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homebrew strobe LED backlight guide?

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homebrew strobe LED backlight guide?

Postby Patrick » 13 Mar 2019, 21:48

First off, wow- what an incredible source of information! I've learned more about how displays work from reading the articles on this site than I have from any other source, especially in regards to motion blur and input lag.

I just got done reading the following:

https://www.blurbusters.com/240-watts-o ... r-monitor/

1. This article is a few years old. Is this article describing the same thing as LED full array? Are current LED-lit LCDs bright enough to do very short strobes/dark 90% of the time?

2. What about scanlines for 240p games? That's a further 50% reduction in brightness. Are current LED-lit LCDs bright enough to do the above AND scanlines?

3. If this is describing something different from LED full array on current displays: is it realistic to think that a novice would be able to add their own LED backlight array to a display following a how-to guide?
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Re: homebrew LED backlight guide?

Postby Chief Blur Buster » 16 Mar 2019, 19:13

That was very old back in the early Blur Busters days;
This article is much better:

- Electronics Hacking: Creating A Strobe Backlight

Also relevant reading material:

- Understanding LCD Scanout Via High Speed Videos
- High Speed Video of Strobe Backlight
- Strobe Crosstalk FAQ
- Strobe Tuning Thread

The art of cramming the GtG elephant into the VBI.

Pixel transitions that are slow, means pixels are still refreshing at bottom of the screen when the top edge of the screen is now beginning to refresh. A GtG fade zone bigger than the VBI, will cause lots of strobe crosstalk.

Also moving this thread to Area 51 Display Engineering. Happy to answer the questions of the art of strobe backlights!
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Re: homebrew LED backlight guide?

Postby Patrick » 17 Mar 2019, 15:44

Chief Blur Buster wrote: Happy to answer the questions of the art of strobe backlights!


Wow, the master wizard himself! :o I am in awe at the technical knowledge on display, here. I'm not sure I'll ever fully understand this stuff, but hopefully I can eventually understand it well enough to stop worrying about the demise of CRTs. Looks like I have quite a bit of reading still to do!

In your opinion, is it possible to get CRT-like motion clarity on an ASUS VG248QE, AND add scanlines to emulated 240p content (1:1 black lines:visible lines, or a 50% reduction in brightness), while still maintaining a good contrast ratio and adequate dim room brightness? Can this be done without opening the LCD and messing around with the actual electronics (fingers crossed)?

Thank you for the incredible work you've done and continue to do!
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Re: homebrew strobe LED backlight guide?

Postby Chief Blur Buster » 17 Mar 2019, 17:51

From what you're writing, I'm assuming you have no experience with strobe backlights. Right?

Don't forget there's multiple brand names of blur reduction for LCDs. See Motion Blur Reduction FAQ. LightBoost was the first really good one.

The VG248QE is an old one and only strobes at 100Hz and 120Hz, which makes it "defacto like a fixed-frequency 100Hz / 120Hz CRT". If you are looking for multisync strobe at any Hz, you're looking at different models such as BenQ Zowie XL2411P that can strobe from 60Hz all the way to 144Hz, albiet with progressively worse strobe crosstalk at higher Hz and smaller vertical totals (smaller VBIs).

Different gaming LCDs have:
- Different levels of quality during strobe mode
- Different refresh rate support that blur reduction is supported at
- Different crosstalk quality (sometimes the crosstalk is practically below human detectable levels for screen centre on some displays)
- Different color quality
- All of them will have poorer black levels than LCDs (at least until local-dimming strobing arrives).
So shopping for the right motion blur reduction mode can be paramount (e.g. Do you just need 120Hz? Or need 60Hz for emulators too? Etc)

CRTs will still win in color quality during motion blur reduction, but there are some LCDs that are getting better and better in color quality during strobe mode. (LightBoost / ULMB / DyAc).

While it's very hard to get good black levels with LCDs, as a general rule of thumb, once GtG is successfully completely hidden in the VBI, there's no upper limit to motion clarity achievable with LCDs. But hiding GtG completely in the dark phase of the strobe backlight is not easy. You can pretty much do it to ~99% with LightBoost but the last 1% is really tough.

Some LCDs I have seen already has less motion blur than CRTs, although with a rather severe brightness-vs-clarity tradeoff. Strobe backlights (unlike CRTs) can have adjustable persistence simply by adjusting the strobe flash length. Some monitors can be configured to flash its strobe backlight for 0.25ms -- that's less than the phosphor decay speed of a Sony GDM-W900 CRT! (medium-persistence phosphor).

Now, if you get one of the brighter strobed models, you can have about 300 nits during blur reduction, which is brighter than many CRTs, and gives some headroom to reduce persistence via its persistence adjustability feature (e.g. BenQ Strobe Duty setting, NVIDIA ULMB Pulse Width setting) -- some strobe backlights are adjustable persistence. So there's a brightness versus clarity tradeoff, but even in the brightest mode, has about 90-95% less motion blur than a typical 60Hz non-strobed LCD.

This is what will happen:

Image

Real photographs, not simulated, at 960 pixels per second at http://www.testufo.com/photo

I can even read the street name labels in a panning map on a strobe-backlight LCD, just like I can with CRT.

Now if you want those scanline effects and all, you can google "MAME HLSL" which actually uses the GPU shader to emulator the phosphor and dotmask in an emulator.

To cover the whole venn diagram of CRT, I'd imagine that a 4K rolling-scan OLED combined with MAME HLSL, will be an almost indistinguishable emulation of a CRT. This may take a few more years, but a somewhat reasonable mimicking can be done with current strobe-backlight LCDs as long as you tolerate the poor black levels and poorer contrast ratio. Motion blur is theoretically no problem (though of varying quality and compromises), it's the other attributes that needs to improve.
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Re: homebrew strobe LED backlight guide?

Postby Patrick » 18 Mar 2019, 19:57

Chief Blur Buster wrote:From what you're writing, I'm assuming you have no experience with strobe backlights. Right?


Yep, n00b here! I've witnessed backlight strobing and the effect it has on a friend's display but am just now getting around to doing this on my own display. I'm primarily interested in motion blur reduction for 240p retro gaming via emulators.

Chief Blur Buster wrote:Awesome stuff


Great info! I feel like I'm still absorbing it all, but it's starting to make sense. :D


Chief Blur Buster wrote:Now if you want those scanline effects and all, you can google "MAME HLSL" which actually uses the GPU shader to emulator the phosphor and dotmask in an emulator.


I'm familiar with shaders in Retroarch, and they can be pretty great when configured right, but have never tried to use MAME HLSL. Does MAME HLSL offer any clear advantages vs Retroarch's shader system, in your opinion?

To cover the whole venn diagram of CRT, I'd imagine that a 4K rolling-scan OLED combined with MAME HLSL, will be an almost indistinguishable emulation of a CRT. This may take a few more years, but a somewhat reasonable mimicking can be done with current strobe-backlight LCDs as long as you tolerate the poor black levels and poorer contrast ratio. Motion blur is theoretically no problem (though of varying quality and compromises), it's the other attributes that needs to improve.


Sounds like I should hang on to my CRTs for a while longer, but you've given me hope for the future!

I think I'll be satisfied with Lightboost if I can get my LCD to 50 cd/m2 with emulated scanlines + strobing while maintaining a decent contrast ratio and color. Just want it to look decent in a dark room, really.

I actually had to order a new computer to play around with Lightboost, since the mini PC I'm using only supports Displayport through HDMI or VGA, and only 60Hz resolutions (lame...) So it'll be a few days before I actually get to try it. I'm psyched, though!
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Re: homebrew strobe LED backlight guide?

Postby Chief Blur Buster » 19 Mar 2019, 19:10

Please note that LightBoost is an older strobe backlight technology. It's the most famous one because it's the first "good" one.

But feature-wise, there are many superior sequels to LightBoost now, see list of LightBoost clone brand names.

- "Motion Blur Reduction" (generic name)
- LightBoost (by NVIDIA)
- ULMB – Ultra Low Motion Blur (by NVIDIA)
- DyAc – Dynamic Accuracy (by BenQ ZOWIE)
- ELMB – Extreme Low Motion Blur (by ASUS)
- VRB – Visual Response Boost (by Acer)
- MotionFlow Impulse (by Sony)
- 1ms MPRT (by LG) — up to 16x clearer motion than “1ms GtG“!

MPRT is a scientific name, Moving Picture Response Time. Achieving 1ms MPRT is only possible with 1ms-flash (strobe backlight) or a 1000fps@1000Hz). GtG pixel response is not the same thing as MPRT pixel response.
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