Joint reversible watermarking and progressive compression of 3D meshes

A new reversible 3D mesh watermarking scheme is proposed in conjunction with progressive compression. Progressive 3D mesh compression permits a progressive refinement of the model from a coarse to a fine representation by using different levels of detail (LoDs). A reversible watermark is embedded into all refinement levels such that (1) the refinement levels are copyright protected, and (2) an authorized user is able to reconstruct the original 3D model after watermark extraction, hence reversible. The progressive compression considers a connectivity-driven algorithm to choose the vertices that are to be refined for each LoD. The proposed watermarking algorithm modifies the geometry information of these vertices based on histogram bin shifting technique. An authorized user can extract the watermark in each LoD and recover the original 3D mesh, while an unauthorized user which has access to the decompression algorithm can only reconstruct a distorted version of the 3D model. Experimental results show that the proposed method is robust to several attack scenarios while maintaining a good compression ratio.     

Fast accessing Web3D contents using lightweight progressive meshes

Accessing Web3D contents is relatively slow through Internet under limited bandwidth. Preprocessing of 3D models can certainly alleviate the problem, such as 3D compression and progressive meshes (PM). But none of them considers the similarity between components of a 3D model, so that we could take advantage of this to further improve the efficiency. This paper proposes a similarity‐aware data reduction method together with PM, called lightweight progressive meshes (LPM). LPM aims to excavate similar components in a 3D model, generates PM representation of each component left after removing redundant components, and organizes all the processed data using a structure called lightweight scene graph. The proposed LPM possesses four significant advantages. First, it can minimize the file size of 3D model dramatically without almost any precision loss. Because of this, minimal data is delivered. Second, PM enables the delivery to be progressive, so called streaming. Third, when rendering at client side, due to lightweight scene graph, decompression is not necessary and instanced rendering is fully exerted. Fourth, it is extremely efficient and effective under very limited bandwidth, especially when delivering large 3D scenes. Performance on real data justifies the effectiveness of our LPM, which improves the state‐of‐the‐art in accessing Web3D contents. Copyright © 2015 John Wiley & Sons, Ltd.     

关于三维网格压缩和渐进传输问题的几点探讨

通过对渐进网格（PM）和压缩渐进网格（CPM）技术的探讨,提出了在采用线性插值的方法分批传输压缩数据的同时,动态细化3D模型的几何网格。相应地,对CPM算法进行了简化,以减少解压时的开销,在CPM的基础上使渐进细化网格有更好的显示效果。     

Combined compression and simplification of dynamic 3D meshes

We present a new approach to dynamic mesh compression, which combines compression with simplification to achieve improved compression results, a natural support for incremental transmission and level of detail. The algorithm allows fast progressive transmission of dynamic 3D content. Our scheme exploits both temporal and spatial coherency of the input data, and is especially efficient for the case of highly detailed dynamic meshes. The algorithm can be seen as an ultimate extension of the clustering and local coordinate frame (LCF)‐based approaches, where each vertex is expressed within its own specific coordinate system. The presented results show that we have achieved better compression efficiency compared to the state of the art methods. Copyright © 2008 John Wiley & Sons, Ltd.     

Progressive 3D mesh compression using MOG-based Bayesian entropy coding and gradual prediction

A progressive 3D triangular mesh compression algorithm built on the MOG-based Bayesian entropy coding and the gradual prediction scheme is proposed in this work. For connectivity coding, we employ MOG models to estimate the posterior probabilities of topology symbols given vertex geometries. Then, we encode the topology symbols using an arithmetic coder with different contexts, which depend on the posterior probabilities. For geometry coding, we propose the gradual prediction labeling and the dual-ring prediction to divide vertices into groups and predict later groups more efficiently using the information in already encoded groups. Simulation results demonstrate that the proposed algorithm provides significantly better performance than the conventional wavemesh coder, with the average bit rate reduction of about 16.9 %.     

Partitioning 3D surface meshes using watershed segmentation

This paper describes a method for partitioning 3D surface meshes into useful segments. The proposed method generalizes morphological watersheds, an image segmentation technique, to 3D surfaces. This surface segmentation uses the total curvature of the surface as an indication of region boundaries. The surface is segmented into patches, where each patch has a relatively consistent curvature throughout, and is bounded by areas of higher, or drastically different, curvature. This algorithm has applications for a variety of important problems in visualization and geometrical modeling including 3D feature extraction, mesh reduction, texture mapping 3D surfaces, and computer aided design     

3D face detection using curvature analysis

Face detection is a crucial preliminary in many applications. Most of the approaches to face detection have focused on the use of two-dimensional images. We present an innovative method that combines a feature-based approach with a holistic one for three-dimensional (3D) face detection. Salient face features, such as the eyes and nose, are detected through an analysis of the curvature of the surface. Each triplet consisting of a candidate nose and two candidate eyes is processed by a PCA-based classifier trained to discriminate between faces and non-faces. The method has been tested, with good results, on some 150 3D faces acquired by a laser range scanner.     

Numerical simulation of multiple 3D fracture propagation using arbitrary meshes

This paper describes a mesh-independent finite element based method for propagating fractures in three dimensions. The iterative algorithm automatically grows fractures in a 3D brittle medium represented by an isotropic linear elastic matrix. Growth is controlled by an input failure and propagation criterion. The geometry and mesh are stored separately, and mesh refinement is topologically guided. Propagation results in the modification of crack geometry, as opposed to changes in the mesh, as the arbitrary tetrahedral mesh adapts to the evolving geometry. Stress intensity factors are computed using the volumetric J Integral on a virtual piecewise cylinder. Modal stress intensity factors are computed using the decomposition method. Mesh and cylinder size effects are studied, as is computational efficiency. A through-going crack embedded in a thick slab, and a horizontal and inclined penny-shape crack, are used to validate the accuracy of the method. The predicted stress intensity factors are in good agreement with analytical solutions. For six integration points per tip segment, integration local to single tips, and a cylinder radius that adapts to the local geometric conditions, results agree with analytical solutions with less than 5% deviation from experimental results.     

Rate-distortion optimization for progressive compression of 3D mesh with color attributes

We propose a new lossless progressive compression algorithm based on rate-distortion optimization for meshes with color attributes; the quantization precision of both the geometry and the color information is adapted to each intermediate mesh during the encoding/decoding process. This quantization precision can either be optimally determined with the use of a mesh distortion measure or quasi-optimally decided based on an analysis of the mesh complexity in order to reduce the calculation time. Furthermore, we propose a new metric which estimates the geometry and color importance of each vertex during the simplification in order to faithfully preserve the feature elements. Experimental results show that our method outperforms the state-of-the-art algorithm for colored meshes and competes with the most efficient algorithms for non-colored meshes.     

Efficient view-dependent refinement of 3D meshes using sqrt{3}-subdivision

In this paper we introduce an efficient view-dependent refinement technique well suited to adaptive visualization of 3D triangle meshes on a graphic terminal. Our main goal is the design of fast and robust, smooth surface reconstruction from coarse meshes. We demonstrate that the sqrt{3}-subdivision operator recently introduced by Kobbelt offers many benefits, including view-dependent refinement, removal of polygonal aspect and a highly tunable level of detail adaptation. In particular, we propose a new data structure that requires neither edges nor hierarchies for efficient and reversible view-dependent refinement. Results on various 3D meshes illustrate the relevance of the technique.     

Generation of 3D mixed element meshes using a flexible refinement approach

This paper describes and discusses the main characteristics and implementation issues of a 3D mixed element mesh generator based on a generalization of the modified octree approach. This mesh generator uses primitive elements of different type as internal nodes, a flexible refinement approach as refinement strategy (primitive elements are not always bisected), and bricks, pyramids, prisms and tetrahedra as final elements. The mesh generation process is divided in several steps: the generation of the initial mesh composed of primitive elements, the refinement of primitive elements until the point density requirements are fulfilled, the generation of a graded mesh between dense and coarse regions, and finally, the recognition of the final elements. The main algorithms and data structures are described in detail for each step of the mesh generation process. As result, examples of meshes that satisfy the Delaunay condition and that can be used with the control volume method are shown.     

Metamorphosis of 3D polyhedral models using progressive connectivity transformations

Three-dimensional (3D) metamorphosis is a powerful technique to produce a 3D shape transformation between two or more existing models. We propose a novel 3D morphing technique that avoids creating a merged embedding that contains the faces, edges, and vertices of two given embeddings. This novel 3D morphing technique dynamically adds or removes vertices to gradually transform the connectivity of 3D polyhedrons from a source model into a target model and simultaneously creates the intermediate shapes. In addition, a priority control function provides the animators with control of arising or dissolving of input models' features in a morphing sequence. This is a useful tool to control a morphing sequence more easily and flexibly. Several examples of aesthetically pleasing morphs are demonstrated using the proposed method.     

A progressive transmission capable diagnostically lossless compression scheme for 3D medical image sets

This paper presents a novel and efficient diagnostically lossless compression for 3D medical image sets. This compression scheme provides the 3D medical image sets with a progressive transmission capability. An automated filter-and-threshold based preprocessing technique is used to remove noise outside the diagnostic region. Then a wavelet decomposition feature vector based approach is applied to determine the reference image for the entire 3D medical image set. The selected reference image contains the most discernible anatomical structures within a relative large diagnostic region. It is progressively encoded by a lossless embedded zerotree wavelet method so the validity of an entire set can be determined early. This preprocessing technique is followed by an optimal predictor plus a 1st-level integer wavelet transform to de-correlate the 3D medical image set. Run-length and arithmetic coding are used to further remove coding redundancy. This diagnostically lossless compression method achieves an average compression of 2.1038, 2.4292, and 1.6826 bits per pixel for three types of 3D magnetic resonance image sets. The integrated progressive transmission capability degrades the compression performance by an average of 7.25%, 6.60%, and 4.49% for the above three types. Moreover, our compression without and with progressive transmission achieves better compression than the state-of-the-art.     

Conformal spherical representation of 3D genus-zero meshes

This paper describes an approach of representing 3D shape by using a set of invariant spherical harmonic (SH) coefficients after conformal mapping. Specifically, a genus-zero 3D mesh object is first conformally mapped onto the unit sphere by using a modified discrete conformal mapping, where the modification is based on Möbius factorization and aims at obtaining a canonical conformal mapping. Then a SH analysis is applied to the resulting conformal spherical mesh. The obtained SH coefficients are further made invariant to translation and rotation, while at the same time retain the completeness, thanks to which the original shape information has been faithfully preserved.     

Predictive compression of animated 3D models by optimized weighted blending of key‐frames

Efficient compression techniques are required for animated mesh sequences with fixed connectivity and time‐varying geometry. In this paper, we propose a key‐frame‐based technique for three‐dimensional dynamic mesh compression. First, key‐frames are extracted from the animated sequence. Extracted key‐frames are then linearly combined using blending weights to predict the vertex locations of the other frames. These blending weights play a key role in the proposed algorithm because the prediction performance and the required number of key‐frames greatly depend on these weights. We present a novel method in order to compute the optimum blending weight that makes it possible to predict location of the vertices of the non‐key frames with the minimum number of key‐frames. The residual prediction errors are finally quantized and encoded using Huffman coding and another heuristic method. Experimental results on different test sequences with various sizes, topologies, and geometries demonstrate the privileged performance of the proposed method compared with the previous techniques. Copyright © 2015 John Wiley & Sons, Ltd.     

An optimized GPU implementation of a 2D free surface simulation model on unstructured meshes

This work is related with the implementation of a finite volume method to solve the 2D Shallow Water Equations on Graphic Processing Units (GPU). The strategy is fully oriented to work efficiently with unstructured meshes which are widely used in many fields of Engineering. Due to the design of the GPU cards, structured meshes are better suited to work with than unstructured meshes. In order to overcome this situation, some strategies are proposed and analyzed in terms of computational gain, by means of introducing certain ordering on the unstructured meshes. The necessity of performing the simulations using unstructured instead of structured meshes is also justified by means of some test cases with analytical solution.     

A 3D stroke based representation of sign language signs using key maximum curvature points and 3D chain codes

Multimedia Tools and Applications - Sign Language is a visual spatial language used by deaf and dumb community to convey their thoughts and ideas with the help of hand gestures and facial...     

External force generation for object segmentation on 3D ultrasound images using simplex meshes

Three algorithms of simplex mesh external force generation are presented. The algorithms are used for simplex meshes adaptation to manually traced object boundaries on several representative non-parallel cross sections of 3D ultrasound images. A morphing algorithm for the transformation between two simplex meshes is also considered. The text was submitted by the authors in English. This work was supported by ISTC, project no. B-517.     

Detail control in line drawings of 3D meshes

We address the problem of rendering a 3D mesh in the style of a line drawing, in which little or no shading is used and instead shape cues are provided by silhouettes and suggestive contours. Our specific goal is to depict shape features at a chosen scale. For example, when mesh triangles project into the image plane at subpixel sizes, both suggestive contours and silhouettes may form dense networks that convey shape poorly. The solution we propose is to convert the input mesh to a multiresolution representation (specifically, a progressive mesh), then view-dependently refine or coarsen the mesh to control the size of its triangles in image space. We thereby control the scale of shape features that are depicted via silhouettes and suggestive contours. We propose a novel refinement criterion that achieves this goal and address the problem of maintaining temporal coherence of silhouette and suggestive contours when extracting them from a changing mesh.     

Analysis of an EMST-based path for 3D meshes

For several 3D data applications such as data-hiding or compression, data ordering is a major problem. We need to know how to achieve the same 3D mesh path between the coding and decoding stages. Various algorithms have been proposed in recent years, but we focus on methods based on Euclidean Minimum Spanning Trees (EMST). In this paper, we analyse the sensitivity of the EMST structure to obtain a more robust synchronization. We present a new theoretical analysis and a way to visualize EMST robustness. Moreover, this analysis can be useful in 3D data-hiding in order to detect fragile area and to predict the 3D object robustness during transmission on a noisy channel.