Blur reduction and 240Hz monitors

Motion blur eliminating strobe backlights found in gaming monitors. This includes NVIDIA LightBoost, Ultra Low Motion Blur (ULMB), EIZO Turbo240, ToastyX Strobelight utility, etc.

Re: Blur reduction and 240Hz monitors

Postby Chief Blur Buster » 26 Nov 2016, 21:35

Very huge ratio of visible:blanking interval, would pull this off.

Example: 3.5 millisecond blanking interval (using a fast 1/288sec LCD scan at 144Hz). As in a 50%:50% visible:blanking ratio, rather than the usual 95%:5% ratio. This would be quite tantamount to a huge Vertical Total (e.g. Vertical Total 2160 = 1080 active rows of visible pixels + 1080 vblank between refresh cycles -- for a 1080p signal), but done internally inside the display, where the LCD is scanned more quickly per refresh, to allow a larger pause between refresh cycles. Metaphorically speaking, this would be like that 1970s analog TV with a rolling picture -- with the VHOLD black bar -- except the VHOLD black bar becomes much thicker, as tall as the preceding/succeeding image -- a massive blanking interval between refresh cycles. This has huge benefits in greatly reducing strobe crosstalk.

This reduces GtG asymmetry between top and bottom edges of screen.

Some displays like EIZO FG2421 achieved fairly good top-to-bottom crosstalk consistency (at least when the screen was warmed up). It actually scanned the panel at something like 1/240sec, during 120Hz mode. So the blanking interval was mondoo huge, big enough to drive the "slow VA 4ms transition" semi-trailer truck through the gapingly-large VBLANK interval.

Someone would need to (1) enable strobing mode, then (2) hardwire the backlight continuously on, and (3) aim a really good high speed camera .... and then we could determine how the LCD is succeeding in lowering strobe crosstalk.

Whenever strobe crosstalk is consistent from top-to-bottom edge of screen, that often means the top-to-bottom scan is being done really quickly. In theory, you could scan faster than the GtG transition -- for VA pixels of 4ms transition time, and a scan that takes only 3.5ms at 1/288sec scan (for 144Hz) you've refreshed the whole screen so quickly that you're triggering the beginnings of the pixel transition (GtG) for the bottom edge of the screen BEFORE the top edge of the screen has completed transitions (GtG). Now if you've got a large blankning interval pause (e.g. at least 4ms -- often critical for VA-based strobed displays, as VA is slower than TN) ... you've got lots of time for all the GtG pixel transitions to complete. The GtG asymmetry of top/bottom edges can be quite much more subdued with much larger blanking intervals.

The bigger the blanking interval (whether internally done like in VA displays, or manually done like in BENQ XL2720Z "Vertical Total"), the easier it is to reduce GtG asymmetry during backlight strobing (less difference between top/center/bottom edges) and also reduce strobe crosstalk -- since it's easier to hide the LCD GtG pixel transitions between refresh cycles and flash the strobe backlight when the pixel transitions are complete. Ideally, you want GtG as small as possible and the blanking interval as long as possible -- for the cleanest possible strobing.

NOTE: For those familiar with XL2720Z "strobe phase adjustment" -- the horizontal strobe crosstalk band -- is much easier to hide inside a larger blanking interval. Meaning, you can move the "double image" band very far off the bottom edge of the screen long before it reappears back at the top edge of the screen. (Strobe crosstalk is massively amplified when the display flashes the blur-reduction backlight while the LCD pixels are still in the middle of their GtG transitions)

TN 240Hz LCDs can probably achieve super-clean look simply by doing this too for 120Hz and 144Hz strobing, too. Assuming the LCD scan is at the full speed (1/240sec) with a large idle period between refresh cycles. For an 8.3ms refresh cycle, 4ms of scan and 4ms of pause (blanking interval. One could even give the LCD 1ms GtG transition a full healthy 3ms to completely settle, before doing a 1ms strobe flash, before beginning the next refresh cycle. This would produce extremely clean refreshes.

Alternatively, a two-pass refresh cycle is a great alternative to a massive blanking interval. Instead of doing a large blanking interval at 50%:50% visible:blanking, you refresh the whole screen twice with the same frame.

Going even further, a 240Hz LCD panel running in 120Hz mode (or 288Hz LCD panel running in 144Hz) could refresh the whole screen twice (The EIZO FG2421 does this) for the same refresh cycle. This helps clean GtG transition imperfections up even further (ghosting, crosstalk, etc). You'd want to strobe at the very end fo the 2nd refresh pass. The two refresh cycles serves to erase as much of the GtG transition artifacts far before the strobe flash. This creates a very clean image. Since some VA displays do the double-pass refresh trick to clean-up their refresh artifacts (GtG/ghosting/etc) -- this may also be why strobe crosstalk is so low for this display.

I highly recommend 240Hz monitor vendors include an ultra-clean strobed 120Hz mode (two-pass refresh + strobe near the end of the 2nd-pass refresh), as it will reduce strobe crosstalk by more than an order of magnitude. In fact, you don't need large blanking intervals for two-pass refresh techniques -- because you can strobe pretty much almost *anytime*, even in the middle of the second pass, since the first pass already did most of the job already, and still have less strobe crosstalk than single-pass refresh methodologies. The second pass is frosting on the cake. Ideal timing of the strobe will still be near the end of the second pass, but just before the first pass of the next refresh cycle, for even fainter strobe crosstalk. The single pass refresh cycle would never be seen by the human eye, as only second-pass refresh cycles would be strobed -- the only purpose of the two-pass refresh cycles is to clean up the GtG artifacts quicker and reduce asymmetry between top/bottom edges as early as possible before the strobe flash of the most perfect-possible-moment of LCD refresh state.
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Re: Blur reduction and 240Hz monitors

Postby Sirslicey » 26 Nov 2016, 23:32

So still no worthwhile upgrade from the BenQ XL2720Z for MBR users? Though the future may look promising for us, just may take a while.
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Re: Blur reduction and 240Hz monitors

Postby Chief Blur Buster » 26 Nov 2016, 23:40

Sirslicey wrote:So still no worthwhile upgrade from the BenQ XL2720Z for MBR users? Though the future may look promising for us, just may take a while.

If you don't care about 60Hz single-strobe, there's already superior strobed monitors than the XL2720Z.

There are already IPS and VA strobed displays, for example.... Even if none of them do 60 Hz single-strobe.
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Re: Blur reduction and 240Hz monitors

Postby Sirslicey » 27 Nov 2016, 02:23

Well I love the idea of an IPS or VA monitor, but
Chief Blur Buster wrote:
Sirslicey wrote:So still no worthwhile upgrade from the BenQ XL2720Z for MBR users? Though the future may look promising for us, just may take a while.

If you don't care about 60Hz single-strobe, there's already superior strobed monitors than the XL2720Z.

There are already IPS and VA strobed displays, for example.... Even if none of them do 60 Hz single-strobe.
Well I love the idea of an IPS or VA monitor, even 1440p or g-sync would be awesome, but I prize MBR performance more than anything else on my list. Unfortunately I don't totally understand everything you guys talk about as I'm relatively new to all of this. Don't know what 60Hz single-strobe is vs what I currently use. I'm assuming currently I have 120Hz single strobe, and that would be my minimum I think.

I have to say the the mbr performance of my monitor is REALLY good. I don't personally know what monitor's have the best strobing performance vs the xl2720z, but I'd love to know!
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Re: Blur reduction and 240Hz monitors

Postby Chief Blur Buster » 27 Nov 2016, 11:26

Sirslicey wrote:Well I love the idea of an IPS or VA monitor, even 1440p or g-sync would be awesome, but I prize MBR performance more than anything else on my list. Unfortunately I don't totally understand everything you guys talk about as I'm relatively new to all of this.

Firstly.... Do you mean:

"I prize MBR performance more than anything else on my list"
...equals "The XL2720Z is the first strobed monitor I have ever seen, and I'm damn impressed with the motion blur reduction. However, I can't tell apart Stobe Length (Duty Cycle) 0.5ms versus 1.0ms versus 2.0ms, and I can't tell apart input lag of strobed and non-strobed mode..."
(The newbie POV)

*OR*

"I prize MBR performance more than anything else on my list"
...equals "I've seen many strobed monitors, and I crave minimum lag, and I see improvements with all the fiddling I do with the XL2720Z, and I actually see the improvements in the real-world competition games I play..."
(The experienced POV)

......

The bottom line is all strobed monitors generally have equally (approximately) dramatic improvements in motion clarity when enabling/disabling MBR features (strobing) for motion whose framerate-matches-refreshrate..... And the further adjustments (that some monitors give) gives minor further improvements (clarity, colors, input lag, etc). If you're a competition gamers, details will matter very much to you -- the XL2720Z is one of the best for tweaking strobe settings to your likings, at the cost of other advantages. On the other hand you're someone who wants the best-color MBR at 120Hz and with less strobe crosstalk, then the XL2720Z isn't the one. But if you crave motion clarity while running emulators at 60fps at 60Hz, then you want single-strobe on XL2720Z (at least for emulators that do not have a black frame insertion feature, like UAE and certain versions of MAME).

About 60Hz single-strobe -- Proper MBR clarity requires one backlight flash per refresh cycle, you don't want two -- and monitor manufacturers who do MBR at 60Hz often use two flashes per refresh cycle (to try to reduce flicker) and that causes a double-image effect (like 30fps@60Hz on a CRT -- the same issue happens with 60fps@120Hz). So 60Hz double-strobed looks like 60fps@120Hz strobed. While 60Hz single-strobed has very good motion clarity but flickers a lot more. Pretty much a pick-your-poison.
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Re: Blur reduction and 240Hz monitors

Postby Sirslicey » 27 Nov 2016, 21:03

I think a bit of both. The XL2720Z is the first strobed LCD monitor I have ever seen.(I used to use CRT's) I am damn impressed with the motion blur reduction. I haven't tested the difference between 0.5ms versus 1.0ms because of the brightness being too low and it seems to be a point of diminishing returns given the lower brightness. (I currently use 1.4ms). I -THINK- I can tell a difference in input lag from strobed to non strobed. I think strobed has a little bit more lag, but hard to tell. It's a very small amount if so, and seems to not have been a hindrance. The strobing was more beneficial for me that I didn't question it. I crave minimum lag WITH strobing. I do see improvements with the fiddling. BBSU, Vertical total tweaks(1500) etc. 120Hz. I do see improvements in my competitive gameplay.

I do not care much about 60Hz single strobing.(is that for like console games emulators?) Better than 120hz MBR?

Given that, what are the ideal settings for my preferences? (obviously lowest persistence, brightness allowing)
But is earliest strobe phase best? What are the effects of strobe phase other than visible crosstalk?
What about V-sync? I used to use V-sync on(double-buffered) but have since tried no v-sync and didn't notice much difference other than tearing(no big deal). The reason I tried no v-sync is because I heard that having highest FPS = least amount of input lag because the frames that are being inserted in the refresh are technically "newer." is there truth to that? What about Framerate smoothing? I see some games like the new Unreal Tournament with that option in the menus.

Anyways given my preferences, I'm not aware of a better monitor, though there may be one.

Maybe I should have made my own topic! :oops:

Edit: Looks like I should have done my homework better. So earlier strobe phase does reduce input lag.
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Re: Blur reduction and 240Hz monitors

Postby Falkentyne » 28 Nov 2016, 00:45

Earlier strobe phase does reduce input lag, but on the XL2720Z, an earlier strobe phase is a HIGHER value of strobe phase in the service menu (up to 100, max limit is reduced when using a vertical total tweak).

You can test this very easily. On the XL2720Z, use TestUFO Alien invasion fullscreen test, press F11, then change the strobephase from 0 to 100 (~50 with a Vertical total tweak applied at 100 and 120hz as the backlight shuts off at >059 strobe phase at 100hz / VT 1350 and VT 1500, and >049 strobephase at 120hz, VT 1350/1500 applied).

Watch the position of the vertical red bar on testufo alieninvasion.

http://www.testufo.com/#test=photo&phot ... &height=-1

As you change the strobe phase from 0 to 100, notice that the bar moves 1 'frame' to the RIGHT? That means you are improving input lag (From the bottom of the screen to the top) by up to 1 frame). As you reduce strobe phase down to 000, the bar moves 1 frame to the LEFT (higher input lag).
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Re: Blur reduction and 240Hz monitors

Postby Chief Blur Buster » 28 Nov 2016, 11:33

Falkentyne wrote:As you change the strobe phase from 0 to 100, notice that the bar moves 1 'frame' to the RIGHT? That means you are improving input lag (From the bottom of the screen to the top) by up to 1 frame). As you reduce strobe phase down to 000, the bar moves 1 frame to the LEFT (higher input lag).

Yes.

Early/late strobe phases interaction with input lag can be weird/complex.

If you make a strobe flash 50% out-of-phase, you have a strobe crosstalk bar across the middle of the screen -- and half of your screen has 1 extra frame of input lag compared to the other half! Opposite sides of the strobe crosstalk zone for out-of-phase adjustments, will be 1-frame-lag-apart. So it's important to tweak Strobe Phase correctly.

If you use a full-screen "Alien Invasion" pattern while adjusting Strobe Phase, you'll be moving the crosstalk band upwards/downards. Typically, the bottom half will be the lagged part and the top half will be the less lagged part. Most stuff at the bottom edge of the screen is unimportant, so you can technically move the strobe crosstalk band upwards to roughly the gun-barrel level (in a FPS shooter), since you really need to see the minimum lag at roughly crosshairs levels. Many enemies do not often come from below the level of your gun barrel (e.g. snipers on the floor, etc). Basically, move that strobe crosstalk band to roughly below feet level of the enemies showing up on your screen. So in theory you could move the strobe crosstalk band about 1/4th screen height upwards from the bottom. That will reduce your strobed input lag by roughly 1-2 milliseconds, but at the cost of ugly double-image effect on the bottom 1/4th of the screen.

This may also be why original XL2720Z's are calibrated the way they are (in V1, this is non-adjustable) -- with the ugly crosstalk problem. Lot of MBR users hate this because they like using MBR for enjoying clarity. But some competition gamers may actually prefer the default setting, to minimize lag at crosshairs level, if they're not distracted/slowed down by the ugly crosstalk near the bottom of the screen.

Image

The above is a photo of the strobe crosstalk artifact (double-image effect during 120fps@120Hz motion).

Instead of the Strobe Utility, most people often use the Service Menu to adjust the strobe phase setting -- it can be ajdusted from there in the service menu.

Now, back on the topic of 240Hz monitors, strobe crosstalk will be a big problem for 240Hz strobing -- you could technically strobe at 240Hz but the blanking intervals between 240Hz refresh cycles will be so tiny, not giving enough time for clean strobes on fully refreshed frames (Not enough time for LCD GtG transitions completed in darkness -- at 240Hz, next refresh cycle scan will begin again at top edge, well before bottom edge of screen has fully completed LCD GtG transitions).

My calculations shows you can likely have reasonably good strobing at 175-200Hz refresh cycle, for a 1/240sec scan -- sufficient time for a pause (to permit LCD GtG transitions to finish) between refresh cycle. For flawless 240Hz strobing, you'd need an LCD capable of ~1/300sec scan (or a bit faster, possibly). We're really pushing the limits of LCD displays, here...
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Re: Blur reduction and 240Hz monitors

Postby Sirslicey » 28 Nov 2016, 15:34

What "service menu" are you guys referring to? I don't see anything referring to strobe phase in the OSD.

From the BBSU utility, I've adjusted the Crosstalk setting to 4 notches to the right, from the left. At the top it seems to be slightly ahead, and the bottom seems to be slightly behind. Is that a correct setting for me?
Last edited by Sirslicey on 28 Nov 2016, 15:45, edited 1 time in total.
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Re: Blur reduction and 240Hz monitors

Postby Paul » 28 Nov 2016, 15:39

Sirslicey wrote:What "service menu" are you guys referring to? I don't see anything referring to strobe phase in the OSD.


In XL2720Z you can enter service menu by doing this:
1) Press power button to power down your monitor.
2) Above the power button there are 5 buttons. Press and hold the 4th one (counting from the top).
3) While holding the 4th button, press the power button to power on the monitor.
4) Keep holding the 4th button until you can see your desktop.
5) Release the 4th button, wait a few seconds then press it again to enter service menu. You can operate it with the pilot.
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