The International Telecommunications Union’s (ITU) Rec. 2020 standard for wide color gamut, which has been set as a target for next-generation 4K Ultra HDTV displays and is included in the recently published Ultra HD Blu-ray specification, may be achievable more quickly than many industry experts thought.
That was the assessment of quantum dot technology specialists from 3M’s Display Materials and Systems Division attending last week’s SID Display Week show. The company intended its statements and demonstrations at the show to contribute to a discussion on how to set guidelines for displays to qualify as Rec. 2020 complaint.
More on 3M’s Quantum Dot Enhancement Film and Rec. 2020 after the break:
Among the areas that should be brought into consideration in setting guidelines, the company said, is the application in which the display is to be used, explaining that guidelines for displays used for professional colorists, for example, can be different than commercial home displays where certain details and color ranges will not be perceived by general audiences.
Standards setting bodies, including the CEA, are currently working on new definitions determining expanded performance characteristics of next-generation 4K Ultra HDTVs including what will determine a Rec. 2020-complaint display.
Sources familiar with the work underway by the Ultra HD Alliance told HD Guru that one of the challenges in arriving at standards for wide color gamut and high dynamic range is the varying performance levels of displays based on different technologies, which may require setting different performance criteria for different technology. For example, OLED displays have lower overall brightness levels than LED TVs but come out of absolute black, while some LED TVs can achieve brightness levels of 1,000 Nits, but lack the ability to achieve the “infinite” black levels of OLED displays, which typically produce up to 300 Nits of brightness.
For LED TVs, 3M developed a Quantum Dot Enhancement Film designed to carry quantum dot particles that will be used in some next-generation 4K Ultra HD TVs to produce a wide color gamut.
“Rec. 2020 color performance was thought to be in the distant future, but with the addition of Quantum Dot technology and the 3M Quantum Dot Enhancement Film, this performance is available today,” James Thielen, 3M Product Development Specialist, said in statement released for a SID Display Week symposium.
At the show, 3M demonstrated flat panel displays of varying sizes using its enhancement film that is said to produce “up to 93.7 percent Rec. 2020 color gamut, one of the largest known color gamuts in any display.”
High-end 4K Ultra HD TVs with wide color gamut capability introduced this year by Sony, Samsung, LG, Panasonic and others are achieving most of the Digital Cinema Initiative’s P3 wide color gamut recommendation for professional digital movie theaters, but P3 represents a color space significantly smaller than Rec. 2020.
The color space in Rec. 2020 represents about 75 percent of the total visual color spectrum, while P3 covers approximately 53 percent. The current Rec. 709 color standard selected as the color space for HDTVs and early generation 4K Ultra HDTVs covers about 35 percent of the total visual color spectrum, and isn’t significantly different from what was established for analog color TV.
The expanded color gamut outlined in Rec. 2020 stretches mostly into shades of green, blue-green and into yellow, with some additional red shades. The blue color area isn’t increased as much.
To get LED-based LCD screens to achieve a color space approaching Rec. 2020, manufacturers are using so-called quantum dot technology, which is sometimes called nanocrystal technology. Technologies employing laser light in professional theater projectors and eventually in some flat-panel applications, are also expected to produce displays capable of achieving much of the Rec. 2020 standard, particularly in the green areas.
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“The International Telecommunications Union (ITU) published recommendations for ultra-high definition television aimed at enhancing visual experience (ITU-R BT.2246-2 & BT.2020) in 2012,” James Hillis, 3M Vision Science Specialist, said in a statement released at the show. “The recommendations include an expanded color reproduction capability with the intent to best encompass natural colors. Current mass-produced technology is unable to achieve this target, but of existing technologies only lasers and Quantum Dots have demonstrated potential to come close to the standard.”
Quantum dot technology uses a chemical/electrical phenomenon to boost brightness and color in LED LCD screens, it is also used to produce high dynamic range (HDR). The technology uses a special compound made up of many different elements, including heavy metals. Nano-sized particles of this compound in the form of tiny dots, called quantum dots or nanocrystals, are bombarded with high intensity energy, like a photon from an LED, producing a quantum effect that gives off energy in the form of visible light.
The physical size of each dot determines the wave length of the energy that they emit. So one size dot will produce green light, a larger dot gives off red light and a smaller dot gives off blue light. The quantum dot compounds are embedded in an optical film, which in 3M’s case is its Quantum Dot Enhancement Film. This film is used in tandem with quantum dot nanocrystals produced by 3M partner Nanosys.
Although some quantum dot compounds can use toxic substances, 3M’s market development manager Art Lathrop told HD Guru that in 3M’s approach, the dots are encapsulated in the film, ensuring the substances don’t escape into the environment.
“Quantum dot enhancement film has been tested in a leach test — a means to see if it will release cadmium in a landfill,” Lathrop said. “In the test, cadmium was not detected.”
The enhancement film carrying quantum dots is put in the path of the LED backlight behind the LCD. Typically, blue LEDs are used as the energy source for the light. Blue light photons from the LEDs collide with the quantum dots, and these inorganic particles produce colored light.
Among the benefits of the technology is a very predictable and stable light source, capable of delivering much brighter and much more saturated colors than have been possible on TV screens before, and more closely approximating what we see in everyday life. Additionally, quantum dots do not have a differential aging issue found in OLEDs and phosphors (used in CRTs, plasma and other emissive displays), so certain shades of color won’t degrade faster than others.
The technology also helps solve a problem with traditional LED LCD TVs, which tend to wash out reds and greens. Quantum dots can overcome this because the harder they are driven the brighter they become without losing saturation, until they hit a level of brightness much higher than using phosphors or even color filters.
3M’s prototype product showcase at the SID event included a 31-inch LCD desktop monitor that was said to produce one of the largest color gamuts from an LCD panel to date. It supposedly produced up to 93.7 percent of the color shades encompassed in Rec. 2020, which 3M said is “large enough to accurately represent 99.4 percent of the 53,497 color samples in the Standard Object Color Spectra database.”
3M said it recently conducted a study showing that “98 percent coverage of Rec. 2020 would be perceptually indistinguishable from the ITU Rec. 2020 standard,” to average viewers, adding that its technology sets a new benchmark for display manufacturers looking to achieve a high coverage Rec. 2020 display.
“The Rec. 2020 color gamut brings an incredible new viewing experience to consumers. It has been our pleasure to partner with 3M to demonstrate this capability to the market and to finally be able to see all of the colors found in the natural world on our displays,” stated Jason Hartlove, CEO of Nanosys.
3M’s Lathrop stated that: “The Rec. 2020 standard has been a difficult standard to meet because the primaries of the gamut are particularly pure compared to previously met standards such as Rec. 709 and Adobe RGB. But now, 3M has developed a solution to bring these broad color capabilities to displays over four years ahead of the standards’ namesake year, 2020, with already commercially available materials.”
By Greg Tarr
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