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post #1 of 12 Old 10-02-2015, 10:53 AM - Thread Starter
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All About Quantum Dots

John Ho, Advanced Development Manager at QD Vision, explains what quantum dots are, how they are used in the backlights of LCD TVs, how they facilitate the expansion of the color gamut to over 90% of BT.2020, the problem of narrow-band primaries and observer metamerism, perceived brightness versus measured luminance and the HK effect, the importance of mastering monitors with the same color gamut as consumer displays, using quantum dots in direct-emissive displays, answers to chat-room questions, and more.

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post #2 of 12 Old 10-02-2015, 09:47 PM
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Good one, very informative.

I'm glad that we're finally moving from BT.709 to a wider standard.
BT.2020 is a very wise choice in the UHD BluRay standard as a container even though current display tech is not even close.
At first content on UHD-BR will be mastered in the DCI-P3 range, but I believe it will keep the information beyond that on the disk for future displays.
In other words, the studio can master to a certain triangle chromaticity points but also leave the info beyond intact and not clipping it.

The UHD-BluRay standard is still quiet about how the stored rec.20202 gamut on the disc will be displayed on TVs with unknown gamut.
Will there be some range conversion or simple clipping?
In any case, the new HDMI 2.0a supporting TVs should know what to do with the incomming rec.2020 colors and not simply display them at the native chromaticity points as current rec.709 TVs do.

So now that we have several gamut variables at the hardware ends, the non-tech-savvy users like my parents may be watching rec.2020 on rec.709 TV and wonder why the colors are practically non existent (de-saturated).
The Player and the TV should know the capabilities and signal type of one another to properly display content.
The manufacturers know this and should be addressing that as we speak.
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post #3 of 12 Old 10-03-2015, 07:10 AM
 
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Sounds like the guy knows his stuff. Unfortunately, QD Vision concentrates mostly on making QD for edge lit LCD sets instead of QD Film for FALD LCD. Nanosys licened by 3M seems to do QDF. Although they may branch out to QDF soon. Also, was there any mention of how OLED can reach REC 2020? Can OLED even use QD?
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post #4 of 12 Old 10-03-2015, 12:17 PM - Thread Starter
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Quote:
Originally Posted by sytech View Post
Sounds like the guy knows his stuff. Unfortunately, QD Vision concentrates mostly on making QD for edge lit LCD sets instead of QD Film for FALD LCD. Nanosys licened by 3M seems to do QDF. Although they may branch out to QDF soon. Also, was there any mention of how OLED can reach REC 2020? Can OLED even use QD?
We didn't really talk much about OLED, since that's not what his company does. OLED can't use QD, since OLED is direct-emissive technology. However, we did talk about using QDs are direct-emissive subpixels, which would make it a direct competitor to OLED.
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post #5 of 12 Old 10-03-2015, 02:46 PM
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It is really embarrassing how badly some professionals misuse the H-K effect. The CIE definition of H-K is a "change in brightness of perceived colour produced by increasing the purity of a colour stimulus while keeping its luminance constant within the range of photopic vision." Increasing purity doesn't mean narrower spectral bandwidth. It means increasing saturation relative to white. You can see this by going back to Helmholt'z original coordinate system which was defined in terms of a dominant wavelength and purity (which is equivalent to saturation). A lot of later research on H-K was performed by Nayatani, who models the effect in CIELUV coordinates. Again, a colorimetric space. Not spectral. Whether you have a LED backlight, quantum dot, or anything else… it doesn't change the H-K effect. The H-K effect exists for everything from daylight to laser illumination, and it simply means that our perception of brightness is a product of both luminance and saturation. Luminance, by itself, does not predict perceived brightness.

When people make the claim that a color made by mixing narrow primaries appears different than mixing broad primaries, what they are trying to describe is a color additivity failure. In other words, a breakdown of Grassmann's Law. That is different than the H-K effect. See here: http://www.cie.co.at/index.php?i_ca_id=708

Unfortunately, some people are willfully misusing the H-K effect to claim increased brightness by comparing the native primaries of a narrow spectrum display against the native primaries of a broad spectrum display. Manufacturers of projectors are especially guilty of quoting scientific research out of context (I'm looking at you LG) because they want to sell consumers on the idea that they can produce a brighter image at lower power. Yes, if you look at a spectrally pure red and compare it against a less saturated red, both at the same measured luminance, then the spectrally pure red looks brighter. However, they are also completely different colors. Once you mix that pure red with enough green and blue to bring its saturation back in line with the second red then the H-K effect is nullified. The H-K effect is only a factor when you cheat by artificially increasing saturation beyond what it is supposed to be.

/end rant

Last edited by EvLee; 10-03-2015 at 02:54 PM.
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post #6 of 12 Old 10-03-2015, 03:59 PM
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Didn't John Ho talk about a "Hybrid Quantum dot display"?
Seems like he mentioned , instead of using the color filters that OLED's now use, that the filters could be replaced by quantum dots. So the light source would be the Oled, but the color filter would be the QD's.


I think He said we would see these "Hybrid Displays", before we finally see direct emitting quantum dots, which (were I younger), I would hold out for!


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post #7 of 12 Old 10-04-2015, 11:02 AM
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I still regret not picking up a Sony KDL-55W900A with the QD Vision backlighting system! Likely the best gaming 1080p HDTV that will ever be made. That could change if the new QD partners release a 1080p TV with a good game mode. However, I'd imagine they will only be UHD.





This is a pretty sweet demo! Really wish DIY kits for computer monitors were available for purchase.
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post #8 of 12 Old 10-10-2015, 01:06 AM
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Just wondering.
Can't you replace the normal LCD subpixel filter with a QD film?

LCD tv's use following configuration:

Backlight(white) -> red LCD-subpixel -> red filter.

With a QD based subpixel filter:

Backlight(blue,UV) > red LCD-subpixel -> QD layer tuned to red

That would eliminate 2 LCD problems
1. No visible bleeding when using UV backlight
2. Wide(r) viewing angles because the QD filter is emmisive.

.
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post #9 of 12 Old 10-10-2015, 04:25 PM
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Quote:
Originally Posted by bitsflew View Post
Just wondering.
Can't you replace the normal LCD subpixel filter with a QD film?

LCD tv's use following configuration:

Backlight(white) -> red LCD-subpixel -> red filter.

With a QD based subpixel filter:

Backlight(blue,UV) > red LCD-subpixel -> QD layer tuned to red

That would eliminate 2 LCD problems
1. No visible bleeding when using UV backlight
2. Wide(r) viewing angles because the QD filter is emmisive.

.
You'd have tremendous off-axis color shifts with that layout. Blue light would still be limited in viewing angle by the LCD while the QD emission would be wide angle without any light shaping film in front of it. You need the light shaping film (aka: BEF, brightness enhancement film) in order to get higher luminance in the normal viewing angles, but that same film also scatters lights so it can't be placed after the LCD panel.

Last edited by EvLee; 10-10-2015 at 04:31 PM.
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post #10 of 12 Old 10-11-2015, 08:11 AM
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Quote:
Originally Posted by EvLee View Post
You'd have tremendous off-axis color shifts with that layout. Blue light would still be limited in viewing angle by the LCD
Maybe I should have been more clear.
The example I gave was only for one subpixel (red)!

A complete system would look like:

Backlight (UV) -> red LCD subpixel -> QD filter tuned to red
Backlight (UV) -> green LCD subpixel -> QD filter tuned to green
Backlight (UV) -> blue LCD subpixel -> QD filter tuned to blue

In effect the standard LCD subpixel filters are replaced with appropriately tuned QD versions.
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post #11 of 12 Old 10-11-2015, 11:32 AM
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Quote:
Originally Posted by bitsflew View Post
Maybe I should have been more clear.
The example I gave was only for one subpixel (red)!

A complete system would look like:

Backlight (UV) -> red LCD subpixel -> QD filter tuned to red
Backlight (UV) -> green LCD subpixel -> QD filter tuned to green
Backlight (UV) -> blue LCD subpixel -> QD filter tuned to blue

In effect the standard LCD subpixel filters are replaced with appropriately tuned QD versions.
Okay, I thought were talking about the blue being passed through unfiltered. I still think this design would face a challenge because it can't use a normal brightness enhancement film. You would get more light being directed off-axis and would lose a lot of brightness in the main viewing angles. It could be in a similar situation as OLED in terms of not achieving the high luminance that is expected from LCD.

Last edited by EvLee; 10-11-2015 at 11:43 AM.
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post #12 of 12 Old 11-04-2015, 07:51 AM
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I watched this when it came out, but I kept forgetting to say thank you for providing such a technical look at QD technology. You see a lot of marketing hype with trade names touting the miracle and numbers with no basis for comparison like "4x more saturated than other technologies!" which for me means nothing. It is refreshing to see an actual fact-based discussion of spectral intensities at different wavelengths, how the edge lit technology actually works, and to John Ho's credit even some of the limitations of the technology.

I am looking forward to purchasing a QD television in the next few months and this really helped me feel more knowledgeable about the technology and not just "I dunno, it's just better somehow", which makes me a more confident consumer. I especially found it interesting that the cost of incorporating the QD Vision edge vial is on the order of $10 for a standard sized display which means hopefully we'll see this in mid-range smaller displays and monitors hopefully soon!
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