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.Mark Rejhon wrote:EDIT 2018:
I've created an updated Blur Busters article about display persistence:
Blur Busters Law: The Amazing Journey To Future 1000Hz Displays
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/d ... ing-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:
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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.
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Simplified illustration for eye-tracking at 60fps @ 60Hz sample-and-hold (e.g. LCD)
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Simplified illustration for eye-tracking at 120fps @ 120Hz sample-and-hold (e.g. LCD).
Less motion blur.
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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).
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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.
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Continuous illumination (e.g. most LCD)
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Half persistence (the frame is illuminated half the time)
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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
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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.
Mark Rejhon wrote:EDIT 2018:
I've created an updated Blur Busters article about display persistence:
Blur Busters Law: The Amazing Journey To Future 1000Hz Displays