Blur Busters Forums

Who you gonna call? The Blur Busters! For Everything Better Than 60Hz™ Skip to content

Two LCD Layers to amplify 1000:1 contrast to 1,000,000:1

Breaking news in the gaming monitor industry! Press releases, new monitors, rumors. IPS, OLED, 144Hz, G-SYNC, Ultrawides, etc. Submit news you see on the Net!

Re: why hasn't anyone thought of this before?

Postby Sparky » 01 Dec 2016, 22:12

So it's basically just putting the color LCD on top of a monochrome LCD?

The obvious answer to the titular question is that they did, but they thought it would be too expensive.
Sparky
 
Posts: 535
Joined: 15 Jan 2014, 02:29

Re: why hasn't anyone thought of this before?

Postby flood » 01 Dec 2016, 22:25

wonder how it affects ips glow/viewing angles
flood
 
Posts: 881
Joined: 21 Dec 2013, 01:25

Re: why hasn't anyone thought of this before?

Postby Sparky » 01 Dec 2016, 22:38

I'm guessing it will reduce both IPS glow and viewing angles

Hypothetically it would let you calibrate out the IPS glow on a pixel by pixel basis, though I doubt that would end up becoming a reality.
Sparky
 
Posts: 535
Joined: 15 Jan 2014, 02:29

Re: why hasn't anyone thought of this before?

Postby flood » 01 Dec 2016, 22:46

well i meant the glow at diagonal angles.
if the monochrome layer has no similar angle-dependent contrast, it would reduce the glow by ~1000x which may be good enough
flood
 
Posts: 881
Joined: 21 Dec 2013, 01:25

Two LCD Layers to amplify 1000:1 contrast to 1,000,000:1

Postby Chief Blur Buster » 02 Dec 2016, 00:47

Amplifying contrast with two LCD layers, requires an extremely intense backlight/edgelight.

Transmission effiicency of an LCD has long been shockingly low, and has only improved sufficiently enough (along with high-efficiency LEDs that doesn't create as much heat as yesterday's backlights) in order to make contrast-ratio-amplification possible this way without igniting a fire in the room...

The theory of contrast ratio amplification by two layers of LCD is mathematically sound. (1/1000th of 1/1000th) versus (1000/1000th of 1000/1000th) is a 1000000:1 ratio.

But....

For many years, it didn't work. Light scattering between the two layers is the main contrast-kill. Even when solving this, vendors have tried to deal with eliminating other artifacts (e.g. polarization issues, viewing angle issues, amplified glow issues, moire issues, uniformity issues, pulsating interference artifacts from FRC beating against FRC or inversion beating against inversion) that amplify with two LCD layers... It has been tried for decades to ugly failures ...but it looks like "Eureka!" has finally arrived!

It is great that tech has finally advanced well enough to successfully use two layers to amplify contrast ratio, without major disadvantages anymore. That is, two 1000:1 LCD layers, done successfully, can create a 1,000,000:1 LCD in theory. It's as good as per-pixel local backlight dimming, just by using an LCD for local dimming.

Apple also patented something very similar
(but the principle is the same: two layers of same contrast ratio, as contrast ratio amplification):

Apple's dual-layer LCD technology promises high-contrast, lifelike HDR images

Looks like this just bought LCD technology another decade (or two).
Head of Blur Busters - BlurBusters.com | TestUFO.com | Follow @BlurBusters on Twitter!
User avatar
Chief Blur Buster
Site Admin
 
Posts: 3659
Joined: 05 Dec 2013, 15:44

Re: Two LCD Layers to amplify 1000:1 contrast to 1,000,000:1

Postby Chief Blur Buster » 02 Dec 2016, 01:09

I was thinking....

The 2nd layer can be used to lower persistence! (to as little as roughly double GtG of the 2nd layer).

[i]...What if the 2nd layer (monochrome) LCD or light shutter (e.g. mechanical shutters or monochrome OLED, etc) could act as a motion-blur reduction. Behave like a scanning backlight, except the 2nd layer LCD is *the* scanning backlight itself. As long as the GtG of the 2nd layer is less than half a refresh cycle, and strobed 180 degrees out of phase of the 1st layer -- this is fast enough to become an alternative to strobe backlights, by using a rolling-scan strobing that's slightly behind the GtG of the first layer (adustable phase, for lag-versus-motion-clarity adjustment). Obviously, this will reduce contrast ratio, in exchange for gaining short-persistence capability, but this could in theory become a simple mode-switch.

A 120Hz double-layer LCD, 8ms refresh cycles and 1ms GtG for each layer, is capable of reducing persistence down to approximately 2ms(ish) via a rolling-shutter-style scan on the 2nd layer. That's LightBoost quality, with less display latency than LightBoost (added lag of approximately 1-2ms) if you adjust phase to roughly 90 degrees offset (2ms trailing rolling scan), just barely enough to hide the GtG transitions of the first layer. Strobe crosstalk will be perfectly uniform from top to bottom edge, because the 1st and 2nd LCD scanning will be in sync. Ghosting artifacts will be identical for top and bottom edge, while input lag will be less than a strobe backlight (even when an LCD is doing the job of strobing.

The only real requirement is that both layers of LCD needs to have GtG less than half a refresh cycle, for this to work.

The rolling scan delay could be adjustable as a input-lag-versus-artifacts tradeoff (the closer you strobe behind GtG, the more strobe ghosting will occur).

A clear LCD "bar" that scrolls downwards on a mostly opaque black LCD -- as a substitute for a scanning backlight. Obviously, you'd lose the million-to-one contrast ratio, but you'd gain the low persistence. But it could be a mode switch toggle.
Head of Blur Busters - BlurBusters.com | TestUFO.com | Follow @BlurBusters on Twitter!
User avatar
Chief Blur Buster
Site Admin
 
Posts: 3659
Joined: 05 Dec 2013, 15:44

Re: Two LCD Layers to amplify 1000:1 contrast to 1,000,000:1

Postby flood » 02 Dec 2016, 12:49

Chief Blur Buster wrote:The theory of contrast ratio amplification by two layers of LCD is mathematically sound. (1/1000th of 1/1000th) versus (1000/1000th of 1000/1000th) is a 1000000:1 ratio.

for each wavelength of light, yes, but the perceived brightness depends on a weighted spectrum

for example
suppose layer 1, turned all the way to "black", transmits blue light 100% and red/green 0%.
suppose layer 2 does exactly the same thing. then stacking the two doesn't make "black" any darker.

or suppose layer 2, turned all the way to "black", transmits red light 100% and blue/green 0%. then stacking the two gives a completely dark black.

of course this isn't talking very precisely since light doesn't just divide into red/green/blue. similarly, there's the issue of polarization.

in equations, ignoring polarization:
if the backlight has the spectrum B(x)
layer 1 has the transmittance function T1(x)
layer 2 has the transmittance function T2(x)
and the luminosity function (https://en.wikipedia.org/wiki/Luminosity_function) is V(x)

the luminosity using only layer 1 is
integral dx V(x) T1(x) B(x)

the luminosity using both layers is
integral dx V(x) T1(x) T2(x) B(x)
flood
 
Posts: 881
Joined: 21 Dec 2013, 01:25

Re: Two LCD Layers to amplify 1000:1 contrast to 1,000,000:1

Postby RLBURNSIDE » 19 Feb 2017, 19:31

I've built a dual layer LCD proof of concept from some 1440p 5 inch LCDs from Topfoison:

http://www.avsforum.com/forum/24-digita ... st50006521

It's quite easy.

Problem:

1) Aperture ratio / transmissivity losses:

To make a mega contrast LCD, you need to incur the losses from both panels. Right from the start, the backlight having unpolarized light loses 50% to get beyond the back panel's polarizing grid. Ok, that's normal for all LCDs. Then you talk about aperture ratio which is around 60% for a grayscale panel, 80% for grayscale + low res (800 x 480). Low res + grayscale is good enough for the back panel, but good luck getting the exact same size + alignment with a colour LCD front panel.

Next: Between panels, you need to rotate the polarization angle by 90 degrees so see anything whatsoever. This is because coming out the front of the back panel, entering the rear of the front panel, the light needs to be rotated back to the direction of the polarizing grid. You can get around this by using differently aligned panels (harder) or placing them back to front (easier) + reverse the signal electronically or use a piece of cellophane aka Feynman's trick (easiest + trivial).

So, assuming two identital panels:

If your light source can do X lumens on its own (say, my 1600 lumen LED torch):

-50% loss from first polarizing filter.
-60% pass-through from each panel (aperture ratio). So 0.6 X 0.6 = 0.36.

You're already at 0.18 X => 288 lumens. Ouch.

Then you need to light up, say, a 120 inch screen. And get HDR too ideally.

If I use a relay lens and a grayscale LCD with low res and higher aperture ratio, I could get it to 0.8 X 0.6. And if I use an Epson 3LCD projector and double up each grayscale LCD (grayscale has much better transparency ratio when it's fully "white"), then it should be possible to do HDR10, assuming of course that you boost the back light to like 13,000 lumens.

The other thing is that if you use a 3LCD tech and RGB lasers, then you can have dynamic dimming (all the way to off) and have excellent dynamic contrast ratio per colour. AND reach rec 2020 with the appropriate laser wavelength / primaries. AND potentially even avoid the 50% polarization losses just by aligning the lasers to the back panel's polarization grid.

To be continued...
Last edited by RLBURNSIDE on 20 Feb 2017, 09:16, edited 2 times in total.
RLBURNSIDE
 
Posts: 104
Joined: 06 Apr 2015, 16:09

Re: Two LCD Layers to amplify 1000:1 contrast to 1,000,000:1

Postby Chief Blur Buster » 19 Feb 2017, 20:36

That's a pretty neat brainstorm.

Yes, the light loses of using 2 LCD's in a row is quite abysmal. 13,000 lumens? Ouch.
Head of Blur Busters - BlurBusters.com | TestUFO.com | Follow @BlurBusters on Twitter!
User avatar
Chief Blur Buster
Site Admin
 
Posts: 3659
Joined: 05 Dec 2013, 15:44

Next

Return to News / Rumors / Conventions

Who is online

Users browsing this forum: No registered users and 1 guest