Remote Colorimetric and Structural Diagnosis by RGB-ITR Color Laser Scanner Prototype

Since several years ENEA's Artificial Vision laboratory is involved in electrooptics systems development. In the last period the efforts are concentrated on cultural heritage remote diagnosis, trying to develop instruments suitable for multiple purposes concerning restoration, cataloguing, and education. Since last five years a new 3D (three-dimensional) laser scanner prototype (RGB-ITR) based on three amplitude-modulated monochromatic laser sources mixed together by dichroic filters is under development. Five pieces of information per each sampled point (pixel) are collected by three avalanche photodiodes and dedicated electronics: two distances and three target reflectivity signals for each channel, red, green, and blue. The combination of these pieces of information opens new scenarios for remote colorimetry allowing diagnoses without the use of scaffolds. Results concerning the use of RGB-ITR as colorimeter are presented. 1. Introduction One of the biggest problems concerning cultural heritage environment is the study and then the reproduction of pigment color. This difficulty is mainly caused by the tendency to consider the color almost exclusively as subject of visual perception and individual sensibility. It is important to underline that the color is also a physical propriety of the object itself and not only an observer experience that can be measured [1] yet in a nontrivial way. The first work of colorimetry applied to cultural heritage field was in 1953 by Istituto Centrale per il Restauro di Roma for a preliminary study on the restoration of “Maestà” by Duccio di Boninsegna [2]. After that, 40 years elapsed before colorimetry found new applications in this field, mainly in Italy [3]. This is also the consequence of finding in commerce tested and optimized electronic instruments which are mainly developed for industrial inspection. The migration of this type of instruments, suitable for the measure of uniform colored surfaces, in cultural heritage environment is limited by the complexity and continuous variation of polychromatic surfaces. For this reason it is important to have a colorimeter, which is able to measure very small areas better if punctual. Traditional colorimeters [4] work in a very closed range, 0–30？cm, which can be acceptable for canvas or small frescos placed at few meters. For investigating large surfaces in a range of several meters, that is, painted chapels, commercial colorimeters are time-consuming systems and the use of scaffolds is necessary. For all these reasons a remote and punctual system is desirable, but a new