Digital Signage at Display Week 2017
Projection, LCD, direct-view LED, and other technologies represented the state of the art in digital signage at the show in Los Angeles.
by Gary Feather
Digital signage, which now represents a sizable segment of the display market, includes the indoor LED direct-view signage business at $2 billion (growing to $4 billion by 2021); outdoor LED at $2 billion; projection at $3.5 billion; professional LCDs at $1.9 billion; and video cubes at $.45 billion. The market has evolved significantly over the past decade in terms of both technology and applications. Static displays, which replaced many nondigital roadside signs, are being replaced in turn by those offering full-motion and full-color video. Pixel pitches of 25 mm have shrunk to below 0.9 mm.
Display Week 2017 was an excellent place to learn about these and other trends; the show floor highlighted direct-view LED and reflective displays, and the technical program featured presentations on how to overcome challenges specific to digital signage. (Since all displays are technically “digital signage,” this article focuses primarily on products that are bigger than 90 inches diagonal and have a luminance higher than 500 nits.)
Large-Area Display Systems: Narrow Pixel Pitches and Direct-View LEDs
Some background may be helpful in better understanding the digital-signage developments at Display Week. In the early 1990s at Texas Instruments (TI), researchers imagined a better solution to the CRT direct-view and CRT three-gun projection systems that were prevalent at the time. The vision was a 2,048 × 1,152 reflective spatial light modulator (SLM) that could be refreshed using pulse-width modulation (PWM) to create full-motion, full-color video with a luminance of more than 4,000 nits and a bit depth greater than 10 bits per color. TI demonstrated the first HD cinema prototype in 1993 in Seattle at Display Week. (See Fig. 1 for a schematic of the chip on which that prototype was based.) The Texas Instruments SLM was operated in a digital mode and was very fast. The product was patented as a DMD, both Digital and Deformable Mirror Device. In 1994 the company decided that a market name would be helpful for product applications, and thus was born digital light processing, or DLP.
Fig. 1: This schematic originally appeared in the 1993 July/August issue of Information Display. It depicts a chip (one of thousands) used to power TI’s HD cinema prototype, which was shown at Display Week in 1993.
After this, large-area projection systems became a standard for indoor digital signage, as high-luminance, full-color, and full bit-depth images were now realizable.
In 2003, after years of development, Sharp launched an affordable line of LCD TVs with 15-in. and 20-in. diagonals worldwide. While the industry scoffed at the possibility of ever building larger-format LCD TVs with HD resolution and image quality, Sharp (and eventually other companies) pushed forward to launch >30-in. LCD TVs in 2004. In 2005, LCD TVs were in every major manufacturer’s booth at the Consumer Electronics Show (CES). Digital signage makers took note and began to incorporate LCD into stand-alone solutions as well as tiled video walls. By 2016, LCD video walls had hit sales of ~$2 billion. Manufacturers are working hard to sustain that growth through new features including narrow bezels (lines) and self-calibration for uniformity.
Meanwhile, direct-view LED signs have, for the past 15-plus years, represented the ever-improving large outdoor displays we see along our roadsides. Those direct-view LED displays started moving indoors a decade ago and are now competing with LCD and DLP technology in both image quality and pixel pitch.
Direct-View LED Joins LCD and DLP Projection
Today, LED video walls have many advantages although they also face a number of challenges they must overcome if they are ever to surpass LCD video walls. From a total market-growth perspective, many analysts predict the compound annual growth rate (CAGR) for direct-view LED displays in the fine-pitch and ultra-fine-pitch area to be greater than 36 percent compared to a mere 10 percent for LCD. By 2020 the sales revenue of fine-pitch LED video will match that of LCD video walls.
The pixel pitch for an LCD with a 60-in. panel at HD resolution is about 0.75 mm. For most large-area digital signage applications, that pixel pitch exceeds the capability of the viewer’s eye at a normal viewing distance to appreciate and value the resolution. LED digital walls are therefore specified to a pixel pitch in which the user gets the maximum content but does not see the individual pixels.
Direct-view LED has been moving quickly into the classic LCD space. One advantage of LED displays is that they can be made in any extended size without the noticeable borders or “mullions” associated with multiple conjoined LCDs. Also, the display is calibrated as a full display rather than individual displays, which aids in image uniformity. LCD video walls have a cost advantage, which will help them maintain their current position in the market. The current 2.5-mm LED pixel pitch is competitive with the best-of-class narrow bezel LCD, and if the resolution (in pixels per inch) is sufficient, the LED is the superior choice.
Direct-view LED digital signage has offerings in many pixel pitches and any practical resolution size. The market has 2.5-mm, 1.87-mm, 1.6-mm, 1.5-mm, 1.25-mm, and now 0.9-mm RGB pixel-pitch solutions in production. The building-block approach to direct-view LED displays makes them adaptable to practically any shape, any size, and any resolution. So with worldwide sales of LED fine-pitch (less than 2.5-mm pixel pitch) digital signage moving from $1 billion today to more than $2 billion in 2022, the challenge ahead will be to educate the market on performance and reliability capabilities so that customers purchase technology that aligns to their needs during this transition of display technologies.
The future of digital signage will be heavily affected by technical, performance, and cost improvements in coming years.
Display Week 2017 Perspectives
Display Week 2017 brought together leading industry experts and top researchers for an array of invited papers and technology presentations. Among the questions posed and sometimes answered in these discussions were:
• Will projection-display applications based on DLP continue to shift to direct-view LED, or is the cost and visual-performance advantage of DLP maintained through most current applications?
• Will LCD maintain its place in the digital signage industry, or will direct-view LED continue to grow its share as a better match to large-format applications?
• Will digital cinema ever move to a direct-view LED display?
• Are there applications for reflective technologies for outdoor and indoor applications?
• What new development in any of the technology areas can create new market growth?
The three sessions and eleven presentations covering digital signage at Display Week 2017 touched on many of the top areas of technology and product opportunity spaces.
SMT RGB LED Display Emitters
In a paper from Cree, Jovani Torres covered details on the release of the 1-mm × 1-mm surface-mount technology (SMT) red-green-blue (RGB) LED for the finer pixel-pitch patterns. Current performance shows support of luminance and color control along with efficacy to address the needs of 1.25-mm pixel-pitch LED display products currently on the market. The output luminance supports displays in the 500-nit-candelas-per-square-meter (cd/m2) range, which is a match for the needs of the industry at this time. Improvements in the contrast ratio are attained through the masking of reflective elements, and the new “sandwich design” supports the low profile required for the tighter pitch. With all the improvements in this RGB LED offering, the industry requirements for next year will be much greater. With current pixel pitches passing 0.9 mm and demonstrations at 0.7 mm, it will be very important for this 1-mm 1010 (refers to package size) LED to continue to be reduced in size. The 0.9-mm pixel pitch requires an 0606 RGB SMT LED (36 percent of the 1010) with all the same optical performance and reduced output flux proportionately. Likely the final requirement for discrete LED SMT packaged solutions will be 0.7-mm pixel pitch, so packages may need to become a little smaller.
Transmissive Displays
National Chiao Tung University’s Zong Qin provided much-needed insight into the proper implantation of transparent displays in the paper, “Pixel-Structure Evaluation Regarding See-Through Image Quality for Transparent Displays: A Study Based on Diffraction Calculation and Full-Reference Image-Quality Assessment.” The transparent display has captured imaginations and won some implementations in the past five years. The open issue is that it has proved difficult to design a “system” solution that makes the display perform at maximum visual impact. The methods and algorithms in Qin’s paper clearly outlined the considerations for addressing image quality and the viewer perception of a transparent digital sign. This is an exciting opportunity in transparent displays, and we hope that implementations based on these design parameters will grow more compelling in the years to come.
Reflective Displays
There are no deployed solutions in reflective digital signage that are getting much attention, and yet there is a great interest in the potential for this technology. Outdoor displays in specific use forms may work best if based on reflective technology. The advantages of reflective technology are in relation to its low power usage and its readability in the outdoor sun. If reflective light management is managed properly, the display will avoid thermal issues as well.
At Display Week 2017, there were three presentations of interest in the reflective color space. In a paper titled “Development of a Novel Reflective Display System with Multi-Primary Color for Digital Signage,” Tatsuya Yata of JDI presented an LCD-based design for reflective outdoor signage with a focus on multiple primary colors. These examples were limited in size to that of a typical LCD panel, but the reflective solution removes the need for super-bright backlights. These displays also supported moving images. The challenges to overcome include cost and long-term reliability in high ambient light.
Another LCD-derived reflective panel, described by JDI’s Tadafumi Ozaki in the paper “Development of New Error-Diffusion Dithering Method for Reflective Memory-In-Pixel (MIP) LCDs,” discussed image quality with dither. The implementation and validation showed useful results. Again, the challenges of the added cost vs. benefits are still in the details of the application.
A unique solution using micro-electrical mechanical systems (MEMs) technology was proposed by Zhong Ji of Yuanse Technology in the paper “Large-Pixel Reflective-Color Display for Outdoor Applications.” While in early feasibility stages, the approach and described method offer a possible path to a prototype. The large pixel size lends itself to outdoor applications. Yet the display is limited in size and doesn’t allow for seamless tiling. It could, however, be considered for particular applications.
In addition to these three presentations, there were three related booth exhibits that sparked interest. From E Ink, we saw the larger-format reflective display with near-full-color performance (Fig. 2).
Fig. 2: E Ink showed new versions of its Advanced Color Display at Display Week. The displays can be tiled.
These displays demonstrated on the floor at Display Week were complete and ready for applications. Most outdoor signage that can be viewed by a moving car is not video but changing static displays; that use aligns to this display. While the size is a smaller format, a number of installations in outdoor environments only need smaller-format displays. E Ink was pushing the display for direct-sunlight applications. Marketing of the product is in progress.
The reflective-digital-signage offering from New Visual Media Group was a macro-sized MEMs device. With a manufacturing process that is validated, the system provides shutters that can provide a reflective display through a dither and switching solution. While it is only a prototype test unit at this point, many on the show floor were very interested in the technology and intrigued by the possible system and addressing schema that might make this useful.
CLEARink surprised many on the exhibition floor with a video-capable electronic paper display. The technology touted e-book applications, and a key feature was sunlight readability and reflectivity. Still in the early stages with regard to larger-format signage, this CLEARink solution has the potential to be another player in outdoor information and entertainment products. (For more about CLEARink, see the Materials article in this issue.)
Signage Market Overview
As an invited speaker for the first Digital Signage session of the Symposium, Samantha Phenix of Planar/Leyard took a step back to discuss all aspects of the digital-signage industry. The key takeaways from her presentation were that market growth, technology evolution, and possible revolutions are all yet to come. The vast availability of video content and the return on investment in bringing displays to the public in any of the growing markets will lead to an additional $1 billion in sales over the next four years. While Phenix discussed LCD solutions (large and tiled), the spotlight was on LED business growth. Trends involve the finer pitches (below 2 mm) and standardization on HD (2K) and now UHD 4K, which are being met with smaller SMT RGB LEDs (1010 to 00505). There are no technical barriers for implementation; the focus now is on better-quality displays and lower costs. In addition, the technology changes to uLED solutions and active-matrix LED (AMLED) backplanes open another huge growth area with regard to performance and cost reductions over the next five years.
“Active Backplane Design for Digital Video Walls,” a presentation by D.R. Dykaar of DifTek Lasers, Inc., laid out the path toward an AMLED backplane. This scalable active-matrix backplane leveraging single-crystal silicon spheres opens the door to a targeted project for early introduction of the next generation of direct-view LED and possible OLED solutions.
OLED and LCD Tiling
Digital signage is usually a large display, often bigger than a single-panel solution for OLED or LCD. Minimizing the gaps (or mullions) from tiling LCD and OLED panels (2 × 2, 3 × 3, etc.) was addressed by Seijin Lee of LG Display with the paper “Development of a Zero-Bezel Display Utilizing a Waveguide Image-Transformation Element.” The solutions are focused on both the optical management and the data management of a display matrix to reduce the visibility of the gaps between the panels. Panel displays have reduced the bezel to 0.9 mm; it’s not enough to be good enough. Both of these presentations are an attempt to electronically shift the image and the light to a spatial position to effectively “fill in” the gap. The results are effective in reduction of the gap, but unfortunately complete elimination remains elusive.
Display and Image Quality
An invited paper from Jorge Perez Bravo of NanoLumens on image quality actually dared to consider matching and improving on the display quality from the best large-format LED and OLED displays. A demonstration of products now shipping in HD and UHD clearly showed the capabilities in the industry. The paper identified the display elements that create limitations to video quality, presented methods to mitigate those limitations, and discussed the competitive capabilities of LED as compared with LCD. Of course, LED has the advantage over LCD when it comes to building a very large display (10 ft2 to >1,000 ft2) without any mullions. This is only offered by LED.
The details of artifacts or characteristics of the LED drive that cause some limitations in display quality were addressed clearly in a paper from ELDIM. Both on the exhibition floor and in the technical presentation, the system approach to presenting information on the display to avoid visual (temporal and spatial) artifacts was a clear improvement.
Digital Signage Continues to Gain Momentum
Display Week 2017 opened the door to more information on digital signage than ever before. With the growing market and the considerable advancements in technology, it is clear that companies focused on these technologies can expect significant demand for their products in this market segment. Figure 3 shows one example of the kinds of applications that are now possible. Combining the inventions with the innovations and the implementations at the system level will assure digital-signage displays will lead to greater demand and higher value. •
Fig. 3: This 4K cinema installation for Telstra in Sydney, Australia, represents but one possible direction for digital signage. Image courtesy of NanoLumens.
Gary Feather is the CTO of NanoLumens, a large-area visualization company in Atlanta, GA. Prior to joining NanoLumens, he led LCD system development at Sharp Laboratories in the transition to HD and Internet-connected products. Previously he was part of the TI team that commercialized DLP in both business projectors and cinema systems. He can be reached at GFeather@nanolumens.com.