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Need 1000fps@1000Hz for 1ms persistence without strobing

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Need 1000fps@1000Hz for 1ms persistence without strobing

Postby Chief Blur Buster » 14 Jan 2014, 13:51

One of my favourite posts, which I wrote on AVSFORUM, covers the subject of attempting to get low-persistence using steady light output, without needing flicker / strobing / light modulation / phosphor.

One would prefer taking your cake and eating it too (getting low-persistence without strobing). But to achieve 1ms persistence, you need to fill all timeslots, and there's 1,000 timeslots per second to achieve 1ms persistence. So you got 1000ms to fill with frames, divided by 1ms persistence = 1000 frames per second required to avoid black periods -- that's 1000fps@1000Hz in order to get completely strobe-free / flicker-free / steady-light output simultaneous with 1ms low-persistence. Ouch.

This is in the pursuit of achieving the fuller "Holodeck" experience without strobe effect / wagonwheel effect / mousedropping effect / motion blur effect. The only way to really solve all such image artifacts simultaneously, is attempting to resemble something closer to framerateless continuous-motion (or infinite framerate). Currently, we are stuck with needing finite refresh cycles in order to artifically display moving imagery (films, televisions, monitors, screens, etc), so strobing (ala LightBoost/ULMB) is a much easier/simpler way to achieve low persistence using today's technology.

Here's my AVSFORUM post in its entirety:
Michael Abrash of Valve Software has a great article about the problems of trying to simultaneously solve motion blur, judder and strobing when using virtual reality headsets. (In Comments section, Michael also complimented the work Blur Busters is doing). He has several great explanations about these problems, and also touches upon the benefits of 1000Hz-refresh displays.

"Down the VR rabbit hole: Fixing judder"
http://blogs.valvesoftware.com/abrash/down-the-vr-rabbit-hole-fixing-judder

Essentially, the Cliff Notes version of his article:
- Low framerates -- problematic for both motion blur and/or judder
- High framerates -- better, but still have motion blur even at 120fps@120Hz
- Strobing -- solves motion blur but adds problems (flicker problem/stroboscopic problem)
- 1000fps@1000Hz -- Simultaneously fix motion blur, fix flicker, fix stroboscopic/stepping effects

Problem: Motion blur of eye-tracking motion blur on discrete-refresh displays:
.
Using Michael Abrash's diagrams, and corroborated by his vision researcher friends, I've arranged the diagrams in way that helps people understand why true 1000fps@1000Hz will eventually become necessary sometime later this century.
.
Image
Simplified illustration for eye-tracking at 60fps @ 60Hz sample-and-hold (e.g. LCD)
.

Image
Simplified illustration for eye-tracking at 120fps @ 120Hz sample-and-hold (e.g. LCD).
Less motion blur.
.

Image
Simplified illustration for eye-tracking at 60fps @ 60Hz flicker driven (e.g. CRT).
Less motion blur too. But problem if you stare stationary (see next section).
.

Image
Simplified illustration for eye-tracking in real life.
No motion blur bottleneck. No stroboscopic problem.



Problem: Persistence, the stroboscopic stepping effect while staring stationary while object moves past

This creates stroboscopic stepping effects (at low framerates, this is the common sensation of judder). The stepping effect can still be visible even at 120Hz and 240Hz. Visualize a fast moving object which creates a non-continuous trail, e.g. object moving 240 inches per second leaves a 1-inch dotted trail if you're just staring straight ahead. This is fixed by adding motion blur, but that is undesirable in many situations. For VR, you want perfect clarity without motion blur.
.
Image
Continuous illumination (e.g. most LCD)
.

Image
Half persistence (the frame is illuminated half the time)
.

Image
Zero persistence (e.g. laser displays and short-persistence CRT's resembles this)



Problem: Persistence, the stroboscopic stepping effect while staring stationary while object moves past

.
Blur Busters UFO Motion Tests

I let Michael Abrash know about the UFO motion tests, of which Michael likes very much. This is very relevant into the "pick-your-poison" problems of finite-framerate displays. Before proceeding, make sure you understand how these animations work. View these links on a recent fast computer using Google Chrome or another browser supporting perfect framerate=Hz animation.

An excellent animation of eye-tracking-based motion blur:
http://www.testufo.com/#test=eyetracking (use a supported browser)

An excellent animation of how strobing reduces motion blur:
http://www.testufo.com/#test=blackframes (use a supported browser)
This also brings some strobing disadvantages

The problem when using virtual reality headsets, you've got head turning that creates very fast horizontal motion. This creates fast panning which can be quite motion blurred. Fast head-turning can create lots of motion blur.

First, look at the stationary image of the Eiffel tower.
http://www.testufo.com/#test=photo&phot ... .jpg&pps=0
This is very clear on almost all displays.
- You can count the number of cars under the Eiffel Tower
- You can count the lattices in the Eiffel Tower

Let's simulate even just a slow head turning speed that's approximately 30 degrees per second (VR headsets):
http://www.testufo.com/#test=photo&pps= ... eiffel.jpg (use a supported browser)
Maximize your web browser window on your display (computer or HDTV). Stare fairly close, at a view distance approximately equal to screen width. Now you're viewing motion that's moving approximately 30 degrees per second. That's only a slow head turning speed.
Look at how motion blurry it is on your LCD.
- LCD will show a lot of motion blur
- CRT will show stroboscopic stepping effects
- Even at 120Hz.
- Even at 240Hz.
- Yes, even at perfectly-done 480Hz.

Animation Self-Test Challenges

Challenge for motion blur.
http://www.testufo.com/#test=photo&pps= ... eiffel.jpg (use a supported browser)
Track your eyes on the details of the moving photo above
- Try to count the number of cars under the Eiffel Tower
- Try to count the lattices in the Eiffel Tower
You can do typically easily do this on a CRT, but not on most LCD's (except LightBoost)
On a CRT with short-persistence phosphor, the fast moving image remains crystal-sharp.
Also crystal sharp on a LightBoost 120Hz monitor running ToastyX Strobelight programmed to 1.4ms strobes (Control+Alt+1).

Challenge for stroboscopic effect:
http://www.testufo.com/#test=photo&pps= ... eiffel.jpg (use a supported browser)
Stare stationary ahead.
- Put your finger along the top edge of the moving photo, at the vertical level where the Eiffel Tower antenna passes underneath.
- Now stare at the finger.
- Notice the strobing effect of the Eiffel Tower antenna, as it passes underneath. You see multiple antennas near the finger.
- Even with 240fps frame interpolation, the strobing effect still remains if you're viewing at this fixed point during 30-degree-per-second motion (the speed of a slow head turn). So 240fps is not enough to fix the stroboscopic effect. There is no consumer display/monitor/HDTV that exists in the world, that fixes this stroboscopic effect problem. It's an artifact that exists on all finite-framerate displays, and diminishes as you go higher in framerate/Hz.

And this is Why 1000fps@1000Hz is Useful Progress

From the perspective of fast-action computer gamers, the persistence of having 1ms frame samples is benefical (the CRT effect) in completely eliminating perceptible motion blur, but even at high-refresh-rate CRT gaming when staring at the videogame crosshairs while doing strafes or turns in video games, you can see stroboscopic effects of finite-framerates (even on 21" high bandwidth professional CRT's being driven at 240Hz). Adding motion blur fixes this, but then you've got the motion blur problem. How do you fix motion blur AND the stroboscopic effect? Simple. 1000fps@1000Hz (or beyond).

So, this century, we will have a use for 1000fps@1000Hz -- in some applications such as FPS gaming, simulators, racing, military training, VR headsets, and everything else that requires all human eye effects to be done naturally (e.g. display doesn't enforce stroboscopic and motion blur limitations upon you). Otherwise, we will never reach Holodeck-league imagery.
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Re: Need 1000fps@1000Hz for 1ms persistence without strobing

Postby RealNC » 14 Jan 2014, 16:21

Maybe Chief O'Brien can come up with something. He's in transporter room 2 :-P
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Re: Need 1000fps@1000Hz for 1ms persistence without strobing

Postby Chief Blur Buster » 14 Jan 2014, 16:25

RealNC wrote:Maybe Chief O'Brien can come up with something. He's in transporter room 2 :-P

There are some experimental ultrahigh-refreshrate displays in production right now for vision science.
vpixx.com has a 500Hz true refresh rate DLP for researchers. (I think the 500Hz mode is in monochrome, due to bandwidth limitations).

Image

I've heard of rumors of a 1000Hz full-color scientific display coming in the near future. Don't expect to pay less than five or six figures for those, however. However, you will need what is tantamount to a supercomputer, to output 1000fps during a game, unless you're playing real old games (e.g. original Quake engine, which can easily run at 1000fps on today's graphics cards).

Realistically, the best we can hope for in the next decade is probably low-persistence (strobed) triple-digit frame rates, which still looks beautiful if done properly.
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Re: Need 1000fps@1000Hz for 1ms persistence without strobing

Postby Karnaj » 14 Jan 2014, 19:12

I was wondering what this stroboscopic effect was called for quite some time while playing FPS games. When I panned my view in-game very fast on my VG248QE, my surroundings seemed to literally multiply in the direction of the pan. I tested this with LightBoost 100/120 Hz @ 10% and had no idea whether this was motion blur (which should have been minimized to under 2 pixels) or a different motion artifact. At least I know what it's called now. :D

Not many FPS gamers seem to be bothered by this since aiming at enemies takes precedence over viewing the surrounding geometry during fast panning. Yet it can be quite difficult to aim at units flying past you at high speeds horizontally or diagonally - especially at close range. Tracking multiple enemies in this manner makes you rely more on prediction since your eyes can only focus on one object (or multiple moving in similar directions) at a time.

Excellent article once again.
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Re: Need 1000fps@1000Hz for 1ms persistence without strobing

Postby RealNC » 15 Jan 2014, 07:34

There's still something I don't fully understand in regards to strobing and persistence. These methods are intended to make persistent displays behave like CRTs. Why is FPS important? Back in the CRT days, games had the same problems we have today; they often would fall below the vertical frequency of the monitor. Playing a game at 30FPS would look just as sharp on my 120Hz CRT as a 60 or 120FPS game.

So why is high FPS important for blur-free display on LCDs, if it wasn't important on CRTs?
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Re: Need 1000fps@1000Hz for 1ms persistence without strobing

Postby HeLLoWorld » 15 Jan 2014, 12:26

You can already have 500fps@500Hz on a good secondhand 50$ CRT.
Note I didn't mention y resolution :)
But it's cool, I did it.

So It's hard not to think that by having pushed this tech further (and with focus on this) we could have had very cool things by now.
It all comes down to bandwidth and horz freq, maybe by modding we could already have more.
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Re: Need 1000fps@1000Hz for 1ms persistence without strobing

Postby Chief Blur Buster » 15 Jan 2014, 13:30

RealNC wrote:There's still something I don't fully understand in regards to strobing and persistence. These methods are intended to make persistent displays behave like CRTs. Why is FPS important? Back in the CRT days, games had the same problems we have today; they often would fall below the vertical frequency of the monitor. Playing a game at 30FPS would look just as sharp on my 120Hz CRT as a 60 or 120FPS game.

So why is high FPS important for blur-free display on LCDs, if it wasn't important on CRTs?
Only because LCD is flickerfree.

Flickerfree creates high persistence (long frame visibility time).
There are only two ways to reduce persistence:
1. Add more frames to shorten persistence (shorter frame visibility time); and
2. Add black periods between frames to shorten persistence (also shorter frame visibility time)

CRTs naturally flicker, so they have a natural black period between flickers.
LCD could not do this technique as a motion blur elimination method, until recently.

Don't think of "CRT" or "LCD"
Think of motion blur as "persistence" == "frame visibility time"
1ms of persistence equals 1 pixel of motion blurring during 1000 pixels/second.
Certainly factors such as phosphor decay, does fuzzy up this math, but the math is fairly simple for squarewave persistence (e.g. strobe backlights, rolling scan OLED found in the japanese paper, etc).

Here's a longer explanation: Understanding persistence: strobed & nonstrobed, CRT vs LCD.
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Re: Need 1000fps@1000Hz for 1ms persistence without strobing

Postby Chief Blur Buster » 15 Jan 2014, 16:37

Also, even non-strobed 1000fps @ 1000Hz can potentially be a limiting factor for VR. With this, you still get 4 pixels of motion blurring during 4000 pixels/second panning -- say, turning your head while wearing 4K VR goggles.

You've heard of talk by multiple parties (Oculus, John Carmack, Valve Software) retorting that VR would benefit hugely from ultrahigh refresh rates. But that's hard, so low persistence via other means, is simpler. With VR, you've got bigger field of view coverage. With games and VR, you got faster panning speeds than video which can make motion blur problems more noticeable. With higher-def displays, you got more pixels to pan through. With computer graphics sharper than video, motion blur sensitivity is much higher. With faster-responding displays and smoother input, display limitations become even more visible. Alas, multiple parties have done test that already confirms that even going to high triple-digit or low-quad-digit doesn't completely sovle all display problems simultaneously, though you do get much closer to a continuous-motion (framerateless display).

Even at 1000fps@1000Hz (strobefree / flickerfree / continuous light / sample-and-hold) -- fast head turning could go 10,000 pixels per second, and thus create 10 pixels of motion blurring if you had 1ms persistence (mathematically minimum possible persistence of a flickerfree 1000fps display). Here, even 4000fps@4000Hz would actually be more beneficial over 1000fps@1000Hz, if you wanted a simultaneously blur-free strobe-free experience. This is unobtainium currently, so low-persistence strobing is much easier -- a much simpler solution, technologically, especially if you need sub-millisecond persistence.

Around Blur Busters, 1000fps @ 1000Hz is not crazy -- the people of Oculus, John Carmack, and the people of Valve Software (Michael Abrash), along with Blur Busters, are among the people who considers finite frame rates a limiting factor for virtual reality and theoretical Holodecks. For the already-explained reasons, getting only 1000fps @ 1000Hz is definitely not enough for the theoretical Holodeck turning test: as in, "Wow, I didn't know I was standing in Holodeck" or "Wow, I didn't know I was wearing VR goggles instead of wearing transparent glass ski goggles". To successfully pass the VR turning test or the Holodeck turing test, you would need a framerateless display (continuous motion) or ultra-high refresh rate on a retina-league display (e.g. perhaps a 10KHz refresh rate combined with 0.1ms motion blurring to eliminate wagonwheel effects). At least at the focal point, where humans are most sensitive to motion blur effects caused by the static frame hold effect (sample and hold), a display could theoretically refresh faster only where the human eye is pointing at, for some bandwidth simplifications.
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Re: Need 1000fps@1000Hz for 1ms persistence without strobing

Postby sharknice » 15 Jan 2014, 17:02

RealNC wrote:There's still something I don't fully understand in regards to strobing and persistence. These methods are intended to make persistent displays behave like CRTs. Why is FPS important? Back in the CRT days, games had the same problems we have today; they often would fall below the vertical frequency of the monitor. Playing a game at 30FPS would look just as sharp on my 120Hz CRT as a 60 or 120FPS game.

So why is high FPS important for blur-free display on LCDs, if it wasn't important on CRTs?


Yes it was just as sharp at 30hz, but it was extremely flickery. You could make a strobed LCD that strobes at 30hz and it would be the same way.
The acceptable flicker threshold for most people seems to be around 85hz. Anything below that and the flickering becomes bothersome. A lot of people would prefer having motion blur over flicker.
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Re: Need 1000fps@1000Hz for 1ms persistence without strobing

Postby Chief Blur Buster » 15 Jan 2014, 17:10

sharknice wrote:The acceptable flicker threshold for most people seems to be around 85hz. Anything below that and the flickering becomes bothersome. A lot of people would prefer having motion blur over flicker.

Yes, that's correct, as strobe backlights work best at framerate == refreshrate == stroberate (perfect sync).

This is where G-SYNC provides a very good substitute for those frame rates too low for strobing. It eliminates the stutters during variable framerate situations -- G-SYNC behaves like a CVT (continuously variable transmission) while traditional VSYNC behaves more like a gearshift (stutters during framerate variability).
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