LED Displays: From Digital Signage to Digital Cinema

10/11/2017 9:30:00 AM
By Gary Feather, NanoLumens
LED displays and full digital visualization solutions are moving forward at an accelerated rate as technology advances. These advancements in display technology are leading to increased reliability with decreased weight, as well as greater efficacy and an improved picture quality. The picture quality improvements in particular have transformed digital signage to the point where it now rivals the quality seen on the best LCD and OLED TVs. Direct-view LED displays, long considered competitive only in digital signage, are on the threshold of becoming competitive with DLP by Digital Cinema Initiative standards, and with such continuous improvements in RGB SMD LED displays, a new large integrators market may be on the horizon. This market could potentially be worth $10 billion over the next 10 years!

The current Digital Cinema Initiative started with the “opportunity” provided by the Texas Instruments DLP device and the total cinema system solution. That system, first demonstrated in 1996 and launched in 1999, has led to more than 144,000 DLP Digital Cinema installations. These systems were installed over a 20-year period, as cinema transitioned from film to digital projections, and LED can now at last rival DLP in every regard. When direct-view LED displays address the LED performance capabilities of high dynamic range, improved contrast ratio, higher brightness, wider color gamut, and motion processing in a compliant manner, a revolution of DLP replacements could occur.

Imagine the new business opportunities that will be created as hundreds, then thousands, of DLP Cinema systems are replaced every year by LED displays. These replacements will often include dramatic refurbishment of the system solution as well, and the LED display will of course change from DLP projection to direct view LED. The audio systems will incorporate new psychoacoustics and speaker systems to manage the different audio performance of the LED screen over the projection screen, and the same theater auditoriums will also be modified to provide a unique experience never before achievable with DLP projection. From NanoLumens’ perspective this “Active Screen experience,” or ASXTM, has ahead of it a deterministic technology development path to attain and surpass these goals. With the help of studios and cinematographers, countless things will become possible with direct-view LED in cinema.

The technical requirements for a cinema quality display are, as of right now, party to industry specifications. However, the actual acceptance of a new display solution that can replace the current deeply entrenched DLP solution will be driven by the experts in the movie and storytelling business. DLP went through years of assessment and improvement to support the experts’ requirements to transition from film to digital projection cinema. The steps toward direct-view LED cinema or ASXTM will require a similar process. Experts and standards groups must come together with cinematographers and studios to assure that the end result, “a story well told,” is attained and (ideally) enhanced beyond current DLP.

Emissive displays like LED have visually perceivable characteristics far different from those of a DLP projector on a screen. The creative experts (and audiences) are only interested in the final image and the impression it makes, so all the factors that impact that image must be considered in order to create films that capture true life. The list of challenges is significant, but not overwhelming.

The LED display industry has already accomplished much in improving LED direct-view technology. Minimal color requirements are being met with careful selection of the LEDs; focus is on DCI-P3. Some would like to set rec. 2020 as a goal. Bit depth currently supports 18 bits of processing and 12 bits RGB, as displayed in recently launched systems. Work is still required, however, on supporting bit accuracy and precision with respect to the actual lumen output of the LEDs. Improvement is needed in system design, drivers, and calibration.

LED display has demonstrated a brightness capability not possible with projection today, and brightness levels at 1500 nits are normal for an LED. Cinema nominally requires only 14ftL (50 nits) with some presentation considerations as high as 20-28ftL. The exception to that in cinema is the desire for sufficient light to support extremely bright areas (specular highlights) like reflections of the sun on a windshield in HDR. With updates in design, LED can reach extremely bright peaks while still supporting deep bit depths in the darker images. Based upon cinema scenes, LED display will support a higher efficacy in W/m2 when contrasted with DLP, and dark images should benefit from the LED being off when the image is black. LED contrast ratios are demonstrated at two to 20 times that of standard DLP, and LED easily supports many 4K resolutions installations today, with 8K emerging where required.

LED display has limitations to overcome, but each of these seems possible. The final image looks and feels compelling to cinematographers and movie theater experts, but that is a hard metric to quantify. An active screen is different than a projected image, and reliability and maintenance must align to normal theater maintenance. Additionally, any visible structure in the screen must be mitigated, so fixed pattern noise is invisible to the viewer. Perhaps most importantly, the cost of the LED display must approach that of the DLP.

One new attribute of LED display is that it can be curved. A curved screen from projection can be dramatically improved upon by an emissive LED display solution with no issues of focus or keystone. The LED display image can also be enhanced with periodic calibration to assure image quality is always in spec. The commercial display industry has an exciting new market emerging in LED display for the highest performance solutions. With challenges overcome, installations and support of thousands of new displays will transform the experience in entertainment and cinema.

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