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Ask Slashdot: Why Don't Graphics Cards For VR Use Real-Time Motion Compensation?
dryriver writes: Graphics cards manufacturers like Nvidia and AMD have gone to great pains recently to point out that in order to experience virtual reality with a VR headset properly, you need a GPU capable of pushing at least a steady 90 FPS per eye, or a total of at least 180 FPS for both eyes, and at high resolutions to boot. This of course requires the purchase of the latest, greatest high-end GPUs made by these manufacturers, alongside the money you are already plonking down for your new VR headset, and a good, fast gaming-class PC. This raises an interesting question: virtually every LCD/LED TV manufactured in the last 5 or 6 years has a 'Real-Time Motion Compensation' feature built in. This is the not-so-new-at-all technique of taking, say, a football match broadcast live at 30 FPS or Hz, and algorithmically generating extra in-between frames in real time, thus giving you a hyper-smooth 200-400 FPS/Hz image on the TV set with no visible stutter or strobing whatsoever. This technology is not new. It is cheap enough to include in virtually every TV set at every price level (thus the hardware that performs the real-time motion compensating cannot cost more than a few dollars total). And the technique should, in theory, work just fine with the output of a GPU trying to drive a VR headset. Now suppose you have an entry level or mid-range GPU capable of pushing only 40-60 FPS in a VR application (or a measly 20-30 FPS per eye, making for a truly terrible VR experience). You could, in theory, add some cheap motion compensation circuitry to that GPU and get 100-200 FPS or more per eye. Heck, you might even be able to program a few GPU cores to run the motion compensation as a real-time GPU shader as the rest of the GPU is rendering a game or VR experience.
So my question: Why don't GPUs for VR use real-time motion compensation techniques to increase the FPS pushed into the VR headset? Would this not make far more financial sense for the average VR user than having to buy a monstrously powerful GPU to experience VR at all?
So my question: Why don't GPUs for VR use real-time motion compensation techniques to increase the FPS pushed into the VR headset? Would this not make far more financial sense for the average VR user than having to buy a monstrously powerful GPU to experience VR at all?
I find the effect sickening on a flat TV. I'd gather it's worse in goggles.
You can't change the angle at which the scene is rendered by interpolating between frames.
It's not the raw framerate. It's that the scene your viewing has to match where you're looking that quickly or you get motion sick.
You can rely on a 24 FPS steady signal when outputting to a television and interpolating the incoming frames is safe and predictable. When your FPS is dynamic due to varying quantities of draw calls, the interpolation becomes far less predictable, and will result in artifacting.
Also, VR headsets render the whole screen, so its not a magical '180 FPS' number when multiplied by two eyes. Two render channels each rendering at 90 FPS doesn't mean the GPU is taxed at '180 FPS', the GPU load depends on pixel density, and high end VR headsets are extremely pixel dense.
Feels like the submitter is a child of some sort...
Look up "asynchronous time-warp". /thread
Broadcast TV with this stuff on has considerable latency. It looks at the next frame and then interpolates its way there, might work reasonably well to watch a recorded show but would be pretty horrible for real time motion from VR. Next question?
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That's the other side of multi-sided coin they are fighting. Motion compensation has to have two frames already processed, then add one in between so it is 2 frames behind. Adding 1 frame is already too much of an issue. Same reason you don't use motion compensation for gaming on TVs.
It's not throughput that matters, it's latency. If there's more than a tiny delay between turning your head and your eyes seeing the viewport move, then many people get bad motion sickness.
In order to add a frame between 1 and 2, you have to have received both frame 1 and frame 2. People are already getting sick because what they see and do don't match, you're going to make it worse by making what they see lag further behind what little the headset picks up.
If I have been able to see further than others, it is because I bought a pair of binoculars.
You would need to draw the next frame before you could interpolate. You may as well blast the next frame instead of waiting to draw one in between. Latency reduces immediacy, which induces motion sickness.
The FPS requirements on VR are less about the number of frames rendered and more about the latency of computing the frame, so that the position that your head was in when the frame started rendering is as close as possible to the position it is in after rendering completed. However, if rendering a frame only takes 10 ms, then there is no reason not to render 100 FPS. On the other hand, the pipeline techniques will tend to result in subsequent frames having started rendering while the previous frame is still in progress, which means that 90 FPS doesn't strictly guarantee a latency of 11 ms for the frame.
Creating extra frames causes latency in the video feed. That would be worse than low frame rate.
The televisions are interpolating between two frames. The issue with the graphics is that you need a new frame reflecting the more recent position of your head. Since that data isn't available until you render the scene from the updated camera position, you would have to use stale data, which is out of sync with how you moved your head, and is more likely to make you sick.
You could render a lower resolution image and just pixel double it, or just have a simpler scene if you are concerned about the GPU cost.
Some of the more modern cards also include optimizations to be less accurate on the outer pixels, which can make things more efficient. This is because unlike a monitor, where you look at all parts of the screen, the head mounted displays generally have whatever you are looking at in the middle, and the outer pixels are for your peripheral vision. Of course, you'll have to wait a generation before those are in the entry level cards.
Another optimization is that since the scene contents don't change between the eyes, you should be able to draw from both camera positions (one for each eye) without clearing the card's information about the scene, but again, this is something that won't be on entry level cards for a bit.
High frame rate is important for motion data, but it's also (and perhaps primarily) about latency. It is *much* more jarring in my Rift to experience latency -- akin to rapid sea-sickness -- than to have a lower frame rate.
Getting more motion information would be great but we can't sacrifice latency for it, and those TVs tend to have a very noticeable amount of latency. Not that this is an unsolvable problem -- I just haven't seen it yet.
As people have been saying, motion compensation introduces unacceptable lag. There is however a similar feature that does work with VR, called Asynchronous Timewarp which slightly warps the image to match the most recently sampled head position to compensate for motion between render and display time.
https://developer.oculus.com/blog/asynchronous-timewarp-on-oculus-rift/
Slashdot used to have interesting topics and wise comments. Now it's just wack-a-mole.
Aren't they already doing these things?
The biggest reason is latency. People start getting nauseous when they turn their head in a VR headset and their view doesn't change quickly to match the head movement. Motion Compensation on TVs relies on having at least two frames (or 22ms worth of frames at 90fps if this were a current-gen VR headset) already at the TV in order to do the calculations for a frame in between, and in practice they could be buffering 2-3 seconds worth of frames for their calculations and you'd never notice that your TV is displaying your channel 2-3 seconds behind everyone else because it's not interactive.
Unfortunately even 22ms of desynchronization between our heads and our eyes is uncomfortable for most people.
I imagine that at a high enough refresh-rate (180hz?), you could get away with the added delay (11ms at 180hz, 6ms at 360hz), but at that point the image would already be very smooth so you wouldn't be gaining anything of value.
I'm more concerned about when fove ate rendering will become standard...that will reduce card spec requirements significantly.
It doesn't help that the technique is also *very* prone to artifacts, and those artifacts would differ per eye, making them even more noticeable in 3D.
VR is Virtual reality - everything you see is rendered.
You don't particularly need a super high frame rate, and overall system latency is the real killer (latency is the overall time it takes for a render operation to occur and finish displaying the image). So real time motion compensation is not really necessary.
AR is Augmented reality - virtual objects are overlayed on real world data.
Here latency is is even more crucial, as without super-low latency, objects appear to jitter and swim around chasing your view (since the virtual object and the real life objects are moving differenetly). Again, frame rate is not sure crucial.
All sorts of corrections are done to minimize the latency, including using motion sensors and dedicated hardware. Microsoft's Hololens actually does an amazing job at this, and their engineers deserve major kudos for making it possible to anchor objects so well.
50% more input lag, coming soon!
you need a GPU capable of pushing at least a steady 90 FPS per eye, or a total of at least 180 FPS for both eyes
Um, what? That's entirely wrong. You need a steady 90 fps, that's it. There's no doubling because of eyes, this isn't 3D TVs where you need to alternate frames. The only other concern is that the resolution is higher than 1080p.
It works in a TV broadcast because it's a stream. It will work in a 3d streaming video to a headset but that's without head tracking.
It can't work for interactive head tracking. It's a thing called latency and it's the reason people get headaches from VR. Your brain does it's own head tracking and when what you see doesn't match you get vertigo and or a headache.
You also get vertigo from confusing your brain by spending too much time in zero G. A ride in an elevator can make you lose your cookies. That's because it remembers both what it expects with gravity and without. You feel motion but you don't see it and your brain is drawing two different opposing conjectures.
Actually, motion compensation requires both the current frame and one or more future frames to be able to compute intermediate frames. With a media player where the full video already exists it is simple enough to access "future" frames. With a TV showing video inbound from a broadcaster, cable company or media device, you can delay the output by 1/30th or 1/24th of a second, delay sound similarly, and no one is the wiser. P>
But in video gaming, delaying the video by 1/30 or 1/24 or even 1/20 of a second has serious effects on game play. You really don't want a gaming device that delays the video just so that it can insert extra frames, you need to see the most recent frame as soon as you can.
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They already have this for VR. It's called Asynchronous Time Warp. If a frame isn't delivered in time then the previous frame is rendered with the new head position and warped around. It's not ideal as for me even at 90fps on the consumer rift I can tell when timewarp is occurring for a dropped frame.
As others have said, its not real time. The frames are delayed before being displayed and any delay in VR causes sickness in VR. So as you turn your head, there is latency added for motion compensation before it is displayed.
Though not in the way you are asking.
First what the TV is doing is doing an intelligent interpolation of two frames to create something that is *usaully* a decent approximation of what the frames missed. Not in animation, it frequently does a bad job.
In 3D gaming, the closest analog would be motion blur (actually it's the exact opposite). 30 FPS is very low compared to what the eye can make out, but we generally don't notice it because exposure time on the captured frame is long enough to do a bit of blurring. 3d engines can imitate this so the sudden 'stutter' is less noticable.
What VR does is render a larger scene. Between the actual rendering engine updating the world, the users head movement is used to move around the most recently available scene. Valve does not do this, Oculus does (called time warp) at one point they were supporting both orientation and positioning (which was quite awesome, you could render at ~40fps and be none the wiser), but have since stopped doing positional time warp, but still does the rotational, which can smooth over gaps,but not nearly as seamlessly. It was intended as a late-stage correction to mitigate the mal effects of unavoidable latency, but it is able to mitigate lost frames as well. Translational movement will undo it pretty quickly.
I never did hear why Oculus stopped doing positional, it was quite awesome.
The Oculus Rift already does something to a similar effect, asynchronous time warp:
https://developer.oculus.com/blog/asynchronous-timewarp-examined/
Basically, for missed frames, the software compensates by distorting the image based on the difference between your head's current rotation and the rotation when the image was rendered. Effectively, imagine the game rendering out a quad for each eye that gets fixed in space, and then that quad gets fixed in space some distance in front of your eyes. You can rotate your head, and even without new rendered frames, your eyes will see something reasonable (until you turn too far, or if your head is translating). The texture and position of the quad then update once a new frame actually completes, and repeat. This is a lightweight operation that runs at 90Hz, regardless of the game's framerate. It's not as good as actually hitting framerate, but it's a solid heuristic to smooth things out.
Valve, occulus, and sony are doing research on this sort of thing. It doesn't work very well at anything below 60 fps.
Because you are an idiot?
In order to generate extra in between frames you need at least 2 frames. For TV this means that the output is delayed for a few milliseconds which isn't a problem because TV is not interactive but for a VR which is interactive you just added more delay into the controller response system.
Its all about latency. Your head needs to move in game at near the exact speed in real life. Smoothing wouldn't do anything to increase the latency, only the framerate.
Feels like the submitter is a child of some sort...
I thought oooh, someone saw a term wanted to pretend smurtness .
Amazing that someone can ask such a question when a simple understanding of motion tracking exists and has been around for.. uh, well over half a century. I know.. easier to get the cheat sheet than do any homework at all.. but you give away your ignorance when you try to convince people that you did some homework.
NVIDIA does exactly that : warps the image according to most recent (or even predicted) head position.
Works on their recent high end cards
http://www.slashgear.com/nvidi...
Oculus 1.3 runtime for the Rift was released with async timewarp. When it was released DK2 users used to earlier runtimes without it were all over the boards with phrases like "holy shit" and "DK3" to explain how ATW changed everything for them. Jitter issues magically disappeared overnight with only a simple software update.
More generally there is one and only one "trick" for improving VR quality going forward and that is foveated rendering. This technology is absolutely critical to any serious vision of future HMDs.
To provide some context cones of our eyes cover a massive (cough cough) 15 degrees of arc. That's it. You can't even lean back and read 1/4 of what is on your monitor without moving your eyeballs around to do it. 4k is overkill.. 1080 is overkill... The future in VR is entirely locked up in sensing eye orientation and optical and or electronic steering of relatively low resolution displays in response.
It wouldn't do the job unless increased motion-sickness is the intended goal.
Give gamers a frame rate of 100 to 200 FPS (more accurately a latency of 5 to 10 mS) to track head motion. But only refresh the scene at 30 FPS. And pretty soon, somebody will figure this out and go all autistic about how the high refresh rate/low latency isn't legit. And their subconscious will convince them that they should be getting sick. So they will.
This actually happened some years ago where, due to a driver glitch, a new graphics card wasn't actually living up to its advertised specifications. Everyone read the numbers on the box and figured that this was the best performing h/w on the market. And it's performance demonstrably better than older models. People didn't start to get headaches from the flicker until the news broke about the driver glitch.
Setting the latency issue aside, the human visual system appears to be evolving at exactly the rate that graphics vendors are coming out with new hardware. Or I must have missed the 20 to 30 percent of moviegoers that ran out of 24 FPS theaters 25 years ago with headaches, vomiting. Latency IS a legitimate issue with systems that have to track head motion. So a system that could rotate or shift a scene at 200 FPS would seem to have benefit. Even if the scene content were rendered at a slower rate, like 30 FPS.
a) What you're describing is frame doubling or similar tricks (every manufacturer has it's own name for it). It only makes the system APPEAR better and brighter. This is often done by simply doubling the frames or turning the backlights on and off between changing frames. This makes it appear "crisper", brighter and smoother, it's only a trick though and most displays already do it, it doesn't actually improve the actual experience, only tricks your brain into thinking it is at first glance and often when you do have a real 60 or 120fps source, it interferes with it (and thus needs to be disabled, either manually or automatically). It does increase fatigue.
b) VR needs to be as close as realtime as possible. When you move your head, your brain expects the world to move right away (most current research pegs the human eye's temporal resolution to be at about 10ms or ~100Hz in bright environments). So when you make your 60Hz game (~16ms latency) into a VR game, you WILL get some issues because you are basically lagging an entire 5-10 frames behind the whole time (your input latency on very high end systems is typically ~10ms, processing latency and video card latency add another 20-50ms and then LCD latency (the time it takes for an LCD to go from black-to-white, not gray-to-gray) is typically another 10ms).
c) Most frame doubling that uses a 'smoothing engine' requires the next frame to be available. You're now adding 32ms of latency (on a 60Hz system or ~3 "frames" for your eyes) just to get a smoother image so that is entirely useless.
A 'good' VR system would require end-to-end control over the individual pixel arrays of the LCD displays as well as direct access to any sensor inputs (which all have inherent latency as well). The second you say "USB" you've already lost 10-100ms and when you say HDMI/VGA/DVI, you've lost another 8-16ms (because those are built for streaming images to "TV's". Hell, most video cards these days also use some form of double or even triple buffering (meaning your image comes out 1-2 frames too late already) in order to do all sorts of post-processing tricks (aliasing etc).
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These are not the same problems at all. Look at gaming monitors and Ping times to better understand the problem. (These aren't the same thing, but at least the underlying reasoning is closer). The VR problem is one of synchronicity. If your sitting looking at a screen of a movie or something, you don't need to change the image very often, and your brain will work it out. If there is something you are carefully paying attention too, like a ball in a sporting event. 30 FPS is not smooth enough (you will see gaps.), this also is worse with Tv's without phosphor display. And the ball will noticeably skip. So this trick gives you more frames with less time between them, so it won't skip. It's not perfect and some people get weirded out by the effect. BUT this has NOTHING to do with the VR problem. In this case it's synchronicity. Think about it, real life is relatively continues, there is no 30 fps per second, and there is reasonable belief that synchronicity has a much much faster ruler. You have a near perfect understanding between doing something and watching what happens when you do it. And if it seems real, but it's not. Turns out a large part of the population will get weirded out. And in the ol venn diagram way of thinking about it, that population and influential gamers is pretty damn high. So no it has to be fast ass cards. (there is a little bit of similarity, but one of the other problems has to do with speed of action. If your fast enough you solve by far the largest of synchronism issues. (remember when the rift first came out. Everyone was excited because they largely solved the synchronicity issue, but on low-res screens. The low res screen is problematic with moving input that is trying to reflect reality.If you move at the right speed you will get stuttering. While the timing will be right,but resolution stuttering will weird some people out. So it has to be fast enough to allow synchronicity enough, it has to be pixel dense enough that it doesn't skip unexpectedly differently from real life. None of this can be cheated, because we are not watching movies in real life. We don't ADAPT like when watching a movie.
I have a nexus player which I like, but if I cast anything to it, or play local content with MX player I get the soap opera effect making a 24 fps movie look like it's at 60. Is it the Nexus player doing this or my TV? I've posted elsewhere and some said it's my TV but if so, wouldn't it do it with everything? Like Netflix YouTube etc.
Drives me nuts.
The proposed technology has nothing to do with why VR needs to be at 90fps.
There's a lot of reasons but the simplest is that VR must, absolutely must, keep up with your head movement. If you move your head and the frame takes too long to catch up you're going to barf. And it turns out people move their heads pretty damned quickly while turning side to side. Because you don't know exactly where the players head is going to move (and yes there are prediction algorithms already) you don't have any data as to what is at the the area the player is moving their head towards until your render it. So there's no interpolation possible. You either miss the frame, and the head's movement doesn't correspond to their vision and they barf, or there's just a flicker of giant black nothingness which takes you out of the experience.
Considering there's already a ton of other things that still make you barf in VR that need work, dropping frames just isn't really possible right now.
Many posters have pointed out that latency in the graphics card is an inherent problem.
There's also latency in the monitor, and latency in the computer which creates each frame. Merging the functions of the monitor and the graphics card should allow a latency reduction of 1 frame (at the display rate). (This brings up new problems, of course. Interfaces change, and the monitor has to handle the weight and heat of the graphics card function - a problem if the monitor is a VR headset.)
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... does exactly this, and it works a treat. Only difference to TV's is, it is only used when your framerate goes below 90 fps.
It does look weird when it goes on for longer periods, but the alternative would be juddering which is insta-puke-city.
A good VR experience (and preventing motion sickness) requires fast response time. This requires low latency of the entire chain from the motion sensing device, through the USB connection, OS process scheduling, scene calculation and rendering and any buffering in the video card and display.
A system that is able to respond quickly can obviously produce more frames per second. But just creating more frames per second without reducing latency will not help the experience feel more convincing (or prevent you from feeling queezy). It will just look a bit smoother.
In playback of canned video latency does not matter much. In fact, generating these in-between images actually increases overall latency as the system has to delay the next image while calculating and displaying the in-between image. As long as an equivalent delay is inserted into the audio nobody notices this. But it won't work for VR.
There is, however, a method to produce faster response without calculating more images per second. The most critical movements are those of the head and the change in the scene from such motions can be approximated by simple panning. It's not perfect, but does work to reduce motion sickness.
Stop worrying about the risks of nuclear power and start worrying about the risks of not using nuclear power.
There are already GPUs that can do 90FPS without interpolation techniques which would not provide as good of a latency or eye tracking. In a couple of years the same level of performance will be cheap and widespread. Why would manufacturers focus on short term tricks and not the real thing?
It's great if the objects on screen are moving in predictable patterns, but if they're not then it looks horrific.
Isn't the PSVR actually using this? Since it's doubtful the internal PS4 hardware is capable of pushing 90 fps as sometimes even normal games have a hard time maintaining 60 fps.
VR people are the rich hipster dicks who run out and buy a new processor or video card when it comes out because the old one is "obsolete". The reason that you're asking this is because you're one of the poors.
what good would extra 60 frames _from the past_ do to your VR experience? other than make you puke
BTW Microsoft once championed the idea of generating 3D from a bunch of 2D tiles, this would enable tricks like motion compensation for tile reusing. It went pretty well for everyone involved (read billions invested/wasted by all MS 'partners').
https://en.wikipedia.org/wiki/...
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The first step in almost any TV calibration guide is to turn of the soap opera effect. The only reason TV manufactures still both with this junk is so that they can boast(lie) 120hz from a 60hz panel. All they are doing is averaging every two frames and inserting it in-between them. So the content still is not actually being updated at 60 fps. Further this takes so much computation that it adds a significant amount of input lag, over 100ms on many TVs, so it would completely unusable for games.
Seriously. This is way below any acceptable standard for interesting articles.
Parent doesn't understand the technology in question, despite mentioning it's an old and well known technology. Then produces a fantasy about how he/she thinks it should work for vr and asks the world "WHY!?".
First of all, it's not 'real-time motion compensation. It's 'after the facts frame interpolation'.
So immediately several problems become clear.
1. since it's an interpolation, you need to delay the output because you can't create an interpolated frame if you don't know what the next frame is going to be. So the output is delayed by at least an extra frame, more if you want to do better interpolation.
2. even with multi-frame interpolation these algorithms regularly suck ass and do all kinds of weird stuttering if the images are complex. THat is because it's a predictive algorithm and you can't possibly predict everything just from the pixels. This would be super ultra shitty for VR and would make you seasick in minutes. And not just if you're sensitive to it. It would be a positively puke-inducing experience. Besides this you would also get all kinds of artefacting going on between the eyes that would be super jarring.
3. there is already a far superior technique that fits the problem much better. I think they call it Time Warp or something like that.
So the writer of this article is just lazy and didn't do his homework.
This is a really dumb question, because the answer is "they already do". Whoever asked this knows nothing about the state of VR.
Carmack programmed time-warp to do exactly this like over a year ago. This is old-hat technology in VR. We've been doing this forever.
PSVR even does this. Games render at 60-90hz and are interpolated up to 100-120hz.
Clueless post.
You ask why we don't generate a video frame that's halfway between the current video frame and ONE THAT WILL HAPPEN IN THE FUTURE. That is quite probably the stupidest question I've heard a nerd make.
I find it sickening when it's disabled, as motion is much more jittery and stutters while panning on today's blur-free LCD panels.
On earlier TVs that would mask this with blurring or phosphor fade between frames, this was not an issue. Today's sets have high refresh rates with little artifacts and blur, so pans and motion appear full of stutter, especially on a large set where an object/person in motion travels larger physical distances between frames
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FPS isn't cumulative like that. 90 FPS "per eye" is just 90 FPS overall. It's the draw area (number of pixels) that increases. And, with what we currently have, it doesn't actually increase. Both Oculus and Vive are 2160 x 1200, 25% more than the usual 1920 x 1080.
Would this not make far more financial sense for the average VR user than having to buy a monstrously powerful GPU to experience VR at all?
awnsered your own question, capitalism at work
Stealing all our interpolation.
gear vr and oculus and i think vive too already support changing the angle "midframe" basically, render a slightly bigger imagethan fits the display(s) and as it comes out of the render pipeline adjust it based on movement that happened since the frame went into rendering. you can notice it on gearvr by turning 180 quickly and seeing the black areas.
i think the question asker isnt up to date on how the current gen vr works.. its not important if the content is 90fps. its important that the angle changes 90fps+.
gearvr also uses trickery to time the blitting perfectly with this scheme, which makes the screen look weird if you look at it all at once. shame its such a wanabe closed ecosystem. oculus is really fucking itself up with the closed swhw combo angle they are trying to go for.
also next android should have something similar support built in(mid-frame head movement compensation).
You need to know what the next frame will be before you can interpolate towards it. This means delaying everything, That's a big no-no in VR.
Also, motion compensation is not perfect. That's why all these "60fps!" trailers people like to put on YouTube look quite underwhelming.
Real 48/60fps video looks a lot nicer.
systemd is Roko's Basilisk.
Latency...all that motion interpolation takes GPU time, which just means there's more lag between the actual signal input and when the image gets drawn on the screen. The main reason VR is attempting to push 90FPS all the time is to minimize latency as much as possible between when the system detects your head moving and the image is drawn on the display.
TV's have to do it because they only get 30 FPS to work with, so they're essentially tweening in frames generated out of thin air (I mean computed from the previous and next frame). However, if you try playing a videogame that requires precise timing using one of these so-called 120-240Hz modes, you'll find that there's input lag on the order of 100-150ms or so, depending on the TV. This is why many TV's have a specific "Game" mode that disables all of the TV's post processing to minimize input lag.
Can't do that as it creates lag between perceive image and head tracking position, this will make you feel drunk and likely get sick the frame rate needs to be as close to realtime information not what was buffered and postprocessed after the act.