David's Take: Quantum Dot Technology and UHD

David Susilo

Published: 05/17/2017 08:37:53 AM EST in David Susilo

David's Take: Quantum Dot Technology and UHD

At one time or another, Sony, LG, and Samsung hailed Quantum Dot (or its variants) as the next big thing in LCD TV technology. I'm not here to argue the efficacy of the technology, but to explain "what is Quantum Dot?"

Quantum Dot is a manufactured semiconductor nano-crystal that converts incoming light into colours. The size of the Quantum Dot precisely dictates the colour it will emit (see the graphic provided below by QD producer Nanosys). As they relate to TVs, Quantum Dots affect colour performance in an LED/LCD TV. We're not talking about a new display technology here. We're talking about a new way of constructing an LED/LCD TV.

In these new QD-constructed TVs, a Quantum Dot layer is placed in front of the light guide panel. Instead of white LEDs for the back/edge lighting (or, more specifically, blue LEDs with yellow phosphor applied to make them white), these TVs use pure blue LEDs, which serves two purposes. First, the blue LEDs provide the blue element of the light. Second, the blue light passes through the Quantum Dot layer to create red and green. This combination of pure blue, red, and green creates a more accurate white light that moves through the rest of the LED/LCD TV chain. Because the white light is so precise, the TV's blue, red, and green colour filters don't have to be designed to filter out so many unwanted colours, which preserves brightness. This does not mean calibration is no longer necessary. However, this means a better end result after the display has been calibrated and will stay calibrated for a longer period of time.

So, the benefits of using Quantum Dots include purer colour, increased colour saturation, better brightness, and reduced electrical consumption. It allows LED/LCD colour performance to be more competitive with OLED colour performance, yet it's far less expensive for TV manufacturers to implement right now. LG is currently the only gigantic company introducing new OLED TVs to the market alongside other brands like Skyworth, Hisense and TCL for the Chinese market. But that technology is expensive to produce, thus the TVs are expensive to purchase. Compared with existing LED/LCD TVs, QD-based LED/LCDs can offer a step up in colour performance without demanding such a big step up in price.

At CES, a variety of manufacturers showed off QD LED/LCD TVs, including LG, TCL, Hisense, and Samsung. (Samsung didn't use the phrase Quantum Dot but instead went with NanoCrystals and Quantum LED or QLED). Different display manufacturers have teamed up with different quantum dot producers, including Nanosys, QD Vision, and DOW Chemical. Sony was actually the first LCD maker to use Quantum Dots in 2013, partnering with QD Vision for its Triluminos TVs.

Some manufacturers are quick to point out that Quantum Dots aren't the only way to create a wider colour gamut in an LCD. Both Sony and Panasonic claimed at CES that their current colour technologies can produce a comparably wide colour gamut, and LG is actually using two different approaches to colour reproduction in its UHD TVs: some models use Quantum Dots, and others use LG's proprietary Wide Color Gamut LED.

What will we do with all this great colour, you ask? This is where standards come in. Currently, our whole HD system is based on the Rec 709 colour standard-from the content's creation to its display on your TV. When we calibrate HDTVs, we try to dial in the colour points to be as close as possible to Rec 709 for accurate performance. A wider colour gamut equals a less accurate colour gamut by the Rec 709 standard. However, the proposed UHD Rec 2020 standard calls for a lot more colour. I mean, a lot more. Check out the graph below.

The thing is, none of the TVs on display at CES 2017 were touted as being capable of Rec 2020 colour. In fact, the TV manufacturers I spoke with at CES 2017 asserted that the Rec 2020 standard simply isn't attainable yet on the display side. Instead, the manufacturers touted that the "wide colour gamut" TVs could reproduce (or at least get very close to) the DCI-P3 colour space that's currently used in theatrical film content. DCI-P3 is a wider colour space than Rec 709 but it's not as wide as Rec 2020. However, since the whole point of home theatre is to reproduce the colour gamut of a movie theatre, DCI-P3 is a perfect match.

How will this difference play out with upcoming UHD content, including Ultra HD Blu-ray? When I asked this question to the Blu-ray Disc Association's Ron Martin, the Vice Chairman of the U.S. Promotions Committee, he answered, "We describe BT2020 [aka Rec 2020] as a ‘container,' meaning it is a signal specification that can allow a progression of colour standards. BT2020 is very wide and covers a great amount of the human visible colours as a transmission signal. In the initial stages, that will be BT709, which most HDTVs carry now with normal gamma referred to as BT1886. Next will come the PQ gamma and HDR signaling that allows for high dynamic range displays. Then, as technology moves forward, the expanded colour range of BT2020 will mature and become available on future TVs."

Samsung QLED

Article Tags:  david's take, quantum dot, uhd, 4k, television, rec 2020


David's Take: Quantum Dot Technology and UHD

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