Reading old books is a delicate process. As they age, books often become brittle, and great care must be taken when cracking their covers. But thanks to a new camera developed by researchers at the Massachusetts Institute of Technology (MIT) and Georgia Tech, historians might one day be able to examine the contents of old books without ever opening them.
The prototype camera uses terahertz radiation, a low-frequency form of radiation that sits between microwave and infrared on the electromagnetic spectrum. Terahertz radiation is frequently used in equipment like the full-body scanners often found at major airports, Carl Engelking reports for Discover Magazine. While those devices are designed to detect things like metals and plastics, this camera is calibrated to tell the difference between blank paper and ink inscribed on the pages of a book—even through a closed cover.
“The Metropolitan Museum in New York showed a lot of interest in this, because they want to, for example, look into some antique books that they don’t even want to touch,” MIT researcher Barmak Heshmat says in a statement.
Because terahertz radiation reacts differently to different chemicals, the scientists can use it to tell the difference between blank pages and the words written or printed on them. By firing quick radiation pulses at stacks of paper nine pages deep, each with a single letter printed on them, Heshmat and his colleagues were able to demonstrate that their device could tell the difference between ink and blank paper, allowing them to decipher the unseen text, Andrew Liszewski reports for Gizmodo.
While terahertz radiation has long been used in imaging technology, the researchers had to figure out a way to interpret the signals they got back from the test scans. The group developed a set of computer algorithms that analyzed the frequencies of radiation as they hit the pages and filtered out any distortion so the hidden pages could be read. In order to determine the difference between stacked pages, the algorithm can decipher when the signal bounces off of the 20-micrometer-thick air gaps between them, Liszewski reports.
“It’s actually kind of scary,” Heshmat says in a statement. “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 result is a set of images that are much higher resolution and easier to read than similar images taken using x-rays or ultrasounds. While the images quickly get more distorted when a stack of pages taller than nine sheets are scanned, the technology is still new. The camera still has a ways to go before it would be ready for museum use, but one day it could become a critical tool for conservationists.