Fringe projection profilometry for recovering 2.5D shape of ancient coins

Abstract

Given its importance in many fields, ranging from quality control to medicine, from robotics to solid modelling, surveys of surface profiles by means of non-contact optical systems is the subject of extensive studies [1]: • In the field of cultural heritage, 3D acquisition is used primarily for documentation, comparative studies [2], [3], remote examination [4], [5] and degradation monitoring [6] as well as to create virtual museums [7, 8]. • In medicine, 3D scanners are useful for obtaining accurate anthropometric body segment parameters for the biomechanical analysis of human motion [9] and for the accurate acquisition of patient dentition [10]. • In the field of forensics, 3D reconstructions are helpful for the analysis of writing [11], [12], the virtual reconstruction of crime scenes [13], firearm examination proficiency tests [14] and face recognition [15], [16] • In quality control, 3D scanning can be used for production control and tool wear analysis [17]-[20]. Furthermore, it can be used for underwater 3D reconstruction [21], [22]. In the field of cultural heritage conservation, both the determination of surface finish (surface texture) and its variations over time are important. In fact, in order to establish the actual vulnerability of cultural assets, one of the most important parameters to determine is the loss of material or, more generally, the determination of microstructural changes in the exposed surface (currently, for these determinations, indirect methods are used). Therefore, the objective of the present research is to develop a non-contact optoelectronic system capable of analysing, at high resolution, the surface profile of artistic finds. The basic methodology to be used for the development of the system is the one known as grating projection or structured light [23]-[25]. This method, supported by optoelectronic signalprocessing techniques, allows the development of a system characterised by its high precision, small footprint and relatively low production cost.