A system for high-volume acquisition and matching of fresco fragments

Abstract

Figure 1: Our acquisition system, deployed at the Akrotiri Excavation, Thera. We use a flatbed scanner to capture high-resolution images and normals of wall painting fragments (shown at left), and multiple 3-D scanners to acquire geometry. A single user can operate up to four scanners simultaneously, while a second user operates the flatbed scanner and verifies processing results. This yields a throughput of approximately 10 fragments per hour. Our matching algorithm correctly finds the only two matches in this data set using the scanned 3-D geometry. AbstractAlthough mature technologies exist for acquiring images, geometry, and normals of small objects, they remain cumbersome and time-consuming for non-experts to employ on a large scale. In an archaeological setting, a practical acquisition system for routine use on every artifact and fragment would open new possibilities for archiving, analysis, and dissemination. We present an inexpensive system for acquiring all three types of information, and associated metadata, for small objects such as fragments of wall paintings. The acquisition system requires minimal supervision, so that a single, non-expert user can scan at least 10 fragments per hour. To achieve this performance, we introduce new algorithms to robustly and automatically align range scans, register 2-D scans to 3-D geometry, and compute normals from 2-D scans. As an illustrative application, we present a novel 3-D matching algorithm that efficiently searches for matching fragments using the scanned geometry.

Merge2-3D: Combining Multiple Normal Maps with 3D Surfaces

“…First, we use a relatively highresolution NextEngine scanner, which is based on laser stripe triangulation. We follow the steps in [21] to reconstruct the surface. Secondly, to explore even lowerresolution geometric input, we have also experimented with Kinect [22], with the Skanect [23] software used to reconstruct the surface from the captured data.…”

Imaging Techniques in Conservation

“…Uses of laser scanning are better recognized and more commonly employed for creating digital models for display and documentation. Its application for reconstruction of fragmentary objects has also been investigated in the US (Velios et al 2003: 88;Brown et al 2008). However, it is not routinely used to its full potential.…”

Aligning surfaces without aligning surfaces

“…When reassembling thick/volumetric objects like a stone-carved statue, for example, fractures will expose a common break-surface between matching fragments. Numerous approaches [2,7,17] use the dense correspondences embedded in this common surface both to find matching fragments, and to align them. When the matching fragments are too thin to share a common surface, these methods may not be applied.…”

“…The standard approach is then to iterate between finding common points in both views, and estimating the transformation that aligns them. This assumption holds for certain applications, such as constructing 3D models from several range-scans, or in digital archaeology where broken fragments have a thick break-surface in common as a result of the fracture [1,2,6,7,17].…”