Browsing by Author "Marroquim, Ricardo"

Now showing 1 - 6 of 6
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    Accessible Digitisation and Visualisation of Open Cultural Heritage Assets
    (The Eurographics Association, 2019) Medeiros e Sá, Asla; Ibañez Vila, Adolfo Bartolome; Rodriguez Echavarria, Karina; Marroquim, Ricardo; Luiz Fonseca, Vivian; Rizvic, Selma and Rodriguez Echavarria, Karina
    In this research, we proposed a methodology for documenting open and medium-large scale cultural heritage assets. By open we mean both in the sense of their location in open spaces and the fact that they are openly accessible to the public. We take advantage of the maturity of 3D digital technologies for enabling communities across the world to support the documentation of Cultural Heritage (CH) assets that are accessible to the public. For the present project, we focus on producing digital replicas of public sculptures from the Modern period situated in public spaces in Rio de Janeiro. We propose the adoption of an open-source pipeline, based on photogrammetry, which is implemented in separate phases: identification, data acquisition, processing, evaluation, and access. These phases present various challenges, in particular given the medium-large scale of such assets and the variety of spaces in which the assets are located including open spaces and other locations in which it is difficult to control the digitisation conditions. The evaluation and access of the resulting documentation is a key component of such projects. We suggest that community-led approaches have the potential to generate digital resources that are relevant both for professionals and the general public. We discuss various options for access, such as web-based solutions, Augmented Reality (AR) applications, as well as 3D printed digital replicas.
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    AR-Assisted Craniotomy Planning for Tumour Resection
    (The Eurographics Association, 2021) Wooning, Joost; Benmahdjoub, Mohamed; Walsum, Theo van; Marroquim, Ricardo; Oeltze-Jafra, Steffen and Smit, Noeska N. and Sommer, Björn and Nieselt, Kay and Schultz, Thomas
    Craniotomy is a procedure where neurosurgeons open the patient's skull to gain direct access to the brain. The craniotomy's position defines the access path from the skull surface to the tumour and, consequently, the healthy brain tissue to be removed to reach the tumour. This is a complex procedure where a neurosurgeon is required to mentally reconstruct spatial relations of important brain structures to avoid removing them as much as possible. We propose a visualisation method using Augmented Reality to assist in the planning of a craniotomy. The goal of this study is to visualise important brain structures aligned with the physical position of the patient and to allow a better perception of the spatial relations of the structures. Additionally, a heat map was developed that is projected on top of the skull to provide a quick overview of the structures between a chosen location on the skull and the tumour. In the experiments, tracking accuracy was assessed, and colour maps were assessed for use in an AR device. Additionally, we conducted a user study amongst neurosurgeons and surgeons from other fields to evaluate the proposed visualisation using a phantom head. Most participants indeed agree that the visualisation can assist in planning a craniotomy and feedback on future improvements towards the clinical scenario was collected.
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    A New Baseline for Feature Description on Multimodal Imaging of Paintings
    (The Eurographics Association, 2022) Toorn, Jules van der; Wiersma, Ruben; Vandivere, Abbie; Marroquim, Ricardo; Eisemann, Elmar; Ponchio, Federico; Pintus, Ruggero
    Multimodal imaging is used by conservators and scientists to study the composition of paintings. To aid the combined analysis of these digitisations, such images must first be aligned. Rather than proposing a new domain-specific descriptor, we explore and evaluate how existing feature descriptors from related fields can improve the performance of feature-based painting digitisation registration. We benchmark these descriptors on pixel-precise, manually aligned digitisations of ''Girl with a Pearl Earring'' by Johannes Vermeer (c. 1665, Mauritshuis) and of ''18th-Century Portrait of a Woman''. As a baseline we compare against the well-established classical SIFT descriptor. We consider two recent descriptors: the handcrafted multimodal MFD descriptor, and the learned unimodal SuperPoint descriptor. Experiments show that SuperPoint starkly increases description matching accuracy by 40% for modalities with little modality-specific artefacts. Further, performing craquelure segmentation and using the MFD descriptor results in significant description matching accuracy improvements for modalities with many modalityspecific artefacts.
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    A Practical and Efficient Approach for Correct Z-Pass Stencil Shadow Volumes
    (The Eurographics Association, 2019) Usta, Baran; Scandolo, Leonardo; Billeter, Markus; Marroquim, Ricardo; Eisemann, Elmar; Steinberger, Markus and Foley, Tim
    Shadow volumes are a popular technique to compute pixel-accurate hard shadows in 3D scenes. Many variants exist that trade off accuracy and efficiency. In this work, we present an artifact-free, efficient, and easy-to-implement stencil shadow volume method. We compare our method to established stencil shadow volume techniques and show that it outperforms the alternatives.
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    Semi-Automatic Perspective Lines from Paintings
    (The Eurographics Association, 2022) Coudert-Osmont, Yoann; Eisemann, Elmar; Marroquim, Ricardo; Ponchio, Federico; Pintus, Ruggero
    Perspective cues play an important role in painting analysis as it may unveil important characteristics about the painter's techniques and creation process. Nevertheless, extracting perspective lines and their corresponding vanishing points is usually a laborious manual task. Moreover, small variations in the lines may lead to large variations in the vanishing points. In this work, we propose a semi-automatic method to extract perspective lines from paintings in order to mitigate the human variability factor and reduce the workload.
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    What is the Reddening Effect and does it really exist?
    (The Eurographics Association, 2019) Clausen, Olaf; Marroquim, Ricardo; Fuhrmann, Arnulph; Weigand, Holger; Klein, Reinhard and Rushmeier, Holly
    The simulation of light-matter interaction is a major challenge in computer graphics. Particularly challenging is the modelling of light-matter interaction of rough surfaces, which contain several different scales of roughness where many different scattering phenomena take place. There are still appearance critical phenomena that are weakly approximated or even not included at all by current BRDF models. One of these phenomena is the reddening effect, which describes a tilting of the reflectance spectra towards long wavelengths especially in the specular reflection. The observation that the reddening effect takes place on rough surfaces is new and the characteristics and source of the reddening effect have not been thoroughly researched and explained. Furthermore, it was not even clear whether the reddening really exists or the observed effect resulted from measurement errors. In this work we give a short introduction to the reddening effect and show that it is indeed a property of the material reflectance function, and does not originate from measurement errors or optical aberrations.