Non-destructive analytical imaging of metallic surfaces using spectral measurements and ultrahigh-resolution scanning for cultural heritage investigation

This paper presents a new approach for analyzing spectroscopic characteristic of metallic surfaces using spectroscopic and image analysis. This method is useful for contactless and non destructive analysis of cultural heritage. Spectral luminance, CIELAB, and CIEXYZ value of more than 80 metallic surfaces were measured with spectrometer and scanned to examine spectroscopic characteristics of foils by using multiband images. This analysis through imaging can improve the method for extracting difference related to types of metallic foils. Firstly, the spectral reflectance of each foil was measured ranging from 220 to 850 nm in steps of 1 nm. The images were captured with color and monochromatic camera using color filter in order to analyze the targets by multispectral approach. Then, principal component analysis (PCA) was conducted with image pixel value of each target. The results have shown that the spectral reflectance whose peak and change rate at a particular wavelength region differed from each foils, and that the multispectral images extracted the difference in spectral characteristics related to different types of metallic foils and Japanese papers. This could be useful in distinguishing among foils. This provides some promise that unknown metallic foils can be identified through the measurement of their spectroscopic features.