Extending Hyper-Spectral Imaging from Vis to NIR spectral regions: a novel scanner for the in-depth analysis of polychrome surfaces

In recent years Hyper-Spectral Imaging (HSI) technologies have become well-established for applications in the field of Cultural Heritage, and in particular for non-invasive analysis and high quality documentation of paintings and other polychrome surfaces. This paper reports on the latest developments of the on-going research at IFAC-CNR, where a new prototype of a high-performance hyper-spectral scanner, operating in the NIR spectral region (900-1700nm range), was designed, assembled and tested. This new NIR scan-head was designed to be mounted on the same mechanical structure used for the earlier IFAC-CNR scanner prototype, which operated in the 400-900nm range. As ultimate goal the whole system would be intended to provide 2D hyper-spectral data on the extended 400-1700nm range, so as to strongly improve the capability of pigment discrimination, and to increase the possibility of visualizing the underlying features of the polychrome surfaces (such as under-drawings, pentimenti, etc.). In the present version, the NIR scan-head operates with a spectral sampling rate of about 2 nm, and a spatial sampling rate of about 9 dots per millimeter. The results of testing and characterization of the new high resolution NIR IFAC-CNR scanner are presented, with a focus on the main technical problems tackled in customizing the new system for the investigation and documentation of paintings.