18 March 2008 Post-capture data analysis as an aid to the interpretation of ultraviolet-induced fluorescence images
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Abstract
Although digital multispectral imaging-particularly ultraviolet-induced fluorescence imaging-is a very common examination tool, its interpretation remains fraught with difficulties. Interpretation is strongly dependent on the capture methodology, requires an understanding of the physical and chemical characteristics and interactions among materials in artworks and is affected by data-analysis procedures. The present research, which began with imaging of paint materials of known composition and proceeded to a range of representative case studies, confirmed that fluorescence emissions by painting materials-such as organic binders or colorants-are generally severely affected by the presence of absorbing non-fluorescing materials, such as inorganic pigments. Application of a mathematical model based on the Kubelka-Munk theory, resulted in the possibility of distinguishing between real and apparent fluorescence emissions. Real emissions correspond to the presence of materials which de facto exhibit fluorescent properties (typically organic binders and colorants), while apparent emissions relate to the optical interactions among fluorescent materials and surrounding non-fluorescent materials (typically inorganic pigments). Correction for the 'pigment-binder interaction' can also provide useful information on the presence of materials whose fluorescence is almost obliterated by absorbing pigmented particles. Therefore, this image-processing methodology can be used to characterise and reveal emissions that are dimmed or altered by re-absorption. This capacity to reveal the presence of weakly fluorescing emitters has important conservation implications and informs the sampling strategy for further analytical investigations. Examples of the application of this data analysis to images made at the Grotto Site in Dunhuang, China, and at the British Museum are presented.
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Giovanni Verri, Daniela Comelli, Sharon Cather, David Saunders, Francesca Piqué, "Post-capture data analysis as an aid to the interpretation of ultraviolet-induced fluorescence images", Proc. SPIE 6810, Computer Image Analysis in the Study of Art, 681002 (18 March 2008); doi: 10.1117/12.764463; https://doi.org/10.1117/12.764463
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