Creating a software overdrive driver (for slow panels)

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IamFrog
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Joined: 29 Sep 2021, 10:26

Re: How do I do laptop panel overdrive?

Post by IamFrog » 05 Jul 2024, 09:05

Thanks for the quick answer chief, just wanted to add something

I do understand the way overdrive works but I always thought that overdriving beyond 255/0 could be possible only if the maximum/minimum values were digitally reduced (kind of how reducing contrast in TNs would result in greatly improved response times for transitions ending in the top end of the 8bit range, or how LG IPS panels also have virtually reduced contrast iirc). That would still be possible under full software based overdrive right?

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Chief Blur Buster
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Re: How do I do laptop panel overdrive?

Post by Chief Blur Buster » 05 Jul 2024, 19:35

IamFrog wrote:
05 Jul 2024, 09:05
Thanks for the quick answer chief, just wanted to add something

I do understand the way overdrive works but I always thought that overdriving beyond 255/0 could be possible only if the maximum/minimum values were digitally reduced (kind of how reducing contrast in TNs would result in greatly improved response times for transitions ending in the top end of the 8bit range, or how LG IPS panels also have virtually reduced contrast iirc). That would still be possible under full software based overdrive right?
Yes, you can intentionally reduce dynamic range to get more overshoot/undershoot headroom.

There is precedent here. 3DTVs and LightBoost strobe backlights used this trick to reduce strobe crosstalk by speeding up LCD GtG to fit in the interval between strobe backlight flashes. So 3D mode often was a lower-contrast mode too, with poor colors. More recent strobe backlights tolerate a slight amount of crosstalk, and/or use different techniques, to avoid the need to reduce dynamic range.

You can do this with software, e.g. adjust whites slightly dimmer and blacks slightly brighter, and keep the rest for overdrive headroom for a GPU shader based overdrive algorithm.

Giving the user the option is the most ideal.

In some screens the voltage range may be slightly extendable in the hardware (e.g. voltages above maximum). However, one of the extremes is 0 volts (white or black depending on LCD) so physical overvoltage only works to solve one end of the range. In practice, this is never done anymore, and overdrive is done completely in the FPGA / ASIC (the scaler/TCON) but you most certainly can do it at the GPU shader level instead.

Also, if using GPU for overdrive for a strobe backlight (which is global flash), Y-axis-based overdrive gain is another enhancement to consider -- basically yet another variable in the overdrive formula. Using more aggressive overdrive towards bottom edge of screen (since bottom edge pixels refreshes last as seen in high speed videos, www.blurbusters.com/scanout ...) which is what some advanced strobe backlight based overdrive does sometimes (NVIDIA LightBoost and NVIDIA ULMB2 will do this). I bet that GSYNC Pulsar's overdrive algorithm is astoundingly complex.
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