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  • Morpho-volumetric measurement tools for abdominal distension diagnose

     Monclús Lahoya, Eva; Muñoz Pandiella, Imanol; Navazo Alvaro, Isabel; Vazquez Alcocer, Pere Pau; Accarino Garaventa, Anna María; Barba, Elisabeth; Quiroga, Sergi; Azpiroz Vidaur, Fernando
    Congreso Español de Informática Gráfica
    Presentation's date: 2013-09-18
    Presentation of work at congresses

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    Digestive bloating is a very common disease, that, though tightly linked to other better known functional diseases such as functional dyspepsia and irritable intestine syndrome, often appears as isolated disfunction itself. Patients refer episodes of abdominal pressure that are difficult to explain. Through the analysis of CT captures of the patients, using a series of measuring tools developed ad-hoc, we have obtained a better comprehension of these functional digestive diseases that have lead to a proper diagnosis and treatment of such patients. In this paper we present the tools that have been developed to assist physicians in obtaining measures of different morpho-volumetric parameters of the abdominal and pulmonary structures and how these are used in the clinical practice to effectively diagnosing digestive bloating.

  • DAAPMed: a data-aware anchor point selection tool for medical Models in VR environments

     Monclús Lahoya, Eva; Vazquez Alcocer, Pere Pau; Navazo Alvaro, Isabel
    International Joint Conference on Computer Vision, Imaging and Computer Graphics Theory and Applications
    Presentation's date: 2013-02-22
    Presentation of work at congresses

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  • Enhanced Perception in Volume Visualization  Open access

     Díaz Iriberri, José
    Defense's date: 2013-04-26
    Universitat Politècnica de Catalunya
    Theses

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    Due to the nature of scientic data sets, the generation of convenient visualizations may be a difficult task, but crucial to correctly convey the relevant information of the data. When working with complex volume models, such as the anatomical ones, it is important to provide accurate representations, since a misinterpretation can lead to serious mistakes while diagnosing a disease or planning surgery. In these cases, enhancing the perception of the features of interest usually helps to properly understand the data. Throughout years, researchers have focused on different methods to improve the visualization of volume data sets. For instance, the definition of good transfer functions is a key issue in Volume Visualization, since transfer functions determine how materials are classified. Other approaches are based on simulating realistic illumination models to enhance the spatial perception, or using illustrative effects to provide the level of abstraction needed to correctly interpret the data. This thesis contributes with new approaches to enhance the visual and spatial perception in Volume Visualization. Thanks to the new computing capabilities of modern graphics hardware, the proposed algorithms are capable of modifying the illumination model and simulating illustrative motifs in real time. In order to enhance local details, which are useful to better perceive the shape and the surfaces of the volume, our first contribution is an algorithm that employs a common sharpening operator to modify the lighting applied. As a result, the overall contrast of the visualization is enhanced by brightening the salient features and darkening the deeper regions of the volume model. The enhancement of depth perception in Direct Volume Rendering is also covered in the thesis. To do this, we propose two algorithms to simulate ambient occlusion: a screen-space technique based on using depth information to estimate the amount of light occluded, and a view-independent method that uses the density values of the data set to estimate the occlusion. Additionally, depth perception is also enhanced by adding halos around the structures of interest. Maximum Intensity Projection images provide a good understanding of the high intensity features of the data, but lack any contextual information. In order to enhance the depth perception in such a case, we present a novel technique based on changing how intensity is accumulated. Furthermore, the perception of the spatial arrangement of the displayed structures is also enhanced by adding certain colour cues. The last contribution is a new manipulation tool designed for adding contextual information when cutting the volume. Based on traditional illustrative effects, this method allows the user to directly extrude structures from the cross-section of the cut. As a result, the clipped structures are displayed at different heights, preserving the information needed to correctly perceive them.

    Debido a la naturaleza de los datos científicos, visualizarlos correctamente puede ser una tarea complicada, pero crucial para interpretarlos de forma adecuada. Cuando se trabaja con modelos de volumen complejos, como es el caso de los modelos anatómicos, es importante generar imágenes precisas, ya que una mala interpretación de las mismas puede producir errores graves en el diagnóstico de enfermedades o en la planificación de operaciones quirúrgicas. En estos casos, mejorar la percepción de las zonas de interés, facilita la comprensión de la información inherente a los datos. Durante décadas, los investigadores se han centrado en el desarrollo de técnicas para mejorar la visualización de datos volumétricos. Por ejemplo, los métodos que permiten definir buenas funciones de transferencia son clave, ya que éstas determinan cómo se clasifican los materiales. Otros ejemplos son las técnicas que simulan modelos de iluminación realista, que permiten percibir mejor la distribución espacial de los elementos del volumen, o bien los que imitan efectos ilustrativos, que proporcionan el nivel de abstracción necesario para interpretar correctamente los datos. El trabajo presentado en esta tesis se centra en mejorar la percepción de los elementos del volumen, ya sea modificando el modelo de iluminación aplicado en la visualización, o simulando efectos ilustrativos. Aprovechando la capacidad de cálculo de los nuevos procesadores gráficos, se describen un conjunto de algoritmos que permiten obtener los resultados en tiempo real. Para mejorar la percepción de detalles locales, proponemos modificar el modelo de iluminación utilizando una conocida herramienta de procesado de imágenes (unsharp masking). Iluminando aquellos detalles que sobresalen de las superficies y oscureciendo las zonas profundas, se mejora el contraste local de la imagen, con lo que se consigue realzar los detalles de superficie. También se presentan diferentes técnicas para mejorar la percepción de la profundidad en Direct Volume Rendering. Concretamente, se propone modificar la iluminación teniendo en cuenta la oclusión ambiente de dos maneras diferentes: la primera utiliza los valores de profundidad en espacio imagen para calcular el factor de oclusión del entorno de cada pixel, mientras que la segunda utiliza los valores de densidad del volumen para aproximar dicha oclusión en cada vóxel. Además de estas dos técnicas, también se propone mejorar la percepción espacial y de la profundidad de ciertas estructuras mediante la generación de halos. La técnica conocida como Maximum Intensity Projection (MIP) permite visualizar los elementos de mayor intensidad del volumen, pero no aporta ningún tipo de información contextual. Para mejorar la percepción de la profundidad, proponemos una nueva técnica basada en cambiar la forma en la que se acumula la intensidad en MIP. También se describe un esquema de color para mejorar la percepción espacial de los elementos visualizados. La última contribución de la tesis es una herramienta de manipulación directa de los datos, que permite preservar la información contextual cuando se realizan cortes en el modelo de volumen. Basada en técnicas ilustrativas tradicionales, esta técnica permite al usuario estirar las estructuras visibles en las secciones de los cortes. Como resultado, las estructuras de interés se visualizan a diferentes alturas sobre la sección, lo que permite al observador percibirlas correctamente.

  • Efficient algorithms for the realistic simulation of fluids  Open access

     Ojeda Contreras, Jesus
    Defense's date: 2013-05-28
    Universitat Politècnica de Catalunya
    Theses

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    Nowadays there is great demand for realistic simulations in the computer graphics field. Physically-based animations are commonly used, and one of the more complex problems in this field is fluid simulation, more so if real-time applications are the goal. Videogames, in particular, resort to different techniques that, in order to represent fluids, just simulate the consequence and not the cause, using procedural or parametric methods and often discriminating the physical solution. This need motivates the present thesis, the interactive simulation of free-surface flows, usually liquids, which are the feature of interest in most common applications. Due to the complexity of fluid simulation, in order to achieve real-time framerates, we have resorted to use the high parallelism provided by actual consumer-level GPUs. The simulation algorithm, the Lattice Boltzmann Method, has been chosen accordingly due to its efficiency and the direct mapping to the hardware architecture because of its local operations. We have created two free-surface simulations in the GPU: one fully in 3D and another restricted only to the upper surface of a big bulk of fluid, limiting the simulation domain to 2D. We have extended the latter to track dry regions and is also coupled with obstacles in a geometry-independent fashion. As it is restricted to 2D, the simulation loses some features due to the impossibility of simulating vertical separation of the fluid. To account for this we have coupled the surface simulation to a generic particle system with breaking wave conditions; the simulations are totally independent and only the coupling binds the LBM with the chosen particle system. Furthermore, the visualization of both systems is also done in a realistic way within the interactive framerates; raycasting techniques are used to provide the expected light-related effects as refractions, reflections and caustics. Other techniques that improve the overall detail are also applied as low-level detail ripples and surface foam.

  • Best Student paper award of the International Conference on Computer Graphics Theory and Applications

     Monclús Lahoya, Eva; Navazo Alvaro, Isabel; Vazquez Alcocer, Pere Pau
    Award or recognition

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  • Adaptive cross-sections of anatomical models

     Díaz Iriberri, José; Monclús Lahoya, Eva; Navazo Alvaro, Isabel; Vazquez Alcocer, Pere Pau
    Computer graphics forum
    Date of publication: 2012-09
    Journal article

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    Medical illustrations have been used for a long time for teaching and communicating information for diagnosis or surgery planning. Illustrative visualization systems create methods and tools that adapt traditional illustration techniques to enhance the result of renderings. Clipping the volume is a popular operation in volume rendering for inspecting the inner parts, though it may remove some information of the context that is worth preserving. In this paper we present a new editing technique based on the use of clipping planes, direct structure extrusion, and illustrative methods, which preserves the context by adapting the extruded region to the structures of interest of the volumetric model. We will show that users may interactively modify the clipping plane and edit the structures to highlight, in order to easily create the desired result. Our approach works with segmented volume models and non-segmented ones. In the last case, a local segmentation is performed on-the-fly. We will demonstrate the efficiency and utility of our method.

  • Efficient selection of representative views and navigation paths for volume data exploration

     Monclús Lahoya, Eva; Vazquez Alcocer, Pere Pau; Navazo Alvaro, Isabel
    Date of publication: 2012
    Book chapter

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  • Uncertainty visualization of brain fibers

     Hermosilla, Pedro; Brecheisen, Ralph; Vazquez Alcocer, Pere Pau; Vilanova, Anna
    Congreso Español de Informática Gráfica
    Presentation's date: 2012-09-12
    Presentation of work at congresses

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    Full high-dynamic range images for dynamic scenes  Open access

     Ramirez Orozco, Raissel; Martín, Ignacio; Loscos, Céline; Vazquez Alcocer, Pere Pau
    SPIE Photonics Europe: Optics, Photonics, and Digital Technologies for Multimedia
    Presentation's date: 2012-04-17
    Presentation of work at congresses

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    The limited dynamic range of digital images can be extended by composing photographs of the same scene taken with the same camera at the same view point at di erent exposure times. This is a standard procedure for static scenes but a challenging task for dynamic ones. Several methods have been presented but few recover high dynamic range within moving areas. We present a method to recover full high dynamic range (HDR) images from dynamic scenes, even in moving regions. Our method has 3 steps. Firstly, areas a ected by motion are detected to generate a ghost mask. Secondly, we register dynamic objects over a reference image (the best exposed image in the input sequence). Thirdly, we combine the registered input photographs to recover HDR values in a whole image using a weighted average function. Once matching is found, the assembling step guarantees that all aligned pixels will contribute to the nal result, including dynamic content. Tests were made on more than 20 sets of sequences, with moving cars or pedestrians and di erent background. Our results show that Image Mapping Function approach detects best motion regions while Normalized Cross Correlation o ers the best deal speed-accuracy for image registration. Results from our method o ers better result when moving object are roughly rigid and their movement is mostly rigid. The nal composition is an HDR image with no ghosting and all dynamic content present in HDR values.

  • Practical volume rendering in mobile devices

     Balsa Rodriguez, Marcos; Vazquez Alcocer, Pere Pau
    International Symposium on Visual Computing
    Presentation's date: 2012
    Presentation of work at congresses

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  • Using Normalized Compression Distance for image similarity measurement: an experimental study

     Vazquez Alcocer, Pere Pau; Marco Gomez, Jordi
    The visual computer
    Date of publication: 2012-11
    Journal article

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    Similarity metrics are widely used in computer graphics. In this paper, we will concentrate on a new, algorithmic complexity-based metric called Normalized Compression Distance. It is a universal distance used to compare strings. This measure has also been used in computer graphics for image registration or viewpoint selection. However, there is no previous study on how the measure should be used: which compressor and image format are the most suitable. This paper presents a practical study of the Normalized Compression Distance (NCD) applied to color images. The questions we try to answer are: Is NCD a suitable metric for image comparison? How robust is it to rotation, translation, and scaling? Which are the most adequate image formats and compression algorithms? The results of our study show that NCD can be used to address some of the selected image comparison problems, but care must be taken on the compressor and image format selected.

  • Fast illustrative visualization of fiber tracts

     Díaz García, Jesus; Vazquez Alcocer, Pere Pau
    Lecture notes in computer science
    Date of publication: 2012
    Journal article

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  • Multi-modal medical image registration using normalized compression distance

     Vazquez Alcocer, Pere Pau; Marco Gomez, Jordi
    IADIs international journal on computer science and information systems
    Date of publication: 2012
    Journal article

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  • Accurate multi-modal image registration using compression

     Vazquez Alcocer, Pere Pau; Marco Gomez, Jordi
    Computer Graphics, Visualization, Computer Vision and Image Processing
    Presentation's date: 2011-07-26
    Presentation of work at congresses

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    Image registration is an important task in medicine, especially when images have been acquired by different scanner/sensor types, since they provide information on different body structures (bones, muscles, vessels...). Several techniques have been proposed in the past, and among those, Normalized Mutual Information has been proven as successful in many cases. Normalized Compression Distance has been proposed as a simple yet effective technique for image registration. It is especially suitable for the case of CT-MRI registration. However, other image modalities such as PET pose some problems and do not achieve accurate registration. In this paper we analyse and propose a valid approach for image registration using compression that works properly for different combinations of CT, MRI and PET images.

  • Avances en realidad virtual para aplicaciones punteras

     Lligadas Rodriguez, Xavier; Susin Sanchez, Antonio; Brunet Crosa, Pere; Vinacua Pla, Alvaro; Fairen Gonzalez, Marta; Andujar Gran, Carlos A.; Monclús Lahoya, Eva; Vazquez Alcocer, Pere Pau; Campoalegre Vera, Lazaro; Argelaguet Sanz, Fernando; Pelechano Gomez, Nuria; Díaz Iriberri, José; Chica Calaf, Antonio; Cervero Abello, Maria Angels; Ojeda Contreras, Jesus; Beacco Porres, Alejandro; Navazo Alvaro, Isabel
    Participation in a competitive project

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    The ViRVIG institute  Open access

     Andujar Gran, Carlos A.; Navazo Alvaro, Isabel; Vazquez Alcocer, Pere Pau; Patow, Gustavo Ariel; Pueyo, Xavier
    SBC Journal on 3D interactive systems
    Date of publication: 2011-11-16
    Journal article

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    In this paper we present the ViRVIG Institute, a recently created institution that joins two well-known research groups: MOVING in Barcelona, and GGG in Girona. Our main research topics are Virtual Reality devices and interaction techniques, complex data models, realistic materials and lighting, geometry processing, and medical image visualization. We briefly introduce the history of both research groups and present some representative projects. Finally, we sketch our lines for future research.

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    Depth-enhanced maximum intensity projection  Open access

     Díaz Iriberri, José; Vazquez Alcocer, Pere Pau
    International Symposium on Volume Graphics
    Presentation's date: 2010-05
    Presentation of work at congresses

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    The two most common methods for the visualization of volumetric data are Direct Volume Rendering (DVR) and Maximum Intensity Projection (MIP). Direct Volume Rendering is superior to MIP in providing a larger amount of properly shaded details, because it employs a more complex shading model together with the use of user-defined transfer functions. However, the generation of adequate transfer functions is a laborious and time costly task, even for expert users. As a consequence, medical doctors often use MIP because it does not require the definition of complex transfer functions and because it gives good results on contrasted images. Unfortunately, MIP does not allow to perceive depth ordering and therefore spatial context is lost. In this paper we present a new approach to MIP rendering that uses depth and simple color blending to disambiguate the ordering of internal structures, while maintaining most of the details visible through MIP. It is usually faster than DVR and only requires the transfer function used by MIP rendering.

    Postprint (author’s final draft)

  • Cost-effective feature enhancement for volume datasets

     Díaz Iriberri, José; Marco Gomez, Jordi; Vazquez Alcocer, Pere Pau
    Vision, Modeling, and Visualization
    Presentation's date: 2010-11-17
    Presentation of work at congresses

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    Volume models often show high complexity. Local details and overall shape may sometimes be difficult to perceive. Unsharp masking techniques improve the perception of those small features by increasing the local contrast. In this paper we present a simple and fast method for feature enhancement based on 3D mipmaps. In contrast to other approaches, in addition to increasing luminance on the feature details, we also darken the valleys of the volume thus increasing local contrast and making neighboring details more visible. Our approach is fast and simple, with small memory requirements thanks to the use of 3D mipmaps. We also propose a color selection strategy, based on harmonic colors, that further enhances the salient features without abrupt or uncomfortable color changes.

  • NPR effects using the Geometry Shader

     Hermosilla, Pedro; Vazquez Alcocer, Pere Pau
    Date of publication: 2010-06
    Book chapter

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  • INTERACTIVE FRAME RATES FOR GLOBALLY ILLUMINATED SCENES IN PRESENCE OF PARTICIPATING MEDIA

     JIMENEZ PEREZ, JUAN ROBERTO
    Defense's date: 2010-12-16
    Department of Software, Universitat Politècnica de Catalunya
    Theses

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  • Real-time ambient occlusion and halos with Summed Area Tables

     Díaz Iriberri, José; Vazquez Alcocer, Pere Pau; Navazo Alvaro, Isabel; Duguet, Florent
    Computers & graphics
    Date of publication: 2010-08
    Journal article

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  • Single pass GPU stylized edges

     Hermosilla, Pedro; Vazquez Alcocer, Pere Pau
    Ibero-American Symposium in Computer Graphics
    Presentation's date: 2009
    Presentation of work at congresses

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    Silhouette detection is a key issue in many non-photorealistic rendering algorithms. Silhouettes play an important role in shape recognition because they provide one of the main cues for figure-to-ground distinction. However, since silhouettes are view-dependent, they must be computed per frame. There has been a lot of research tailored to find an efficient way to do this in real time, although most algorithms require either a precomputation, and/or multiple rendering passes. In this paper we present an algorithm that is able to generate silhouettes in realtime by using the geometric shader stage. In contrast to other approaches, our silhouettes do not suffer from discontinuities. A second contribution is the definition of a continuous set of texture coordinates that allows us coherently texture the object, independently on the length and orientation of the edges. This texture coordinates are also robust to translation and does not produce sudden changes during rotation.

  • GRUP DE RECERCA EN VISUALITZACIO, REALITAT VIRTUAL I INTERACCIO GRAFICA (VIRVIG)

     Vinacua Pla, Alvaro; Chica Calaf, Antonio; Díaz Iriberri, José; Vazquez Alcocer, Pere Pau; Susin Sanchez, Antonio; Monclús Lahoya, Eva; Andujar Gran, Carlos A.; Fairen Gonzalez, Marta; Cervero Abello, Maria Angels; Ojeda Contreras, Jesus; Lligadas Rodriguez, Xavier; Argelaguet Sanz, Fernando; Pelechano Gomez, Nuria; Campoalegre Vera, Lazaro; Navazo Alvaro, Isabel; Brunet Crosa, Pere
    Participation in a competitive project

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    The Virtual Magic Lantern: an interaction metaphor for enhanced medical data inspection  Open access

     Monclús Lahoya, Eva; Díaz Iriberri, José; Vazquez Alcocer, Pere Pau; Navazo Alvaro, Isabel
    ACM Symposium on Virtual Reality Software and Technology
    Presentation's date: 2009-11-19
    Presentation of work at congresses

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    In this paper we present the Virtual Magic Lantern (VML), an interaction tool tailored to facilitate volumetric data inspection. It behaves like a lantern whose virtual illumination cone provides the focal region which is visualized using a secondary transfer function or different rendering style. This may be used for simple visual inspection, surgery planning, or injure diagnosis. The VML is a particularly friendly and intuitive interaction tool suitable for an immersive Virtual Reality setup with a large screen, where the user moves a Wanda device, like a lantern pointing to the model. We show that this inspection metaphor can be efficiently and easily adapted to a GPU ray casting volume visualization algorithm. We also present the Virtual Magic Window (VMW) metaphor as an efficient collateral implementation of the VML, that can be seen as a restricted case where the lantern illuminates following the viewing direction, through a virtual window created as the intersection of the virtual lantern (guided by the Wanda device) and the bounding box of the volume.

    Postprint (author’s final draft)

  • Automatic view selection through depth-based view stability analysis

     Vazquez Alcocer, Pere Pau
    The visual computer
    Date of publication: 2009-05
    Journal article

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  • MTCut: real time marching tetra cuts

     Monclús Lahoya, Eva; Navazo Alvaro, Isabel; Vazquez Alcocer, Pere Pau
    Theory and Practice of Computer Graphics
    Presentation's date: 2008
    Presentation of work at congresses

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    Isosurface construction and rendering based on tetrahedral grids has been adequately implemented on programmable graphics hardware. In this paper we present MTCut: a volume cutting algorithm that is able to cut isosurfaces obtained by a Marching Tetrahedra algorithm on volume data. It does not require a tetrahedal representation and runs in real time for complex meshes of up to 1.8M triangles. Our algorithm takes as input the isosurface to be cut, and produces the cut geometry in response to the user interaction with a haptic device. The result is a watertight manifold model that can be interactively recovered back to CPU upon user request.

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    Representative views and paths for volume models  Open access

     Vazquez Alcocer, Pere Pau; Monclús Lahoya, Eva; Navazo Alvaro, Isabel
    International Symposium on Smart Graphics
    Presentation's date: 2008
    Presentation of work at congresses

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    Volume data models are becoming larger and larger as the capture technology improves. Thus, their visualization requires high computational power. The automatic presentation of volume models through representative images and/or exploration paths becomes more and more useful. Representative views are also useful for document illustration, fast data quality evaluation, or model libraries documentation. Exploration paths are also useful for video demonstrations and previsualization of captured data. In this paper we present a fast, adaptive method for the selection of representative views and the automatic generation of exploration paths for volume models. Our algorithm is based on multi-scale entropy and algorithmic complexity. These views and paths reveal informative parts of a model given a certain transfer function. We show that our method is simple and easy to incorporate in medical visualization tools.

    Postprint (author’s final draft)

  • S3Dc: a 3Dc-based volume compression algorithm

     Yela, H; Navazo Alvaro, Isabel; Vazquez Alcocer, Pere Pau
    Congreso Español de Informática Gráfica
    Presentation's date: 2008
    Presentation of work at congresses

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    Volumes acquired for medical purposes are continuously increasing in size, faster than graphic cards memory capacity. Large volumetric datasets do not fit into GPU memory and therefore direct rendering is not possible. Even large volumes that still fit into GPU memory make frame rates decay. In order to reduce the size of large volumetric models, we present a new compression scheme. In this paper we present S3Dc, a lossy volume compression algorithm suitable for scalar values. It is inspired in hardware-accelerated 3Dc normal compression technique. S3Dc allows us to compress the volume in CPU up to a 4:1 or 8:1 ratio, while still yielding good quality results. We provide details on the compression scheme and show how to render directly from a S3Dc compressed texture. Furthermore, we analyze the image quality theoretical error and the average error with several images in order to assess the results.

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    Automatic generation of exploration paths for medical models  Open access

     Monclús Lahoya, Eva; Navazo Alvaro, Isabel; Vazquez Alcocer, Pere Pau; Herrero Jover, Javier; López, Jordi
    International journal of computer assisted radiology and sugery (Online)
    Date of publication: 2008
    Journal article

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    Although the visualization techniques are becoming faster and faster, the datasets also increase, and the time the radiologists are able to devote to a single analysis is limited. In this sense, we propose some techniques to help the specialists to find adequate views of the datasets in an efficient way.

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    Vicinity occlusion maps: enhanced depth perception of volumetric models  Open access

     Díaz Iriberri, José; Yela Reneses, Hector; Vazquez Alcocer, Pere Pau
    Computer Graphics International
    Presentation's date: 2008-06-09
    Presentation of work at congresses

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    Volume models often show high depth complexity. This poses di±culties to the observer in judging the spatial relationships accurately. Illustrators usually use certain techniques such as halos or edge darkening in order to enhance depth perception of certain structures. Halos may be dark or light, and even colored. Halo construction on a volumetric basis impacts rendering performance due to the complexity of the construction process. In this paper we present Vicinity Occlusion Maps: a simple and fast method to compute the light occlusion due to neighboring voxels. Vicinity Occlusion Maps may be used to generate flexible halos around objects or selected structures in order to enhance depth perception or accentuate the presence of some structures in volumetric models at a low cost. The user may freely select the structure that requires the halos to be generated, its color and size, and our proposed application generates those in real time. They may also be used to perform vicinity shading in realtime, or even to combine both effects.

    Postprint (author’s final draft)

  • A 3D virtual model for training in endoscopical repair of subcondylar fractures of the mandible

     Hueto, J A; Díaz Iriberri, José; Monclús Lahoya, Eva; Navazo Alvaro, Isabel; Vazquez Alcocer, Pere Pau; Raspall, G
    International journal of computer assisted radiology and sugery
    Date of publication: 2008-09
    Journal article

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    Conventional treatment of the subcondylar fractures of the mandible is challenging because of the medial and anterior displacement of the condylar fragment and the limited surgical field. Proximity of facial nerve, carotid artery branches, parotid gland, and ear canal are risk factors to open surgical procedures. In these fractures a proper reduction and osteosynthesis are always difficult, even if using open procedures. The recent endoscopic approach allows a perfect control and vision of the fragments, and it also permits an anatomic reduction and plating of the fracture avoiding risks associated to the open surgery. Surgical training for these endoscopic procedures is difficult, especially in those cases in which surgeons are not familiar with endoscopic interventions and they still don’t have skills to work while looking at the screen. Simulators are friendly and risk free systems to train surgeons to operate with endoscopes.

  • An interactive 3D framework for anatomical education

     Vazquez Alcocer, Pere Pau; Götzelmann, Timo; Hartmann, Knut; Nürnberger, Andreas
    International journal of computer assisted radiology and sugery
    Date of publication: 2008-12
    Journal article

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    Object: This paper presents a 3D framework for Anatomy teaching. We are mainly concerned with the proper understanding of human anatomical 3D structures. Materials and methods: The main idea of our approach is taking an electronic book such as Henry Gray’s Anatomy of the human body, and a set of 3D models properly labeled, and constructing the correct linking that allows users to perform mutual searches between both media. Results: We implemented a system where learners can interactively explore textual descriptions and 3D visualizations. Conclusion: Our approach allows easily performing two search tasks: first, the user may select a text region and get a view showing the objects that contain the selected structures, and second, using the interactive exploration of a 3D model the user may automatically search for the textual description of the structures visible in the current view.

  • Rendering falling leaves on graphics hardware

     Vazquez Alcocer, Pere Pau; Balsa, Marcos
    Journal of virtual reality and broadcasting
    Date of publication: 2008-03
    Journal article

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  • Omni-directional relief impostors

     Andujar Gran, Carlos A.; Boo, J; Brunet Crosa, Pere; Fairen Gonzalez, Marta; Navazo Alvaro, Isabel; Vazquez Alcocer, Pere Pau; Vinacua Pla, Alvaro
    Computer graphics forum
    Date of publication: 2007-07
    Journal article

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  • Tessellation-Independent Best View Selection

     Vazquez Alcocer, Pere Pau; Andujar Gran, Carlos A.
    International Conference on Computer Graphics and Artificial Intelligence
    Presentation of work at congresses

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  • Correlating text and images: concept and evaluation

     Götzelmann, Timo; Vazquez Alcocer, Pere Pau; Hartmann, Knut; Nürnberger, Andreas; Strothotte, Thomas
    International Symposium on Smart Graphics
    Presentation's date: 2007-06
    Presentation of work at congresses

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    This paper presents the concept and an evaluation of a novel approach to support students to understand complex spatial relations and to learn unknown terms of a domain-specific terminology with coordinated textual descriptions and illustrations. Our approach transforms user interactions into queries to an information retrieval system. By selecting text segments or by adjusting the view to interesting domain objects, learners can request additional contextual information. Therefore, the system uses pre-computed multi-level representations of the content of explanatory text and of views on 3D models to suggest textual descriptions or views on 3D objects that might support the current learning task. Our experimental application is evaluated by a user study that analyzes (i) similarity measures that are used by the information retrieval system to coordinate the content of descriptive texts and computer-generated illustrations and (ii) the impact of the individual components of these measures. Our study revealed that the retrieved results match the preferences of the users. Furthermore, the statistical analysis suggests a rough value to cut-off retrieval results according to their relevancy.

  • MTCut: GPU-based Marching Tetra Cuts

     Monclús Lahoya, Eva; Navazo Alvaro, Isabel; Vazquez Alcocer, Pere Pau
    Date: 2007-01
    Report

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  • MTCut: GPU-based Marching Tetra Cuts

     Monclús Lahoya, Eva; Navazo Alvaro, Isabel; Vazquez Alcocer, Pere Pau
    Date: 2007-01
    Report

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  • Real Time Falling Leaves

     Vazquez Alcocer, Pere Pau; Balsa, Marcos
    Date: 2007-01
    Report

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  • Real Time Falling Leaves

     Vazquez Alcocer, Pere Pau; Balsa, Marcos
    Second International Conference on Computer Graphics Theory and Applications, 2007
    Presentation of work at congresses

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  • Access to the full text
    Automatic light source placement for maximum visual information recovery  Open access

     Vazquez Alcocer, Pere Pau
    Computer graphics forum
    Date of publication: 2007-06
    Journal article

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    The automatic selection of good viewing parameters is a very complex problem. In most cases, the notion of good strongly depends on the concrete application. Moreover, when an intuitive definition of good view is available, it is often difficult to establish a measure that brings it to the practice. Commonly, two kinds of viewing parameters must be set: camera parameters (position and orientation) and lighting parameters (number of light sources, its position and eventually the orientation of the spot). The first ones will determine how much of the geometry can be captured and the latter will influence on how much of it is revealed (i. e. illuminated) to the user. Unfortunately, ensuring that certain parts of a scene are lit does not make sure that the details will be communicated to the user, as the amount of illumination might be too small or too high. In this paper we define a metric to calculate the amount of information relative to an object that is effectively communicated to the user given a fixed camera position. This measure is based on an information-based concept, the Shannon entropy, and will be applied to the problem of automatic selection of light positions in order to adequately illuminate an object. In order to validate the results, we have carried out an experiment on users, this experiment helped us to explore other related measures.

    The definitive version is available at http://onlinelibrary.wiley.com/doi/10.1111/j.1467-8659.2007.00944.x/abstract

  • Programación en C++ para ingenieros

     Xhafa Xhafa, Fatos; Vazquez Alcocer, Pere Pau; Marco Gomez, Jordi; Molinero Albareda, Xavier; Martin Prat, Angela
    Date of publication: 2006-04
    Book

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  • Semi-presencialitat a través de la compartició de la informació i del coneixement virtualment (SCIC-v)

     Xhafa Xhafa, Fatos; Marco Gomez, Jordi; Vazquez Alcocer, Pere Pau
    Jornada d'Innovació Docent UPC
    Presentation of work at congresses

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  • A programmable Tutor for OpenGL Transformations

     Vazquez Alcocer, Pere Pau; Andujar Gran, Carlos A.
    EuroGraphics
    Presentation of work at congresses

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  • Realtime automatic selection of good molecular views

     Vazquez Alcocer, Pere Pau
    Computers & graphics
    Date of publication: 2006-02
    Journal article

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  • Generación de penumbras con hardware gráfico

     Susín, Dani; Vazquez Alcocer, Pere Pau
    Novática: revista de la Asociación de Técnicos de Informática
    Date of publication: 2005-10
    Journal article

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  • Using Computer-Supported Collaborative Work in Fundamental Programming Subjects

     Xhafa Xhafa, Fatos; Vazquez Alcocer, Pere Pau; Marco Gomez, Jordi; Martin Prat, Angela
    Congrés Internacional de Docència Universitària i Innovació
    Presentation of work at congresses

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  • Bandwidth reduction for remote navigation systems through view prediction and progressive transmission

     Vazquez Alcocer, Pere Pau; Sbert Cassasayas, Mateu
    Future generation computer systems
    Date of publication: 2004
    Journal article

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    Remote navigation systems, such as exploration of virtual 3D worlds or remote surgery, usually require higher bandwidth than the Internet connection commonly available at home. In this paper,we explore a set of techniques to reduce the bandwidth required by these applications. Our system consists of a client PC equipped with a graphics card, and a remote high-end server. The server hosts the remote environment and does the actual rendering of the scenes for several clients, and the new image is passed to them. This scheme is suitable when the data has a copyright or when its size may exceed the rendering capabilities of the client. The general scheme is the following: each time the position changes, the newviewis predicted by both the client and the server and the difference information between the predicted view and the correct one is sent to the client. To reduce bandwidth we can improve the prediction method, and the transmission system. We present here two groups of techniques: First, a set of lossless methods which achieve reductions of up to a 9:1 ratio. These are a combination of a two-level forward warping, that takes advantage of spatial coherence, and a masking method, which allows to transmit only the information that really needs to be updated. Second, a set of lossy methods suitable for very low bandwidth environments which involve both progressive transmission and image reuse. They consider relevant parameters such as the number of pixels, the amount of information they provide, and their colour deviation in order to create a strategy for prioritizing the information transmission. This system allows to improve up to an additional 4:1 ratio. The quality of the generated images is very high, and often indistinguishable from the correct ones.

  • Way-finder: guided tours through complex walkthrough models

     Andujar Gran, Carlos A.; Vazquez Alcocer, Pere Pau; Fairen Gonzalez, Marta
    Computer graphics forum
    Date of publication: 2004-09
    Journal article

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    The exploration of complex walkthrough models is often a difficult task due to the presence of densely occluded regions which pose a serious challenge to online navigation. In this paper we address the problem of algorithmic generation of exploration paths for complex walkthrough models. We present a characterization of suitable properties for camera paths and we discuss an efficient algorithm for computing them with little or no user intervention. Our approach is based on identifying the free-space structure of the scene (represented by a cell and portal graph) and an entropy-based measure of the relevance of a view-point. This metric is key for deciding which cells have to be visited and for computing critical way-points inside each cell. Several results on different model categories are presented and discussed.

  • Introducing semi-open learning/teaching into fundamental programming subjects

     Xhafa Xhafa, Fatos; Marco Gomez, Jordi; Vazquez Alcocer, Pere Pau
    Congrés Internacional de Docència Universitària i Innovació
    Presentation of work at congresses

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