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Acer X27: Linus Shows Off New 4k 144hz Panel/Monitor

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Re: Acer X27: Linus Shows Off New 4k 144hz Panel/Monitor

Postby Vega » 11 Jun 2018, 14:09

I haven't seen anything that states the ASUS version will have ULMB. In fact since this panel and G-Sync chip were worked on heavily by NVIDIA I am almost positive it won't.
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Re: Acer X27: Linus Shows Off New 4k 144hz Panel/Monitor

Postby Chief Blur Buster » 11 Jun 2018, 14:35

Vega wrote:I haven't seen anything that states the ASUS version will have ULMB. In fact since this panel and G-Sync chip were worked on heavily by NVIDIA I am almost positive it won't.

Most of the early announcements had ULMB.

There may have been a technical issue that prevented scanning ULMB from looking really good, and they may have removed the feature.

Due to the slow pixel response, scanning backlights can work better than strobe backlights. Locally dimmed panels can make excellent scanning backlights. But there's another tradeoff: Scanning backlights are often prone to strobe crosstalk via internal backlight diffusion -- the leakage of light from the "ON" sections to the "OFF" sections of a scanning backlight. This is why full-flash strobe backlights tends to be superior in strobe crosstalk (at least for most of the screen surface area) than sequential-flash backlights (backlights that flash in sequence with panel scanout).

There may have been other issues or showstoppers that prevented them from being able to do this, e.g. switching frequency limitations of the backlight LEDs, since they must be quite precise when doing a scanned ULMB backlight.

It may in theory, be possible, to be added via a firmware upgrade -- assuming the monitors supports user firmware upgrades. (They should at these price leagues. Samsung already allows gaming monitor firmware upgrade by thumbdrive, for example.)
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Re: Acer X27: Linus Shows Off New 4k 144hz Panel/Monitor

Postby RealNC » 11 Jun 2018, 15:53

The current 165Hz IPS panels already have visible crosstalk in the middle of the screen. The amount of crosstalk is just barely acceptable. Since it seems these new HDR panels have a bit worse pixel response, I would imagine that would bring ULMB crosstalk into the "unacceptable" range for many people.
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Re: Acer X27: Linus Shows Off New 4k 144hz Panel/Monitor

Postby Chief Blur Buster » 11 Jun 2018, 19:37

<TECHICAL>
RealNC wrote:The current 165Hz IPS panels already have visible crosstalk in the middle of the screen. The amount of crosstalk is just barely acceptable. Since it seems these new HDR panels have a bit worse pixel response, I would imagine that would bring ULMB crosstalk into the "unacceptable" range for many people.

Scanning backlights can actually reduce strobe crosstalk for the worst regions -- but at a tradeoff of increasing crosstalk for the best region.

Meaning all screen surface's strobe crosstalk becomes averaged out, to roughly 25% worse than the lowest strobe crosstalk. If the least-worst strobe crosstalk (e.g. screen center or screen top) is extremely good and 25% worse is not bad, then it's actually a huge improvement to the rest of the screen (e.g. screen bottom that has nasty strobe crosstalk).

Basically instead of varying amounts of strobe crosstalk (full strobe backlight versus LCD scanout asymmetry) -- a scanning backlight scanning at the same velocity as LCD panel scanout -- has consistent strobe crosstalk. But the amount of strobe crosstalk would be roughly 25% of the way worse than the lowest strobe crosstalk surface area and 75% of the way better than the worst strobe crosstalk surface area.

Bad: maximum strobe crosstalk
(Bugged strobing, such as early LG MOTION240 or Version 1 of uncalibrated BENQ Blur Reduction. Can makes gaming look visually worse)
Image

Average: acceptable strobe crosstalk
(Typical ULMB at maximum brightness & maximum contrast ratio, typical TN/IPS/VA strobing. Usually not as easily noticed during gaming)
Image

Good: nearly invisible strobe crosstalk
(Samsung 120Hz+ gaming monitors, ASUS VG248QE LightBoost, good TN strobing. This CRT clarity is very sought after by motion-clarity geeks.)
Image

-- In many strobe backlights, you have "Bad" at top/bottom and "Good" at centre.
-- If you convert this into a scanning backlight, the whole screen surface area might become "Average" (top/center/bottom looking same instead).

Since LCDs scan from top-to-bottom (see high speed video), it's potentially advantageous to flash the LEDs on the fully-refreshed LCD parts.

Image

So this can really help a slower LCD which a larger GtG fade zone. The slower the GtG response, the taller the GtG fade zone is -- and then the GtG fade zone overlaps refresh cycles (bottom edge and top edge are in transition) with no fully-clear refresh cycles. But if the LCD pixel response is faster than a refresh cycle, you can strobe between refresh cycles. But if the GtG is a bit long (e.g. 4ms on a 6.9ms refresh cycle) -- then you can attempt to flash the narrow bar outside the now very-tall GtG fade zone (rolling pixel-transition zone). But you run into backlight-row diffusion outside the area you're trying to flash, and start butting against GtG pixel response limits. However, this can be easier (with a well-focussed local dimmed backlight) than with a full-strobe backlight (which guarantees no backlight diffusion, and is easier to control strobe crosstalk if the GtG:refresh ratio is large (e.g. 1ms GtG on an 8.3ms refresh cycle) -- that's when full-flash strobing is usually better.

Now with a scanning backlight instead of a full all-at-once strobe backlight:
The limiting factor is internal backlight diffusion in a scanning backlight.
-- If it is _really_ good, then the strobe crosstalk equallizes (to full screen surface) to the best strobe crosstalk area. "Good" all over.
-- If it is _really_ bad, then the strobe crosstalk equallizes (to full screen surface) to the worst strobe crosstalk area. "Bad" all over.

In theory, a scanning backlight with a 4ms LCD can have less strobe crosstalk than a full-strobe backlight with a 1ms LCD. In practice, scanning backlights can be a lot worse unless you put expensive engineering into it. It depends on a variety of complex parameters (e.g. long blanking intervals, internal backlight diffusion in a scanning backlight, switching precision of backlight rows, custom parabolic mirrors behind all 384 LEDs to focus the light more directly straight forward to avoid internal diffusion, etc). So because of the complicatedness, there are so many engineering variables when it comes to a really good scanning backlight that can exceed a strobe backlight.

In practice, strobe backlights are much simpler, and it doesn't take much engineering to add a strobe backlight (simple combo of custom PWM controller + custom firmware + larger vertical sync interval ideally longer than LCD GtG + ideally well tuned neutral overdrive + slightly narrower contrast dynamic range to prevent ghosting for fullblacks/fullwhites) -- and are already occasionally done in indie / hacker channels. Homebrew strobe backlights, to indie manufacturers such as Zisworks have added relatively decent strobe backlights since the best-practices of a modern strobe backlight is relatively simple.

Really good scanning backlights can be more than 100+ more complex than a simple strobe backlight.

</TECHICAL>
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       To support Blur Busters:
       • Official List of Best Gaming Monitors
       • List of G-SYNC Monitors
       • List of FreeSync Monitors
       • List of Ultrawide Monitors
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Re: Acer X27: Linus Shows Off New 4k 144hz Panel/Monitor

Postby haanuman » 22 Jun 2018, 06:50

Uh no, I will not being paying $2000 for a 27in monitor. If it was under 1200 I would still give a thought to it but it is not a wise decision to spend that much on it. The Alienware AW3418DW for $800 is a much better option I think
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Re: Acer X27: Linus Shows Off New 4k 144hz Panel/Monitor

Postby darzo » 08 Jul 2018, 20:00

Flaws seem to continue to pop up with these monitors. They're starting to seem like a waste of money.
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