Overclocked IPS w/ DIY strobed backlight?

Talk about overclocking displays at a higher refresh rate. This includes homebrew, 165Hz, QNIX, Catleap, Overlord Tempest, SEIKI displays, certain HDTVs, and other overclockable displays.
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nimbulan
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Overclocked IPS w/ DIY strobed backlight?

Post by nimbulan » 09 Jan 2014, 14:11

I was wondering if anyone has ever tried this or considered trying this, since there are IPS displays overclockable to 120 Hz available, and it is possible to build a DIY strobe backlight. I'd be very curious to see a motion blur comparison vs current Lightboost displays.

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Re: Overclocked IPS w/ DIY strobed backlight?

Post by Chief Blur Buster » 09 Jan 2014, 18:34

nimbulan wrote:I was wondering if anyone has ever tried this or considered trying this, since there are IPS displays overclockable to 120 Hz available, and it is possible to build a DIY strobe backlight. I'd be very curious to see a motion blur comparison vs current Lightboost displays.
Yes, it is possible, but will be fairly tricky with IPS.
The lower the refresh rate, the easier it is to build a strobe backlight.
I'd think about 75Hz or 85Hz would be better for a strobe backlight on an IPS display at this time.

See high speed videos of LCD refreshes

Monitors that are too slow to finish refreshing before the next refresh, can overlap multiple refreshes (video of http://www.testufo.com/flicker ...), much like:

Image (older Dell 2007WFP LCD)

You can see three refreshes overlapped. That's what overclocked IPS tends to do, the refreshes begin to overlap quite noticeably beyond about 96Hz ("streaking" -- like the bad old 33ms LCD days; 33ms overlapped multiple refreshes). When this happens, there's no clean fully refreshed screen to strobe a backlight through. (See high speed video of proper strobe backlight)
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PinkysBrain
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Re: Overclocked IPS w/ DIY strobed backlight?

Post by PinkysBrain » 09 Mar 2014, 09:34

Couldn't more accurate overdrive help for this? At the moment overdrive is designed to give an average intensity over time, not to be strobed.

With a fairly short pulse you can overdrive to hit the desired intensity just at the pulse, instead of storing the last frame as-is for the overdrive you'd need to store a relatively accurate estimate of where the intensity will be during the next refresh though (assuming LCD intensity as a function of applied voltage only acts like a first order system). Need to have a temperature sensor and an accurate model of the LCD response, also need to take into account the reduced strobe to refresh time vertically unless you have a scanned backlight (reading up on it, scanned sidelit backlights are not so much a hard problem to solve ... as usual the obvious solution, to segment the lightguide, is just patented).

PS. I think some panels are already using the estimate-frame even for normal overdrive, because they have oscillations in their step response which are otherwise very hard to explain.
Last edited by PinkysBrain on 09 Mar 2014, 11:22, edited 1 time in total.

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Re: Overclocked IPS w/ DIY strobed backlight?

Post by Chief Blur Buster » 09 Mar 2014, 11:06

PinkysBrain wrote:With a fairly short pulse you can overdrive to hit the desired intensity just at the pulse, instead of storing the last frame as-is for the overdrive you'd need to store a relatively accurate estimate of where the intensity will be during the next refresh though (assuming LCD intensity as a function of applied voltage only acts like a first order system). Need to have a temperature sensor and an accurate model of the LCD response, including vertical variation unless you have a scanned backlight.
Yes, if the panel variations were low enough, you could optimize the overdrive to make this happen. It's really hard though (much harder than a simple dumb strobe or scanning -- some brands of strobe backlights don't even use Y-axis-compensated response time acceleration at all). And yes, you definitely need the temperature sensor if you're attempting to time the response. Either a very good accurate modelling of GtG (see Area 51 thread, Seeking Math Formulas for LCD GtG) and/or a bit LUT of self-mesured GtG data. There can be enough variances between individual panels to prevent perfect zero crosstalk (need to hit near final color value with incredible accuracy to do that). As you can see from the diagrams in that thread and within the science papers linked, LCD intensity doesn't always act as a first order system. A lot of overdrive is probably already using estimation algorithms, but this may not be good enough to perfectly zero-out the strobe crosstalk. I've seen some LightBoost panels that were able to do it darn near perfectly for screen center (e.g. could not see any strobe crosstalk in TestUFO from normal arm's length view distance), with only minor ghosting at the top/bottom edge. It's even quite possible NVIDIA is already timing the strobes accordingly.
PinkysBrain wrote:(reading up on it, scanned sidelit backlights are not so much a hard problem to solve ... as usual the obvious solution, to segment the lightguide, is just patented).
Segmented lightguides are patented? Are you able to look up the patent number?
PinkysBrain wrote:PS. I think some panels are already using the estimate-frame even for normal overdrive, because they have oscillations in their step response which are otherwise very hard to explain.
Why don't you create a new thread in Area 51 or contribute to the GtG formula thread? You look like you know some of your stuff on LCDs, or have readily absorbed publicly-available LCD GtG information to make such intelligent observations. We'd love to hear what you have to say. Especially since I am already looking for math formulas to estimate LCD GtG, because I want to create a modern "strobe-aware" web version of PixPerAn's Streaky Pictures feature.
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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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