by Steve Towns
Editor, HP Government
FBI agents investigating a man suspected of
murdering young children recently turned to an innovative
three-dimensional imaging technique developed by HP Labs to help scour for
The suspect kept a notebook listing the names of his alleged victims,
but he'd torn out the incriminating pages before his arrest. Luckily,
a faint imprint of his handwriting remained on the underlying blank pages,
and authorities were able to reveal the hidden information using HP Labs' polynomial
texture mapping (PTM).
"We photographed the pages, and using PTM, we made the surface of the
paper appear highly reflective, which let authorities see those indentations
quite a bit better than they could with the naked eye," said
PTM inventor Thomas Malzbender, a distinguished technologist in HP's Mobile
and Media Systems Laboratory.
After three days of working with the notebook, investigators were able to
recover the name of an additional victim.
The evidence never was used during the trial, but the case offers a glimpse
of why PTM is drawing the attention of not just other law enforcement agencies,
but specialists in such fields as paleontology, archaeology, geology and even
These experts have used PTM to get a clearer picture of everything
from plant fossils to painters' brush strokes to native American
Paleontologists at the Swedish
Museum of Natural History used PTM to see sharp images of trace
fossils of primitive life on a 500 million-year-old stone. Curators
at the National Gallery of Art in London, working with PTM on a
painting by Pointillist Georges Seurat, were able to see a sailboat
the artist had painted over in the course of his work. Other recent
PTM users include the San Francisco Police Department, the Tate
Britian in London and the
West Semitic Research Project at the University of Southern California.
"One of the things about PTM is that it's extremely visual.
You just show it to poeple, and they get enthusiastic," says
Dan Gelb, an HP Labs researcher who has worked with Malzbender
on the technology.
PTM captures images of three-dimensional objects, then allows
users to shine a light on that image from various angles to reveal
hidden surface details. The technique also allows users to change
the color of the lighting or modify the characteristics of an
object's surface, transforming it from dull to metallic, for
The result is what is known as a parametric photograph -- something
that allows users to dial a couple of knobs to change the position
of light in a photograph. The technology is fast, too. It runs
in real-time on consumer-level PCs.
Because it is a purely photographic technique, PTM is also much
less expensive than other methods of producing images of three-dimensional
objects, which rely on costly, elaborate laser scanning systems.
PTM is simpler to use, too, because it involves only the complexity
of taking the photographs.
To produce a PTM model, users capture between 30 to
50 digital images of an object -- each with the light source
in a different location. That's done using a special automated
dome with flashbulbs lining its interior and a digital camera mounted
in a hole at the top. The
device is linked to an HP laptop that automatically collects
50 images at the touch of a key.
(Free software to view and create PTMs is available here.)
Although the device
can be shipped whereever it's needed, the dome can be somewhat cumbersome
to use, particularly in a field
environment. So Malzbender's colleage Gelb developed a more portable
method, gathering images for PTMs using simply a digital camera,
a tripod and a shiny object.
"You put a shiny, reflective object into the scene you're
photographing, then take a number of pictures while moving around
the scene with a handheld flash," Malzbender explains. "It
turns out that with a reflective object in the scene -- a cue ball
works very well -- you can recover the position of the light source."
The simplified technique will allow forensic specialists to produce
PTM images of footprints in the ground, for example, without special
Not only are PTM models relatively simple to create, they're easy
to share, because the technology produces an extremely compact
representation of an object. PTM models are just 30 percent to
40 percent larger than a single image of an object.
Interactive PTM images easily can be posted to Web sites for wide
distribution, which is particularly useful for research
disciplines such as archaeology and paleontology, where researchers
are reluctant to part with priceless physical artifacts.
Last year, HP researchers teamed with a number of well-known paleontologists
to publish a paper
on Cambrian trace fossils that
were roughly 500 million years old. They published
the paper online, which gave readers the ability to download PTMs
of the illustrations and try different enhancement methods themselves.
the researchers are teaming with several universities to digitally
share archaeological artifacts among scholars and make them available
on the Web.
PTM's usefulness extends well beyond Malzbender's original intent
when he cobbled together the dome's prototype in his basement.
The researcher was attempting to solve problems with existing three-dimensional
rendering technologies, looking for a way to improve photorealism
and image rendering efficiency.
Although the technique is finding its way into sophisticated graphics
accelerators inside HP products, PTM also is poised to reshape
fields ranging from police forensics to diagnostic medicine.
"It turns out there are a lot of fields that deal with objects
that have interesting surfaces on them, and they can benefit from
looking at those surfaces under variable lighting conditions," Malzbender