I'm having trouble understanding (Variable) Overdrive...

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vookhan
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I'm having trouble understanding (Variable) Overdrive...

Post by vookhan » 14 Jan 2023, 04:19

Hello all, I'm in the market for a 1440p Gsync monitor. A couple of questions I still have are:

1) Is Overdrive exclusive to Gsync/Freesync monitors?

2) How different is Variable Overdrive from Overdrive? Is Variable Overdrive exclusive to Native Gsync monitors? Are there any Gsync compatible monitors that support Variable Overdrive?

3) Is Variable Overdrive changing its setting automatically or I need to go through the OSD every time to change it manually?

4) Finally, how important is Overdrive/ Variable Overdrive when considering a monitor?

Thanks a lot.

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RealNC
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Re: I'm having trouble understanding (Variable) Overdrive...

Post by RealNC » 14 Jan 2023, 07:17

vookhan wrote:
14 Jan 2023, 04:19
1) Is Overdrive exclusive to Gsync/Freesync monitors?
No. All LCD displays use overdrive.
2) How different is Variable Overdrive from Overdrive? Is Variable Overdrive exclusive to Native Gsync monitors? Are there any Gsync compatible monitors that support Variable Overdrive?
Variable overdrive adapts its strength depending on the current FPS. Normal overdrive doesn't do that, and thus is prone to generate ghosting. There are non-gsync displays with variable overdrive, though I don't keep a list. It used to be rare last time I looked at it. No idea if that's changed now.
3) Is Variable Overdrive changing its setting automatically or I need to go through the OSD every time to change it manually?
It's automatic.
4) Finally, how important is Overdrive/ Variable Overdrive when considering a monitor?
The quality of the overdrive is important. If a review of a monitor points out that there's ghosting at lower FPS when using VRR, then that usually means the overdrive implementation is bad. Unfortunately, not all reviewers test for ghosting in VRR.
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Re: I'm having trouble understanding (Variable) Overdrive...

Post by Discorz » 15 Jan 2023, 08:26

Had this written down. Maybe it helps.

Overdrive gain
Image
VG279QM @280Hz VRR 165FPS or @165Hz 165FPS - OD 0-40-60-80-100, Transition RGB 63-191

Overdrive applies more voltage to pixels which boosts the transitions and speeds up GtG response times (less ghosting). However too much overdrive can overshoot final color target which results in inverse ghosting. Extreme amounts can be quite uncomfortable, so it's recommended to use most balanced overdrive option if available. However if you don't find such artifacts distracting feel free to use any setting. It's a personal preference thing.


Overdrive at different frame rates in VRR (or at fixed refresh rates)
Image
VG279QM @280Hz VRR 240-165-100-85FPS or 240-165-100-85Hz/FPS - OD 80, Transition RGB 63-191

1. On displays without variable overdrive overshoot amount will increase as refresh rate or frame rate (in VRR) decreases due to lingering for longer time (VBI, check online). As you can see from the image initial transition is the same throughout the range, when overdrive is applied transition will keep rising until panel updates to new frame (every 4.2 ms at 240Hz, 6.1 ms at 165Hz...), and then it stabilizes back to target color. Refreshing the panel to new frame simply cuts off or stops the transition from overshooting further. So overdrive level can look good at high but bad at low refresh/frame rate. This is why we sometimes need to manually reduce overdrive - overshoot inconsistency.

2. With variable overdrive (Nvidia G-SYNC module) transitions still linger as refresh/frame rate decreases but the overdrive gain is automatically reducing to keep the initial over/under/shoot amount throughout the VRR range - overshoot consistency. Its a combination of image 1 and 2.

3. Other than gain, there are also other methods to tune the VRR range but I'm not very familiar with those.
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Re: I'm having trouble understanding (Variable) Overdrive...

Post by Chief Blur Buster » 23 Jan 2023, 02:36

Discorz, thanks for a great answer with image embeds where the varying frametimes (refresh intervals) "interrupt" an overdrive curve.

A perfect variable overdrive allows the new frame to interrupt the current GtG momentum right at the moment of the new refresh cycle.

But it does get complicated -- multidimensional overdrive where you're using maybe two previous frametimes, as well as the color associated.

It's almost certainly why G-SYNC Native chip has lots of memory (128MB+), for all the massive overdrive lookup tables.
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Re: I'm having trouble understanding (Variable) Overdrive...

Post by Discorz » 23 Jan 2023, 12:45

Chief Blur Buster wrote:
23 Jan 2023, 02:36
But it does get complicated -- multidimensional overdrive where you're using maybe two previous frametimes, as well as the color associated.
May I ask how color mapping works? Do normal colors when desaturated have the same transition curves as greyscale? For example color transition from RGB 255-255-0 (yellow) to RGB 0-0-255 (blue) when fully desaturated becomes RGB 170-170-170 and RGB 85-85-85. Would the curves of the two be identical or at least very similar? From my observations they do resemble each other a lot.
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Re: I'm having trouble understanding (Variable) Overdrive...

Post by Chief Blur Buster » 24 Jan 2023, 21:08

LCD GtG is per color channel. Treat each color pixel as three separate monochrome pixels.

The GtG on LCDs are usually darn near identical (same microwire thicknesses and driving, on the lithographed panel), but there can be issues where GtG deviates (e.g. phosphor-driven LCD subpixels, like quantum dots or KSF phosphor), which is why GtG of red is slower, www.blurbusters.com/red-phosphor

But for vast majority of screens, just treat each subpixel as their unique GtG, with exactly the same performance.
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