Posted on Feb 18, 2019 by Julian Mitchell
Words: Phil Rhodes
One thing the TV industry really wants is a video display that can achieve black blacks, healthy bright whites, and a wide range of colours all in one unit. For a long time, it’s seemed that organic LED displays – OLEDs – offered a near-perfect solution to the problem, with the ability to treat each individual pixel on the display as a set of lights that could be individually controlled. Crucially, those lights could be turned entirely off, finally producing a technology that could, like no other, achieve a true black. It seemed like a solution.
And for many applications, it’s a very good solution. OLED took a long time to develop, with small demonstration panels shown at trade shows for years before the first broadcast monitors appeared. The key limitation is brightness. The issue was manageable with conventional, standard dynamic range work, which demands a bit more than 100 candles per square metre, abbreviated 100 NITs. HDR finishing, on the other hand, demands whites up to ten times brighter while ideally leaving the blacks as black as they ever were. Sony went some way to meeting this demand with the BVM-X300, which combines the inky blacks of OLED with the soaring brightness and colour performance of 1000-NIT HDR.
“For a long time it’s seemed that organic LED displays offered a near-perfect solution to the problem.”
Laurent Treherne, Chief Technology Officer at Goldcrest Post Production in London, is happy with the company’s five X300s. “We use these monitors for SDR and HDR grading including HDR10 and Dolby Vision passes. The monitor calibration is a critical process for us and the X300 has been easy to align both in SDR and HDR. We regularly check the calibration of each monitor and all of them have been extremely stable so far.”
Goldcrest’s credit history hardly needs repetition, but for the sake of completeness the company’s post-production page lists Jurassic World: Fallen Kingdom, the Kingsman series and Skyfall amongst many others. At this level, Treherne continues, clients are demanding. “Some of the studios are now requesting a monitor profile document as part of the HDR delivery package. This document must show the gamut and precise EOTF of the monitors read by us, using a professional probe, before doing the grade. Again, we never have any problems meeting the spec defined by the studios.”
Then, at IBC 2018, Sony launched the BVM-HX310. It’s a display based on LCD technology, but it has much the same specification as the X300 and targets much the same market as the X300. Why would a company risk competing with its own product, having already created a successful display that was widely received as the holy grail?
Bram Desmet, of monitor specialists Flanders Scientific (FSI), suggests that the answer may be practical. Flanders makes displays based on various technologies from various manufacturers and is a
client of Sony Semiconductor, the branch of the company which manufactures the OLED panels used in X300 (and competing) displays.
Desmet says, simply, that “for pro markets, the top-emission [high-brightness] type OLEDs that are used in the [Flanders Scientific] DM250s, the X300 from Sony, that tech is gone. The manufacturer has pulled out from even trying to make those. Top emission RGB OLED is not going to be around a year from now.” With brightness a sore point of OLED displays, HDR was always going to work them hard. “There were challenges,” Desmet continues. “They’re not that well suited for HDR. There’s a huge challenge with burn-in, lifespan.” A challenge indeed, given that displays using high-brightness OLED panels routinely push £30,000.
Sony’s Daniel Dubreuil, product manager for professional monitors, describes the situation slightly differently, and points out some of the advantages that the BVM-HX310 enjoys as an LCD-based display. “The reason we decided to move that direction was that the new tech has an advantage over OLED. The new technology LCD can display 1000 NITs, but… on the X300 you can’t have the full-screen white at 1000 NITs. You can have 10% of the surface of the screen at 1000 NITs. When you grow that to full screen, you can have only 150 NITs. It’s to protect the panel.”
At the same time, Dubreuil says, the new display maintains the superb contrast performance of the BVM-X300. “It’s not a normal, or a regular LCD like we say today. It’s a new technology that improves the contrast radio to the level of the X300. You can see that benefit in terms of contrast ratio and blacks. The ratio is still a million to one, the same as the X300, [but] it can maintain 1000 NITs at full screen.”
The new Sony HX310 with the extra Light Modulating Cell layer.
The technology used in Sony’s HX310 display may offer a solution. Flanders Scientific’s Desmet explains: “The easiest way to try to think about it is that you have a backlight that’s always on at full blast, and then what you have up front is essentially a standard LCD panel with red, green and blue filters.
Then, in between that you have the light modulating cell layer. The best analogy for what that is, is it’s like a monochromatic LCD. A lot of people call this dual-layer LCD… we prefer light-modulating cell layer, LMCL. That’s what the people who developed it call it. That’s a bit more accurate because it’s not like it’s just two regular LCD panels.”
The technology is perhaps most closely associated with Panasonic, dating back to press releases in 2016, and Desmet suggests they may be supplying TVLogic and Eizo as well as Flanders Scientific and Sony. Dubreuil is keen to emphasise that Sony’s implementation takes full advantage of the company’s long experience in the field. “We call it new tech LCD. The most important for us is the result. A couple of competitors are using similar tech to achieve monitors with 1000 NITs full screen. Sony has exclusivity, the way the LCD [is made] could be similar, but the backlight, surface treatment and other stuff are different, which makes our panel unique.”
Either way, the results shown at IBC were spectacular, competing ably with Sony’s own BVM-X300 in a side-by-side test in the blacked-out tent. “You have pixel level control of that light,” Dubreuil says. “You have something that allows you to have one area of the screen with a black level of about .001 NITs, then you can have 1000 NITs just a few pixels over.”
Laurent Treherne at Goldcrest is cautiously enthusiastic. “The X310 seems to be a natural progression… from the quick review we’ve done so far the picture quality seems to be at least as good as the X300 with the added bonus of the LCDtechnology being able to deliver brighter peak whites at 1000 NITs over a large area. Unfortunately, the viewing angle seems to be much narrower compared to [OLED] which is a real problem when you are grading with clients. Having a client sitting off at an angle from the monitor and commenting on the grade while seeing something slightly different to the colourist who is sitting directly in front is obviously not manageable.”
Sony has, naturally, consulted with the post-production world and is aware of the concern. Dubreuil: “From the experience I had from some of the post houses I visited… some of them think they can accommodate it because they understand the performance compared to the X300. Some of them are strict on the viewing angle. In the long term it will depend on the customer… people want to see it, people want to compare it with the X300, we do side-by-side comparisons. Most of the time they are convinced. When you do a side-by-side comparison it’s very obvious, the advantage of the new tech.”
This competition between OLED displays and LCD displays is fundamental to the display market in 2019. OLEDs are panels made of tiny lights, and break down into two groups: those (like the BVM-X300) which use red, green and blue emitters, and the large panels manufactured by companies such as LG, mainly targeting the domestic market.
RGB OLEDs achieve excellent accuracy, but struggle to get to HDR levels of brightness without risking short lifespan and burn-in. LG’s OLED TVs combine red, green, blue and white, boosting brightness with the white emitters to achieve better peak whites at the expense of colour accuracy. They can be good at displaying standard dynamic range images, but can struggle to achieve accurate colour in bright HDR material.
LCDs are panels made of tiny filters with a light behind them. Peak brightness is controlled by the brightness of the backlight, but some light always leaks through, so the lowest brightness is not entirely black. Illuminating the LCD panel in a series of separate zones makes it possible to display very bright and very dark subjects simultaneously. Since the zones are larger than a single pixel, though, the brightest white and darkest black cannot be displayed in adjacent pixels. Bright areas may appear to bleed into dark ones.
“People want to compare it with the X300. When you do a side-by-side comparison it’s very obvious, the advantage of the new tech.”
LCML may offer advantages beyond sheer imaging performance. Flanders’ Desmet suggests that, “any time a display technology doesn’t have that consumer market, manufacturers don’t get involved and you don’t get economies of scale.” Referring to the high-power backlights, he says that “nobody needs a 55in, two-foot-thick TV. They draw more power, they produce more heat. Every single one of them is going to have at least a few fans built in because they do generate a fair bit of heat.” Even so, it’s likely to be easier to make than OLED. “You can use a lot of the same basic infrastructure you can use to make normal LCDs. You can afford to do this in small runs without having these giant facilities dedicated to nothing but top emission RGB OLED.”
Finally, Desmet suggests that someone may work out how to make very bright OLEDs reliably, but it may not be soon. “We have several semiconductor manufacturers that are trying to make their own RGB OLED. We may have large RGB OLEDs in the future. Even though it’s dead at the moment it may not be dead in two years… there are at least two panel manufacturers that may commercialise next-generation RGB top emission, but it would be kind to even call those nascent technologies at this point.” Given all that, the availability of LCML seems well-timed, and it’s likely to fulfil at least some of that need for the perfect display that’s always seemed just out of reach.
OLED Screen Burn
Tests by influential technology reviews site RTINGS, have found screen burn can set in as quickly as two years after buying a new OLED television and by association, monitor. That’s much quicker than previously expected in OLED TVs.
Screen burn, or burn-in, refers to an effect where part of an image that is no longer displayed is still visible on a different image, such as static logos that stay on the screen when running timecode, watching news channels and playing video games. The latest tests by RTINGS tested OLED for burn-in on a variety of content, from news and general TV to sports and gaming. During the testing period, the technology reviewers assessed and reported on the screens’ brightness and colour renderings every two weeks. The channels and content were respectively displayed in intervals of a five-hour ‘on’ period and one-hour ‘off’ period during a cycle that was repeated four times per day.
The tests found that when the TVs were set to maximum brightness and were showing gaming content and news channels, they were most affected by burn-in, as both pieces of content feature static logos on screen most of the time. After 4000 hours, the TVs testing this content displayed the mark of these logos on the screen, even when the content wasn’t being played.
It is for this reason in part that Samsung decided to stop using OLED technology in its TVs in 2012 and proceeded to develop the new QLED technology. Samsung claims that their QLED TVs’ picture quality lasts for the lifetime of the product and there will not be any visible deterioration in colour over time due to the advanced Quantum dot technology – QLED uses inorganic Quantum dot material which is known to be durable and stays burn-in free. On the other hand, the organic material of OLED TVs potentially wears out over time. As such, Samsung QLED and LED TV sets have received a perfect score (10/10) for image retention in RTINGS’ test.
The impartial tests seem to prove that Samsung’s QLED and Dynamic Crystal Colour UHD TVs aren’t susceptible to screen burn like other TVs and potentially monitors on the market, and as such Samsung is offering a market-leading ten-year screen burn warranty as a testament to the confidence in its QLED technology.