Such a provocative headline at IBC encouraged many to take part in a set of debates that delivered the very latest knowledge on direct view LED technology — and what active screens means in the cinema setting.
Cinema guru and polymath Peter Ludé (technical advisor to RealD) has an encyclopaedic knowledge of the technologies behind the LED screens tentatively being offered to the cinema industry, as well as alternative technologies being researched. At IBC, he took industry insiders behind the scenes of the different manufacturing processes, explaining the variations between the screen-making technologies, ‘chip on board’ and ‘surface mounted’. Not one to shirk the commercial side, he outlined costs per pixel to manufacture, and did the maths to demonstrate why large LED screens currently need to be expensive. Having looked at the market for LEDs and driver chips manufactured in China, Taiwan and the USA (Cree) he expressed confidence that screen costs will drop, due to a combination of lower manufacturing costs, better thermal control and higher pixel densities. He cited one manufacturing technique which uses micro-LEDs of around .01mm which can be transferred to screens at a rate of millions per hour. The modular design of these screens might also make it possible to use them to give wrap- around immersive viewing — the modern equivalent of curved Cinerama.
At IBC, Chris Buchanan of Samsung described their new LED screen offering, proudly explaining that the company has installed the first commercial cinema LED Screen at Lotte Cinema World Tower in Korea. At 10.3m (33.8ft) wide, the Samsung Cinema LED Screen brings HDR picture quality to the big screen, and ultra-sharp 4K resolution (4096 x 2160) with peak brightness levels of 146fL (500 Nits), some 10x greater than that offered by standard projector technologies. The screen surface is matt-black, reducing unwanted reflections, and no masking is needed — you just switch off unwanted pixels to provide ‘Scope or Flat aspect ratios. Marketing teams claim an ’infinity to 1’ contrast ratio, but knowing his audience of engineers, Chris said 100,000:1 was more realistic — still far greater than anything at cinemas today.
He claimed the colour gamut is larger than DCI P3, even at very high brightness levels, and that the low-tone greyscale performance is excellent. The HDR images are perfectly uniform, with no hot-spots, no darkened screen corners, and none of the optical distortion often inevitable with projected images. The system is efficient at turning electricity into light on screen, and although it runs warm, there are no fans required for cooling or heat extraction.
DCI security issues have been addressed using an integrated GDC media block, and this can cope with inputs from a wide range of sources. Concerns about audio dialogue from the screen have been addressed by a collaboration between Harman Professional Solutions and Samsung Audio Lab — speakers above the screen at the front, and special audio processing provide a true-to-life experience, using the ‘psycho-acoustic’ ventriloquist effect.
maintaining a balanced view
Sony’s ground-breaking Crystal LED direct view display technology was on display at IBC, though not in a format intended for cinema use. Sony’s Oliver Pasch provided a balanced overview of the relationship between current and new generations of projectors and direct view screens. Sony is showing this screen technology to cinema professionals to gain feedback on the implications its use might have. Decisions about making such screens available to the cinema industry are under consideration, but initial responses have been enthusiastic. Such screens could go up to 16K resolution and are capable of 120fps — Ang Lee’s Billy Lynn images have been shown. A 4.8m x 2.7m 4K screen was shown at September’s FNCF Congress in Deauville, offering a glimpse of the future. The audio solution there was from Alcons Audio.
A time for new standards?
Before the cinema industry adopts this large flat screen technology, which will eliminate disadvantages of projection such as optical distortion and ensure that images are always in focus, there are many considerations to discuss, including theatre design and layout. As Oliver Pasch explained, the industry will need a standard for a new enhanced brightness level, and maybe it will prove beneficial to have appropriate lighting surrounding the screen — much work was done on this for TV use by companies like Philips. Since this type of display provides the only true cinema HDR capability, the industry will need to agree on an HDR standard. Going further, we will need to look again at DCI specs, which were written with projectors in mind, and to see what changes will need to be made to take account of direct view screens. Even the name of the technology will need to be discussed — active screens, direct view etc.
Oliver came up with the interesting suggestion that, just as we created LIPA to consider all aspects of using laser projection in the cinema business, perhaps the time has come for a similar organisation to look into all aspects of active cinema screens — he suggested The Active Screen Society.
Oliver predicted segmentation between different types of screen in cinemas. Today, exhibitors have an unprecedented choice of lamp and laser-based solutions for presentation in any size theatre. Looking further ahead, that choice will get wider still with LED screens. This will allow exhibitors to pick the right blend of technologies to suit their needs — 4K projection still has a great future.
Gary Feather from Nanolumens, has a long history working on DLP devices at Texas Instruments, so understands the needs of the cinema industry well, and his previous role at Sharp Electronics looking after development of their LED displays gave him a deep understanding of the technology, leaving him qualified to talk about active screens in cinema settings.Three years ago NanoLumens completed development of a direct view LED display suitable for cinemas, and Gary discussed the detailed considerations now taking place on how the company’s 4K 2.5mm pitch LED display screen technology can be tailored to fit high-end cinema applications. The colour space uses Rec 709 (the same as standard HDTV) but work is going on to ensure that this gamut can be extended to P3 and Rec 2020 soon.
Brightness is an interesting topic — LED screens allow for far brighter cinema pictures, but the industry needs to consider exactly how bright it wants them. Too much brightness can lead to fatigue. A high percentage of cinema storytelling is done with dark images, so it is no good aiming for maximum brightness. Light levels must match the story. Theatre design will have to be re-thought too — cinemas must provide the best views of LED screens, especially where these may wrap around the sides of the theatre.
Pixel size is important — we must ensure that tiny LED dots provide as good an image as DMD pixels with a fill factor of 80%, as well as making pixellation imperceptible. Gary said that we can’t consider the screen in isolation, but must look at the process flow for the whole system, including frame rates and motion artifacts. He believes there is a great future for LED in cinema, and will work with the industry to incorporate all viewpoints into the solutions they create. According to Gary, the introduction of LED screens to cinemas will create the most lifelike experiences possible for audiences everywhere, and will effectively create a whole new industry — with many tens of thousands of researchers working on improvements to LED technologies the future is bright for direct view LED screens in cinema.
Peter Ludé highlighted that the advantages of LED displays still need to be proven in cinema.
Cinemas use a wide variety of screen sizes and shapes — all LED products currently on sale are 16:9 aspect ratio. Image scaling might be used, but might produce aliasing. Modern image processing technologies can reduce this.
Colour gamuts of current models don’t match cinema — it will be possible to match P3 and Rec 2020, but it isn’t easy.
Current products show colour shifts at low luminance levels.
Greyscale linearity isn’t uniform. It will probably be necessary to use PWM to drive the displays, rather like with DLP projectors. The non-uniformity is more pronounced nearer to black, and different colours have different non-uniformities in that area.
The different coloured LEDs don’t ‘fire’ at exactly the same time or code value, the result being that near-black areas can appear with a red hue to them as the red LEDs start glowing at lower code values than other colours. Displays will need calibration to account for this.
High contrast ratios can be achieved, but for cinema use, careful design of the substrate is needed.
Off-axis uniformity can be a problem due to the construction of the LEDS. Colours look different as you move off axis. Solutions can be found.
Scanned images can give rise to temporal artefacts which affect some people when they move their head.
We are used to hearing on-screen dialogue via perforations in the screen, so sound processing will need to be used to provide convincing audio. Sound could also be reflected back from the screen. DCI security considerations will need to be found for the multiple display modules that make up a large LED screen.
Peter concluded LED displays are likely to become viable, bringing super-dynamic range to cinemas — and a disruptive experience for the industry.