[Paleopsych] NYT: Fleeting Experience, Mirrored in Your Eyes

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Fleeting Experience, Mirrored in Your Eyes
NYT July 29, 2004

POETS, lovers, and amateur psychologists have long looked
deep into people's eyes to read their thoughts and
feelings. But the reflections in full view on the surface
of the eye rarely receive much attention.

Now two Columbia University scientists have come up with a
computer-based way to extract detailed information from the
fleeting images of the world mirrored on the curved surface
of the eye.

Shree K. Nayar, a professor of computer science and
co-director of the Columbia Vision and Graphics Center,
took high-resolution photographs of people that include
their eyes and, in particular, the transparent part of the
eye called the cornea. Then, with a postdoctoral
researcher, Ko Nishino, he devised computer algorithms that
analyze the images reflected in these natural mirrors,
revealing a wealth of information.

The system can automatically recover wide-angle views of
what people are looking at, including panoramic details to
the left, right and even slightly behind them. It can also
calculate where people are gazing - for instance, at a
single smiling face in a crowd.

Because the algorithms can track exactly where a person is
looking, the system may one day find use in surveillance
cameras that spot suspicious behavior or in interfaces for
quadriplegics who use their gaze to operate a computer.

Dr. Nishino and Dr. Nayar plan to try their corneal imaging
system with archival photographs. "It will be fascinating
to go back and look at photographs of important people like
John Kennedy," Dr. Nayar said. "From a single image of the
eye, we may be able to figure out what was around him and
what he was looking at."

The image-processing system works both with high-resolution
digital photographs and with conventional film that can be
scanned and enlarged for high resolution in the area of the

Analyzing such images might reveal not only new information
about the people's surroundings as the photograph was
taken, but also the precise object or individual the person
photographed was observing.

Jitendra Malik, a professor of electrical engineering and
computer science at the University of California at
Berkeley, described Dr. Nayar's system as a "simple but
elegant idea.''

"Professor Nayar treats the cornea as a mirror, so if you
look at what's imaged in the mirror, you can see many
details of what a person is looking at," he said.

Dr. Nayar, the inventor of a 360-degree omnidirectional
camera called the Omnicam, has long been interested in
imaging systems that combine lenses and mirrors, called
catadioptric systems.

About a year ago, he and Dr. Nishino realized that the
cornea could be viewed as the mirror in such a system, and
the lenses as the camera.

The detailed wide-angle information recovered by the new
system is possible because the image reflected by the
cornea is broader than that captured on the retina. The
retinal field of view is considerably less than a
hemisphere - 160 degrees horizontally and 130 degrees
vertically. But the corneal image is roughly about a
hemisphere or more, permitting objects to the side and
behind the person to be seen so long as the person is not
looking away from the camera at an extreme angle.

"My hunch is that the best applications of this work will
be with human-computer interactions," like using one's gaze
to start a computer, Dr. Malik said. "The advantage of the
technique is that it's passive," and does not direct
additional energy at the eye, he added. (With some common
eye-tracking methods, infrared light is projected into the
user's eyes.)

The crucial algorithm in the system automatically computes
the relative position and orientation of the cornea in
relation to the camera, using the elliptical shape of the
limbus, or border, between the cornea and the white of the
eye. "The shape of the limbus tells you where the eye is in
the three-dimensional scene and which direction the eyeball
is pointing," Dr. Nayar said. The wide-angle image can then
be created from this information.

Dr. Malik said the technique was particularly timely
because of the advent of high-resolution cameras. "Now it
makes sense to exploit the information we can get from

The system may be a boon to marketers who use cameras to
track what people are looking at in a room or in a store.
It may also prove important to journalists, said John V.
Pavlik, a professor and chairman of the department of
journalism and media studies at Rutgers University. "One
problem with eyewitness accounts that journalists and
others rely on is that these accounts are limited," he
said, by people's ability to recall accurately what they
have seen.

"This technique could reveal things that were in front of
them that they weren't aware of seeing so that we can
understand the truth of what happened, and advance the
veracity of eyewitness accounts," he said.

Dr. Nayar suggested that the system could also be applied
to security cameras, although the picture would have to be
of high quality and the eye would have to be in focus. The
Columbia group shot high-resolution pictures, typically of
3,000 by 2,000 pixels, with the eye taking up a circle of
about 120 pixels by 120 pixels.

The algorithms may also play a part in computer graphics,
for example, to recover the original lighting in old movies
from information reflected in actors' eyes. Then virtual
objects could be inserted in the films that blended in
realistically with the original images.

Takeo Kanade, a professor of computer science and robotics
at Carnegie Mellon University, said the new system would
have many other applications, too. "It's really intriguing
to use the eye as a natural mirror to reflect the world,"
he said. "You observe this every day, and yet no one had
ever thought to use it for computer image processing."

E-mail: eisenberg at nytimes.com


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