The bottom line is, over the long term, we need strobe backlights to eventually become shorter persistence (less than 1ms). I can tell apart 1ms and 2ms persistence (See LightBoost 10% vs 50% vs 100%), which manifests itself as 1 pixel of motion blurring during 1000 pixels/second motion versus 2 pixels of motion blurring during 1000 pixels/second motion.Mark Rejhon wrote:Wrong. Actually, backlight strobing is a light-output issue, not a clarity issue.Interesting, but gimmicky technology. If you need slow-mo capture to notice a significant "difference" then it is not worth worrying about unless you are one of those anal-retentive videophile types that must have perfect image fidelity no matter the cost.
Tearing is over-exaggerated. You only notice it when you pan the screen around like an ADHD, caffeine junkie or you are having some kind of seizure. Even if these cases, it is a you blink and you'll miss it type of deal.
The problem is the strobe lengths (1ms-2.5ms) are longer than a short-persistence CRT (<1ms). There is not enough light output in the backlight in order to shorten the strobes.
Several newer TN LCD's are already able to transition pixels fast enough to be virtually finished before the next refresh cycle. Motion blur on a good strobe-backlight LCD is dictated by the strobe length, and not by the LCD pixel transition speed. Pixel transition speed limits show up as a faint crosstalk effect (like 3D crosstalk, but as a chasing ghost). On the better LCD's, the crosstalk is not visible.
Since I test these for Blur Busters, I have all 4 monitors (several LightBoost monitors, an Eizo FG2421 with Turbo240, a GSYNC monitor NVIDIA sent, and a beta BENQ XL2720Z with BENQ Blur Reduction, that BENQ sent) .
Using my oscilloscope, here are the strobe flash lengths:
-- LightBoost. Strobe flash length 1ms to 2.5ms. (usually 1.4ms to 2.4ms range)
-- EIZO Turbo240, found in FG2421. Strobe flash length 2.3ms
-- ULMB (Ultra Low Motion Blur) on GSYNC monitors. Strobe flash length 2.0ms.
-- BENQ Blur Reduction in Z-Series (XL2720Z, XL2411Z, XL2420Z). Strobe flash length 2.0ms
So you can see, the strobe lengths mimic medium-persistence CRT phosphor.
We need future strobe-backlight monitors that have shorter flash lengths (e.g. 0.5ms strobe flash, once per refresh, and shorter), without the screen becoming dark. We also need ability to strobe at lower refresh rates (e.g. strobing at 75Hz), since LightBoost is like a CRT forced to only work at 100-120Hz. Motion on Impulse-driven displays always looks best at stroberate=refreshrate, and sometimes GPU's are not powerful enough to allow 120fps@120Hz.
The side effect of slow LCD pixel transitions are already negligible on ULMB and the newer (1ms) LightBoost monitors, while it is more of an issue on the Eizo Turbo240. It shows up as a faint crosstalk between refreshes (<1% intensity -- sometimes only 1 color off -- much like greyscale 254 versus greyscale 255) since the black period hides most of the LCD pixel transitions now. This is lost in the visual clutter of game motion. Motion clarity noticeably improves with shorter strobe lengths (Example: LightBoost 10% versus 50% versus 100% when viewing fast-panning motion -- shorter strobe lengths are pretty noticeably clearer).
My tests confirm that motion clarity is bottlenecked by light output because the shorter you flash, the darker the picture becomes. CRT phosphor shine insanely bright (as much as ~5000cd/m2) for the short duration of illumination, often for less than 1ms. LED backlights can't shine that brightly, so strobed monitors compensate, by using a persistence compromise (~2ms flash)
Laboratory tests have already shown that there is no limits to motion clarity on strobe-backlight LCD's -- once manufacturers build in brighter strobe backlights, they can flash the backlights more briefly, to mimic a shorter-persistence CRT. Tests confirm that motion clarity is proportional to persistence (1ms of strobe length translates to 1 pixel of motion blurring during 1000 pixels/second motion).
Millions of dollars of engineering went into LCD's that finally could finish refreshing before the next refresh, because of something called stereoscopic 3D. During 2010-2011, they did not do a good job, but during 2012-2013, with the advent of strobe backlights, finally, 3D crosstalk fell almost below human detectability threshold (on some of the best LCD's), and this automatically ended the era of "pixel transitions are the motion blur limiting factor". So your talk is silly.
The motion clarity limitations is no longer caused by the LCD pixel transition speed, once most pixel transition is complete before the next refresh cycle. The LCD pixel transition can be slow, but as long as it's in total darkness, and the pixel transition is practically finished (>99%+) before the next strobe. When inter-refresh crosstalk is this faint, it gets lost in the noise floor of detailed imagery, while the motion clarity stands out (e.g. fine details during fast panning motion). The pixel transition speed became a moot issue once the inter-refresh crosstalk fell below a threshold -- because motion clarity is dictated by strobe flash length. And strobe flash length can be shorter than pixel transitions. The strobe flash just has to be timed on the clearest, fully refreshed LCD.
I, and several others, confirmed this. Do you have an oscilloscope, photodiode, and a high speed camera like I do? Do you have all four under the same roof: Eizo Turbo240, BENQ XL2720Z Blur Reduction, LightBoost, and GSYNC's ULMB -- like I do? Thusly, I call-out your pixel-transition-speed limitation myth (at least for newer LightBoost and the ULMB models), since some of those models actually push the inter-refresh crosstalk finally below human perceptibility thresholds for nearly all combinations of GtG transitions: Which means darn near completely clean refreshes for strobing.
Given a sufficiently bright backlight, LCD can be made to have far less motion blur than even short-persistence CRT's. LED's can be flashed very fast, so it's a matter of cost (engineering enough LED brightness) in order to achieve a sufficiently-bright ultra-low-persistence strobe backlight (Say, 0.1ms for starters).
But you are right, CRT's still produce great colors and unbeatable blacks. No argument.
But, LightBoost 10% is quite dark, which illustrates the light-output problem during short strobes. And when motion runs fast enough (e.g. TestUFO Panning Map Test, I begin to see the limitations of 1ms persistence: It manifests itself as about 3 pixel of motion blurring during 3000 pixels/second.)
Certainly this is a far cry from regular 60Hz LCD's (16.7ms persistence even for a 2ms GtG response LCD), which creates about 50 pixels of motion blurring during 3000 pixels/second motion. However, 1ms persistence should not be the final frontier, especially as we go to 4K. Fast flick mouse turns at several thousand pixels per second panning. 4K displays panning at several thousand pixels per second panning. VR goggles head turning at several thousand pixels per second panning.
We need to see persistence fall towards the sub-millisecond league within a few years. Either in OLED or strobed LCD's.
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