8K Ultra HDTVs are now coming to retail stores, but just as with 4K before it, skeptics are beginning to wonder if the extra pixels the technology will afford really makes a visible difference worthy of the extra cost.
First, keep in mind that 8K displays are generally assumed to have larger average screen sizes than typical 4K displays. This is why Samsung introduced an 85-inch model as the first 8K Ultra HD QLED TV in the United States last year. Since then, Samsung has announced plans to introduce some smaller screens in 8K coming in 2019, while Sony has announced plans to introduce a pair of 8K Ultra HD full-array LED-LCD TVs – 85- and 98 inches — in its Master Series Z9G line later this year.
Other manufacturers including LG (OLED and NanoCell LED LCD) and TCL (8K QLED LED-LCD) have also announced 8K plans for the year ahead.
During special technology Sony “black box” sessions at CES 2019, Toshiyuki Ogura, Sony Technical Strategy Office, Sony Visual Products TV Division Chief Distinguished Engineer, made a convincing case that all of the extra pixels (7680 x 4320) in 8K are not only visible, they make images look more like real objects than 4K when viewed from proper distances.
The benefit is huge in the development of next-generation televisions that are designed to both preserve the artistic vision of the content creator, and to produce images that look closer to real objects than ever before.
Viewing distance for these TVs is a key element, Ogura explains because while more picture information is visible the closer a viewer gets to a screen, the more visible the pixel structure of the screen also becomes, destroying the illusion of reality to the viewer.
Ogura said his personal observations of 8K and those of experts from the Japanese broadcasting company NHK, have determined that two pixel arc minutes, or 1.5 H – 1.5 times the height of the screen — is proper for reproducing the look of reality, where .75 H is adequate for seeing greater image “information,” which is important for things like medical applications. But for presenting convincingly real images, 1.5 H is ideal.
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Ogura explained that real-looking images will have increased color volume, in which the number of visible colors increases along with a smooth gradation of colors without obvious steps to the point that subjects begin to look three dimensional. One of the challenges TV manufacturers have with 8K is eliminating these visible gradations or bands of colors as brightness of the picture increases. Ogura pointed out that once steps in color gradations begin to appear in bright images, the illusion of reality is shattered.
To avoid this, Sony’s advanced image processing systems are designed to increase the number of pixels and refine the gradation steps so they are no longer obvious. This requires increasing the number of pixels to better present the smooth color gradient using a greater gamut of colors, approaching BT. 2020. At the same time, when the brightness of the television is boosted more pixels are required to accommodate it. The larger color volume draws the need for higher brightness.
The best 8K displays will be capable of delivering the pixel density and brightness levels that reproduce images that look like reality.
In 4K displays, an optimal viewing distance of 1.5H is good for seeing greater picture “information,” he said. To see images that look real in 4K this must be doubled to 3H, which narrows the viewing angle. If the screen is small, the amount of information also decreases because the viewing distance is farther away. With a peak distance of 3H, the degree of realism is lowered. Meanwhile, the expected viewing angle in 8K is 60 degrees, and the level of realism rises steadily in the content resulting from a balance of the three key elements.
Interestingly, as these elements rise, he said, a greater sense of immersion results that is not always measurable.
So, the benefit of the best performing 8K TVs will be their ability to present a more realistic pallet of colors with large color volume and a high level of brightness. Sony believes that this combined with high resolution presents an ideal canvas for content creators, and has been taken into account in the development of the Z9G 8K TV series.
In developing 4K TVs, Ogura said Sony has sought to match images as closely as possible to how they appear on the Sony BVM-X300 OLED mastering monitor that is in wide use today by movie producers/directors in color and light grading. But that monitor has a relatively small, 30-inch screen and 1,000 nits of peak brightness, where most consumer OLEDs top out at about 800 nits. Larger 4K screens have less pixel density that detracts from the sense of realism. But the added pixel density provided by 8K screens in larger screen sizes is a closer match to the density of the pixels of the mastering monitor.
Meanwhile, the veritable absence of native 8K content for the foreseeable future, means the upscaling and video processing systems in these new televisions will be more critical than ever. Sony is equipping its Z9G 2019 8K TVs with the X1 Ultimate processor that affords object-based super resolution that will up-convert lower resolution content and maintains the feeling of pixel density needed to create a sense of realism.
By Greg Tarr
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