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Reading the unreadable

22 May 2013

Pioneering X-ray technology is making it possible to read fragile rolled-up historical documents for the first time in centuries, thanks to technology developed by the University.

Old parchment is often extremely dry and liable to crack and crumble if any attempt is made to physically unroll or unfold it. The new technology, however, eliminates the need to do so by enabling parchment to be unrolled or unfolded 'virtually' and the contents displayed on a computer screen.

Developed by Cardiff School of Optometry and Vision Sciences, and Cardiff School of Computer Science and Informatics, the breakthrough means historians will be able to access previously unusable written sources and gain new insight into the past.

The Cardiff team worked with colleagues in Queen Mary, University of London and the Engineering and Physical Sciences Research Council (EPSRC), the project received just under £1.3M funding.

No other technique developed anywhere in the world has the capability to make text concealed in rolled or folded historical parchments genuinely legible. The system has now been tested successfully on a nineteenth century legal scroll provided by the Norfolk Record Office.

In a completely innovative approach to the problem, the technique works by scanning parchment with X-rays in order to detect the presence of iron contained in 'iron gall ink' – the most commonly used ink in Europe between the 12th and 19th centuries.

Using a method called microtomography, a 3-dimensional 'map' showing the ink's exact location is built up by creating images made from a series of X-ray 'slices' taken through the parchment.

Advanced software specially developed by the Cardiff project team combines the data obtained with information about the way the parchment is rolled or folded up and calculates exactly where the ink sits on the parchment. An image of the document as it would appear unrolled or unfolded can then be produced.      

The key difference between the new method and other techniques previously developed to read un-openable historical documents is the unprecedentedly high contrast resolution it provides to distinguish between ink and parchment. This means the ink shows up very well against the parchment and is genuinely readable.

Professor Paul Rosin, Cardiff School of Computer Science and Informatics: "Our major technical challenge was to separate the parchment layers in the 3D X-ray volume before performing the flattening of the parchment and projection of the ink from the 3D volume onto the flattened 2D surface. The task was complicated by the variable nature of the parchments, which are irregular and contain variable sponge-like internal structure. Furthermore, their degradation over time has caused fragmentation, while the tight rolling has joined adjacent surfaces together. We tested state of the art image processing techniques, but found that none were able to deal with such difficult data. Consequently, over the last few years we have built a specialised computer system that has been designed to virtually unroll such
challenging scanned parchments."

The scanning takes place at the Institute of Dentistry at Queen Mary, University of London led by Dr Graham Davis: "Because no commercial or research X-ray tomography scanners were capable of providing the quality of image we needed, we've developed our own advanced scanner which is also being adapted for a diverse range of other scientific uses, including those within our own Institute of Dentistry where enhanced, high contrast images are enabling the detection and analysis of features in teeth that we haven't been able to see before."

You can find out more about the research in an audio slide show on the EPSRC YouTube channel.