LCD motion blur: Eye-tracking now dominant cause of motion blur (not pixel transition/GtG) - Page 7 - AVS Forum
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post #181 of 184 Old 11-07-2013, 08:17 PM - Thread Starter
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Originally Posted by MrBonk View Post

It's not just the eye though.
The heart of it lies in the content. Much of the content has that blur (Especially motion blur) to begin with.
Freeze frame during any film or TV with the camera in motion.
That's why Blur Busters focusses on motion blur elimination for computers and video games:

1. Close viewing distances (1:1 view distance). Motion blur becomes easier to see.
2. Ultra high definition (1080p and up). Motion blur becomes easier to see relative to stationary images.
3. Faster movement speeds (faster than video/movie panning)
4. No content-based motion blur (unlike movies/video), or GPU blur effects easily disabled in Game Options

We have run into situations where we even see motion blur with just 2ms of persistence -- which translates to 2 pixels of motion blurring during 1000 pixels/second motion.
(persistence, not GtG -- persistence and transitions are two different things -- see www.testufo.com/eyetracking ) ... Tomorrow, it's virtual reality goggles strapped to our faces, where we turn our heads. Here, even 1ms of persistence becomes a problem -- 4 pixels of motion blurring during 4000 pixels/second motion (full screen width per second for a 4K display). Imagine turning your head and suddenly seeing unwanted display-based motion blur being forced upon you. Whether it's 1ms of persistence caused by strobing (1ms flashes), or 1ms of persistence from short frames (1000fps@1000Hz). There would still be human visible motion blur caused by flickerfree 1000fps@1000Hz (1ms persistence per refresh) even if transitions is instantaneous at 0ms. Short-persistence CRT's have less motion blur than that (e.g. 0.1ms persistence)

And video games / computer use is generally so demanding of low latency, that interpolation is verboten unless it can be achieved at low latencies. For example, native 240fps@240Hz could be interpolated to 960fps@960Hz with only an added ~4.1ms of latency with 1-frame-lookahead. But at current (today's) native refresh rates, interpolation is simply not an option, as no supercomputer can accurately do interpolation without frame lookahead (which requires buffering, which causes input lag). So many of today's "960Hz" televisions with interpolation, don't work very well for video games...

Finite/discrete refresh rate displays are always going to cause problems for blurfree media such as videogames and virtual reality, as in tomorrow's holodecks.
Longer run, dynamic higher-speed refreshing where the eye is pointing is at, to other exotic refreshrateless display technologies (continuous movement without the need for interval-based refreshing), may save the day. Zero strobing, zero phosphor, zero laser scanning, perfectly continuous light. But for a long time, the refreshrate-driven display metaphor will stick with us for a long time.

The good news is manufacturers are FINALLY starting to recognize computer/game-friendly strobe backlights, to fill needs.

- NVIDIA LightBoost -- the one that started it all! -- unofficial for 2D
- NEW: NVIDIA G-SYNC's optional strobe mode -- Official "sequel" to LightBoost
- NEW: Eizo Turbo240 Mode (FG2421) -- official strobe backlight
- NEW: BENQ Blur Reduction Mode (XL2720Z) -- official strobe backlight
- Samsung 120Hz 3D Mode -- unofficial for 2D
- Sony Motionflow Impulse -- 60Hz interpolation-free low-latency mode available in Game Mode on certain models.

As you can see, today, we've come a long way -- and what I said last year was prescient/correct.
Today, LCD's that beat CRT motion clarity, now exist today. (at least for LightBoost=10%, benchmarked against a Sony FW900 CRT -- testimonials) --
My predictions one year ago is correct.
The day of CRT-motion-quality computer monitors -- that aren't CRT's -- have finally arrived.
These ultra-high-efficiency strobe backlight displays are vastly superior to scanning backlights in terms of motion quality; as they have none of the inefficiencies caused by scanning backlights.

As we approach Holodeck towards the end of this century (bigger displays, bigger FOV, bigger resolution, less content motion blur, more human-natural motion blur, less display-forced motion blur), the elimination of unavoidable display-based motion blur through various technologies are necessary. Strobe backlights are only a band-aid stop gap for now, simply because we can't achieve low-persistence with steady-light-output displays (non-light-modulated, zero flicker even under high speed camera). So we need scanning, strobing, phosphor, subfields, or another form of light modulation (for now), and strobe backlights are a great, inexpensive improvement to today's LCD's, now that it's become much easier to bypass LCD pixel speed limits (on modern/fast panels) as the motion blur limiting factor for games/computers. Massive order-of-magnitude motion blur improvements are now today routinely possible with fast-response LCD's through ultra-high-efficiency backlight strobing. A good big incremental step to enjoy while waiting for OLED's to mature.

Thanks,
Mark Rejhon

www.BlurBusters.com

BlurBusters Blog -- Eliminating Motion Blur by 90%+ on LCD for games and computers

Rooting for upcoming low-persistence rolling-scan OLEDs too!

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post #182 of 184 Old 01-22-2014, 11:55 AM - Thread Starter
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Hello,
Thanks to the site admin for editing the post title.

The topic has now been renamed.
Incorrect: "LCD motion blur: Eye-tracking now dominant cause of motion blur (not pixel persistence)"
Correct: "LCD motion blur: Eye-tracking now dominant cause of motion blur (not pixel transition/GtG)"

Back when I posted this thread, I was using the PixPerAn motion testing tool, called "Pixel Persistence Analyzer". This old motion blur testing software application, "PixPerAn" (written in the era before good backlight strobing), perpetuated the confusion between persistence and GtG, especially as persistence was roughly equal to GtG for many years, until GtG became far less than a refresh cycle, then motion blur was bottlenecked by the refresh cycle length (1/60sec = 16.7ms) even as GtG continued falling to sub-frame lengths (meaning little difference between 1ms, 2ms, and 5ms LCDs). The divergence of persistence and GtG, makes it necessary to really clearly industry standardize the separate factors, and the industry has finally chosen the word persistence.

Myself, Blur Busters, John Carmack, Oculus, Valve Software, and many parties, have all unamiously agreed "pixel persistence" is a totally different meaning from "pixel transition/GtG"

persistence == sample and hold == pixel visibility/static time

transition == GtG == pixel switching time == pixel transition time == pixel movement time

Thanks,
Mark Rejhon

www.BlurBusters.com

BlurBusters Blog -- Eliminating Motion Blur by 90%+ on LCD for games and computers

Rooting for upcoming low-persistence rolling-scan OLEDs too!

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post #183 of 184 Old 01-31-2014, 01:22 PM
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Quote:
Originally Posted by Mark Rejhon View Post

Another item from the Scanning Backlight FAQ is ...

Q: How do you bypass pixel persistence as a motion blur barrier? (with a scanning backlight)

A: Thanks to tests on new LCD panels, it has now recently become possible to bypass the pixel persistence barrier. In some displays, the vast majority of pixel persistence is less than a single frame of a refresh. This provides an excellent window of opportunity for a massive motion-blur reduction from a scanning backlight. It is possible to wait for pixels to finish refreshing, and then strobe the backlight after the pixels have largely finished refreshing, but before the next refresh. A single refresh at 60Hz takes about 16.67 milliseconds, and pixel persistence has now become far less than this.

Example LCD Refresh cycle
T+0ms - Refresh begins (unseen in dark)
T+2ms - Most of the refresh is finished (unseen in dark)
T+14ms - Residual ghosting is practically gone (unseen in dark)
T+15ms - Strobe backlight brightly for 0.5 milliseconds (seen by human eye)
T+16.67ms - Next refresh begins (unseen in dark)

The human eye sees the 0.5 millisecond strobe portion of a refresh that is visible, instead of the pixel persistence portion of the refresh that is now made invisible by a turned-off backlight. Thus, the human eye no longer sees motion blur caused by pixel persistence limitations, provided the display is able to finish refreshing before the next refresh cycle.

Mark,

this information is fascinating, and while I don't have the energy to explore the subject as deeply as you, I would like to understand if I have the major points right:

1/ modern 120Hz refresh panels have succeeded to reduce motion blur by 50% versus older 60Hz refresh panels because pixel persistence has been significantly reduced in order to reduce ghosting or more importantly, crosstalk between 'eyes' in the case of active 3D.

2/ combining a 120Hz refresh panel with a scanning backlight can eliminate motion blur caused by pixel persistence and ghosting at the expense of a 50% loss of image brightness.

3/ in this case, motion blur caused by eye tracking will still exist (but will still be half of what it would be without a 50/50 scanning backlight).

4/ the only way to further reduce apparent motion blur is to further reduce the duty cycle of the strobe (with a corresponding reduction in image brightness). Strobing at 10% duty cycle will reduce eye-tracking-based motion blur to 10% of what it would be without a scanning backlight (and also with a resulting image that is only 10% as bright).

Is all of that essentially correct (and if not, appreciate clarification).

Also, I believe the example you have provided above is for a 60Hz refresh panel (14ms for the residual ghosting to be practically gone).

Would it be possible for you to show a similar example for typical timing of a 120Hz panel with a 50% scanning backlight?

One detail I am a bit confused about; is the use of multi-segment scanning backlights (ie: 4 or 5 segments). Are these used to effectively strobe 'ON' 75% or 80% of the time and if so, wouldn't that mean that eye-tracking-based blur would be worse than it would be with a 50% strobe (and the resulting image also brighter than it would be with a 50% strobe)? Or are the multi-segment scanning backlights used to strobe 25% or 20% of the time and so deliver a further reduction in eye-tracking-based motion blur versus a 2-segment scanning backlight (and with a corresponding reduction in image brightness)?

-fafrd
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post #184 of 184 Old 02-02-2014, 02:39 PM
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Quote:
Originally Posted by Mark Rejhon View Post

Another item from the Scanning Backlight FAQ is ...

Q: How do you bypass pixel persistence as a motion blur barrier? (with a scanning backlight)

A: Thanks to tests on new LCD panels, it has now recently become possible to bypass the pixel persistence barrier. In some displays, the vast majority of pixel persistence is less than a single frame of a refresh. This provides an excellent window of opportunity for a massive motion-blur reduction from a scanning backlight. It is possible to wait for pixels to finish refreshing, and then strobe the backlight after the pixels have largely finished refreshing, but before the next refresh. A single refresh at 60Hz takes about 16.67 milliseconds, and pixel persistence has now become far less than this.

Example LCD Refresh cycle
T+0ms - Refresh begins (unseen in dark)
T+2ms - Most of the refresh is finished (unseen in dark)
T+14ms - Residual ghosting is practically gone (unseen in dark)
T+15ms - Strobe backlight brightly for 0.5 milliseconds (seen by human eye)
T+16.67ms - Next refresh begins (unseen in dark)

The human eye sees the 0.5 millisecond strobe portion of a refresh that is visible, instead of the pixel persistence portion of the refresh that is now made invisible by a turned-off backlight. Thus, the human eye no longer sees motion blur caused by pixel persistence limitations, provided the display is able to finish refreshing before the next refresh cycle.

Mark,

a follow-on question for you. The 2014 Vizio P Series will apparently be based on a panel with 120Hz native refresh rate combined with a scanning backlight for 960Hz 'Clear Action Rate'.

If I've understood all this stuff about scanning backlights correctly, this either means they have an 8-zone scanning backlight or a 4-zone scanning backlight combined with insertion of 4 black frames (since the panel is Full-Array Local Dimming with 64 dimming zones probably organizes as an array of 8 across X 8 down, the scanning backlight is probably 8-zone).

Either way, I believe this means that rather than strobing pixels for the entire 8.34ms, pixels will only be strobed for 1/8th of that time meaning 1.4ms...

This is about 3 times the example you sketched above, but it is still a big step in that direction.

The Vizio Reference Series has a 'Clear Action Rate' of 1800Hz. This is probably implemented with a 120Hz native refresh panel combined with an 8-zone scanning backlight and insertion of 7 black frames. But whatever, it means that the pixel strobe time should be reduced from 8.34 to 0.56 milliseconds.

So my question for you is, does the Vizio Reference Series essentially implement the massive motion-blur reduction as you have outlined above??? (and the P-Series implementation get to within a factor of 2?)

-fafrd
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