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Item SynthPS: a Benchmark for Evaluation of Photometric Stereo Algorithms for Cultural Heritage Applications(The Eurographics Association, 2020) Dulecha, Tinsae Gebrechristos; Pintus, Ruggero; Gobbetti, Enrico; Giachetti, Andrea; Spagnuolo, Michela and Melero, Francisco JavierPhotometric Stereo (PS) is a technique for estimating surface normals from a collection of images captured from a fixed viewpoint and with variable lighting. Over the years, several methods have been proposed for the task, trying to cope with different materials, lights, and camera calibration issues. An accurate evaluation and selection of the best PS methods for different materials and acquisition setups is a fundamental step for the accurate quantitative reconstruction of objects' shapes. In particular, it would boost quantitative reconstruction in the Cultural Heritage domain, where a large amount of Multi-Light Image Collections are captured with light domes or handheld Reflectance Transformation Imaging protocols. However, the lack of benchmarks specifically designed for this goal makes it difficult to compare the available methods and choose the most suitable technique for practical applications. An ideal benchmark should enable the evaluation of the quality of the reconstructed normals on the kind of surfaces typically captured in real-world applications, possibly evaluating performance variability as a function of material properties, light distribution, and image quality. The evaluation should not depend on light and camera calibration issues. In this paper, we propose a benchmark of this kind, SynthPS, which includes synthetic, physically-based renderings of Cultural Heritage object models with different assigned materials. SynthPS allowed us to evaluate the performance of classical, robust and learning-based Photometric Stereo approaches on different materials with different light distributions, also analyzing their robustness against errors typically arising in practical acquisition settings, including robustness against gamma correction and light calibration errors.Item STRONGER: Simple TRajectory-based ONline GEsture Recognizer(The Eurographics Association, 2021) Emporio, Marco; Caputo, Ariel; Giachetti, Andrea; Frosini, Patrizio and Giorgi, Daniela and Melzi, Simone and Rodolà , EmanueleIn this paper, we present STRONGER, a client-server solution for the online gesture recognition from captured hands' joints sequences. The system leverages a CNN-based recognizer improving current state-of-the-art solutions for segmented gestures classification, trained and tested for the online gesture recognition task on a recent benchmark including heterogeneous gestures. The recognizer provides good classification accuracy and a limited number of false positives on most of the gesture classes of the benchmark used and has been used to create a demo application in a Mixed Reality scenario using an Hololens 2 optical see through Head-Mounted Display with hand tracking capability.Item FloralSurf: Space-Filling Geodesic Ornaments(The Eurographics Association, 2023) Albano, Valerio; Fanni, Filippo Andrea; Giachetti, Andrea; Pellacini, Fabio; Ritschel, Tobias; Weidlich, AndreaWe propose a method to generate floral patterns on manifolds without relying on parametrizations. Taking inspiration from the literature on procedural space-filling vegetation, these patterns are made of non-intersecting ornaments that are grown on the surface by repeatedly adding different types of decorative elements, until the whole surface is covered. Each decorative element is defined by a set of geodesic Bézier splines and a set of growth points from which to continue growing the ornaments. Ornaments are grown in a greedy fashion, one decorative element at a time. At each step, we analyze a set of candidates, and retain the one that maximizes surface coverage, while ensuring that it does not intersect other ornaments. All operations in our method are performed in the intrinsic metric of the surface, thus ensuring that the derived decorations have good coverage, with neither distortions nor discontinuities, and can be grown on complex surfaces. In our method, users control the decorations by selecting the size and shape of the decorative elements and the position of the growth points.We demonstrate decorations that vary in the length of the ornaments' lines, and the number, scale and orientation of the placed decorations. We show that these patterns mimic closely the design of hand-drawn objects. Our algorithm supports any manifold surface represented as triangle meshes. In particular, we demonstrate patterns generated on surfaces with high genus, with and without borders and holes, and that can include a mixture of thin and large features.Item SHREC 2020 Track: River Gravel Characterization(The Eurographics Association, 2020) Giachetti, Andrea; Biasotti, Silvia; Moscoso Thompson, Elia; Fraccarollo, Luigi; Nguyen, Quang; Nguyen, Hai-Dang; Tran, Minh-Triet; Arvanitis, Gerasimos; Romanelis, Ioannis; Fotis, Vlasis; Moustakas, Konstantinos; Tortorici, Claudio; Werghi, Naoufel; Berretti, Stefano; Schreck, Tobias and Theoharis, Theoharis and Pratikakis, Ioannis and Spagnuolo, Michela and Veltkamp, Remco C.The quantitative analysis of the distribution of the different types of sands, gravels and cobbles shaping river beds is a very important task performed by hydrologists to derive useful information on fluvial dynamics and related processes (e.g., hydraulic resistance, sediment transport and erosion, habitat suitability. As the methods currently employed in the practice to perform this evaluation are expensive and time-consuming, the development of fast and accurate methods able to provide a reasonable estimate of the gravel distribution based on images or 3D scanning data would be extremely useful to support hydrologists in their work. To evaluate the suitability of state-of-the-art geometry processing tool to estimate the distribution from digital surface data, we created, therefore, a dataset including real captures of riverbed mockups, designed a retrieval task on it and proposed them as a challenge of the 3D Shape Retrieval Contest (SHREC) 2020. In this paper, we discuss the results obtained by the methods proposed by the groups participating in the contest and baseline methods provided by the organizers. Retrieval methods have been compared using the precision-recall curves, nearest neighbor, first tier, second tier, normalized discounted cumulated gain and average dynamic recall. Results show the feasibility of gravels characterization from captured surfaces and issues in the discrimination of mixture of gravels of different size.Item Effective Interactive Visualization of Neural Relightable Images in a Web-based Multi-layered Framework(The Eurographics Association, 2023) Righetto, Leonardo; Bettio, Fabio; Ponchio, Federico; Giachetti, Andrea; Gobbetti, Enrico; Bucciero, Alberto; Fanini, Bruno; Graf, Holger; Pescarin, Sofia; Rizvic, SelmaRelightable images created from Multi-Light Image Collections (MLICs) are one of the most commonly employed models for interactive object exploration in cultural heritage. In recent years, neural representations have been shown to produce higherquality images, at similar storage costs, with respect to the more classic analytical models such as Polynomial Texture Maps (PTM) or Hemispherical Harmonics (HSH). However, their integration in practical interactive tools has so far been limited due to the higher evaluation cost, making it difficult to employ them for interactive inspection of large images, and to the difficulty in integration cost, due to the need to incorporate deep-learning libraries in relightable renderers. In this paper, we illustrate how a state-of-the-art neural reflectance model can be directly evaluated, using common WebGL shader features, inside a multiplatform renderer. We then show how this solution can be embedded in a scalable framework capable to handle multi-layered relightable models in web settings. We finally show the performance and capabilities of the method on cultural heritage objects.Item Approximating Shapes with Standard and Custom 3D Printed LEGO Bricks(The Eurographics Association, 2021) Fanni, Filippo Andrea; Dal Bello, Alberto; Sbardellini, Simone; Giachetti, Andrea; Frosini, Patrizio and Giorgi, Daniela and Melzi, Simone and Rodolà , EmanueleIn this paper, we present a work-in-progress aimed at developing a pipeline for the fabrication of shapes reproducing digital models with a combination of standard LEGO bricks and 3D printed custom elements. The pipeline starts searching for the ideal alignment of the 3D model with the brick grid. It then employs a novel approach for shape "legolization" using a outside-in heuristic to limit critical configuration, and separates an external shell and an internal part. Finally, it exploits shape booleans to create the external custom parts to be 3D printed.Item Remote and Deviceless Manipulation of Virtual Objects in Mixed Reality(The Eurographics Association, 2023) Caputo, Ariel; Bartolomioli, Riccardo; Giachetti, Andrea; Banterle, Francesco; Caggianese, Giuseppe; Capece, Nicola; Erra, Ugo; Lupinetti, Katia; Manfredi, GildaDeviceless manipulation of virtual objects in mixed reality (MR) environments is technically achievable with the current generation of Head-Mounted Displays (HMDs), as they track finger movements and allow you to use gestures to control the transformation. However, when the object manipulation is performed at some distance, and when the transform includes scaling, it is not obvious how to remap the hand motions over the degrees of freedom of the object. Different solutions have been implemented in software toolkits, but there are still usability issues and a lack of clear guidelines for the interaction design. We present a user study evaluating three solutions for the remote translation, rotation, and scaling of virtual objects in the real environment without using handheld devices. We analyze their usability on the practical task of docking virtual cubes on a tangible shelf from varying distances. The outcomes of our study show that the usability of the methods is strongly affected by the use of separate or integrated control of the degrees of freedom, by the use of the hands in a symmetric or specialized way, by the visual feedback, and by the previous experience of the users.Item Outside-in Priority-based Approximation of 3D Models in LEGO Bricks(The Eurographics Association, 2022) Fanni, Filippo Andrea; Rossi, Elisa De; Giachetti, Andrea; Cabiddu, Daniela; Schneider, Teseo; Allegra, Dario; Catalano, Chiara Eva; Cherchi, Gianmarco; Scateni, RiccardoIn this paper, we discuss the problem of converting a 3D mesh into an assembly of LEGO blocks. The major challenge of this task is how to aggregate the voxels derived by the shape discretization into a set of standard bricks guaranteeing global connectivity. We propose an outside-in priority-based heuristic method based on the analysis of the critical regions that are more likely to cause the creation of a legal assembly to fail. We show that our graph-building heuristic provides relevant advantages, making it easier to obtain a connected graph with good properties with respect to the layer-based or random aggregation strategies applied in most of the optimization approaches. We also propose BRICKS, a novel dataset for the evaluation of aggregation strategies. It includes voxelizations at 3 different resolutions of 33 shapes and allows the easy comparison of different voxel aggregation strategies independently of the shape discretization step and also considering their scalability. We use it to evaluate our approach with respect to graph-based connectivity measures, showing the advantages of the proposed strategy.