Reduced-Contrast Trick To Reduce Strobe Crosstalk / Ghosting

[Chief Blur Buster]

You've lowered refresh rates, you used other tricks, and you managed to make framerates permanently match refresh rate (framerate = stroberate = refreshrate) via the various low-latency VSYNC ON techniques.... But still hugely bothered by strobe crosstalk? And you're looking for an additional method of further reducing strobe crosstalk? Here it is!

Instructions for dynamic range reduction for reduced strobe crosstalk

Follow these instructions ONLY if you're unsatisfied with all your monitor's overdrive

First, configure your monitor to the least-worst overdrive setting.
(or perhaps slightly more corona than your preferred overdrive setting, you may need to repeat these instructions at different overdrive settings for best results).

Next, you need to digitally compress your color range without touching the monitor's backlight.
Overdrive has biggest problems with the brightest colors.
So you trick the monitor to avoid ever using the brightest colors.

1. Go to NVIDIA Control Panel -> Adjust Desktop color settings -> Use NVIDIA settings -> Slide both "Brightness" and "Contrast" downwards in NVIDIA Control Panel.
2. They both default +50%.
...Lower both to same settings if you only want to chop the top end of your color range.
...Contrast should be slightly lower than Brightness if you're chopping both ends of your color range.
3. Play the sliders while watching http://www.testufo.com/ghosting

The final settings would be closer to usually Brightness=+40% and Contrast=+30%. Or try Brightness=+30% and Contrast=+10%. The exact numbers will be a personal preference, and depend greatly on the display.

This brightens your blacks and darkens your whites without touching your backlight, forcing the monitor's overdrive to avoid the most problematic ghosty pixel colors.

- This range-reduce trick works best in conjunction with middle-setting overdrive (e.g. "BenQ AMA High" rather than "BenQ AMA Premium")
- This range-reduce trick works best with VRR displays with true dynamic overdrive (e.g. true native NVIDIA GSYNC)
- This range-reduce trick will also reduce strobe crosstalk if you use blur reduction modes (ULMB, ELMB, DyAc, etc)
- This range-reduce trick will, to a lesser extent, partially help non-dynamically-overdriven FreeSync monitors too.

There are cons, like worse colors and reduced contrast ratio, but sometimes the "contrast-loss" of 5% for a "ghosting-disappear" of 75% for some models, and sometimes a worthy tradeoff, on certain models.

This is not a 100% solution and will not erase all overdrive problems but can "dim" bright coronas by 50%-90%, making them between half-visible to tenth-visible, depending on monitor. And text scrolling can suddenly jump from ghosty to perfectly clear.

[lizardpeter]

Chief, I have a question about this method. You mention that there is no adjustment of the display's backlight itself. Does changing the brightness setting on the monitor itself (the backlight brightness, I would assume) do anything to affect ghosting? I believe the contrast setting on the monitor does, and I have traditionally increased the monitor's brightness while decreasing the contrast (on the display itself). I wanted to try that method in combination with these NVIDIA settings.

[Chief Blur Buster]

Chief, I have a question about this method. You mention that there is no adjustment of the display's backlight itself. Does changing the brightness setting on the monitor itself (the backlight brightness, I would assume) do anything to affect ghosting? I believe the contrast setting on the monitor does, and I have traditionally increased the monitor's brightness while decreasing the contrast (on the display itself). I wanted to try that method in combination with these NVIDIA settings.

There are separate behaviours that can increase crosstalk
These are two different crosstalk-increasers, and they can stack on each other for an even worse effect.

(1) Backlight pulse width (Which affects strobe backlight brightness) can enroach into still-incomplete LCD GtG. The longer the pulse width, the less time LCD GtG has to complete in total darkness between refresh cycles. Increasing crosstalk.

(2) Panel contrast ratio may create fully saturated colors (without overdrive headroom) that ends up having slower LCD GtG.
Fully-saturated colors moving on non-saturated colors, are the worst ghosting offenders;
For 8 bit color, there are 2^8 = 256 levels of brightnesses for each subpixel color (R, G, B). It's color-by-numbers from 0 to 255, essentially.
By reducing contrast ratio, you stay away from the 0's and 255's that ghost a lot on non-0 and non-255 backgrounds, and only have, say pixel transitions between 10-245 or 16-235 or 5-250 instead, where overdrive overshoot/undershoot headroom allows faster pixel response. Overdrive needs overshoot/undershoot room.

e.g. using value 255 to speed a GtG pixel response transition faster from 20 to 240.

A car analogy to help explain "overdrive"

Overdrive is briefly flooring the pixel's gas pedal, in a manner of speaking, like accelerating a car from 0mph to 20mph as quickly as possible by briefly flooring the gas pedal down. You don't NEED to floor a gas pedal to make car reach 20mph. But briefly flooring it DOES help you reach 20mph faster (Even though that same pedal flooring is often also used to reach 100mph too on raceways).

Overshoot (coronas, bright ghosting) is when in your attempt to speed 0mph to 20mph as fast as possible, you accidentally reach 25mph. You have to let go of the gas pedal at the right time. Good overdrive calibration is hard. Especially since temperatures can change LCD GtG, much like how winters and hot summers can affect a car engine's performance.

If your car's engine speed limit is 100mph and it can only be achieved by flooring the pedal, there's no way to achieve 100mph faster. So you reduce contrast ratio (e.g. reduce the maximum speed you ever use the car at down to, say, 80mph). Then you can either almost floor the pedal to reach 80mph, or you can fully floor the panel faster (and then let go on time) to reach 80mph faster. That's the overshoot headroom -- unused performance above/below your dynamic range -- to improve overdrive logic.

Your priority is improving the speed of how fast your car can change its velocity to a desired exact driving speed as quickly as possible. The game of LCD GtG pixel response is simply a game of how fast a pixel can change colors from A to B.

The word overdrive should help turn this car analogy to understanding how overdrive speeds up LCD GtG pixel response. it helps some people understand the purpose of LCD overdrive, and helps understand why slightly reduced dynamic range speeds up LCD GtG.

Note: The car analogy is not always a perfect analogy -- since another complication, sometimes the slowest colors are near-zero and near-max (e.g. value 1 and value 254, instead of value 0 and 255), so there's a heavy amount of pixel response non-linearity at the near-black and near-fullbright colors. This is especially worse with VA LCDs where you see really bad numbers in the 2nd row/column rather than 1st row/column of the RTINGS/HardwareUnboxed GtG heatmaps for some LCDs. So you've got additional complications like certain "bad" areas of the GtG heatmap that requires you to reduce your dynamic range even further in order to avoid the slow areas of a LCD
GtG pixel response heatmap

[RonsonPL]

I hate to go against the Chief here but I'll write it anyway

From my observations, it's exactly high contrast and vibrant color content which benefits the most from clear motion reproduction.
I even have a theory that this is strongly connected to why the certain visual styles in games are more popular now than before. Same with aliasing - it's not better to have fog as close to the camera as in Turok 1 game, but it helps hide aliasing. The blurry displays cannot handle clear, vibrant image in motion anyway, so designers (I think) naturally lean towards the art style which works well, especially if it helps with aliasing. Even modern temporal anti-aliasing techniques take a way some contrast and vibrancy, not just the sharpness.

But I digressed. There's very little high contrast and vibrant colors content already. If a dev reads this thread...

If people choose a display where they sacrifice motion reproduction for better contrast and colors (slower VA panels for example) this is rather pointless. I think it would be wiser to simply opt for a better display (better in terms of motion)
Laymans already are doing harm to our cause (reaching the time where clear motion comes back to mainstream) by saying the low persistence feature is useless or not important, when they review monitors which struggle from significant crosstalk. I'd rather see them saying "if you value motion, get something else, this monitor deosn't have a proper low persistence mode) rather than saying "this has many flaws and some of you tell me it's usable if you sacrifice the contrast"

We have to fight against bad PR for strobed/LP modes already. Dim, not bright enough, worse LCD panels. Adding "and washed out colors" to the list of what average Joe knows about strobed/LP displays won't help.

That said, I see the value of this thread for people who are forced to use their current displayes riddled with crosstalk issues. I just would hate to see anyone choosing a display with serious crosstalk issue thinking "oh no problem, I can fix it by lowering contrast". It's a workaround, not a fix. A layman not knowing all the benefits of clear motion might not even know what they are about to lose. On blurry displays the image in motion is completely washed out anyway.