The design of a compact spectrometer for analysis of artworks is presented. Its operation is based on the use of a variable
transmission filter associated with an array detector. The instrument allows the measurement of the spectral reflectance
factor and combines the acquisition of data in a continuous spectrum with the small dimension that is of primary
importance for in-situ spectral imaging.
Surface topography is very important for many applications. Today the most used techniques on artworks and stone artifacts
require long acquisition times and invasive interventions. For this reason, here a non-contact device improved in portability
is described. It can acquire wide areas in short times, so it is suitable for topography reconstruction with spatial resolution
of some tens of micrometers.
The starting point is a commercial conoscopic probe, the Optimet Conoline, that is able to reconstruct the depth profile
of a surface line probed by a built-in laser. Its accuracy and acquisition speed are as high as to return wide measured areas
in short times; its resolution permits fine details reproduction. Low interference with the artwork, high portability and low
response to environmental noise are the ingredients for the instrumental setup.
In this paper we present a scanning device for multispectral imaging of paintings in the 380-800 nm spectral region; the
system is based on a spectrophotometer for contact-less single-point measurements of the spectral reflectance with 10
nm resolution. Two orthogonal XY translation stages allow to scan up to 1,5 m2 with spatial resolution up to 8 dots/mm.
As an application we present the results of the measurements carried out on Ritratto Trivulzio by Antonello da Messina
and Madonna in gloria tra Santi by Andrea Mantegna. Besides spectra comparison also multivariate image analyses
(MIA) have been performed by considering the multi-spectral images as three-way data set.
In order to point out the slight spectral differences of two areas of a painting we analyzed its multispectral data cube by
means of the Principal Component Analysis (PCA) and the K-Nearest-Neighbouring Cluster Analysis (KNN).
We present a scanning device for 32-band multi-spectral imaging of paintings in the 380÷800 nm spectral region. The system is based on contact-less and single-point measurement of the spectral reflectance factor. Multi-spectral images are obtained by scanning the painted surface under investigation. An adjustment procedure was established and calibration was performed by means of a set of seven matt ceramic color tiles certified by National Physical Laboratory (UK). Colorimetric calculations were carried out in the XYZ colorimetric space, by following the CIE recommendations and choosing the D65 standard illuminant and the 1931 standard observer. Measurement campaigns were carried out on several paintings in situ and at the INOA Optical Metrology Laboratory located inside the Opificio delle Pietre Dure in Florence. As an example we report herein on the measurements carried out on the Madonna in gloria tra Santi by Andrea Mantegna, (at present in the Pinacoteque of the Castello Sforzesco in Milan). Multivariate image analyses (MIA) were performed by considering the multi-spectral images as three-way data set. The stack of detected images were unfolded in a 2D data matrix and analyzed by the conventional Principal Component Analysis (PCA).
In the last few years multispectral imaging has entered the field of painting diagnostics and conservation because of its effectiveness and safety. It provides spectral and colorimetric characterization of the whole paint layer, suitable to document the conservation state of the artwork and useful in the study for the identification of pigments.
Here we present a high-resolution scanning system for 32-band multispectral imaging of paintings in the 380÷800 nm spectral region. This system is based on a fast spectrometer for contact-less single-point measures mounted on two orthogonal XY translation stages. It can scan an area of 1 m2 with a spatial resolution of 4 dots/mm and a spectral resolution of 10 nm.
Spectral reflection factor and tristimulus value measurements were carried out on coloured ceramic tiles and the results were compared with the corresponding certified values.
Multispectral analysis was performed on a few ancient paintings and spectrophotometric results are shown.