Recovering illegible writings in fire-damaged medieval manuscripts through data treatment of UV-fluorescence photography

Abstract When faced with legibility issues on a historical document, several approaches can be explored to recover the degraded contents, such as hyperspectral imaging, XRF scanning or X-ray tomography. Unfortunately due to the time, costs and technical skills required, these imaging techniques cannot be applied to the numerous faded/altered documents present in library collections. Hence, there is a need for a simple imaging procedure that could be applied on a large scale, in the same way libraries and archives are being digitized. The great sensitivity of modern digital camera sensors used for digitization campaigns added to the development of simple image post-treatment tools offer new potentialities regarding this issue. This paper presents a fast and low-cost methodology to archive current aspect and reveal hidden contents of documents: UV-fluorescence photography used in combination with contrast enhancement treatments (principal component analysis, color space conversion and decorrelation stretch). The efficiency of this approach is demonstrated on the fire-damaged medieval manuscripts collection from Chartres in France.