Design of a semi-automatic methodology supporting the graphic documentation for the restoration of artifacts

To motivate the proposed research, it is necessary to clearly define the role and usefulness in cultural heritage of the two main topics dealt with: graphic documentation and diagnostic imaging. The geometric-dimensional cognition of the object of historical-artistic interest and the study of its constituent materials have a fundamental role in all the disciplines concerning the activity of preservation and conservation (or restoration). They represent a unique opportunity to transcribe reality through graphic and photographic interpretation. Hand drawing and diagnostic imaging are the instruments with which the conservator-restorer interrogates the artifact, transforming dialogue into a process of representation, giving at graphic and photography, not the role of expressive tools but languages focused on the methodological developments expressed by the culture of restoration. Photographic and graphic documentation, diagnostic investigations together with the conservation/technical report and written report, “represent a “dossier” still considered the current standard for all interventions performed on artifacts to allow the recognition and definition of each procedure carried out, leaving an organized description of that done today to allow a proper maintenance of that artifact tomorrow, providing the basis for any new restoration and communicating the additional knowledge obtained in the restoration process” [Translation] - (Sacco, 2002, p.28). Numerous factors contribute to the realization of appropriate graphic documentation and involve problems of theoretical and methodological nature. What must be recorded is the set of aesthetic, static, technical, and historical parameters, as well as those relevant to the preservation conditions. It is often necessary to define for each case the system of consistency of all the measures taken, choosing different schedules, modalities and operational criteria of a technical/executive type, depending on the object to be documented. In addition to the listed factors, there are also difficulties related to the interpretation of diagnostic images that are currently visually inspected with the naked eye by conservator-restorers, or at most optimized through pre-processing by diagnosticians. The detected characteristics are concurrently manually reported in ad hoc graphic surveys, denominated Graphic Documentation. The software tools currently used to support these tasks only allow the manual tracing of drawings on a photographic basis, thus making this process subjective, challenging, and time-consuming. The complexity of the whole process induces conservator-restorers to only record essential information, rendering their documentation incomplete and far from ensuring the reproducibility of the results. To date, as far as the automatic extraction of drawings from raster images is concerned, a specific technique has been adopted only in the archaeological field. It is developed to produce illustrations in raster format, extracted from photographs of archaeological objects (Bezzi n.d.; Bezzi and Bezzi 2011). Unfortunately, these drawing extraction techniques do not meet the requirements of graphic documentation in restoration, which instead requires the design of a non-illustrative, non-raster vector drawing, i.e., without shading and with topographically coherent closed polygons. The aim of this research is to propose a semi-automated methodology based on the use of image analysis algorithms that may help cultural heritage operators interpret diagnostic images, recording their findings and performing image analysis through statistical methods. The set of relevant available images can be handled as a whole, and the regions of interest segmented and extracted by Blind Source Separation Methods (BSS) and binarization. Then, region boundaries are vectorized to allow the graphic documentation and statistical analysis of results. The procedure facilitates conservator-restorers’ work, making it faster and less subjective, allowing them the freedom to choose what is essential to their purposes from the wealth of information that is automatically extracted from the images. These computerized processing procedures, defined as morphological and segmentation procedures, allow images to be divided into their constituent objects, though not ensuring optimal results in all fields of application. Their accuracy and ease in identification are closely linked to variations in the following characteristics: edge models that distinguish objects; similarities between regions; spatial resolution in pixels; bit depth per channel; color pattern/space. Various identification problems also occur according to the type of artifact and the formal geometric requirements that conservation and restoration interventions may require. The different phases of the methodology are supported by two software applications: QGIS, a Geographic Information System (GIS) application, and Matlab. The results are comparable and compatible with currently used Computer-Aided Drafting (CAD) software and SICAR. The thesis is organized as follows. Chapter 1 presents the birth and development of documentation in the field of cultural heritage, analyzing specific regulations on the matter and various applications. In addition, the current graphic and thematic information structure, and software currently used to create and manage such information, are described. In chapter 2 we discuss still unsolved problems concerning graphic documentation and diagnostic image analysis. A list of studies and researches aimed at solving such problems is also included. Chapter 3 illustrates the theoretic principles on which the proposed methodology is based and presents reasons and reflections which led to its definition. The software applications (MatLab Version 9.7 R2019b and QGIS version 3.10.2-A Coruña, whit Grass 7.8.2.) selected to practically carry out the methodology itself are also analyzed. In chapter 4, the methodology structure is presented and described: each section presents a brief introductory description and an applicative part in which some steps of the chosen software applications are briefly demonstrated. To show the outcome of methodology application, chapter 5 presents the results obtained in real study cases. Bezzi, Luca. “ArcheOS and UAVP, a Free and Open Source Platform for Remote Sensing.” https://www.researchgate.net/profile/Luca_Bezzi/publication/281462322_2012_03_28_caa_arc-team_v05/links/55e9a9dc08ae65b6389b09b7/2012-03-28-caa-arc-team-v05.pdf?origin=publication_list (May 19, 2020). Bezzi, Luca, and Alessandro Bezzi. 2011. “Proposta per Un Metodo Informatizzato Di Disegno Archeologico Il Disegno Archeologico.” In ArcheoFOSS. Open Source, Free Software e Open Format Nei Processi Di Ricerca Archeologici. Foggia 5-6 Maggio 2010., eds. Giuliano De Felice and Maria Giuseppina Sibilano. Puglia: Edipuglia, 113–23. 1. In this paper, the term preservation will be used to indicate planned maintenance performed on the artefacts, for example, all interventions aimed at preserving their microclimate, elimination of surface debris such as fine particles, etc. The term conservation will instead be used to indicate direct restoration interventions on the artefacts.