Real-time Surface Analysis and Tagged Material Cleansing for Virtual Colonoscopy

Abstract

The most common representation of volumetric models is a regular grid of cubical voxels with one value each, from which a smooth scalar field is reconstructed. However, common real-world situations include cases in which volumes represent physical objects with well defined boundaries separating different materials, giving rise to models with quasi-impulsive gradient fields. In our split-voxel representation, we replace blocks of N 3 voxels by one single voxel that is split by a feature plane into two regions with constant values. This representation has little overhead over storing precomputed gradients, and has the advantage that feature planes provide minimal geometric information about the underlying volume regions that can be effectively exploited for volume rendering. We show how to convert a standard mono-resolution representation into a out-of-core multiresolution structure, both for labeled and continuous scalar volumes. We also show how to interactively explore the models using a multiresolution GPU raycasting framework. The technique supports real-time transfer function manipulation and proves particularly useful for fast multiresolution rendering, since accurate silhouettes are preserved even at very coarse levels of detail.