Automatic analysis of UV-induced fluorescence imagery of historical violins

In recent years, UV-induced fluorescence (UVIFL) photography has proven to be very effective when studying the surface of historical musical instruments, such as violins. This technique makes it possible to highlight superficial details not clearly perceptible with visible light (e.g., retouchings, superficial distribution of varnishes, or wear). The data retrieved are also an important guide for further noninvasive spectroscopic analyses used when the chemical composition of the surface needs to be investigated. However, UVIFL imagery interpretation of a historical violin is no trivial task. In fact, constant playing and the multiple restorations over the centuries have produced very complex surfaces. This work presents an automatic tool designed to facilitate this kind of analysis. Using a quantized histogram in HSV color space, the distribution of the main fluorescence colors on an instrument's surface can be highlighted, recurrence of the same color in different areas of the same violin can be detected, or different violins can be compared. UVIFL images of seven Stradivarius violins kept in the Museo del Violino in Cremona, Italy, were used as a test set. The results achieved endorse the validity of the proposed approach.