Brightness Vs. Blur
New Projectors Provide Ultra-Brightness, But Trade-Offs Remain
Liquid crystal on silicon (LCoS) displays have long been admired for their spectacular brightness, ultra-high resolution and low-maintenance costs - and shunned for the way they blur moving images.
Now, new smear-suppression technologies have some of the biggest players in the simulation industry rushing to use LCoS displays in place of dimmer, maintenance-heavy cathode ray tubes.
Those fixes include simple shuttering techniques to unique and complex fixes patented and closely guarded by company engineering departments.
This year, training-and-sim giant CAE switched to LCoS, Barco's new SIM 7, as its standard projector system. As of June, all CAE simulators that were delivered arrived with LCoS systems.
"CRTs have essentially stopped their progress and CAE has elected to use Barco SIM 7C LCoS for its Medallion 6000 image generators. They are 10 times brighter than CRTs and produce better night-vision-goggle stimulation," said Philippe Perey, CAE's engineering director for visualization products. "The CRT workhorse is being actively phased out faster than many of us thought."
In simple terms, LCoS displays are a cross between liquid crystal displays (LCD) and silicon processors. The silicon is an electronic back-plane with a highly reflective top layer that controls the orientation of the liquid crystal molecules. This makes for smaller and less complex electronics and good, dark blacks.
But LCoS systems also take about twice as long as CRTs to turn individual pixels on and off - about 4 or 5 milliseconds. The longer illumination stimulates a larger portion of the eye's retina and is perceived as blur.
So, not everyone is sold. Barbara Sweet, an aerospace engineer at the NASA Ames Research Center, told attendees at the IMAGE 2007 conference in Scottsdale, Ariz., in July that motion-induced blur "is a highly salient and potentially objectionable issue." And in NASA Ames tests using an LCoS helmet-mounted display, even the lowest levels of perceived blur were above that experienced with CRT and would "likely produce very salient and objectionable differences in perceived resolution as a function of image motion," she said.
"Other technologies offer advantages beyond CRT projectors that make them attractive," Sweet concluded. "However, these projectors need to improve their moving picture response to validate the continued interest by the simulator industry."
Reducing Blur
Working with the U.S. Air Force Research Laboratory's Mesa Visual Systems Development unit, the NASA Ames research engineers came to several conclusions.
First, reducing hold time down to 8 milliseconds reduces blur, as does shuttering.
"On fighter air-to-air missions, applying shuttering produced a dramatic reduction in blur. It's very promising. It appears that shuttering is a worthwhile strategy," Sweet said.
Agreeing to a standard for measuring and comparing different technologies and displays is also important, Sweet said.
"A common measurement standard must be developed to allow side-by-side comparisons of the different models and technologies of today, and to allow more cogent discussions on projector performance," Sweet's paper concludes. "For these standards to be usable to inform design decisions, a clear correlation needs to be established between the sensor-based measurement metrics and human perception, across varying levels of contrast, luminance and resolution."
More controversially, Sweet proposed doubling the current typical frame refresh rates from 60 Hertz to 120 Hertz - 120 cycles per second. Increasing the refresh rate rather than shuttering would reduce hold time without loss of luminance. But it's expensive and technically difficult to achieve with LCoS. Geoff Blackham, chief technical officer at SEOS, said he was not aware of any 120 Hertz LCoS solutions available today, although he said he believes they will become available in the future.
"It would need double the IG capacity, and that would increase the cost," he said.
Barco, which provided much of the hardware for NASA's and AFRL's research work, uses a shuttering technique on its SIM 7 projector and also applies true motion reproduction to compensate for response-time smearing effects.
Paul Lyon of Barco's Simulation & Training Group based in Xenia, Ohio, agreed that brightness was lost with shuttering but said: "At 2,500 lumens unshuttered, we are still the best in the industry even after shuttering - we are still over 1,000 lumens."
The simulators visuals industry has always been about trade-offs and fixes.
"You probably could not do LCoS at 120 Hertz, so you would have to go back to CRT and then you would lose all the lifecycle costs and brightness benefits that you get with LCoS," said James Davis, a member of the American Institute of Aeronautics and Astronautics Modeling & Simulation Technical Committee. "You have to ask yourself, which benefits are important and which are just good to have? But for a dome display, for example, CRTs don't give you enough light.
"LCoS is very affordable and it's good technology that's being aggressively pursued. It will only get better, even if at this point there might be some high-end military applications where it will be found wanting," Davis said.
"But if pilots are complaining, two things might be happening. First, they might be using a cheap LCoS system where better systems are available. And second, separate issues could be happening that really good engineers could work a fix for." ■
E-mail: kwalker@defensenews.com.
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