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Isolating Watermarks in Antique Paper

About this Project

We are currently desiging software and associated optimal conditions of capture to isolate images of watermarks and internal paper structure in archival paper. The method uses visible light phogotraphs and requires only a camera, a computer, and a light table to implement. We hope to produce images that rival those produced with the standard watermark imaging technique of beta-radiography in terms of efficiency of capture and accuracy.

The Process

Out technique uses photographs taken in two lighting conditions, one with a light table beneath the paper being imaged and the other in ambient lighting.  The software in development uses the ambient light image, in which only features on the surface are visible, to suppress those features in the transmitted light image, which contains both surface information and subtle changes in brightness due to shifts in paper density. In the resulting image only the paper structure is visible. We are currently working through a variety of test cases to develop algorithms that are robust to different challenging conditions like heavily inked surfaces, sheets in different mounting and preservation conditions, and sheets with ink on both sides.

Motivation

The internal structure of paper including laid lines, chain lines, watermarks and any production related changes in density are diagnostic of the conditions, date and location of a sheet of paper’s production. In particular our method seeks to access the information contained in paper structure in a way that is minimally invasive, and time, cost, and expertise efficient. To that end we have focused on implementing a method that relies only on readily available, inexpensive easy to operate equipment. Our hope is that such a method will be conducive to high volume digitization of watermarks with accuracy sufficient to inspire database construction and even machine learning or further large scale digital projects.

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