Clearing the Image: A Quantitative Analysis of Historical Documents Using Hyperspectral Measurements

Poster presented at the AIC 37th Annual Meeting, May 20–23, 2009, Los Angeles, California. condition for future generations. For the first task, new quantitative techniques are required that help to extract as much information as possible from already-degraded and fragile documents in a completely non-destructive way. For the second task, quantitative techniques are required to support an objective evaluation of the document condition and environmental influences therein. Hyperspectral Imaging (HSI) is a technique with which objects are imaged in tens or even hundreds of wavelength bands. Typically, HSI covers not only the visible, but also the near-ultraviolet and near-infrared, spectral range. This technique has already proven its worth in various fields such as agricultural research, space exploration, environmental investigations, and defense (Stein et al. 2001; Kruse et al. 2003; Lawrence et al. 2003). Often, these HSI systems are mounted on airborne or space-borne vehicles. On a microscopic scale, HSI technology is increasingly becoming a valued research tool especially in biomedical research (Schultz et al. 2001, Qin and Lu 2006). However, it is also possible to use HSI for investigation of objects of cultural heritage. In the last few years this technique has been introduced for research in the area of document conservation and document analysis (Melessanaki et al. 2001; Mansfield et al. 2002; Casini et al. 2002; Attas et al. 2003; Klein et al. 2006; Kubik 2007; Padoan et al. 2008; Klein et al. 2008). In this contribution we discuss the application of advanced numerical hyperspectral image processing techniques applied to the analysis of historical documents. Powerful computer algorithms for spectral feature extraction and classification allow one to detect even very subtle correlations in the hyperspectral data that cannot be detected with conventional visual comparison. Such algorithms can provide reproducible, quantitative results that enable a comparison of different objects or of the same object measured at different times, so that it becomes possible to establish databases and to measure the influences of treatments or aging. In the following, two particular applications will be discussed: 1) Evaluation of iron-gall ink corrosion and 2) detection of underdrawings. ABSTRACT