GCH 2018 - Eurographics Workshop on Graphics and Cultural Heritage

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https://diglib.eg.org/handle/10.2312/2632673

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An Investigation of Optimal Light Source Setups for Photometric Stereo Reconstruction of Historical Coins
(The Eurographics Association, 2018) Brenner, Simon; Zambanini, Sebastian; Sablatnig, Robert; Sablatnig, Robert and Wimmer, Michael
In this paper, we address the 3D reconstruction of historical coins by means of Photometric Stereo. We investigate the influence of the number and arrangement of lights to the reconstruction quality by comparing mean angular errors on 22 historical coin models. Our results demonstrate that 6 lights circularly placed at an optimal elevation angle do not show a significant loss of reconstruction quality compared to a full semispherical dome setup with 54 lights. This represents a considerable saving of acquisition time and system complexity when it comes to the mass digitization of historical coins.
Browsing Spatial Photography for Dissemination of Cultural Heritage Research Results using Augmented Models
(The Eurographics Association, 2018) Niebling, Florian; Bruschke, Jonas; Latoschik, Marc Erich; Sablatnig, Robert and Wimmer, Michael
Both digital and physical 3D models of buildings as well as historical photographs of architecture are used for a wide range of needs, from research in humanities and information technologies, museum contexts and library studies, to touristic applications. Spatially oriented photographs play an important role in visualizing and browsing contemporary as well as historical architecture, starting with the ground-breaking Photo Tourism project [SSS06]. We present a technique to combine physical, 3D-printed models of buildings with spatially registered historical photographic documents in a hand-held Augmented Reality (AR) environment. Users are enabled to spatially explore historical views of architecture by selecting photos from a collection of images, which are then utilized as textures for the physical model rendered on their respective mobile device. We compare different methods to spatially select photos registered to a physical model in hand-held AR.
Granitic Recumbent Statue Reproduction by a Seven Axes Robotic Milling Machine
(The Eurographics Association, 2018) Barreau, Jean-Baptiste; Jouneau, Joëlle; Mérelle, Johnny; Maillard, Loïc; Bernard, Yann; Quesnel, Laurent; Sablatnig, Robert and Wimmer, Michael
Facing the sea, the rocks sculpted by the "Abbé Fouré" at the "Pointe du Christ" and the "Pointe de la Haie" in Rothéneuf (Brittany, France) attract many visitors. Winds, rains and sea spray erode each day a little more the sculptures carved in granite more than a century ago. In order to preserve the heritage, the "Association des Amis de l'Oeuvre de l'Abbé Fouré" tried to start an innovative project: recreate a statue sculpted by the "Ermite of Rothéneuf" at the end of the 19th century thanks to 3D technologies and robotics. With a first 3D scanning of the sculpture of the "Pointe du Christ", a stonecutters' company was approached to reproduce identically this recumbent statue, identified as John IV, Duke of Brittany. Thanks to a robotic milling machine working on seven axes, by cutting layers in the granite at each passage, the company realized 60% of the work in less than a month. Then, a sculptor of the company was responsible, from documents collected by the association, to give the granite block the features of the original recumbent statue. This replica is currently the centerpiece of several French exhibitions dedicated to the general public.
Frontmatter: Eurographics Workshop on Graphics and Cultural Heritage
(The Eurographics Association, 2018) Sablatnig, Robert; Wimmer, Michael; Sablatnig, Robert and Wimmer, Michael
Visualizing Networks of Maya Glyphs by Clustering Subglyphs
(The Eurographics Association, 2018) Bogacz, Bartosz; Feldmann, Felix; Prager, Christian; Mara, Hubert; Sablatnig, Robert and Wimmer, Michael
Deciphering the Maya writing is an ongoing process that has already started in the early 19th century. Among the reasons why Maya hieroglyphic script and language are still undeciphered are inexpertly-created drawings of Maya writing systems resulting in a large number of misinterpretations concerning the contents of these glyphs. As a consequence, the decipherment of Maya writing systems has experienced several setbacks. Modern research in the domain of cultural heritage requires a maximum amount of precision in capturing and analyzing artifacts so that scholars can work on - preferably - unmodified data as much as possible. This work presents an approach to visualize similar Maya glyphs and parts thereof and enable discovering novel connections between glyphs based on a machine learning pipeline. The algorithm is demonstrated on 3D scans from sculptured monuments, which have been filtered using a Multiscale Integral Invariant Filter (MSII) and then projected as a 2D image. Maya glyphs are segmented from 2D images using projection profiles to generate a grid of columns and rows. Then, the glyphs themselves are segmented using the random walker approach, where background and foreground is separated based on the surface curvature of the original 3D surface. The retrieved subglyphs are first clustered by their sizes into a set of common sizes. For each glyph a feature vector based on Histogram of Gradients (HOG) is computed and used for a subsequent hierarchical clustering. The resultant clusters of glyph parts are used to discover and visualize connections between glyphs using a force directed network layout.
Development of a High Resolution Topography and Color Scanner to Capture Crack Patterns of Paintings
(The Eurographics Association, 2018) Hengstum, Mathijs J. W. van; Essers, Tessa T. W.; Elkhuizen, Willemijn S.; Dodou, Dimitra; Song, Yu; Geraedts, Jo M. P.; Dik, Joris; Sablatnig, Robert and Wimmer, Michael
The aging of paintings is inevitable and over the years degradation occurs due to exposure to a variety of environmental influences. One of these degradations is craquelure, fracture patterns in the paint. 3D imaging techniques offer opportunities to capture the surface of a painting and these patterns at high resolution. In this paper we present a 3D scanner that is able to capture surface topography and color of oil paintings at high resolution utilizing fringe-encoded stereo imaging scanning system. The scanner is capable of automated capture of an area of 1x1m2, capturing a painting at a spatial resolution of 7 micron and a depth accuracy of 34 microns. Scanning at this resolution creates potential research opportunities for documentation and monitoring oil paintings under its environmental influences. A scan was made of 'Girl with a Pearl Earring' (c.1665), painted by Johannes Vermeer, which exhibits fine craquelure patterns. The scanner is able to capture the painting of 39x44.5 cm within 2 hours with a tile overlap of 25%. The results showed that the craquelure has more often a ridge-shaped profile instead of the expected inward valleys. The documentation of these variations in crack profiles create interesting paths for future research.
Virtual Restoration of Wooden Artifacts by Non-Rigid 3D Shape Assembly: A Case of the First Solar Boat of King Khufu
(The Eurographics Association, 2018) Nemoto, Takashi; Kobayashi, Tetsuya; Oishi, Takeshi; Kagesawa, Masataka; Kurokochi, Hiromasa; Yoshimura, Sakuji; Ziddan, Eissa; Taha, Mamdouh; Sablatnig, Robert and Wimmer, Michael
In this paper, we present a method to digitally reassemble an object to its original form given the 3D data of its component which are assumed to be non-rigidly deformed. Targeting wooden artifacts, we developed an algorithm to deform the components parametrically, and constraints based on the physical properties of wood are imposed on the deformation. We apply our method to a deformed cultural asset, specifically the first solar boat of King Khufu which is made of wood.
Gloss Calibration and Gloss Gamut Mapping for Material Appearance Reproduction of Paintings
(The Eurographics Association, 2018) Elkhuizen, Willemijn S.; Essers, Tessa T. W.; Song, Yu; Pont, Sylvia C.; Geraedts, Jo M. P.; Dik, Joris; Sablatnig, Robert and Wimmer, Michael
Being able to link captured material characteristics and fabricable material appearance attributes is important for creating life-like reproductions. In this paper we propose a method for gloss calibration, and an approach for gloss gamut mapping, as part of an integrated approach for color, topography and gloss reproduction. For gloss calibration, gloss calibration targets were printed in the primary printing colors (CMYK and White), with uniform gloss in equal distant gloss levels. These targets were scanned using the proposed gloss scanner. To create the gloss gamut map, a monotonic curve was fitted to the mean gloss scan values at different gloss levels. Analysis of fitted curves indicated that the gloss mapping is independent of the diffuse colors. As a case study, the painting 'Fruit Still Life' by Cornelis de Heem was scanned, and the measured gloss was mapped to printable gloss levels using the relation described by the fitted curve. The printed result shows good correspondence to the painting's appearance, with clearly distinguishable gloss features for the in-gamut glass values.
Data Visualization of Decoration Occurrence and Distribution. A Comparative Study of Late Egyptian Funerary Decoration in Thebes
(The Eurographics Association, 2018) Wutte, Anja; Sablatnig, Robert and Wimmer, Michael
Decoration in Ancient Egyptian funerary monuments represents an important part of the monuments layout. Beside scenes displaying the owner, scenes of daily life, fabrication, offerings and hieroglyphic texts are found. Not only topics of self-presentation but also decoration for the translation to the afterlife were predominant. Therefore, this paper suggests approaches to analyze distribution and occurrence of decorations of several ancient monuments of the same style, with data visualization and quantitative methods. As a case study ancient Egyptian funerary monuments of High Officials from the Late Period, twenty-fifth to twenty-sixth dynasty, were studied. The decorative scenes were categorized and tagged in terms of their content. The positions in the monument were highlighted and included in abstracted 3-dimensional models. This computational implementation offers users to search for decoration categories, highlight, locate and finally compare the position of a scene between the monuments. The visualized data include the position and orientation of a categorized scene in the monument, their occurrence and distribution among the analyzed monuments. In a further step the analysis data was studied statistically in order to be able to query detailed results of the prevalence, distribution and preservation of decorations and specific scenes. Both introduced solutions provide a user friendly information interface to visualize, compare and request quantitative data.
Aging Prediction of Cultural Heritage Samples Based on Surface Microgeometry
(The Eurographics Association, 2018) Ciortan, Irina Mihaela; Marchioro, Giacomo; Daffara, Claudia; Pintus, Ruggero; Gobbetti, Enrico; Giachetti, Andrea; Sablatnig, Robert and Wimmer, Michael
A critical and challenging aspect for the study of Cultural Heritage (CH) assets is related to the characterization of the materials that compose them and to the variation of these materials with time. In this paper, we exploit a realistic dataset of artificially aged metallic samples treated with different coatings commonly used for artworks' protection in order to evaluate different approaches to extract material features from high-resolution depth maps. In particular, we estimated, on microprofilometric surface acquisitions of the samples, performed at different aging steps, standard roughness descriptors used in materials science as well as classical and recent image texture descriptors. We analyzed the ability of the features to discriminate different aging steps and performed supervised classification tests showing the feasibility of a texture-based aging analysis and the effectiveness of coatings in reducing the surfaces' change with time.
On Combining Epigraphy, TLS, Photogrammetry, and Interactive Media for Heritage Documentation: The Case Study of Djehutihotep's Tomb in Dayr al-Barsha
(The Eurographics Association, 2018) Lima, Roberto de; Sykora, Toon; Meyer, Marleen De; Willems, Harco; Vergauwen, Maarten; Sablatnig, Robert and Wimmer, Michael
The governors' tombs located at Dayr al-Barsha are considered among the most important monuments of the Egyptian Middle Kingdom. Unfortunately, due to quarrying activities, looting, and natural catastrophes, the archaeological remains are now in a dilapidated state. Their documentation therefore becomes a necessary task towards the preservation and research of this provincial elite cemetery. Traditional geomatics-based heritage recording methods and sensors are, however, not sufficient to yield a full and comprehensive documentation. Inspired by emergent technologies, this paper proposes a symbiosis of digital epigraphy, Terrestrial Laser Scanning (TLS), image-based digitalization techniques, and 3D visualization platforms, to provide experts with a digital tool able to yield high-level information in terms of accurate digital drawings of decorated sections and dense 3D mesh models. Results show that the proposed approach provides a reliable alternative to answer research questions, especially in the context of ancient Egyptian heritage, as the level of detail captured enables the academic community to further explore decoration techniques, damage recognition, and digital reconstruction.
New Haven Building Archive: A Database for the Collection, Study, and Communication of Local Built Heritage
(The Eurographics Association, 2018) Rubin, Elihu; Akhtar, Saima; Brown, Benedict; Rushmeier, Holly; Sablatnig, Robert and Wimmer, Michael
The New Haven Building Archive (NHBA) is a digital, mobile, and interactive field guide to New Haven, Connecticut's built heritage. As an interactive digital guide and database for local buildings, the NHBA harnesses digital mapping technologies, place-based storytelling and community-based research. Ultimately, the development of the NHBA will aid in the co-production of knowledge about the city by students, academic researchers and local citizens in a way that will facilitate conversations about the historical patterns and future development of New Haven while suggesting a model for engaged teaching and research for urban studies more broadly.
Multi-Light Energy Map
(The Eurographics Association, 2018) Lardeux, Florian; Marchand, Sylvain; Gomez-Krämer, Petra; Sablatnig, Robert and Wimmer, Michael
We propose a model to represent quasi-flat objects, such as coins or amphora stamps. These objects are flat surfaces, meaning their length and their width largely exceed their height, and feature a distinctive relief. This relief characterizes the object and its perception is directly influenced by the position of the object, the light direction and the viewer's direction. Our model is a single image representation containing the underlying structural variations of the object. This model, that we call 'Multi-Light Energy Map', is constructed out of several classic images taken with several illumination directions without computing the object's surface normals. We found a way to extract useful information out of this sequence of images and compile it into our map. We eventually explain how we can use this model in the case of image registration of ancient coins.
Deep Mapping Tarn Hows: Automated Generation of 3D Historic Landscapes
(The Eurographics Association, 2018) Reinhold, Alexander; Gregory, Ian; Rayson, Paul; Sablatnig, Robert and Wimmer, Michael
Changing landscape presents a problem for both conservation and education at heritage sites. We consider the site of Tarn Hows in the English Lake District National Park, a site which has had significant landscape change over the past 200 years, from developing tree coverage, to the merging of three lakes into one. We created an automated process that combines an elevation map and a vegetation map to build a 3D representation of the landscape. We used this tool to create a 3D Deep Map of Tarn Hows, representing the site's landscape at multiple periods over time, allowing them to be viewed side by side and explored in an interactive environment. This 3D Deep Map provides an exploratory resource for site authorities to educate the public about the historic environment, with embedded multimedia in the application to provide additional information to users that might be disruptive or impractical to display on site. The 3D Deep Map also provides a tool for conservators to plan site maintenance to best maintain the integrity of the historic landscape without negatively impacting visitors' experience of the iconic site.
Elastic Flattening of Painted Pottery Surfaces
(The Eurographics Association, 2018) Preiner, Reinhold; Karl, Stephan; Bayer, Paul; Schreck, Tobias; Sablatnig, Robert and Wimmer, Michael
Generating flat images from paintings on curved surfaces is an important task in Archaeological analysis of ancient pottery. It allows comparing styles and painting techniques, e.g, for style and workshop attribution, and serves as basis for domain publications which typically use 2d images. To obtain such flat images from scanned textured 3d models of the pottery objects, current practice is to perform so-called rollouts using approximating shape primitives like cones or spheres, onto which the mesh surfaces are projected. While this process provides in intuitive deformation metaphor for the users, it naturally introduces unwanted distortions in the mapping of the surface, especially for vessels with high-curvature profiles. In this work, we perform an elastic flattening of these projected meshes, where stretch energy is minimized by simulating a physical relaxation process on a damped elastic spring model. We propose an intuitive contraction-directed physical setup which allows for an efficient relaxation while ensuring a controlled convergence. Our work has shown to produce images of significantly improved suitability for domain experts' tasks like interpretation, documentation and attribution of ancient pottery.
An Image-based Approach for Detecting Faces Carved in Heritage Monuments
(The Eurographics Association, 2018) Lai, Yu-Kun; Echavarria, Karina Rodriguez; Song, Ran; Rosin, Paul L.; Sablatnig, Robert and Wimmer, Michael
Heritage monuments such as columns, memorials and buildings are typically carved with a variety of visual features, including figural content, illustrating scenes from battles or historical narratives. Understanding such visual features is of interest to heritage professionals as it can facilitate the study of such monuments and their conservation. However, this visual analysis can be challenging due to the large-scale size, the amount of carvings and difficulty of access to monuments across the world. This paper makes a contribution towards this goal by presenting work-in-progress for developing image-based approaches for detecting visual features in 3D models, in particular of human faces. The motivation for focusing on faces is the prominence of human figures throughout monuments in the world. The methods are tested on a 3D model of a section of the Trajan Column cast at the Victoria and Albert (V&A) Museum in London, UK. The initial results suggest that methods based on machine learning can provide useful tools for heritage professionals to deal with the large-scale challenges presented by such large monuments.
Objective and Subjective Evaluation of Virtual Relighting from Reflectance Transformation Imaging Data
(The Eurographics Association, 2018) Pintus, Ruggero; Dulecha, Tinsae; Jaspe, Alberto; Giachetti, Andrea; Ciortan, Irina; Gobbetti, Enrico; Sablatnig, Robert and Wimmer, Michael
Reflectance Transformation Imaging (RTI) is widely used to produce relightable models from multi-light image collections. These models are used for a variety of tasks in the Cultural Heritage field. In this work, we carry out an objective and subjective evaluation of RTI data visualization. We start from the acquisition of a series of objects with different geometry and appearance characteristics using a common dome-based configuration. We then transform the acquired data into relightable representations using different approaches: PTM, HSH, and RBF. We then perform an objective error estimation by comparing ground truth images with relighted ones in a leave-one-out framework using PSNR and SSIM error metrics. Moreover, we carry out a subjective investigation through perceptual experiments involving end users with a variety of backgrounds. Objective and subjective tests are shown to behave consistently, and significant differences are found between the various methods. While the proposed analysis has been performed on three common and state-of-the-art RTI visualization methods, our approach is general enough to be extended and applied in the future to new developed multi-light processing pipelines and rendering solutions, to assess their numerical precision and accuracy, and their perceptual visual quality.
Towards an Automatic 3D Patterns Classification: the GRAVITATE Use Case
(The Eurographics Association, 2018) Thompson, Elia Moscoso; Biasotti, Silvia; Sorrentino, Giusi; Polig, Martina; Hermon, Sorin; Sablatnig, Robert and Wimmer, Michael
When cataloging archaeological fragments, decorative patterns are an indicator of the stylistic canon an object belongs to. In this paper we address a quantitative classification of the decorative pattern elements that characterize the models in the GRAVITATE use case, discussing the performance of a recent algorithm for pattern recognition over triangle meshes.
Towards the Reconstruction of Wide Historical Sites: A Local Graph-based Representation to Resample Gigantic Acquisitions
(The Eurographics Association, 2018) Bletterer, Arnaud; Payan, Frédéric; Antonini, Marc; Meftah, Anis; Sablatnig, Robert and Wimmer, Michael
Nowadays, LiDAR scanners are able to digitize very wide historical sites, leading to point clouds composed of billions of points. These point clouds are able to describe very small objects or elements disseminated in these sites, but also exhibit numerous defects in terms of sampling quality. Moreover, they sometimes contain too many samples to be processed as they are. In this paper, we propose a local graph-based structure to deal with the set of LiDAR acquisitions of a digitization campaign. Each acquisition is considered as a graph representing the local behavior of the captured surface. Those local graphs are then connected together to obtain a single and global representation of the original scene. This structure is particularly suitable for resampling gigantic points clouds. We show how we can reduce the number of points drastically while preserving the visual quality of large and complex sites, whatever the number of acquisitions.
Proxy Painting
(The Eurographics Association, 2018) Lange, Vanessa; Kurth, Philipp; Keinert, Benjamin; Boss, Martin; Stamminger, Marc; Bauer, Frank; Sablatnig, Robert and Wimmer, Michael
For archaeologists it is often desireable to present statues in their original coloration. With projection mapping real-world surfaces are augmented by digital content to create compelling alterations of the scene's visual appearance without actually altering or even damaging the object. While there are frequent advances in projection quality, content creation is still a chal- lenging and often unintuitive task, especially for non-experts. In our presented system we combine the advantages of digital content creation such as rapid prototyping with the convenience of an analog workflow. Users paint on smaller versions of the projection mapping target, employing real-world brushes and pencils, while the results are presented live on its large counter- part. We further demonstrate the integration of our system into a state-of-art game engine. By leveraging a powerful rendering and material workflow we make creating compelling materials and lighting situations an intuitive experience.

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