren't concerned about showing lower framerates exactly.

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The logical next step is 600Hz, to handle 50fps PAL content as well. –  Mark Jul 11 at 0:27
    
A very good answer! –  Michael Jul 15 at 20:07

A similar question (except about 60Hz) was raised on Skeptics Stack Exchange.

The answers there discuss how the human eyes works differently to screens and cameras, and doesn't have a frame rate, and that being able to distinguish flicker and being to perceive that we distinguish it may be separate concepts.

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Immediately created an account for skeptics.stackexchange.com :) –  jan Jul 11 at 6:57

As per my knowledge television sets are clocked to 60 hz refresh rate. As it goes on increasing like 120 Hz the pictures will look more smoother. but lets say for 200 performance will enhance a bit. But for 600 Hz or so our eyes will not feel much difference than 200 Hz. So as per my opinion its not necessary to have refresh rate as high as possible in other hand it should be moderate.

check following link they have tried to explain it more clearly.: http://www.pcmag.com/article2/0,2817,2379206,00.asp

hope this will help you

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This article was very helpful. Thanks! –  jan Jul 10 at 12:56
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You are welcome :) –  dking Jul 10 at 13:22
    
That article isn't particularly clear, the main problem with higher refresh rates in those contexts is that the frames are being invented, not that they are occurring. –  AJ Henderson Jul 10 at 13:54
    
@AJ Henderson ohk. Do you know any other particular article focusing on more technical stuff about the refresh rates? if yes then do share here. –  dking Jul 10 at 14:05
    
@dking - see my answer for more details. –  AJ Henderson Jul 10 at 14:10

As a gamer, I notice a huge difference between a regular 60hz monitor and a 120/144hz one. The smoothness of fast movements is impressive!

BenQ L2420TE

Asus VG248QE

EDIT - Televisions have input lag, so it doesn't feel as smooth as these monitors.

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It is worth noting that input lag doesn't impact video playback as long as it is consistent lag. It does impact gaming or computer use though. –  AJ Henderson Jul 11 at 15:34

Most topics have been very well discussed already, I just want to add a case were even more than 400hz is very much needed. As previously stated by Oddthinking, the eye and human brain don't work like a TV or Camera.

This especially counts for cases where our other senses are involved. E.g. video games, high-frame rates of 60-120hz are very well perceived by most people in this case. Because our "motoric senses" are connected to what happens on the screens and we expect a certain action to occur on the screen within a given time frame.

This gets driven to the extreme with Virtual Reality which has been an increasingly hot topic over the past 2 years thanks to the Oculus Rift. When it comes to your head movement, even the slightest "lag" in our vision is perceived which puts VR infront of a big problem. Suddenly much more than 1000FPS become something very viable, though this isn't really possible in games at the moment without huge losses in graphical fidelity. So they implement tricks like inserting black frames in between actual frames to trick out brain that it sees fluid motion.

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