Abstract
A visual hull is an approximation of a three-dimensional (3-D) object generated by the shape-from-silhouettes (SfS) technique. Because a visual hull is calculated from silhouettes, a visual hull can be represented by silhouette images, encoded by a small number of bits. However, it is challenging to represent the concave regions of a visual hull. In this paper, we model voxel data with a set of visual hulls, thereby handling the concave regions of voxel data. To accomplish this, silhouettes are generated from input voxel data using virtual cameras, and a visual hull is computed by SfS using the silhouettes. To handle the concave regions, we calculate the residuals of visual hulls, and the residuals are represented by visual hulls again. This process is repeated until all concave regions are processed, and a hierarchical data structure, i.e., a visual hull tree, is generated. Because the visual hull tree is constituted from a set of visual hulls, it can represent the details of the voxel data even in the root node. Also, because a set of visual hulls can be represented by silhouettes, a visual hull tree has a small number of bits. From the experiments, we compare our method to the octree-based representation, and our method demonstrates good encoding performance.
Highlights
To represent three-dimensional (3-D) geometry data efficiently, a variety of methods have been proposed
We find the concave regions based on the differences between the 3-D geometry and its visual hull
SfS computes a visual hull using silhouettes, which means that a visual hull is represented by silhouettes that have a small amount of data
Summary
To represent three-dimensional (3-D) geometry data efficiently, a variety of methods have been proposed. We propose a visual hull tree to represent voxel data. We represent voxels as a set of silhouettes used for computing a visual hull using SfS. This implies that while the majority of previous research uses SfS as a tool for generating 3-D contents, we instead use it as a 3-D geometry decoder. Jang et al.: Visual Hull Tree: A New Progressive Method to Represent Voxel Data tree [7]–[9]. The residuals, are represented by silhouettes again This process is repeated until all residuals are calculated, and the visual hull tree is generated.
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