Louis Borgeat

BigBrain: an ultrahigh-resolution 3D human brain model.

Reconstructing the Human Brain Reference brains have become a standard tool in human brain research. Reference brains presently in the public domain provide a spatial framework at the macroscopic level. Amunts et al. (p. 1472) present a high-resolution (20 µm) three-dimensional reconstruction of a human brain. The tool will be freely available to help with interpreting functional neuroimaging studies, fiber tract analyses, and assigning molecular and gene expression data. A freely available microscopic model of human brain architecture with a spatial resolution of 20 micrometers is presented. Reference brains are indispensable tools in human brain mapping, enabling integration of multimodal data into an anatomically realistic standard space. Available reference brains, however, are restricted to the macroscopic scale and do not provide information on the functionally important microscopic dimension. We created an ultrahigh-resolution three-dimensional (3D) model of a human brain at nearly cellular resolution of 20 micrometers, based on the reconstruction of 7404 histological sections. “BigBrain” is a free, publicly available tool that provides considerable neuroanatomical insight into the human brain, thereby allowing the extraction of microscopic data for modeling and simulation. BigBrain enables testing of hypotheses on optimal path lengths between interconnected cortical regions or on spatial organization of genetic patterning, redefining the traditional neuroanatomy maps such as those of Brodmann and von Economo.

GoLD: interactive display of huge colored and textured models

This paper presents a new technique for fast, view-dependent, real-time visualization of large multiresolution geometric models with color or texture information. This method uses geomorphing to smoothly interpolate between geometric patches composing a hierarchical level-of-detail structure, and to maintain seamless continuity between neighboring patches of the model. It combines the advantages of view-dependent rendering with numerous additional features: the high performance rendering associated with static preoptimized geometry, the capability to display at both low and high resolution with minimal artefacts, and a low CPU usage since all the geomorphing is done on the GPU. Furthermore, the hierarchical subdivision of the model into a tree structure can be accomplished according to any spatial or topological criteria. This property is particularly useful in dealing with models with high resolution textures derived from digital photographs. Results are presented for both highly tesselated models (372 million triangles), and for models which also contain large quantities of texture (200 million triangles + 20 GB of compressed texture). The method also incorporates asynchronous out-of-core model management. Performances obtained on commodity hardware are in the range of 50 million geomorphed triangles/second for a benchmark model such as Stanfords St. Matthew dataset.

Visualizing and Analyzing the Mona Lisa

As technologies for acquiring 3D data and algorithms for constructing integrated models evolve, very large data sets representing objects or environments are emerging in various application areas. As a result, significant research in computer graphics has aimed to interactively render such models on affordable commodity computers. Interest is growing in the possibility of integrating real-time analysis and transformation tools in interactive visualization environments as they become more available.

A framework for the registration of color images with 3D models

This paper describes an environment to automatically or semi-automatically compute the precise mapping between a set of 2D images and a triangulated 3D model built from high-resolution 3D range data. This environment is part of our Atelier3D framework for the modeling, visualization and analysis of large sensor-based datasets. This work was done to initially support three cultural heritage application projects: the modeling of the Grotta dei Cervi in Italy, of the Erechtheion in Athens, Greece, and of Leonardos Mona Lisa. The proposed method combines image-based registration, feature matching, robust estimation techniques and advanced multi-resolution rendering with a powerful user interface.

A fast hybrid geomorphing LOD scheme

A significant amount of recent work on real-time multiresolution rendering of triangulated geometric models is built on the concept of iterative edge contraction(e.g. [Hoppe 1997]). The system we have developed is a hybrid method that integrates aspects of this kind of approach and of more classical discrete Level of Detail (LOD) techniques. Our goal was to produce a multiresolution rendering system that would produce minimal visual artifacts when rendering high resolution scene or object datasets produced from sensor data while maintaining the same graphic performance we get with optimized static versions of those models. The first step of the method is to partition the triangular mesh into a set of groups. The model is then globally decimated into a series of discrete LODs using an algorithm based on vertex pair contraction. Each discrete level is repartitioned along the same boundaries. Groups are shaped based on criteria such as compactness, orientation, texture, and desired granularity. At run-time, LOD levels and geomorph ratios between selected levels are computed for each group of the model, these groups are then rendered as precomputed triangle strips. Border points between groups are geomorphed in order to maintain seamless continuity between neighboring LOD groups at all time. To achieve this, we maintain a connexity graph between the various groups and apply a set of simple rules when morphing these points. Morphing is done for space and texture coordinates, normals and color. Adjusting the granularity of the multiresolution rendering through this grouping process provides us with multiple advantages. First, it allows us to extend smooth geomorphs over numerous frames by morphing more triangles over a longer distance rather than expanding/contracting the model by a few polygons every frame. Secondly, each group having a static topology, it can be efficiently rendered as a set of pre-computed triangle strips. These groups can also serve as the units of an anticipative paging algorithm for larger models. Finally, groups can be shaped so that they correspond to rectangular texture images, therefore optimizing texture memory usage and smoothing texture swapping for high resolution models.

Layered surface fluid simulation for surgical training

We present a novel approach to fluid simulation over complex dynamic geometry designed for the specific context of virtual surgery simulation. The method combines a surface-based fluid simulation model with a multi-layer depth peeling representation to allow realistic yet efficient simulation of bleeding on complex surfaces undergoing geometry and topology modifications. Our implementation allows for fast fluid propagation and accumulation over the entire scene, and runs on the GPU at a constant low cost that is independent of the amount of blood in the scene. The proposed bleeding simulation is integrated in a complete simulator for brain tumor resection, where trainees have to manage blood aspiration and tissue/vessel cauterization while they perform virtual surgery tasks.

Issues in acquiring, processing and visualizing large and detailed 3D models

Modelling from reality using active optical geometric sensing has been a very active research area in computer graphics and vision for the last twenty years. While most elements of the modelling pipeline have reached maturity and have been adopted in several application sectors, several issues remain, particularly in the modelling of large structures and environments, as well as in the management of large, complex and detailed 3D models. This paper describes some of these issues, and outlines some of the solutions that we have proposed. These methods and approaches, as well as their current limitations, are described using different example applications: a monument (the Erechtheion), a painting (Mona Lisa), and a terrain model.

Projector-based dual-resolution stereoscopic display

We present a stereoscopic display system which incorporates a high-resolution inset image, or fovea. We describe the specific problem of false depth cues along the boundaries of the inset image, and propose a solution in which the boundaries of the inset image are dynamically adapted as a function of the geometry of the scene. This method produces comfortable stereoscopic viewing at a low additional computational cost. The four projectors need only be approximately aligned: a single drawing pass is required, regardless of projector alignment, since the warping is applied as part of the 3D rendering process.

Foveated stereoscopic display for the visualization of detailed virtual environments

We present a new method for the stereoscopic display of complex virtual environments using a foveated arrangement of four images. The system runs on four rendering nodes and four projectors, for the fovea and periphery in each eye view. The use of high-resolution insets in a foveated configuration is well known. However, its extension to projector-based stereoscopic displays raises a specific issue: the visible boundary between fovea and periphery present in each eye creates a stereoscopic cue that may conflict with the perceived depth of the underlying scene. A previous solution to this problem displaces the boundary in the images to ensure that it is always positioned over stereoscopically corresponding scene locations. The new method proposed here addresses the same problem, but by relaxing the stereo matching criteria and reformulating the problem as one of spatial partitioning, all computations are performed locally on each node, and require a small and fixed amount of post-rendering processing, independent of scene complexity. We discuss this solution and present an OpenGL implementation; we also discuss acceleration techniques using culling and fragments, and illustrate the use of the method on a complex 3D textured model of a Byzantine crypt built using laser range imaging and digital photography.

More than a poplar plank: the shape and subtle colors of the masterpiece Mona Lisa by Leonardo

During the autumn of 2004, a team of 3D imaging scientists from the National Research Council of Canada (NRC) was invited to Paris to undertake the 3D scanning of Leonardos most famous painting. The objective of this project was to scan the Mona Lisa, obverse and reverse, in order to provide high-resolution 3D image data of the complete painting to help in the study of the structure and technique used by Leonardo. Unlike any other painting scanned to date, the Mona Lisa presented a unique research and development challenge for 3D imaging. This paper describes this challenge and presents results of the modeling and analysis of the 3D and color data.