Managing and controlling modern aircraft in
flight remains one of the primary technology challenges
of the aerospace industry. The vehicle pilot
not only controls the flightpath of the aircraft, but
must communicate path objectives to the air traffic
control system, and receive and respond to directives
from that agency in order to maintain safe and
efficient flight. Additionally, the pilot is the manager
of the on-board systems that are required for flight.
Modern aircraft and aviation systems are highly
complex, and for many of these tasks - control,
management, and communications - modern display
technology has been utilized as the best way to
interface the pilot with the vehicle and system. Map
displays have replaced compass headings on the
aircraft instrument panel, allowing the pilot to see the
flightpath information directly in terms that are easily
understood and difficult to misinterpret. Air traffic
control commands can be visualized directly on
these maps. Additionally, the status of on-board
systems can be graphically presented to the pilot,
reducing his perceptual and cognitive workload, and
reducing the potential to misinterpret more traditional
system indicators. High-information-content display
technology has enabled this transformation of the
man-machine interface in aviation. The goal of this
effort is to improve the fundamental display technology
base in order to make it possible to move
lightweight, portable, untethered display technology
from the low-cost portable-computing environment
to this aviation setting.
Head-mounted displays are currently being
developed that use new technology innovations such
as liquid crystal on silicon and organic light-emitting
diodes. These displays offer revolutionary advancements
in weight and power reduction, enabling
untethered use with minimal effect on pilot mobility
and action in the cockpit. However, there are
remaining challenges - image size, resolution, color,
contrast, and speed - depending on the display
technology. Common expectations about the
requirements for these parameters are based on
decades of experience with cathode-ray tube (CRT)
displays, and not necessarily on perception science.
High-information-content imagery requires broad
information channel capacity to the device in order
to display fine detail, subtle shading, full color, and
continuous motion. However, excess channel
capacity for one of these parameters can often be
used to compensate for a lack in another. A well-known
example of this is the halftones used in
printing, where some spatial resolution is sacrificed
to enhance tone reproduction.
For several years, Ames has been developing a
display optimization tool set known as Visual Display
Engineering and Optimization System (VIDEOS). In
the investigation of the gray-scale/resolution trade-off
for displays, it was found that without dithering, there
was no trade-off; there was both a minimum spatial
resolution and a minimum number of gray levels
required in order to produce an image indistinguishable
from a photo-quality version. With dithering, an
important trade-off region emerged that corresponds
to parameter values achievable by microdisplays
being developed for helmet-mounted systems. A
summary graph for these results is shown in figure 1.
Plot coordinates are spatial resolution (abscissa) and
number of gray levels (ordinate). The shaded upper-right-
hand regions are below threshold for discrimination.
Data points are the threshold results for three
observers in the psychophysical study; continuous
contours were generated by the computational study
using the human vision model and a just noticeable
difference JND = 1 for the threshold. Figure 1a shows
the results for non-dithered images: the rectangular
shape of the below-threshold region indicates the
lack of a gray-scale/resolution trade-off. The triangular
portion of the contour in figure 1b demarcates the
trade-off region for the dithered images. When color
dither for displays was investigated, it was found that
a considerable savings in computational power could
be achieved by dithering in the digital, instead of the
luminance, representation of the image, as long as at
least six levels of each color were used. These six
levels could correspond to what is known as the
"browser-safe" palette commonly used for image
compression on the Internet.
The broad information channel capacity required
for high-information content imagery also requires
high power outlays to support the device communication
needs and to rapidly switch data onto the
display device. The ViDEOS team is developing
methods for reducing these requirements without
sacrificing the visual quality of the images presented
to the user. Because these devices act essentially as
random access memory units, they provide new
opportunities to save communication channel
capacity, power, and, ultimately, weight. The unique
feature of the Ames approach to this technology
problem is that the information quality of the images
drives the optimization of the display system. The
ultimate goal is to provide new venues of visual
information to the pilot thereby improving safety and
efficiency.
Figure 2 shows a commercially available near-to-eye
display system, suitable for avionics. This light-weight
unit can be connected to a flight helmet or
even to a baseball cap. This display was manufactured
by LitEye® Microdisplay Systems.
Point of Contact: J. O. Larimer
(650) 604-5185
jlarimer@mail.arc.nasa.gov
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