| Do You See What I See?
by David Pescovitz
For more than
two decades, computer science professor Brian A. Barsky has suffered
from an eye disease that blurs his vision and increases sensitivity
to glare. But in 1992, Barsky a leader in developing the
computer graphics techniques that bring Hollywood blockbusters to
life took a look at his own research and noticed a possible
solution to his vision problem.
to the frame from Pixar's Tin Toy on top, the lower image
was post-processed to create optically correct blur, simulating
focus on the baby in the background. Note how the tin toy
in the foreground is depicted out of focus.
Brian A. Barsky
Barsky is afflicted with keratoconus, an abnormal thinning and curvature
of the central cornea that often worsens with age and sometimes
can only be relieved through a corneal transplant. The numbers vary
by source, but keratoconus affects between a few hundred thousand
and more than a million people in the United States. For many individuals
with the disease, contact lenses not glasses can bring
their vision back up to par. The problem is that standard symmetrical
contacts don't fit well on the irregularly-shaped corneas of keratoconus
patients. After a global search for contacts that didn't damage
his cornea, Barsky had a revelation.
"At Berkeley, one of our big pushes in graphics research was in
the design of complex shapes like car bodies," says Barsky, who
is also an affiliate professor of optometry and vision science.
"I realized that the problem fitting contact lenses was also about
shape, specifically getting a little piece of plastic to match the
shape of a cornea."
To represent the
corneal shapes, Barsky looked to splines, algorithms used to define
the curves in computer models. Splines, Barsky explains, are named
for the flexible plastic or wooden laths used by a draftsperson
to draw a smooth curve. In computer graphics, 3-D curved objects
can be built using individual splines with varying mathematically-determined
image on the left simulates the vision of an aberration-free
model eye. The right image, processed with Barsky's Vision-Realistic
Rendering filters, simulates the vision of a patient with
Brian A. Barsky
To determine the shape of the cornea, Barsky uses a technology called
corneal topography. The technology enables a precise map to be made
of the cornea's surface. But corneal topography is not without its
faults. Traditionally, Barsky says, the machine's measurements are
dependent on where you're looking even though your eye, of course,
does not change shape. As part of their research, Barsky and his
team have developed new algorithms that produce measurements that
are not affected by a change in gaze direction.
Barsky believes using those measurements could enable a contact
lens to be designed that sits perfectly on even an irregularly-shaped
cornea. The made-to-measure lenses, Barsky says, could be fabricated
on precise new computer-controlled milling machines that cut based
on mathematical instruction.
"Every time I put on a contact lens, it looks like someone shined
up all the objects and drew careful lines around all the edges,"
Barsky says. "Most people get contact lenses for convenience or
cosmetic reasons. But people like me need them to see."
Brian Barsky with a scene from Pixar's Tin Toy animated
short on screen behind him. Barsky's students have gone
on to work for Pixar and Lucas Digital's Industrial Light
(Click for larger image.)
doctors better understand how he and other patients see is the thrust
of Barsky's latest research. Vision-Realistic Rendering, he explains,
is the computer generation of images that appear the way a particular
individual would see them. For example, Barsky can alter a three-dimensional
image to have characteristics like "double edges" around objects,
a common symptom of keratoconus. Vision-Realistic Rendering, Barsky
says, could simulate visual disorders to better educate doctors
and patients. It may even help someone considering LASIK surgery
understand the improvements they could expect and the potential
problems they may face.
Barsky's Vision-Realistic Rendering is enabled by a Shack-Hartmann
Sensor, a device recently acquired by the Berkeley School of Optometry
that precisely measures the aberrations of an individual's eye.
The raw data provided by the Shack-Hartmann Sensor is used by Barsky's
group in the construction of novel computer algorithms to generate
the mathematical functions that quantify blur. Meanwhile, a 3-D
image is sliced into a series of depth images. The blur filters
are then applied to each slice, creating the blur effect. Recombining
the blurred slices results in a picture that incorporates characteristics
of the subject's unique optical system.
Ironically, Vision-Realistic Rendering brings Barsky's computer
graphics research around full circle. Simplified variations of the
same techniques Barsky and his team are developing to study and
alleviate bad vision can also be used to increase the realism of
Hollywood special effects. In this aspect of the research though,
the mathematics simulate not an abnormal eye but the view from a
Brian A. Barsky's home page
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