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3-D Mug Shot
by Rob Meyer
Sam Reese Sheppard, who has long maintained that his father, Dr. Sam Sheppard,
had nothing to do with the killing of Mrs. Sheppard on a July night 45 years
ago, might well have wished that a crime-fighting tool now under development at
MIT's Lincoln Laboratory existed back in 1954. Because that tool is
sophisticated enough that, if it had been employed at the Sheppard crime scene,
it would very likely have ferreted out evidence missed by investigators of the
day - evidence that might have altered the jury's decision.
The tool in question is a laser-imaging system that provides pictures in three
dimensions of target objects using a technique known as Accordion Fringe
Interferometry (AFI). Nathan Derr, a physicist and member of the team that
invented AFI, says that in the future, detectives might bring a portable
version of one of these 3-D cameras to crime scenes, where they could
photograph everything from footprints to tooling marks - scratches or nicks
left by tools or other hard objects.
The system is quick - producing a picture takes seconds - and its images are
sharp: each is accurate to 200 microns, or one-fifth of a millimeter. Further,
the device does not damage or contaminate the evidence itself, allowing future
detectives the ability to, as environmentalists like to say, "take only
photographs."
Diagram of a prototype AFI
system that NOVA Online observed at work in the basement of MIT's Lincoln
Laboratory.
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One of the most promising applications for the new technology is the
three-dimensional mug shot. Traditional 2-D mugs, long the standard in suspect
identification, have obvious limitations. Authorities typically photograph a
suspect from only two angles, under a single lighting condition. A witness to
the crime, however, may have caught a fleeting glimpse of the suspect in the
dark, or a security camera may have captured his or her blurry image from only
one unnatural angle. What if police could access a database of 3-D mug shots
that offered them the ability to rotate a suspect's head and adjust the source
of light shining on his or her face to simulate different lighting conditions?
Well, let's just say the FBI, for one, is very interested in what Lincoln
Laboratory is up to.
Acquiring and processing all the data necessary to render an image precisely
in 3-D used to take weeks; using the Lincoln Laboratory technique, a computer
can record all of the necessary information in seconds. The subject sits in a
dentist's chair facing a camera, all but oblivious to a zebra pattern of
near-infrared light illuminating his face. The system takes a rapid series of
still images and sends the information to a computer, which runs some novel
processing algorithms developed by Dr. Lyle Shirley, head of the group that
invented AFI. Within seconds, a 3-D rendering of the subject's head appears on
the screen. (Presently, the engineers are unable to capture the very back of
the head, but they're exploring the possibility of taking two such pictures
simultaneously in order to get a full 360° view.)
Measuring the dimensions of a human face with such precision presents unique
problems. Minute movements of individual hairs make exact measurement
impossible, and because complex shapes such as a person's nose block
illumination from the laser source, the source must be rigged so as to ensure
optimal coverage of the face. Moreover, any system for real-world usage needs
to be lightning fast. (As team member Matt Kavalauskas notes, "You're not going
to get a suspect to hold perfectly still for five seconds.") The Lincoln
Laboratory engineers feel confident that with faster cameras now on the market,
they will be able to get their device to work in under a second.
Soon, too, they hope to produce such 3-D mug shots in color. Because their
system records the x, y, and z coordinates of every point on the face, they
feel confident that, with the proper equipment, they should be able to record
the color values for every point as well, offering photo-realistic renderings
in full, living color. Authorities could install such a useful instrument in
police stations, where suspects would supply fingerprints, then sit in a
special chair for a 3-D mug.
Continue: So how does AFI work?
Chronology of a Murder |
Science in the Courtroom
Create a DNA Fingerprint |
3-D Mug Shot |
Cleared by DNA
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© | Updated November 2000
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