Multispectral Hypercolorimetry and automatic guided pigment identification: some masterpieces case studies

摘要

A couple of years ago we proposed, in this same session, an extension to the standard colorimetry (CIE '31) that we called Hypercolorimetry. It was based on an even sampling of the 300-1 OOOnm wavelength range, with the definition of 7 hypercolor matching functions optimally shaped to minimize the methamerism. Since then we consolidated the approach through a large number of multispectral analysis and specialized the system to the non invasive diagnosis for paintings and frescos. In this paper we describe the whole process, from the multispectral image acquisition to the final 7 bands computation and we show the results on paintings from Masters of the colour. We describe and propose in this paper a systematic approach to the non invasive diagnosis that is able to change a subjective analysis into a repeatable measure indipendent from the specific lighting conditions and from the specific acquisition system. Along with the Hypercolorimetry and its consolidation in the field of non invasive diagnosis, we developed also a standard spectral reflectance database of pure pigments and pigments painted with different bindings. As we will see, this database could be compared to the reflectances of the painting to help the diagnostician in identifing the proper matter. We used a Nikon D800FR (Full Range) camera. This is a 36megapixel reflex camera modified under a Nikon/Profilocolore common project, to achieve a 300-1000nm range sensitivity. The large amount of data allowed us to perform very accurate pixels comparisions, based on their spectral reflectance. All the original pigments and their binding have been provided by the Opificio delle Pietre Dure, Firenze, Italy, while the analyzed masterpieces belong to the collection of the Pinacoteca Nazionale of Bologna, Italy.