Color-based automatic detection of worn out varnishes on Stradivari's "Scotland University" violin back plate

UV-induced fluorescence (UVIFL) photography is widely used in the study of artworks, in particular for the analysis of historical musical instruments (e.g., violins). This technique allows seeing important details, which cannot be observed with visible light, such as retouching, different paints coats, or worn areas of the superficial varnishes. However, the interpretation of UVIFL images may be very complex, in relation to preservation state of the analyzed artifact. The aim of this work is the development of a new tool able to automatically detect the presence of colors related to worn areas on the back plates of historical violins. The proposed solution is a program able to identify some peculiar color hues related to wear, find their position on the surface and compute their percentage respect to the total area. The study was performed on UVIFL imagery of Stradivari's Scotland University violin (1734) held in the Museo del Violino in Cremona (Italy).