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Item Improving the digitization of shape and color of 3D artworks in a cluttered environment(The Eurographics Association, 2013) Bettio, Fabio; Gobbetti, Enrico; Merella, Emilio; Pintus, Ruggero; -We propose an approach for improving the digitization of shape and color of 3D artworks in a cluttered environment using 3D laser scanning and flash photography. In order to separate clutter from acquired material, semi-automated methods are employed to generate masks for segment the 2D range maps and the color photographs, removing unwanted 3D and color data prior to 3D integration. Sharp shadows generated by flash acquisition are trivially handled by this masking process, and color deviations introduced by the flash light are corrected at color blending time by taking into account the object geometry. The approach has been applied to, and evaluated on, a large scale acquisition campaign of the Mont'e Prama complex, an extraordinary collection of stone fragments from the Nuragic era, depicting larger-than-life archers, warriors, boxers, as well as small models of prehistoric nuraghe (cone-shaped stone towers). The acquisition campaign has covered 36 statues mounted on metallic supports, acquired at 0.25mm resolution, resulting in over 6200 range scans (over 1.3G valid samples) and 3426 10Mpixel photographs.Item Surface Light Field from Video Acquired in Uncontrolled Settings(The Eurographics Association, 2013) Palma, Gianpaolo; Desogus, Nicola; Cignoni, Paolo; Scopigno, Roberto; -This paper presents an algorithm for the estimation of the Surface Light Field using video sequences acquired moving the camera around the object. Unlike other state of the art methods, it does not require a uniform sampling density of the view directions, but it is able to build an approximation of the Surface Light Field starting from a biased video acquisition: dense along the camera path and completely missing in the other directions. The main idea is to separate the estimation of two components: the diffuse color, computed using statistical operations that allow the estimation of a rough approximation of the direction of the main light sources in the acquisition environment; the other residual Surface Light Field effects, modeled as linear combination of spherical functions. From qualitative and numerical evaluations, the final rendering results show a high fidelity and similarity with the input video frames, without ringing and banding effects.Item Characterization of European Lacquers by terahertz (THz) reflectometric imaging(The Eurographics Association, 2013) Dandolo, Corinna Ludovica Koch; Jepsen, Peter Uhd; -In this study a European lacquerware replica has been investigated by terahertz (THz) reflectometric imaging. The inspected lacquerware is a wooden panel covered by multiple complex layers of lacquers and plaster. Utilizing pulsed Terahertz Time-Domain Imaging (THz-TDI) in reflection mode, we observe non-invasively buried layers of the lacquerware replica, including the internal structure of the wooden panel itself. We find that non-invasive terahertz reflectometric imaging analysis of lacquerware is can provide conservators with important information about the condition of the compositional layers, potentially aiding in the development of appropriate conservation treatments. With the same technique we have performed a surface material mapping. The material distribution has been enhanced through reflected THz composite RGB false color rendering, where RGB mapping allows distinction between different materials and textures on the surface of the lacquerware. The contrast between different textures is enabled by wavelength-dependent scattering from the surface, as well as differences in the composition of the surface layer.Item Quick textured mesh generation for massive 3D digitization of museum artifacts(The Eurographics Association, 2013) Gonizzi, Sara; Micoli, Laura L.; Guidi, Gabriele; -The goal of the "3D Icons" European Project, is to provide Europeana with accurate 3D models of Cultural Heritage artifacts. The purpose of this paper is to describe the specific optimized processing pipeline that has been set-up for digitizing a significant part of the Civic Archaeological Museum in Milan (Italy). Many technical and logistic issues for capturing 3D models in a Museum environment are addressed. In such framework the main problem is generating a good result by the technical point of view, minimizing the impact on the usual Museum activity during 3D capture operations, while shortening the processing time to the minimal allowed by the different applicable techniques. This condition led to precise choices related to the 3D acquisition techniques to be used (SfM), and the related data processing. This paper illustrates the aforementioned systematic aspects through three practical examples, showing good practices for image capturing and some 3D processing optimizations that allowed to speed the 3D models production at a level compliant to the final goal of more than 500 models in 36 months.Item Realistic Virtual Reproductions. Image-based modelling of geometry and appearance(The Eurographics Association, 2013) Martos, Antonio; Ruiz, Bernardino; -Existing technologies for contact-less 3D scanning and Image Based Modelling (IBM) methods are being extensively used nowadays to digitize cultural heritage elements. With a convenient degree of automation these methods can properly capture and reproduce shape and basic colour textures. However, there is usually a quite evident lack of fidelity in the resulting appearance of the virtual reproductions when compared with the original items. Even when properly photo-textured, the reproduced surfaces often resemble either plaster or plastic, regardless of the properties of the original materials. What is neither captured nor modelled is the natural dynamic response of the actual materials with respect to changes in observation angle and/or the lighting arrangement. The methodology introduced in this paper tries to improve the three-dimensional digitalization and visualization of cultural heritage elements, by extending the present capabilities of IBM with additional capture and modelling of surface appearance. We show that it is possible to automatically reproduce realistic-looking virtual objects and scenes, even with photographs taken with an uncalibrated single moving camera and while under uncontrolled and intentionally variable lighting conditions. This is achieved not only by reconstructing the shape and projecting colour texture maps from photographs, but also modelling and mapping the apparent optical response of the surfaces to light changes, while also determining the variable distribution of environmental illumination of the original scene. This novel approach integrates Physically Based Render (PBR) concepts in a processing loop that combines capture and visualization. Using the information contained in different photographs, where the appearance of the object surface changes with environmental light variations, we show that it is possible to enhance the information contained in the usual colour texture maps with additional layers. This enables the reproduc- ion of finer details of surface normals and relief, as well as effective approximations of the Bi-directional Reflectance Distribution Function (BRDF). The appearance of the surfaces can then be reproduced with a dedicated render engine providing unusual levels of detail and realism due to enriched multi-layer texture maps and custom shading functions. This methodology will be introduced with a real case-study, to illustrate its practical applicability and flexibility; The virtual reproduction of the Lady of Elche was performed only from archived photographs taken at the museum for different documentation purposes, using uncalibrated optics and an uncontrolled studio light arrangement. We discuss the capture on larger architectural elements as well, with uncontrolled (yet still variable) illumination in outdoor environments and challenging items with difficult to capture surfaces such as the brass sculpture of La Regenta, where proper reproduction of surface reflection and environmental lights are fundamental steps to provide a good visualization experience. These cases will show the feasibility of working with field calibration and initial approximations for the camera model and light-maps, addressing thus the flexibility required for practical field documentation in museum environments or outdoors. The potential for diffusion will be shown with the use of open source software tools for enhanced visualization. The presented capture methods are integrated with the specific adaptation of open-source GPU-based (Graphics Processing Unit) render engines to produce two flavours of 3D inspection/visualization tools with proper relighting capabilities, able to reveal very subtle details: A quasi-real time realistic engine (Blender Cycles), which is also the basis for the capture process and is focused on realistic reproduction, and a real-time version based on customized pixel shaders, for the real-time visualization of lightweight models on web browsers and other interacItem Global refinement of image-to-geometry registration for color projection on 3D models(The Eurographics Association, 2013) Dellepiane, Matteo; Scopigno, Roberto; -The management, processing and visualization of color information is a critical subject in the context of the acquisition and visualization of real objects. Especially in the context of Cultural Heritage, artifacts are so complex or hard-to-handle that the appearance information has to be extracted from a set of images. The images usually have to be registered to the 3D model of the objects, in order to transfer the needed information. Hence, the problem of image-to-geometry registration has been thoroughly studied by the Computer Graphics and Computer Vision community. Several methods have been proposed, but a fully automatic and generic solution is still missing. Moreover, small misalignments often lead to visible artifacts in the final colored 3D models. In this paper, we propose a method to refine the alignment of a group of images which has been already registered to a 3D model. Taking advantage of the overlapping among the images, and applying a statistical global method based on Mutual Information, the registration error is distributed among all the elements of the dataset. Hence, the quality of color projection is improved, especially when dealing with small details. The method was tested on a number of heterogeneous Cultural Heritage objects, bringing to a visible improvement in the rendering quality. The method is fully automatic, and it does not need powerful hardware or long processing time. Hence, it represents a valid solution for a wide application on CH artifacts.Item 3D Laser Scanning in Cave Environment: the Case of Las Cuevas, Belize. Acquisition of the Cave System and Excavation Area(The Eurographics Association, 2013) Lindgren, Stefan; Galeazzi, Fabrizio; -The Las Cuevas site is a Maya administrative and ceremonial center active during the latter part of the Late Classic period (700 900 AD) in Western Belize. It is of particular interest because a large cave resides directly beneath the largest temple in the site core. This paper presents the use of phase shift variation laser scanning technology (Faro Focus 3D) for the acquisition of the cave's network of galleries (9 chambers) and a large excavation area (8×5 m) investigated in the entrance chamber in the summer of 2012. More than 300 scans were made to acquire the entire cave and the amount of 3D data collected was more than 400 GB. The creation of different level of details allowed the alignment and triangulation of the 3D models of the different chambers and units. The dimension (24×20×10 cm; 5 kg) and accuracy (' 2 mm at 10 25 m) of the laser scanner allowed complete documentation of the cave and units in just three weeks of work. The importance of this work relies on the possibility to use the processed data to systematically improve the archaeological understanding of Las Cuevas' complex cave system, favoring the interpretation of socio-cultural dynamics linked to cave environments during the Late Classic. The use of 3D technologies can, in fact, help the understanding of how the space in the cave was used in the past for rituals and ceremonies. Moreover, the 3D millimetric reproduction of the excavation process linked to the 3D survey of the entire cave will be instrumental for the archaeological record's preservation. Future scholars will have the opportunity to retrace the work made by archaeologists at Las Cuevas, starting new discussion and interpretations of the same 3D archaeological context.Item Comparing 3D digitising technologies: where are the differences?(The Eurographics Association, 2013) Mathys, Aurore; Brecko, Jonathan; Semal, Patrick; -We tested five 3D digitization systems and one method of 2D+ recording on one object: a human skull from the Royal Belgian Institute of Natural Sciences collection (RBINS). We chose a skull because it has both simple and complex structures and different materials such as bone and enamel within the same object. The results obtained with the different technologies were compared for 3D shape accuracy, texture quality, digitization and processing time and finally price. Our results show that the structured light scanner provided the best results to record external structures, CT was found to be the best to record internal structures and is also the best for recording reflecting material such as enamel. Photogrammetry is a very good compromise between portability, price and quality. RTI is a method of 2D+ recording and is a complementary technique, using the same equipment than photogrammetry, which can capture small morphological features that are not easily digitized with the 3D techniques.