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Asus 240hz native new screen

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Re: Asus 240hz native new screen

Postby Chief Blur Buster » 21 Jan 2017, 14:12

Clarifications...

Falkentyne wrote:A CRT at 120hz is 8.3ms of persistence.

No.

Persistence is often a mis-used word, but in many cases, it is being used to describe the length of phosphor fade.

The phosphor fade is a continuous curve, but fade-to-90%-dark is the generally accepted cutoff point for quoting numbers (although not necessarily representative of human eye detectability). In this way, there are CRTs that do this in far less than 1ms, and CRTs that do this in more than 1ms. Either way, the phosphor on a typical CRT fades in less than 8.3 milliseconds. (Except when we're talking about old "memory CRTs" or radar scopes).

In other words, CRT persistence (from the human eye's POV) has a curved sawtooth curve (fast up, curve down) and strobed LCD persistence have a squarewave curve (fast up, fast down). And non-strobed LCD persistence (as seen by the eye) is a slow curve on both sides of the curve.

For the advanced thinkers: Motion blur can occur on either side of the persistence curve. If only one side of the curve is slow, then more motion blurring becomes visible on one side of motion (either leading or trailing) and the appearance of these types of artifacts are described as "ghosting". That's why phosphor-based motion blur is described as phosphor ghosting. Also traditional LCD ghosting due to GtG asymmetries of various forms (fast GtG in rise, slow GtG in fall). But all of them boils to eye-tracking-based-motion-blur physics found at www.testufo.com/eyetracking ...

Falkentyne wrote:However there is no crosstalk (overdrive artifacts don't exist on CRT's)

True, but not really relevant in the same sentence when we're talking about motion blur. Crosstalk occurs when visible persistence exceeds the length of a refresh cycle. Persistence can be longer than a refresh cycle (e.g. old 33ms LCDs, radar CRTs, etc)

Falkentyne wrote:and the response time of phosphors are in the NANOSECONDS.

Only on the illuminate-side. Not the fade-side. However, the nanoseconds have little bearing on actual motion blur -- it's the actual persistence time (length of phosphor fade, or length of strobe) that pretty much determines display motion blur.

Falkentyne wrote:I would estimate that a 120hz CRT would strobe at somewhere around 0.5ms to 1.0ms of true persistence, if you related this to LCD strobing.

That's better.

Falkentyne wrote:At 240hz ULMB, what matters is the persistence. 1.0ms persistence at 240hz will look better than 1.0ms of persistence at 120hz at FAST MOTION. At slow motion, it will look the same. The bigger benefit is you won't notice any flickering.
Yes.
In other words: The motion blur will be identical as it's a function of persistence, but you'll see less flicker / less lag / fewer stroboscopic / fewer wagon-wheel / fewer phantom-array artifacts.
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Re: Asus 240hz native new screen

Postby Falkentyne » 21 Jan 2017, 14:56

I wish Asus or Benq would just hire you to work on their firmwares.

Then we could get some really nice features, and you could have a group of dedicated users to help bug test before going live (as the average pro gamer probably doesn't even know what something like "Single strobe" even is.

The Benq XL2540 doesn't even seem to have a working persistence (Intensity) slider. I don't know if it works at 100hz or 120hz but it sure does NOT work at 240hz. It's like trying to use "Single Strobe" on the old blur reduction Benqs at 50hz refresh rate...the monitor doesn't strobe, but changing strobe duty still affects the brightness. Go too high and overcurrent protection shuts the monitor off hard. These XL2540 monitors ARE Strobing but persistence isn't being affected when changing "Intensity" In the service menu....
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Re: Asus 240hz native new screen

Postby Paul » 21 Jan 2017, 16:49

...Has it been confirmed that ULMB will work at 200+ Hz with that monitor?
If so then I might upgrade from my XL2720Z one day... Probably when the price drops down to "affordable" levels.
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Re: Asus 240hz native new screen

Postby Chief Blur Buster » 21 Jan 2017, 17:40

I suspect that ULMB will look good only up to approximately 75%-85% of the monitor's maximum refresh rate, assuming 1ms TN. I'd guesstimate ULMB would look sufficiently clean up to 180Hz, then start to really get dramatically bad with strobe crosstalk as you approached the LCD's native refresh rate.

Strobing requires a pause between refresh cycles to let pixels settle (finish GtG transitions in dark) before visibly strobing the whole screen.
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Re: Asus 240hz native new screen

Postby Paul » 22 Jan 2017, 06:40

Chief Blur Buster wrote:I suspect that ULMB will look good only up to approximately 75%-85% of the monitor's maximum refresh rate, assuming 1ms TN. I'd guesstimate ULMB would look sufficiently clean up to 180Hz, then start to really get dramatically bad with strobe crosstalk as you approached the LCD's native refresh rate.

Strobing requires a pause between refresh cycles to let pixels settle (finish GtG transitions in dark) before visibly strobing the whole screen.


Chief you should buy that monitor when it comes out and tell us your honest opinion about it : )
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Re: Asus 240hz native new screen

Postby Chief Blur Buster » 22 Jan 2017, 13:05

Since this monitor supports ULMB all the way to 240Hz -- I'm really curious how good/bad the crosstalk is at 240Hz.

<Monitor Engineering Talk>

To get cross-talk free 240Hz, you need to accelerate scan to free up a 1ms blanking interval.
At 240Hz with reduced blanking interval, it would be 1/240sec = ~2.5ms LCD scan.

To create enough time for mostly crosstalk-free strobing at 240Hz, you would need to scan the LCD in 1.5ms (2.5ms slowest possible scan cycle minus 1ms GtG) necessary to create a 1ms pause (blanking interval) between refresh cycles for giving time to settling the LCD GtG pixel transitions (in total darkness) before strobing a fully clear frame. Mathematically this requires a scan cycle of 1.5/1000th of a second = 1/666th of a second for a 1ms TN. Ouch. (A 666Hz+ capable LCD!)

Now, if the GtG of a TN LCD can be reduced to ~0.5ms in a highly aggressive overdrive mode, then you only need to reduce from ~2.5ms to ~2ms (2.5ms minus 0.5ms). So you need an LCD scan cycle of 2/1000th of a second = 1/500th of a second scan. Ouch, again (a scan rate equivalent to a 500Hz LCD). Perhaps the screen is actually doing this (e.g. creative LCD scan optimizations such as addressing multiple rows of pixels simultaneously, to speed up the top-to-bottom scan) -- there is no technical reason why it can't be done. Some manufacturers have been able to do very creative tricks to compensate, to create more time. LCDs have been scanned at 1000Hz in the laboratory, so we haven't hit theoretical limits yet.

For strobe flash timing, you time the strobe flash somewhat late (sometimes after already having begun the next LCD scan) to make sure the strobe crosstalk is balanced between the top edge/bottom edge. For strobe flash length, you don't want it to be too long (enroach the end of previous refresh cycle or beginning of next refresh cycle). The longer the strobe flash length, the longer the blanking interval needs to be for relatively strobe-crosstalk-free operation.

But if NVIDIA let 240Hz strobing happen, then knowing NVIDIA, they've already done some really creative tricks... Or it was moved to the Service Menu because of bad strobe crosstalk.

</Monitor Engineering Talk>

Anyone test for strobe crosstalk at 120Hz versus 180Hz versus 240Hz?

Photographing Strobe Crosstalk
Strobe crosstalk may be fairly bad (at the top and bottom edges) at 240Hz ULMB. The ideal test is the TestUFO Alien Invasion -> full screen mode, speeds of 1440ppf or faster -- 3840ppf works great for photography even if too fast for eyes. Take a fast-shutter photograph of this (preferably 1/240sec shutter speed with a point-and-shoot camera, or SLR), and you've photographically captured strobe crosstalk, worthy of posting in forums. You may want to take separate photos of top edge and bottom edge, if you need clearer close-ups. Even a smartphone camera works well if your screen is adjusted as bright as possible, and your smartphone camera app's exposure compensation as low as it can go (without going too dark), you need the camera photo to capture exactly only 1 strobe flash, not more than 1.
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Re: Asus 240hz native new screen

Postby Chief Blur Buster » 22 Jan 2017, 13:20

flood wrote:btw @chief: if you read this: you should change the speed selection on testufo to multiples of the refresh rate, so that there's no jitter from rounding

It already automatically rounds-off to the nearest "Pixels Per Frame", so just select a few numbers and read the "Pixels Per Frame" value. It always locks motion based on exact PPF, which means "Pixels Per Second" will be inaccurate by default when it's rounded-off (e.g. running TestUFO at custom refresh rates).
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Re: Asus 240hz native new screen

Postby Falkentyne » 22 Jan 2017, 13:35

Chief,
The Samsung monitors avoid any crosstalk at all at 144hz by strobing the backlight in 4 "quadrants" instead of at once. I wonder if the Asus is doing something similar? I just don't want to buy a monitor to test it :( The Samsung panels are suffering from pixels going bad, color purple shift, freesync issues and the works :(
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Re: Asus 240hz native new screen

Postby Chief Blur Buster » 22 Jan 2017, 14:42

Falkentyne wrote:Chief,
The Samsung monitors avoid any crosstalk at all at 144hz by strobing the backlight in 4 "quadrants" instead of at once. I wonder if the Asus is doing something similar? I just don't want to buy a monitor to test it :( The Samsung panels are suffering from pixels going bad, color purple shift, freesync issues and the works :(

A low-resolution scanning backlight (2-section or 4-section) is also a clever way to (on average) reduce strobe crosstalk.

Even an edgelight can in theory do this -- strobe top edge strobe & bottom edge separately. Like a 2-segment super-low-resolution scanning backlight. It is tricky though. The problem is controlling internal light scatter (easier to do with a back light rather than an edge light) so there can still be crosstalk issues with scanning backlights. In exchange for reducing crosstalk at the top/bottom edges, some of them spread crosstalk more evenly throughout the screen because of internal light scatter. Unless light leakage into adjacent sections is strongly controlled, something easier to do with true backlights and local-dimming backlights, than with edgelights. For a 2-flash or 4-flash strobe backlights (aka low-resolution scanning backlight) with poor internal reflection rejection, it might replace 1 strong strobe crosstalk with 4 much-fainter ghosts (at 1/4th spacing or 1/2 spacing). But if Samsung does this well, the multiple ghosts coming from low-resolution scanning backlights might be 10x-100x fainter and be preferable...

Advanced gaming monitors are coming with local dimming capabilities (e.g. PG27UQ) which can be used as a high quality scanning backlight that eliminates the majority of internal reflections.

How good is the 4-quadrant strobe backlight in reducing strobe crosstalk?
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Re: Asus 240hz native new screen

Postby Falkentyne » 22 Jan 2017, 16:27

I don't have that monitor because of the horrible QA issues with it. Did you check the overclock.net thread on it?
There is no visible crosstalk at 144hz, however I don't know if there are other strobe artifacts or not.

http://www.overclock.net/t/1605507/sams ... uantum-dot

A LOT Of people are returning these monitors.
Apparently the C27 27" 1080p version is faring better.
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