The Expanding Vision of Head-Up Displays: HUDs for Cars at Display Week 2017
The goal for HUDs is to provide drivers with critical situational awareness in a non-distracting way. At Display Week 2017, it was clear that manufacturers are overcoming numerous technical challenges to make this goal a reality.
by Steve Sechrist
In the automotive space, head-up displays (HUDs) allow drivers to see information such as speedometer, tachometer, and navigation system data without having to look away from the road while driving. In a conventional windscreen HUD system, this information can be projected from a system mounted in the dash onto a windshield film that provides the appearance
of the information floating outside the vehicle. Next-generation windscreen HUDs called AR (augmented-reality) HUDs will project images on the street and in the environment as we drive. These images will go beyond a simple arrow indicating an upcoming turn; they will entail a series of arrows superimposed on the street and in the lane up to the turn point as we approach. This functionality requires a dramatic increase in the field of view and optics components in order to work in a realistic and reliable fashion.
Compelling as automotive HUDs are, one reason they are not more common is they are expensive. The technology is difficult to mass produce, as it must be made to conform to the complex geometries of unique car model windshields, and few (if any) models achieve the volume required to make the technology viable through economies of scale. Consequently, for
decades, conventional HUD technology has been primarily relegated to high-end luxury cars and avionics applications.
Beyond cost, integration issues still loom for conventional windscreen HUD technology. These center around the competition for volume (space) in the vehicle. Two critical factors car designers face is the trade-off between HUD device package volume, which can range from 4 liters (today), to prototype AR systems that may be up to 20 liters in volume. HUD package volume directly impacts the head-up display object size and image distance (how far it floats above the hood of the car), with the potential to encompass the entire windscreen and field of view of the driver with augmented situation-awareness data (Fig. 1).
Fig. 1: The future of windscreen conventional HUD systems includes a wide field of view that augments the entire windscreen for the driver. The arrows indicate which lane to turn into. Image courtesy of Continental.
Recent HUD design breakthroughs with lower-cost alternatives to conventional windscreen HUD systems are helping to address the need for enhanced critical situational awareness information. These new systems can deliver this information directly into the field of view of the driver, diminishing “eyes-away” distractions and enhancing driver safety. This is in concert with other auto display megatrends that include a dramatic increase in the number of sensors in vehicles.
The primary display development focus in HUD systems today (and near term) is in situational awareness and AR data display. These near-term technology additions include livestreaming of rear-view data to a mirror display from a rear-mounted wide-angle camera. Additional cameras and other sensors such as lane-change assist and warning indicators for side mirrors are available in new vehicles today.
Future “sensorization” of the vehicle includes the addition of artificial intelligence (AI) combined with connectivity between transportation and metropolitan infrastructures that will contribute both mid- and long term to the eventuality of the driverless vehicle. These advances include car-to-car communication as well as car-to-infrastructure (road and highway or building, like a parking garage). At some point in the future, our primary display focus inside the car will switch from situational awareness and monitoring to personal and social information access and entertainment.
Newer, Low-Cost HUDs Solve Windshield Conformity Issues
Recent developments in lower cost “combiner-type” HUD systems involve the projection of an image on a pop-up, see-through glass or plastic optical element. This augments the driver’s field of view with critical situational awareness data, while using a relatively low-cost approach. The key difference to the driver is that the image remains inside the vehicle on the combiner element rather than appearing to float above the hood outside the car, as it does with the more expensive conventional approach. In either case, the display module includes an LED (or sometimes a laser) light source with a liquid-crystal or MEMS projection-type light engine. Critical to car designers is the volume of the module, power (in hybrids), and ruggedness, including the ability to withstand wide temperature ranges in both off state and when operational.
As evidenced at Display Week 2017, and in reports from system integrators, there is strong OEM interest in these lower-cost combiner HUD systems for B- and C-class cars that will help reduce the unit cost of the technology by leveraging its use in more models, and consequently moving the technology into the mainstream car market.
Auto Industry Requirements for Displays
The major specifications of HUD displays are mostly driven by well-established safety standards for vehicle components. In short, automotive displays require additional performance criteria compared to displays used in offices and homes, including:
Picture quality: In automotive HUD systems, the focus is primarily information (rather than entertainment and full-motion video), so higher resolutions are not a critical requirement. As recently as 2014, the HUD display requirement was relegated to a 1.x-in. WQVGA display. This was before the adoption of combiner-type displays.
High contrast/high luminance: A higher contrast ratio is required in order to provide daylight readability in the high-ambient environment of a vehicle, with luminance now being delivered above 8,000 nits.
Adjustable luminance to augment changing time of day, and day-to-night transitions: Displays must provide adjustable dimming from maximum luminance in daytime to lower luminance in evening and at nighttime to avoid interior ghosting and glare.
Color gamut: Displays must maintain color stability under sunlight conditions and in broad viewing angles, but they do not need to produce as many or as wide a range of colors as entertainment-type displays.
Fast response time: 30 milliseconds or better response time is ideal for vehicles as well as entertainment uses that go beyond automotive.
Wide temperature range: Displays must perform consistently regardless of operating temperature; in a range from –40°C to 105°C, which is much wider than typical consumer-grade requirements.
Display Week was the ideal place to catch a glimpse of the current state of the art in automotive HUD systems. And the Market Focus Conference on Automotive Displays on Tuesday at the show was an excellent place to start.
For example, the BOE presentation at the automotive conference showed a good outline of the different types of HUD devices (Fig. 2). The lower cost combiner technology uses an LCD engine powered by LED illumination. Conventional windshield HUDs generally utilize MEMS imagers (like TI’s DLP), plus laser light sources. These are currently 2D systems but long term, 3D will be added, and combined with a much longer virtual image distance that offers a more realistic AR experience than the HUD system. In the Texas Instruments presentation at the automotive conference, the company stated a minimum of 7.5 meters in virtual image distance that can extend up to 20 meters and a field of view that ranges from 5 to 20 degrees will be required for a true AR HUD image (Fig. 3).
A livestreaming video image to a rear-view mirror display represents another HUD-like display type (Fig. 4).
This irregularly shaped display technology is available this year to car makers and system integrators from BOE.
Fig. 2: BOE provided an overview of its HUD technology at Display Week’s Market Focus Conference for Automotive Displays.
Fig. 3: TI’s presentation showed conventional windscreen HUDs moving to “true AR functionality” in the future, but due to optics requirements, this will come at a cost of increased package volume.
Fig. 4: A mirror display shows a streaming camera image from a rear-mounted CCD sensor with a wide-angle lens offering superior situational awareness. Image courtesy BOE.
HUDs on the Show Floor
One company leading the field in automotive HUDs is JDI, which has been providing these types of products for three years now. In 2014, just two years after its founding in 2012 with the joining of display groups from Sony, Toshiba, and Hitachi, the company showed its automotive market “combiner HUD” technology in Yokohama, Japan. This display showed the image on a transparent screen inside the vehicle, rather than projecting the information onto a light field above the car hood, as would a conventional HUD.
A factor to consider is the long lead cycle necessary to get equipment such as displays into car designs. Display makers are then also burdened with long support cycles, as car manufacturers often require replacement parts to be available for 15 years or longer after product end of life.
At Display Week, the JDI booth focused on a highly transparent color display that can be used in a car as a hybrid HUD. The 4-in. diagonal LCD offers up to 80 percent transmittance with a 300 × 360 pixel (117-ppi) resolution sporting 16.77 million colors (Fig. 5). Background images can be clearly seen through the LCD, which requires no color filter or polarizer.
Fig. 5: JDI’s display was shown in both off (left) and on (right) states on the show floor at Display Week. Photograph by Steve Sechrist.
A key benefit is the 80 percent transmittance, which allows users to see displayed images against a real-world background. (As referenced in “Materials and Other Game Changers,” the materials review article in this issue, the US National Highway Traffic Safety Administration requires at least 70 percent transmissivity for an optical element that is placed between a driver and his view of the road.) This technology is targeting AR and MR (mixed-reality) environments and can be used in expanded applications such as car mirrors or even windows.
An additional display for next-generation automobile cockpits is being developed by JDI that targets auto designers’ need for flexibility and content in a non-distracting way. JDI cleverly combined the driver instrument display (DID) content with a data subset displayed on the HUD combiner windscreen (Fig. 6). The technology is meant to deliver a low-cost HUD alternative to car designers by circumventing the expensive windshield HUD approach.
Fig. 6: In 2014 JDI introduced this combiner HUD for application inside the car with data synced to the driver information display; here is a 10-in. cockpit cluster with head-up overlay.
For more detail, we went to the company website and found this description: “JDI offers a display for next-generation automobile cockpits that increases flexibility for both interior design and displayed content to assist drivers by integrating the instrument cluster....”
For the instrument cluster, the curved “IPS-NEO” provides displays that are easily viewable to drivers. The upgraded “White Magic” achieves both a large high-definition screen and low-power consumption. In a safe head-up display that can be viewed without turning the eyes, a larger display area with increased resolution leads to the extension of data display.
In the booth this year, JDI was also featuring an LCD engine for the conventional HUD projection-based devices that have been around for years. These use a local dimming backlight added to the “White Magic” (added white pixel) display JDI has standardized on for the past several years (Fig. 7). The company showed how the local dimming backlight module improves traditional HUD images while lowering power by approximately 45 percent and improving luminance 35 percent.
The company also showed a curved (500-mm radius) 10-in. diagonal prototype cockpit cluster display with a head-up overlay in 2,880 × 1,080 pixel configuration (380 ppi) using an in-plane-switching based LCD. The panel sports a 1,500:1 contrast, and offers a wide gamut.
Fig. 7: An example of JDI’s LCD engine for conventional windscreen HUD systems uses an LED backlight. The company also supports a retractable combiner HUD like the one found in the 2016 Mini Cooper with final components assembled by Bosch.
LGD’s Transparent Display
On the show floor, LG’s automotive exhibit featured its OLED technology and a hybrid of what the company calls MLD (multilayer display), which combines both OLED and liquid crystal in a transparent display meant for relatively low-cost (compared to windscreen-based applications) head-up use (Fig. 8).
Fig. 8: LG’s transparent 12.3-in. hybrid diagonal display combines both LCD and OLED elements.
The MLD has a front resolution of 900 × RG (BG) × 360 pixel and a rear display resolution of 1,920 × RGG × 720 pixels. Other details, like transmissivity, were not published but LG said they will be forthcoming.
LG identified three chronological trends in the automotive display space. In the first, from 2010 to 2014, displays were included as a small part of the dashboard, combined with analog instruments and growing center-stack displays. Starting in 2015, larger size displays, including full cluster displays (rather than those simply mixed in with analog instruments) and much larger center information displays (CID or center stack displays) with touch interface began to proliferate. These will continue to do so through 2019. During this period, we will also see the beginning of pervasive head-up displays. The third trend begins in 2020 and lasts to 2024, during which displays will be seamlessly integrated into the full dashboard, with the potential to include the entire vehicle – everything will be a head-up display.
LG also addresses some of the unique requirements needed by the auto industry in its display integration.
Another example of the evolving head-up display in cars is the move toward using a display and camera system to replace the rear view mirror. In fact, some see the use of traditional mirrors in the car as totally going away. At Display Week, LG showed its version of a 6.13-in. diagonal OLED that will serve as a rear-view mirror replacement. Its display sports 600 × 224 pixel resolution with 105 ppi and a reflectance of >75 percent with over 600 nits white luminance. LG Display’s J. Kang (Fig. 9) told us the OLED panel uses an LTPS backplane.
Fig. 9: LG Project Manager project manager J. Kang stands next to the company’s 6.3-in. OLED mirror display.
Overall, LG seems to be targeting the auto space with its OLED technology over LCD, claiming the self-emitting technology offers better auto-grade reliability, plus the ability to create various shapes (curvatures) to conform to the auto design requirements. OLED’s “perfect black,” high-contrast display capabilities are also in its favor.
LG’s transparent OLED technology offers very high transmissivity and the ability to conform to slim window integration requirements. These displays also feature very low latency – important for situational awareness and safety – and offer a high reflectance level for use in mirror applications.
So LG’s vision long term for HUD may just be display ubiquity in the car with its transparent displays placed on every traditional glass surface in the car today. As driverless (or self driving) vehicles make their way into the mainstream by the next decade, the car interior will evolve into more of a super-efficient living space where people spend time while moving from place to place. That means content consumption, and that points directly to greater use of multiple displays. And remember, this is coming from the company that also showed a 77-in. diagonal “Wallpaper” OLED display with UHD resolution, weighing in at under 3 lbs. and measuring less than 6 mm deep.
Asahi Glass Company also has a focus on automotive displays with windshield and rear view (e-mirror) technology also mentioned, along with dashboard displays (Fig. 10).
Fig. 10: AGC head-up displays are combined with e-mirror display and driver information cluster.
AUO’s booth (and conference presentation) focused on the future of the HUD in the vehicle as a unified 360-degree glass screen where “glass is the fabric that knits the displays together.” To get there, the company said what is needed is curved, molded 3D glass displays (not necessarily “flexible” ones), seamless transition of infotainment from surface to surface, integrated dynamic gesture recognition, touch and HMI, plus high-speed interconnectivity (screen to screen that includes vehicle to vehicle, vehicle to infrastructure, and vehicle to smartphone).
This is an exciting time for automotive HUD technology, whose growth is just beginning to take off. New windscreen technologies and combiner HUD systems are just the beginning. As we move forward into the realm of AR HUD systems, we see the technology growing in prominence. It is sure to be a feature in a car you drive – perhaps sooner rather than later.
From the early days of its adoption in airplane cockpits to the first use in cars dating back to luxury brands in the 1980s, the head-up display has captured the driver’s imagination with the idea of a non-distracting way to update critical situational awareness. This is an idea not lost on auto safety engineers, auto insurance providers and especially cutting-edge drivers wanting that extra edge that enhances the driving experience. And after all, isn’t that what it’s all about? •
Stephen Sechrist is a display industry analyst and long-time SID member since the pen computing days of Apple Newton and Go Corp. (AT&T) EO (remember?) He enjoys display industry writing and talk of the old days when a 1MB HD was hot stuff. He can be reached at firstname.lastname@example.org.