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‘An Imaging System That Can Read Closed Books’

In a report from Nature Communications, Hardesty writes, a prototype of the system is described by researchers: papers were stacked, each with a single letter printed on it. The system was then able to “correctly identify the letters on the top nine sheets.”

One potential application of such technology, of course, has to do with priceless, delicate manuscripts. Barmak Hesmat, a research scientist at the MIT Media lab and “corresponding author” on the paper, tells Hardesty, “The Metropolitan Museum in New York showed a lot of interest in this, because they want to…look into some antique books that they don’t even want to touch.”

Hardesty reports that Heshmat is joined on the paper by Ramesh Raskar, an associate professor of media arts and sciences; Albert Redo Sanchez, a research specialist in the Camera Culture group at Media Lab; and by Justin Romberg and Alireza Aghasi of Georgia Tech.

Hardesty writes:

“The MIT researchers developed the algorithms that acquire images from individual sheets in stacks of paper, and the Georgia Tech researchers developed the algorithm that interprets the often distorted or incomplete images as individual letters.

“’It’s actually kind of scary,’ Heshmat says of the letter-interpretation algorithm. ‘A lot of websites have these letter certifications [captchas] to make sure you’re not a robot, and this algorithm can get through a lot of them.’

“The system uses terahertz radiation, the band of electromagnetic radiation between microwaves and infrared light, which has several advantages over other types of waves that can penetrate surfaces, such as X-rays or sound waves.”

A standard terahertz camera emits extremely short bursts of radiation. The camera’s sensor detects their reflections. Based on their arrival time, the algorithm used by the researchers gauges the distance to pages of the book.

Hardesty writes, “At the moment, the algorithm can correctly deduce the distance from the camera to the top 20 pages in a stack, but past a depth of nine pages, the energy of the reflected signal is so low that the differences between frequency signatures are swamped by noise.”

Laura Waller, an associate professor of electrical engineering and computer science at the University of California at Berkeley tells MIT News:

“So much work has gone into terahertz technology to get the sources and detectors working, with big promises for imaging new and exciting things. This work is one of the first to use these new tools along with advances in computational imaging to get at pictures of things we could never see with optical technologies. Now we can judge a book through its cover.”