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Kutlu, Hasan; Ritz, Martin; Santos, Pedro; Fellner, Dieter W.

Fully Automatic Mechanical Scan Range Extension and Signal to Noise Optimization of a Lens-Shifted Structured Light System

2021

GCH 2021

Eurographics Workshop on Graphics and Cultural Heritage (GCH) <19, 2021, online>

Digitization of cultural heritage is of growing importance, both for its preservation for coming generations in the face of looming dangers of natural decay or intentional destruction, and current generations, that increasingly have access to virtual cultural heritage for interactive exploring or scientific analysis. These goals can only be achieved by 3D replicas at reasonable quality and resolution, to come as close as possible to the original. This brings about several challenges to overcome. The challenge of digitizing huge numbers of artefacts is addressed by CultLab3D, the first fully automatic 3D digitization system. Another challenge is the size of objects, as each digitization system is designed for a certain optimum measurement range, leaving which results in loss of quality. Due to optical and mechanical constraints, most systems are not able to faithfully reconstruct objects under a certain size limit in their full geometric detail. Historic coins are one good example, where the deterioration of the surface structure in most cases has progressed to a degree that it not even is perceptible through the fingernail. This challenge is addressed by a modular extension of CultLab3D, the MesoScanner, which is a structured light system that breaks limits in depth resolution through a mechanical lens-shifting extension, allowing physically shifting of fringe patterns on top of the well-known multi-period phase shift method. This is where this work adds two major improvements: First, the signal to noise ratio and thus reconstruction quality has been improved significantly through several algorithmic processing steps. Second, the physical limitation of the measurement range was removed using a 2D actuator steering the object mount, thus allowing for a measurement range at theoretically arbitrary size. This opens up the fully automatic handling of two scenarios: Complete digitization of objects exceeding the measurement range, and unsupervised digitization of large collections of small objects in one run.

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Kutlu, Hasan; Weinmann, Andreas [Referee]; Ritz, Martin [Co-Referee]

Fully Automatic Mechanical Scan Range Extension of a Lens-Shifted Structured Light System

2020

Darmstadt, Hochschule, Master Thesis, 2020

Cultural heritage are precious goods which need to be preserved for coming generations. Due to many reasons, e.g., wars or natural decay, those objects are in danger of destruction. In order to prevent them from being lost forever, those objects are digitized as 3D models to be accessible for further generations of mankind, the Fraunhofer Institute for computer graphics research offers a fully automatic 3D digitization system called the CultLab3D. There is already a fully functional system for big objects. However, it is more difficult to scan small objects like coins or rings. Those small objects are often referred to as 2.5D objects because they often got engravings and inscriptions on their surface, which cannot even be felt with ones fingers. Scanning such fine detailed objects needs a system that can measure such details. This is accomplished by the MesoScannerV2, an extension of the CultLab3D. It is designed for the digitization of these 2.5D objects without missing details. The MesoScannerV2 is a structured light system which uses a special variation of the phase shift method in order to improve the accuracy of the digitized 3D model of the object. The structured light-based MesoScannerV2 reaches an advanced depth and lateral resolution due to its specialty, the extension of state-of-the-art fringe patterns by a mechanical lens-shifted surface encoding method. Due to bad data acquisition and due to possible uncertainties of numerical algorithms noise is generated which directly influences the digitized 3D models. Therefore, this thesis aims to reduce the generated noise to get cleaner 3D models. Furthermore, the MesoScannerV2 needs to be future-proof, which requires an automation of the scan process of many objects at the same time. The integration of an automation procedure to the MesoScannerV2 is another topic discussed in this thesis. We show that methods are found to reduce the generated noise significantly in particular, we provide a corresponding evaluation. Further, possible solutions to automate the scan process could be found.