Documentation of paintings restoration through photogrammetry and change detection algorithms

Abstract The philosophical and theoretical foundations of the Theory of Restoration, envisioned by Cesare Brandi in 1975, are established around clear and straightforward guidelines on what is ethically acceptable, and unacceptable, in conservation. Specifically, the Italian scholar advocates for the complete reversibility of restoration work and respect for the history of an artwork. Indeed, according to these concepts, all interventions should be fully reversible so to return the object to its initial conditions without any damage. Bearing in mind these assumptions, a detailed documentation of all the steps of the conservation process, and the possibility to retrieve them a posteriori, must be considered essential. This concept especially applies when dealing with paintings restoration characterized by fine and small details. In recent years, the tendency is to favour minimal invasive interventions ranging from consolidation actions, cleaning samples, and colours retouching. Materials change more or less conspicuously over time according to their consistency and the intensity of the changing factors. Icons do not make an exception to this rule. This process affects the icon’s whole structure: the support, the painting itself and the varnish coating. This paper investigates the performance of change detection algorithms, developed in the remote sensing domain, and, in the framework of this research applied at a microscale (paintings). Each phase of the restoration process is documented exploiting a multi-epoch image acquisition. A monitoring methodology coupled with photogrammetry and 3D shape analysis is tested and described. It is anticipated that the proposed innovative use of change detection techniques can be applied to different kinds of painted surfaces. An icon, today preserved at the Byzantine Museum Makarios III Foundation in Nicosia and restored by the Department of Antiquities of Cyprus labs, has been used as a case study