Blur Busters Forums

Who you gonna call? The Blur Busters! For Everything Better Than 60Hz™ Skip to content

[Overcoming LCD limitations] Big rant about LCD's & 120Hz BS

Advanced display talk, display hackers, advanced game programmers, scientists, display researchers, display manufacturers, vision researchers. The masters on Blur Busters.

Re: [Overcoming LCD limitations] Big rant about LCD's & 120H

Postby RealNC » 31 Jul 2017, 03:37

If you want a 60Hz comparison of LCD vs CRT, you can use 120Hz strobing on the LCD and use MAME with black frame insertion. This gives you 60Hz effective.

Anyway, with all that being said, there's more to CRTs than just clarity. Light output, contrast, black levels, color quality, viewing angels, are areas where CRT has the advantage (Someone correct me if I'm wrong, but CRTs could do what we now call "HDR" for decades.) And CRTs are resolution independent too; not using their native resolution doesn't ruin the image.

LCD has some advantages too, however. Sharpness and image geometry are 100% perfect on LCDs. And they can be bigger. I don't think 27" or 30" CRT computer monitors (as opposed to low resolution TVs and arcade "monitors") were very practical.

Overall I agree that going from a CRT to an LCD can feel as a downgrade, especially when going to a VA panel LCD. But you have to consider the advantages too. Playing a game on a 27" LCD (which is true 27" even) compared to a a 21" CRT (which is usually 19" visible or so) is an improvement. Even the Sony GDM-FW900 24" (arguably the best computer gaming CRT) is actually only 22.5".

The experience on a non-blurry high-refresh LCD is actually quite good. I'm using a 165Hz G-Sync 27" IPS and IMO the overall experience is better than a CRT. Yes, a CRT is still better in some areas, but the overall experience seems better on the LCD, especially due to the VRR (G-Sync, in this case), the large size of 27" and the higher pixel density (108PPI).

However, the future seem to be OLED displays. And those solve all problems of LCDs and effectively combine the best of both worlds. Except resolution independence; for that one it's GPU vendors hat need to get their act together and provide non-shitty scaling options.
The views and opinions expressed in my posts are my own and do not necessarily reflect the official policy or position of Blur Busters.
User avatar
RealNC
 
Posts: 1247
Joined: 24 Dec 2013, 18:32

Re: [Overcoming LCD limitations] Big rant about LCD's & 120H

Postby Chief Blur Buster » 31 Jul 2017, 09:39

Hear, hear!

Yes...

Software-based frame insertion to convert 120Hz hardware strobing into 60Hz hardware strobing, as a workaround to manufacturers artificially preventing their monitor from doing 60Hz single-strobe. This black frame insertion feature is built into some emulators, including WinUAE and some ports of MAME, etc.

Light output of OLED is a factor

I should add another issue that display panel makers have gotta solve: Light output of OLED. CRT phosphor is insanely bright for an instant (over 10,000 nits) at the electron gun beam spot.

OLED's inability to do this, makes it harder to shorten the persistence (flash length of pixel pulsing during rolling scan).

We have to work hard to solve that, to make it easier to shorten persistence of OLED. This is where one (unfortunate) advantage of LCD has -- you can outsource the light to a backlight which can be bigger or overkill (even heatsinked / fan-cooled) to permit short pulses.

But honestly, I'd prefer to see 240Hz OLED monitors with 1ms MPRT (pulsed rolling-scan). At 240Hz, you only need to decrease persistence by 75% to get to 1ms MPRT. Whereas with 60Hz, you need to decrease persistence to 1/16.7th the light output of a non-pulsed OLED, to get to 1ms MPRT on a 60Hz rolling-scan OLED -- losing over 90% of light doing so (unless you overvoltage the pulses, not recommended for OLED though -- albiet sometimes used for LCD strobe backlights). Light output has been a big problem for OLED going forward, but a compromise between rolling scan technique & more refresh cycles, will probably be what will happen to balance-out the light-output limitations of OLED during low-persistence operation...

Retina-resolution + MAME HLSL style processing = can essentially solve the resolution independence issue

Resolution independence on fixed pixel arrays can be sorta (indirectly) solved by going "retina" resolutions -- and that gives lots of pixels to emulate the look of phosphor via shader emulation such as MAME HLSL. It even emulates phosphor decay too! MAME HLSL configuration files even supports shadowmask PNG files! It even emulates bouncy scanlines of an imperfect CRT gun (scanline jitter) and even misconvergence (red/green/blue separation at corners). HLSL is a masterpiece work of programming art. The closer to "retina resolution" the OLED from your viewing distance, the more accurate the shadowmask emulation will become.

So with HLSL's support for custom shadowmask PNG files, you can even create your own custom shadowmask/trinitron CRT of a custom dpi, like Trinitron or Mitsubishi.

Certainly, it doesn't look right on low-resolution LCDs but when you go retina-resolution, you can simply emulate a CRT shadowmask instead via the overkill pixels of a retina-league resoution OLED or LCD. Yeah, it's overkill GPU horsepower (e.g. MAME on 4K, 5K or 8K "retina" screen) just to emulate a darn old fashioned CRT's shadowmask. But Retina low-persistence OLED would be a great CRT emulator with HLSL. The MAME HLSL effect will probably look good on low-persistence OLEDs. Be careful, the HLSL effects do look wrong until the values are properly tweaked (e.g. For example, phosphor_life parameter should bias the green phosphor, because most CRT phosphor ghosting is green-ish, because green fade is a little bit slower than red/blue).

The limited black levels (and for TN, poor viewing angles) of LCD throws off the HLSL effects, so you want high contrast ratios (e.g. fine-granularity local dimming or the use of OLED) to get inky blacks. And obviously, the motion blur of sample-and-hold displays need to be avoided, too (which means full-illumination non-impulsed non-strobed OLED/LCD will not look as "CRT correct" with HLSL emulation). Once you have a low-persistence display capable of great colors and inky blacks (ala rolling scan OLED), with sufficient retina resolution to be able to emulate any custom CRT shadowmask, and enough light output to compensate for the low-persistence and the darkening of a GPU-emulated CRT shadowmask (the black area between shadowmask holes...), then it can be made to have a texture that looks indistinguishable to a real CRT. Except for the lack of curvature. (Fortunately, CRTs do come in flat formats).

I imagine MAME HLSL would look kick-ass on the Dell U-3017Q OLED monitor (alas, discontinued) running in single-strobe rolling-scan mode (albiet pulse length is 4ms, which would resemble a somewhat slower-persistence CRT -- but it would look CRT-like). All the benefits of a fixed pixel array, with all the advantages of a fuzzy-scanlines-texture arcade CRT.

Man, putting all those teraflops in a GPU to work just doing CRT shadowmask emulation (ha!)
Head of Blur Busters - BlurBusters.com | TestUFO.com | Follow @BlurBusters on Twitter!
User avatar
Chief Blur Buster
Site Admin
 
Posts: 3659
Joined: 05 Dec 2013, 15:44

Re: [Overcoming LCD limitations] Big rant about LCD's & 120H

Postby anothergol » 31 Jul 2017, 19:06

Chief Blur Buster wrote:A mouse cursor can cross the screen easily in just 1 second. For a 1920x1080 display, that's 1920 pixels per second mouse movement. To eliminate both added motion blur AND stroboscopic effect (CRT clarity without the impulsing/strobing/flicker), you would literally need a razor-sharp individual, unique frame, at every single pixel position. Every 1920 of them.
[/b]


Ok, I was using the "waving finger around" as a real-world example, but let's take the mouse cursor example.

If the mouse cursor was a physical object, and you were moving it around, you -would- also see a motion blur. If I wave my finger around in front of my eyes, the only finger I see are the 2 on each side where I decelerate, but in-between these 2 fingers, it's a plain, filled shape, that can't even be identified as a finger.

I really don't see how the same seen couldn't be seen at 70Hz.

What you describe, a CRT displaying 1000's of frames to display the mouse cursor in all positions, I don't see how that wouldn't result in a motion-blurred cursor to our eyes. It would, just like real motion does in real life.
And I'm pretty sure that this is all displayable at 70Hz.

Really, all I'm trying to say is that if we really could "see" above 70Hz, we would with real life motion, but we don't, we see motion blur, we just can't analyse that many frames, all we see is a blend of them all. Well, the extreme example being a spinning top, say a bi-color one. The result to our eyes is a pure blend of both colors, there is absolutely no motion visible to our eyes. For this extreme case, the motion is exactly the same as a still image. Whether it's displayed as 1 still image that is the compound of 1000's, or displayed as 1000's of FPS, to our eyes it's still the same thing.

(this is for objects in motion in front of us, though. The other problem is that when people think motion blur, it's often when a game does it when you move your view around. But even if this was done perfectly, that would still not map to anything real, because when we move our head around our eyes still focus one thing, and jump to the next thing directly, or in saccades, but never smoothly)


Of course we can argue that outside the fovea we're more sensitive to motion, perhaps that was your point about VR? But we're still only a bit more sensitive outside the fovea.
anothergol
 
Posts: 7
Joined: 28 Jul 2017, 23:47

Re: [Overcoming LCD limitations] Big rant about LCD's & 120H

Postby Sparky » 31 Jul 2017, 19:37

The thing about real life motion blur is that it doesn't impact an object that your eyes are tracking, it does impact everything else. You can't get both of those aspects of real vision at 70hz, just one or the other. If you use full persistence you'll get motion blur of tracked objects. If you use strobing you'll get stepped motion artifacts of objects you're not tracking.

The refresh rate/framerate required to get artifact free motion depends on how fast everything is moving, and how big the object is. For a mouse cursor it's probably something like 10~20khz.
Sparky
 
Posts: 535
Joined: 15 Jan 2014, 02:29

Re: [Overcoming LCD limitations] Big rant about LCD's & 120H

Postby Chief Blur Buster » 31 Jul 2017, 20:27

10-20KHz is quite overkill just for a mouse cursor! (fast-flicks even on 4K-8K displays into a continuous-blur mouse cursor).

Yes. Motion speed, resolution & size of the display is important.

Phone -> Small Desktop -> Big Desktop -> Desktop HDTV -> Narrow VR -> Full FOV VR -> Holodeck

It's not just VR, it's simply the end point.

The bigger the FOV the display covers (and/or) the more pixels (and/or) the faster motion,
...the more refresh rate that will be needed to simultaneously eliminate motion blur & stepping effects.
Head of Blur Busters - BlurBusters.com | TestUFO.com | Follow @BlurBusters on Twitter!
User avatar
Chief Blur Buster
Site Admin
 
Posts: 3659
Joined: 05 Dec 2013, 15:44

Re: [Overcoming LCD limitations] Big rant about LCD's & 120H

Postby Chief Blur Buster » 31 Jul 2017, 20:42

anothergol wrote:Really, all I'm trying to say is that if we really could "see" above 70Hz, we would with real life motion, but we don't, we see motion blur, we just can't analyse that many frames, all we see is a blend of them all. Well, the extreme example being a spinning top, say a bi-color one. The result to our eyes is a pure blend of both colors, there is absolutely no motion visible to our eyes. For this extreme case, the motion is exactly the same as a still image. Whether it's displayed as 1 still image that is the compound of 1000's, or displayed as 1000's of FPS, to our eyes it's still the same thing.

Don't forget these are different questions:

"Can humans see above 70Hz" (flicker fusion threshold question)
versus
"Can humans see motion blur caused by refresh rate limitations?" (indirect side effects: motion blurring)
versus
"Can humans see stroboscopic stepping effects from refresh rate limitations?" (indirect side effects: stroboscopic/wagonwheel/stepping/mousedropping/etc)
versus
Etc.

Certainly, the common answer about flicker fusion threshold is often in the neighborhood of 70Hz, but this isn't the only artifact being concerned about.

Don't forget fixed gaze versus eye-tracking. When you are eye-tracking moving objects on a display, displays behave very differently than when you're doing a fixed gaze.

The bigger the display, the more room there is for eye tracking of motion. And thus, the more noticeable display artifacts (from low refresh rate) is visible. Blending at the display-end (instead of the human brain) creates problems because blending creates an assumption -- blending is designed to work well for fixed-gaze situations but not eye-tracking situations.

During eye tracking, blending fails because whatever blended result is blurrier than the original refresh cycle. Human eyes cannot un-blend/sharpen a blended frame. And eye-tracking motion blur is above-and-beyond (blur is additive). Human eyes/brains cannot de-blur pre-blended pre-blurred frames -- neither can Photoshop very well.

Eye tracking is why lines are thicker in the TestUFO Thin-vs-Thick Lines Animation (view this on an LCD) -- this is not motion blur caused by GtG -- GtG does not change during fixed gaze versus eye tracking situation. So you already know, it's motion blur caused by eye tracking.

When you are eye-tracking, the frame is stationary relative to eye position. So the refresh cycles has to be sharp to be sharp (and stationary relative to eye tracking). Longer visible refresh cycles means your eye gaze are in different positions at the beginnings/ends of frame visibility). The longer the frame is visible for, the more time the frame is blurred. (This is how http://www.testufo.com/eyetracking animation was designed -- view that animation on an LCD or OLED screen).

Also, this YouTube video explains display motion blur caused by eye-tracking very well, jump to 0:59 of this YouTube video. There are scientific papers (on Google Scholar) about the motion blur from eye tracking on displays.
Head of Blur Busters - BlurBusters.com | TestUFO.com | Follow @BlurBusters on Twitter!
User avatar
Chief Blur Buster
Site Admin
 
Posts: 3659
Joined: 05 Dec 2013, 15:44

Re: [Overcoming LCD limitations] Big rant about LCD's & 120H

Postby Sparky » 31 Jul 2017, 21:28

Chief Blur Buster wrote:10-20KHz is quite overkill just for a mouse cursor! (fast-flicks even on 4K-8K displays into a continuous-blur mouse cursor).


Obviously we don't care THAT much about a mouse cursor having perfectly artifact free motion, but we can move a mouse cursor awful fast across the screen. From moving my mouse around I estimate about 50k pixels per second is pretty common. At 1khz that's 50 pixels of displacement per frame. Size of the monitor doesn't particularly matter, except in that it will provide cause for bigger/faster mouse movements.

Obviously you'd need faster USB polling to get that high in the first place. The point is that there's really no such thing as excessive framerate/refresh rate, It's going to be a tradeoff against other considerations for a long time yet.
Sparky
 
Posts: 535
Joined: 15 Jan 2014, 02:29

Re: [Overcoming LCD limitations] Big rant about LCD's & 120H

Postby anothergol » 01 Aug 2017, 03:05

Sparky wrote:The thing about real life motion blur is that it doesn't impact an object that your eyes are tracking, it does impact everything else. You can't get both of those aspects of real vision at 70hz, just one or the other. If you use full persistence you'll get motion blur of tracked objects. If you use strobing you'll get stepped motion artifacts of objects you're not tracking.

The refresh rate/framerate required to get artifact free motion depends on how fast everything is moving, and how big the object is. For a mouse cursor it's probably something like 10~20khz.


But you can't track something that's moving rapidly, just try it. Move your finger around in front of your eyes, tracked or not, it's not gonna be sharp. From the moment you move your finger fast enough for it to become a "blur trail" instead of a finger, there is just no way you can eye track it anymore.
anothergol
 
Posts: 7
Joined: 28 Jul 2017, 23:47

Re: [Overcoming LCD limitations] Big rant about LCD's & 120H

Postby anothergol » 01 Aug 2017, 03:32

Chief Blur Buster wrote:
anothergol wrote:Don't forget fixed gaze versus eye-tracking. When you are eye-tracking moving objects on a display, displays behave very differently than when you're doing a fixed gaze.

Eye tracking is why lines are thicker in the TestUFO Thin-vs-Thick Lines Animation (view this on an LCD) -- this is not motion blur caused by GtG -- GtG does not change during fixed gaze versus eye tracking situation. So you already know, it's motion blur caused by eye tracking.



First, I know I ranted about LCD's, but you've told me that there are LCD's out there that do a proper strobing at 60Hz, so in that aspect, let's forget that part of my rant. If we all do agree that LCD's are still not there, that a CRT is still better for gaming, well there's no real argument anymore.

So let's be clear that I'm debating about ideal rendering framerate vs ideal screen refresh rate, in an ideal situation, which would be a CRT here.

This is my whole point, is 120Hz needed to overcome a problem with LCD's only, or is 120Hz needed because our vision is really that good that we can tell the difference.
But I think I see your point now. In the eye tracking test (with 12 pixels/step), if the frame rate was 12x70FPS instead of 70FPS, the result of the background would be a solid grey, and the result of the bottom UFO, when tracked, would be blurred by 12 pixels. Ok, makes sense. So perhaps high framerate rendering+blend isn't a good idea indeed.
..but still, here at 70Hz
-the bottom UFO moves as smoothly as it could
-I can eyetrack it perfectly
At 120Hz, what would really change?
-the background, when focusing the first UFO, wouldn't be fixed anymore, it would flicker between 2 positions, in 6 pixel increments instead of 12. Would this be better? It would still be far from the blurred background it should theorically be. That is, is "less bandwagon effect" a real improvement? Well.. I'm not sure the problem is the amount of bandwagon effect, rather than the fact that there is bandwagon-ning. Yeah, less bandwagon-ning will probably help seeing the direction of a motion/rotation better, but just doubling the refresh rate should only make a slight difference in some cases of objects moving fast enough but not too fast. All car wheels, helicopter blades, fans, where it's generally a problem, will still look as bad at 120Hz as they do at 70Hz.
-would eye-tracking the second UFO look any better? I doubt it, it's already as smooth as it can be, IMHO. I see smooth motion, no strobing, and at this speed I can still perfectly identify all detail.

But yeah, I would now agree that at an infinite framerate, we would probably see a solid grey image behind the first UFO, and still (probably?) the same 12pix grid when eye-tracking the second UFO. Makes sense, I guess, but we're never gonna reach that infinite framerate, and I don't think that 100, 200 or 300Hz are really an improvement as for the result.
But you're right, I now see how a 1000Hz+ framerate with blending & output at 70Hz would not give proper results for this eyetracking test, my bad.

Perhaps the ideal result would come from a combination of both, btw. Eye-tracking has a speed limit (100deg/sec ?, after a quick googling). Here I now understand why you were talking about VR, when the screen cover your whole vision, yeah a pixel of motion is more degrees than on the screen looked from distance. But shouldn't we able to compute the max refresh rate ever needed, knowing our limit in eye-tracking?
anothergol
 
Posts: 7
Joined: 28 Jul 2017, 23:47

Re: [Overcoming LCD limitations] Big rant about LCD's & 120H

Postby Chief Blur Buster » 01 Aug 2017, 10:23

anothergol wrote:But you can't track something that's moving rapidly, just try it. Move your finger around in front of your eyes, tracked or not, it's not gonna be sharp. From the moment you move your finger fast enough for it to become a "blur trail" instead of a finger, there is just no way you can eye track it anymore.

Correct, that said, we need to cover both bases: Fixed gaze versus eye tracking.

You have mentioned precisely the point.

The required maximum refresh rate needed (for a specific use case) is at the threshold matching your maximum eye tracking speed. Beyond that, it's unnecessary. However, getting beyond all the "points of diminishing returns" extends surprisingly far.

Note: eye "tracking" can also apply to a physically moving screen while keeping eyes stationary in your eyeball sockets (which forces your eyes to essentially track across the screen, by virtue of a physically moving screen). Like moving your OLED Galaxy smartphone horizontally while watching http://www.testufo.com/eyetracking while keeping your eye gaze stationary. Try it on your phone or tablet, load http://www.testufo.com/eyetracking .... Use your hand to move your phone horizontally to keep the 2nd UFO in a fixed-gaze position. Exact same display motion occurs. Same tracking motion blur occurs, but it is commonly called "eye tracking" motion blur -- but it also applies to any vision/camera motion relative to a display's plane (e.g. No matter how you track -- whether be pursuit cameras, tracking cameras trying to photograph fast moving objects (sports,olympics), physically moving displays, eye tracking on displays, turning your head while keeping eyeballs stationary in their eye sockets, head turning in virtual reality, etc -- all of them, all create the same tracking-based motion blur above-and-beyond human brain limitation) It's akin to waving a camera while taking a picture at slow shutter. Creates a blurry photo. In blur-comparision tests, 60fps@60Hz and 240fps@240Hz on sample-and-hold displays (OLEDs, fast TN LCDs with good overdrive, or other display tech where GtG is an insignificant % of refresh cycle) -- at the same relative angle-per-second tracking motionspeed -- the motion blur (angle-of-blurring) of each look just like the blur difference between a 1/60sec vs 1/240sec camera shutter photograph. Slower shutters means more blurry photographs, and the same thing happens to eye-tracking smearing frames across retinas. Scientists/vision researchers/display engineers/VR scientists finally realized that once we removed GtG limitations, this motion blur limitation still remained with displays that is not fixable without going to formerly-laughworthy ultrahigh refresh rate. The use of static imagery to represent moving analog objects, creates motion blur limitations for tracking cases.

Yes, yes, human eyes aren't cameras. However, the principle of static refresh cycles being smeared across your retinas is still the principle of motion blur (that the TestUFO animations so eloquently demonstrate). As the TestUFO Thin-versus-Thick-Lines animations already demonstrate -- this specific type of blur animation is designed to highlight tracking blur instead of GtG. The longer the static refresh cycles are on for, the more time a refresh cycle can smear across your retinas. Once GtG is eliminated (or insignificant), the blur distance is exactly the same distance your eyes tracked between the beginning part of a refresh cycle and the end part of a refresh cycle.

Human eyes "cannot see 240fps" directly. We are simply seeing side effects. 240 blurred frames (whether blurred by tracking or blurred by pre-blending) in one second still shows up as sustained blurring that's now noticed by humans. Simple. That's it.

We just currently solve that by impulsing/flickering like a CRT. That acts like a fast shutter to prevent tracking based motion blurring. Like the special "GearVR Low Persistence Mode" on your phone which flickers your phone's OLED screen like a CRT to fix the motion blur from long frame visibility times.

Turn that mode off, and your OLED is no better in motion blur than a 1ms TN LCD! Yes, the OLED will have better colors and blacks, but, you get "LCD-like motion blur" even at 0ms GtG.

GtG and MPRT must simultaneously be low to eliminate tracking-based display motion blur.

At 960 pixels per second at 60Hz, that's (960/60) = 16 pixels thickness for http://www.testufo.com/blurtrail (configured to Pixel Per Frame = 16) ..... At 960 pixels per second at 240Hz, that's (960/240) = 4 pixels thickness for http://www.testufo.com/blurtrail (configured to Pixel Per Frame = 4). Try it now, change the speed of http://www.testufo.com/blurtrail -- the line becomes thicker on your Samsung Galaxy OLED or your LCD desktop monitor -- during fast line moving speed. But fixed gaze, the line is still 1-pixel thick. But the faster you move that line, the thicker the line becomes in tracking situation.

Try this on your Galaxy OLED smartphone or on a fast LCD monitor (preferably one with GtG far less than refresh cycle).

If your display uses PWM for dimming, adjust to maximum brightness to eliminate PWM-stepping artifacts.
(Note, some newer OLED phones may have a low-persistence mode ("GearVR Low Persistence") to produce CRT-like clarity for Google Cardboard VR mode -- flickering the screen to avoid motion blur. Disable this low-persistence mode during the below test.)

TestUFO Blur Trail at 4 pixel step
TestUFO Blur Trail at 8 pixel step
TestUFO Blur Trail at 16 pixel step
Twice the speed = Twice the tracking-based motion blur (on non-strobed/non-impulsed/non-CRT displays)

Note: you might see shimmering if scaled above 1:1 pixel mapping; e.g. pinch zoomed Galaxy smartphone (or zoomed desktop browser) causing 1-pixel variations in blur trail thickness -- that's simply scaling/aliasing artifact. However, the motion blur should actually outweigh the shimmering artifacts. For the sake of educational exercise, ignore scaling/aliasing artifacts and focus only on the thickness of the overall motion blur.

You'll see that doubling the pixel step will double the tracking-based motion blur. (You can still tell all lines are the same thickness in a fixed-gaze-at-display-center situation). The only now-scientifically-proven way to avoid tracking based motion blur is to shorten frame visibility time (whether shutter in a camera, the flicker of a CRT/strobed LCD/strobed OLED, or the frame duration time on a continuously-illuminated sample-and-hold display = more frames per second (and thus more refresh cycles per second to display each frame in their original razor-sharp formats).

So, thusly:
1ms of frame visibility time = 1 added pixel of motion blur during 1000 pixels/sec motion.

So if you're doing a 240Hz display, sample-and-hold, 4ms frame duration time, that is 4 pixels of motion blurring during 960 pixels/sec. That will still cause TestUFO Panning Map Readability test to fail.

Now if you strobe instead (CRT phosphor, LCD strobe, OLED rolling scan), e.g. 1ms strobe flash length, the TestUFO Panning Map Readability Test stays sharp, avoiding tracking-based blur.

Another way to achieve 1ms frame visibility time is to fill all intermediate eye-tracking spots with sharp frames. (aka 1000fps@1000Hz). That can do essentially the same thing (assuming GtG isn't a limitation preventing such, basically good sub-refresh-cycle GtG).

1ms vs 2ms vs 4ms GtG makes a whole hoot of almost no difference to tracking motion blur 60Hz, but it can be a chasm valley at 240Hz when GtG really enroaches the full refresh cycle length (or even beyond, like 33ms LCDs in the Bad Old Days where LCD refreshes simply ghosted well into each other).

Yes, that's true -- 240Hz (at 0ms GtG, or insignificant percentage of refresh cycle) -- 240fps@240Hz is the same motion blur at the same speed as a 1/240sec camera shutter. That still creates blurry photographs during fast camera panning, like photographing a ski jumper. If you track perfectly, the skiier will be sharp but the background will be blurry. If you don't track, the skiier will be blurry but the background will be sharp. Now imagine a skiing game or skiing video. You can only do EITHER (sharp background or sharp skiier) but not BOTH simultaneously IF you are also needing to simultaneously avoiding stroboscopic stepping effect TOO. A human can randomly decide to track a skiier on a screen, or track the background behind the skiier. Strobing (and CRT) allows tracking to remain sharp, but that adds stroboscopic stepping effect. Stepping effects in background can be seen when tracking skiier (if background is not pre-blurred from slow camera shutter). For a game (GPU effects), you can do the same essentially by pre-blurring/pre-blending the scrolling background to compensate for stepping effect, but that spoils the situation when the human decides to track eyes on the background instead of the skiier. The background will look blurry. (That's also often what happens on a real TV too, the background is still blurry when you eye-track the background, even on a CRT -- if the video camera used a slower shutter than needed to be crisp & clear for your eye's maximum tracking speed).

Moral of the story, you cannot control whether a human decides to track their eyes across a display's plane, unless you're using some high-speed eye tracking sensor and being able to physically (or projection) flit the display around to keep the center of the display at your gaze center. That has the advantage of being able to choose displaying a higher resolution only where it matters (instead of peripheral vision), possibly making 8K unnecessary. Research is already being done on doing this in VR -- e.g. eye-tracking displays that actually move a projected display around to match your eye tracking (e.g. a high-resolution smaller display in the middle of a bigger low-resolution display) -- like this startup. This can be a solution to attempting to solve both tracking situation and fixed-gaze situation simultaneously, without unobtainium refresh/framerates, since it's analog movement of a display to stay in sync with eye tracking -- problem solved in a framerateless manner. Could be done with a projector and a high-speed mirror, to do the same thing on a wall, to have CRT-quality panning without needing impulsing. However, that doesn't help desktop displays which can't physically move to keep in sync with eye tracking.

So, how do you solve everything simultaneously in all of the above paragraph, combined? Yep -- The only way to make it look like reality is to remove the 240 limitation, and go to refreshrate/framerates just right at your maximum eye tracking speed.

In fixed gaze, you can tell there's a stepping effect if you flick fast enough. If the mouse is going 50,000 pixels second in the fastest arm-flick, the mouse arrow tips are going to jump a 5 pixel gap, (50,000 pixels/sec divided by 10 KHz refresh) = 5 pixel step for mouse arrow tips. This is a situation where frame-blending is recommended.

You want a "high enough" refresh rate to a human's eye tracking speed limit. The more pixels, the more pixels to be blurred. If sufficiently razor-sharp enough (e.g. retina display at huge scales -- e.g. 4K or 8K TV, monitor, or VR, covering at least 30+, 45+ or more FOV) the defocussing effect of motion blur can be indirectly noticed. At low resolutions OR narrow FOV, it's not noticeable. But at super-high resolution AND very wide FOV, the effect becomes a problem. Panning scenery defocussing itself (above-and-beyond natural human brain blur). You are very familiar that panning scenery on CRT looks as sharp as stationary scenery, thanks to CRT's short visibility time (phosphor). To be able to do that, without flicker, requires analog-like motion (insanely high frame rates @ high refresh rates).

With your CRT, load TestUFO Panning Map Street Label Readability Test. That will test your maximum eye tracking speed. Most people have said that they are able to still read the street name labels at 960 pixels per second on a CRT. Some can go up to 3000 pixels/second or more -- sometimes the label is not onscreen long enough to read it (limited FOV of CRTs, alas) but with a wider FOV, you have more time to read during eye tracking situations. Like giant retina monitors on a desk, or 4K/8K wall-size TVs (10-foot-size images from projectors etc), or in VR. (CRTs can't get big & sharp (simultaneously) enough for that, so we need other display technologies for those mantles).

But it's actually not necessarily important that you read the label in TestUFO Panning Map Test or not: You'll still notice whether the labels are sharp or blurry. What's important is you can notice/see the text is razor sharp on your CRT even at 960 pixels per second. There isn't the "1-2 pixels of motion blurring" necessary to obscure the small text into non-readability. (1-2 pixels of blurring = frame visibility time is less than 1/960ths or 2/960ths of a second = 1 to 2ms persistence = your CRT phosphor is going essentially dark after less than 1ms or 2ms). You can't keep the street name labels if you shine a frame for longer than that. (And blending won't help here, either).

The defocussing effect (of display motion blur) is something that doesn't happen to physical material being scrolled at the same speed (inches per second at the same physical distance) -- you can tell that a book's text stays crystal sharp if you wave a book slowly across your face -- you won't have time to read text (maybe just one word) on a moving book but you can immediately tell the text is sharp instead of unfocussed (if you eye-track the slowly moving book being waved across your face).

So, naturally, you want a display to be crystal sharp at your eye's fastest tracking speed.

The variables vary (e.g. Smartphone -> small monitor -> big monitor -> huge wall size TV -> narrow FOV VR -> wide FOV VR -> Holodeck) but let's assume a huge HDTV on a desktop.

If you sit only 2 feet from a 4K HDTV (using it like a computer monitor), you will be able to see pixels; it won't be quite "retina" sharp anymore at this distance (as proven by http://www.testufo.com/aliasing-visibility ). You'll definitely notice 1 pixel motion blurring at 960 pixels/sec easily. However, 960 pixels/sec is slow -- that takes 4 seconds for a moving object to go from left edge to right edge of a 4K HDTV. It takes only roughly ~1 second worth of eye tracking (usually less) to notice if an image is not fully crystal sharp (e.g. reading just one word scrolling past the screen). So, 3840 pixels/sec for this specific situation, and that motionspeed still takes 1 second to go from left edge to right edge of a 4K display occupying about 30-40 degrees of FOV. At that FOV and 40-degrees-per-second eye tracking -- eye tracking is sufficiently accurate in most human to detect if something is in-focus or something is out-of-focus (motion-blurred) for non-retina graphic densities.

Obviously, some humans will have better vision than others, and some will have better eye tracking than others, but for the sake of simplicity, we're using the "sitting close enough to a 4K TV to the point that it's no longer retina sharp" -- like when some people repurpose 40-48" 4K 2160p HDTVs as a desktop computer monitor instead of using an 2x2 array of 20"-24" 1080p monitors in multimonitor mode (similar screen surface area, but becomes a single surface).

So, we're going with a conservative 3840 pixels/sec eye tracking speed for this particular use case (4K at 40 degree FOV), as an eye-tracking-speed limit (you can turn your head to keep up, too) -- you will be able tell whether there's 1 added pixel of motion blur added to CRT motion clarity (zero motion blur during tracking situations).

Now, if you want CRT quality with no impulsing, you need to maintain no blurring during all tracking speeds up to your eye tracking speed limit. So, for that particular display (resolution, FOV, and fairly slow eye tracking speed) to become "real life analog motion" (without impulsing / flicker / etc), you'd need 3840fps @ 3840Hz to make it look analog real life (avoid tracking-based blurring). Your eyes are not digital stepper motors, your eye tracking is continually moving as you track. Yes, there are erraticness/saccades, but that only determines your maximum accurate tracking speed; you can still read moving text, like driving past road signs or walking past signs, etc. Display motion blur (eye tracking across statically dispayed refresh cycles, even if they're only 1/240sec each) can affect the clarity of that sort of thing.

However, now if we're using a much smaller display, e.g. 10" LCD, at 10 degrees FOV -- at lower resolution of 1024x768 -- say the iPad Original. Then one human may only be able to track for about approximately 500 or 1000 pixels/second before noticing there's blurring or not. (narrow FOV = less time to track eyes to notice blur). In this case, you'd only need 500fps @ 500Hz for that specific FOV / resolution.

The wider the FOV, the more time your eyes has to track (to notice that things are blurry caused by display (tracking) motion blur)
The bigger the display, the bigger the FOV/pixels become, so you need more pixels. (more resolution)
The higher the resolution, the more pixels to be blurred at the same angles-per-second eye tracking. (up to your eye gaze resolution limit, and tracking speed limit). That's where the diminishing returns finally stop (finally, finally, finally ;) ...LOL)

So at the end of the day, the bigger/sharper/wider FOV, the more problems are created by a display's long refresh cycle duration time (whether it's blended or not). With Microsoft's 1000Hz display, NVIDIA's 16,000Hz Augumented Reality display, Viewpixx 1440Hz lab DLP, etc, many scientists have learned quite a lot since then about display limitations.

Does it matter? Usually, no. We view handheld phones, 40" HDTVs all the way across a big living room, and 24" monitors sitting at the back of a desk. Often 60-70Hz can be good enough and people don't care about display motion blur. It't not important for a lot of use cases like writing emails, reading Internet news and writing documents, anyway! But the bigger/sharper/wider FOV, the bigger the problem becomes when trying to represent reality onscreen. (HDTV "seeing through a window of a moving train" test, or VR "it's just like real life" test, etc).

Once we've solved tracking motion blur (e.g. zero blur at human eye's fastest tracking speed for a particular display/use case), the remander of the solving can be done by blending (e.g. after (X)fps @ (X)Hz (to first solve the motion blur problem), then pre-blend to not need to go above >(X)fps@(X)Hz (to solve the stepping effect problem). And a margin is likely needed too, since the pre-blending may bump X slightly higher to compensate for the pre-blending a little. The variables vary a lot, but for sample-and-hold (no black periods, no flicker, no impulsing), the number X can end up being 100-200 for a specific small handheld display, above >1000 for a specific desktop display, and use cases already exists where certain "different-from-real-life" imperfections becomes visible below ~10,000Hz for wide-FOV retina VR situation for a percentage of people).

And display industry is not the ONLY time where imperfections shows up. The lighting industry has also found this out, e.g. 5000 Hz fluorescent ballasts still doesn't make five-sigma people happy.

Image

From lighting industry paper.

The numbers are apparently uncannily similar to the numbers that many VR scientists have discovered, in terms of stroboscopic stepping effects and/or motion blur limitations (at least at the "near final frontier" league of surround-retina).

TL;DR:
  1. Your maximum eye-tracking speed definitely affects the ideal maximum refresh rate to jump past "diminishing points of returns". However, display angular resolution relative to your eyes (and tracking time available) matters a great deal in determining the "perfect final frontier refresh rate where diminishing points of returns disappear".
  2. Size/FOV/resolution matters a lot.
    e.g. Smartphone -> small monitor -> big monitor -> IMAX or wall height TV -> narrow FOV VR -> wide FOV VR -> Holodeck.
  3. The bigger/sharper/wider FOV, the more time for tracking over more pixels across the display plane, the easier it is to notice imperfections such as blur (tracking across display plane) or stroboscopic stepping effects (gaze in fixed point of display plane).
  4. You cannot control whether a human decides to track or gaze. Thus, doing only blending isn't always a fix-all.
  5. This all doesn't matter if you're just doing email, reading news, editing source code, or writing docs. ;)
  6. Heck, this might not even matter for you, on displays you play on, running specific games (& gameplay tactics) you play today.
Head of Blur Busters - BlurBusters.com | TestUFO.com | Follow @BlurBusters on Twitter!
User avatar
Chief Blur Buster
Site Admin
 
Posts: 3659
Joined: 05 Dec 2013, 15:44

PreviousNext

Return to Area 51: Display Science, Research & Engineering

Who is online

Users browsing this forum: No registered users and 1 guest