With Cruden preparing its first simulator LED wall visual system for a driving simulator, Dennis Marcus and Bastiaan Graafland look at how display technology is evolving for driving simulators. This is the seventh and last in our current Content Series of articles.
Projector-based visual systems have been a mainstay of driving simulators since their inception. Even in the future, at Cruden we expect that many simulators will continue to use multi-channel projection system. With LED projectors now replacing the old-style, lamp-lit ones, both image quality and projector longevity are much better than they were a decade ago.
However, we’ve also been monitoring advances in direct view LED panel technology for some time. You’ll have seen these huge screens in city centres, or at airports or sports venues, often being used to display commercials or other media. Such screens are usually viewed at quite a distance and often have distance between the pixels. But with recent advances for the pixel pitch, which refers to the closeness of the pixels to one another, the door has opened to their use in driving simulators, too.
Let’s begin by looking at the current projector technology. In a driving simulator, a projection system is good for creating a large screen at a distance that is far enough away – typically 3-4m – from the driver for them to feel like they are looking into the distance. A driver naturally focuses on objects that are in the distance, so it is important for the immersion of the simulator not to have those objects projected close-up, for example on a laptop screen.
But projectors also have their challenges. One is that the light path to the screen must always be free of the envelope of positions created by the moving structure of the vehicle mock-up on the motion system. The need to avoid shadows on the screen can often lead to suboptimal projection layouts. Instead of placing the projectors in the centre, in line with the driver’s eyepoint, they are typically moved towards the ceiling.
This shift upwards means that the projectors are closer to the top of the screen than the bottom, so the brightness at the top is correspondingly higher than it is lower down. The same goes for pixel density: the closer the screen is to the projector, the smaller the pixels are on the screen. Further down and further away, the larger pixels compromise the image uniformity that you would have, were the projector in the ideal location. The pixels as well as the projected images are no longer square and the trapezoidal blend zones are wider at the bottom than at the top of the screen, which leads to a spilling of pixels and a reduction in system resolution and brightness.
This brings us to the newer, high-end direct view LED panel solutions, whose pixel-pitch has reduced in recent years from a minimum of around 2.5mm to as little as 0.9 to 1.5mm, which matches the system resolution requirements for an immersive driving simulator visual system. Truly curved LED panels still don’t go down that far, but curved screens suitable for driving simulation can be built from planar LED segments, which come in sections ranging from 8 cm x 11 cm to 60 cm x 35 cm, depending on the solution and vendor. Cruden can provide the customer with a cylinder, U-form or any other screen shape or aspect ratio, simply by stacking the panels horizontally and vertically in the right combination.
The resulting LED panel image will have advantages over that of a projector image, for several reasons. One is the absence of the task of blending adjacent images in order to create a single image from multiple projectors. Also, the geometric correction (warping) of the images is much more straightforward because with LED panels, the location of each pixel is known and can therefore be addressed directly from the image generator that renders the images. No pixels or render performance is spilled as all the rendered pixels will be used to show one synchronous image distributed over adjacent panels.
Removing the blend zones brings further advantages in low-light conditions. Typically, a blend zone is visible on a projection screen displaying night-time sceneries because the projector is not capable of showing true black. The possibility of showing true black with LED panels results in a huge contrast increase compared to images of a projection system with the same luminance.
The human eye is very good at compensating for lack of brightness but can never compensate for lack of contrast. High contrast is therefore a very important aspect in all visual systems, including those in simulation. Here, the LED wall solution is a big improvement because it offers virtually unlimited contrast.
The additional contrast also helps us to create a better-defined image. The driver or test subject in the simulator can recognize subtle details in the image that might otherwise fall away in the very small differences that you would have in the lower-contrast projection solution: a more recognizable bump in the road or clearer road signs in the distance, for example. That in turn leads us again to better immersion, as does an LED visual system’s ability to show a much better-defined image.
Reduced maintenance downtime is a further advantage of the LED panel solution. Since there is no projector attachment to the ceiling, no post-maintenance recalibration of the warping and blending is required after reattachment. Instead, the solid-state LED panels not only have fewer things to go wrong, but when something does, each individual segment can easily be replaced from the front side. The new unit can then be matched with the other segments in the LED visual system and a consistent image will be up and running again straight away.
The system’s longevity is good, too. The degradation in the brightness of the LED visuals in a driving simulator application has been calculated to be negligible.
With such promising fundamentals in place, Cruden has been working with LED panel manufacturers and signal processing developers to fully harness the potential of this technology for driving simulators. The low latency and 120fps frame rate requirements are aspects that we’ve been able to address. This refresh rate isn’t critical for showing a big-screen commercial at an airport and neither is a very low latency but both are essential for driving simulation, so the developers have worked to ensure that this can be implemented.
Effects such as the smearing or ghosting that you sometimes see on a television – the streak of colour that can get left behind a fast-moving object – also need to be eliminated because of the simulator’s reliance on fast-panning visuals. To avoid unwanted ‘artifacts’ you need a careful combination of the right LED panels plus a good-quality driver and signal processing. At Cruden, we have carefully selected solutions to match our application, working with the manufacturers and developers to find our way to optimized image processing that reduce the unwanted phenomena and enable the high frame rates and processing tricks that will improve image quality, without adding latency or other negative effects to the immersive experience.
The LED panels that are used in off-board simulator visual systems are currently not suited to use on-board the simulators – screens mounted directly on the simulator motion system – as the panel structures are not designed for dynamic applications and also the pixel pitch isn’t yet high enough for their use so close to the driver. Instead, Cruden is now busy replacing its custom-developed LED backlit LCD displays that are used on-board its motion platforms, with OLED technology that is also used in televisions. These OLED panels have the further advantage that they can be curved to wrap around the driver. If the space in your facility is limited or the budget isn’t available for a large off-board projection or LED panel type visual system, then onboard OLED visuals are a good alternative.
We believe however that LED panels are setting a new standard for large, off-board visual systems. This is important because, as we’ve noted before, the visual system is by far the most important factor in immersing a human in a driving simulator.
LED panels won’t be for everyone, not least because such a solution can come at about three times the cost of a traditional projection system. But it’s for the enhanced technical capabilities that some of our customers are now requesting this option – especially those who have extensive experience in simulation and projection systems.
Like Cruden, these customers are aware of the limitations of projection solutions and see LED panels as the next step towards high-end visual systems for simulation. LED walls are already used in car companies’ design studios, but we expect to be the first company to implement and deliver the technology in driving simulator visual systems.
For more information on the topics covered in this article, please contact Dennis Marcus via firstname.lastname@example.org or on +31 20 707 4646.
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Other articles in the series:
Article 6: Rendering a world of new possibilities