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Called
"reversible data hiding," the new technique will solve
a dilemma faced by digital image users, particularly in
sensitive military, legal and medical applications. Until now
they have had to choose between an image that's been watermarked
to establish its trustworthiness and one that isn't watermarked
but preserves all the original information, allowing it to be
enlarged or enhanced to show detail. When information is
embedded using the newly discovered method, authorized users can
do both.
The technique,
described in a paper that will be presented at the IEEE 2002
International Conference on Image Processing here on Sept. 24,
was co-developed by Mehmet U. Celik and A. Murat Tekalp of the
university and Gaurav Sharma and Eli Saber of Xerox. Their
collaborative research was done in the Center for Electronic
Imaging Systems (CEIS), a New York State Office of Science,
Technology and Academic Research designated center for advanced
technology.
"Commonly
used techniques for embedding messages such as digital
watermarking irreversibly change the image, resulting in
distortions or information loss. While these distortions are
often imperceptible or tolerable in normal applications, if the
image is enlarged, enhanced, or processed using a computer, the
information loss can be unacceptable," said Gaurav Sharma,
an imaging scientist at Xerox's Solutions and Services
Technology Center in Webster, N.Y.
"With our
new data embedding algorithm, authorized recipients not only can
extract the embedded message but also can recover the original
image intact, identical bit for bit to the image before the data
was added," he said. "The technique offers a
significantly higher capacity for embedding data and/or a
lower-distortion than any of the alternatives."
"The
technique will be widely applicable to situations requiring
authentication of images with detection of changes, and it can
also be used to encode information about the image itself, such
as who took the picture, when or with what camera," said
Murat Tekalp, professor of electrical engineering at the
University of Rochester.
"The
greatest benefit of this technology is in determining if anyone
has clandestinely altered an image. These days many commercial
software systems can be used to manipulate digital images. By
encoding data in this way we can be sure the image has not been
tampered with, and then remove the data within it without
harming the quality of the picture," he said.
Although the
technique is currently implemented in software, it could be
implemented in hardware or firmware in trusted devices where
image integrity is critical to the application, the authors
said. For instance, the technique could be used in a trusted
digital camera used to gather forensic evidence to be later used
at a trial. If information is embedded in the images captured
with the camera using the new algorithms, any subsequent
manipulations of the pictures could be detected and the area
where they occurred pinpointed.
A patent
application on the methods developed for reversible data hiding
has been filed by the University of Rochester; and the
university and Xerox will share the rights to this invention.
CEIS is devoted
to enhancing the economic development of the greater Rochester
region and New York State by developing and transferring
electronic imaging technology to industry for commercialization,
and by educating the next generation of leaders in the field of
electronic imaging.
The University of
Rochester is one of the smallest of the most distinguished
private universities in the country. Fewer than 3,700
undergraduates are enrolled in its College, the home of arts,
sciences and engineering programs.
Xerox
Corporation, one of the world's top technology innovators,
operates research centers in the United States, Canada and
Europe that conduct work in color science, computing, digital
imaging, work practices, novel materials, and other disciplines
related to Xerox's expertise in printing and document
management.
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