Source Codes

Computing Medial Axis Transform with Feature Preservation via Restricted Power Diagram
Abstract: We propose a novel framework for computing the medial axis transform of 3D shapes while preserving their medial features via restricted power diagram (RPD). Medial features, including external features such as the sharp edges and corners of the input mesh surface and internal features such as the seams and junctions of medial axis, are important shape descriptors both topologically and geometrically. However, existing medial axis approximation methods fail to capture and preserve them due to the fundamentally undersampling in the vicinity of medial features, and the difficulty to build their correct connections. In this paper we use the RPD of medial spheres and its affiliated structures to help solve these challenges. The dual structure of RPD provides the connectivity of medial spheres. The surfacic restricted power cell (RPC) of each medial sphere provides the tangential surface regions that these spheres have contact with. The connected components (CC) of surfacic RPC give us the classification of each sphere, to be on a medial sheet, a seam, or a junction. They allow us to detect insufficient sphere sampling around medial features and develop necessary conditions to preserve them. Using this RPD-based framework, we are able to construct high quality medial meshes with features preserved. Compared with existing sampling-based or voxel-based methods, our method is the first one that can preserve not only external features but also internal features of medial axes.
[Paper Download] [Supplement] Ningna Wang, Bin Wang, Wenping Wang, Xiaohu Guo. (2022) "Computing Medial Axis Transform with Feature Preservation via Restricted Power Diagram." ACM Transactions on Graphics (Proceedings of SIGGRAPH Asia 2022), Vol. 41, No. 6, Article No. 188.
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Layered-Garment Net: Generating Multiple Implicit Garment Layers from a Single Image
Abstract: Recent research works have focused on generating human models and garments from their 2D images. However, state-of-the-art researches focus either on only a single layer of the garment on a human model or on generating multiple garment layers without any guarantee of the intersection-free geometric relationship between them. In reality, people wear multiple layers of garments in their daily life, where an inner layer of garment could be partially covered by an outer one. In this paper, we try to address this multi-layer modeling problem and propose the Layered-Garment Net (LGN) that is capable of generating intersection-free multiple layers of garments defined by implicit function fields over the body surface, given the personí»s near front-view image. With a special design of garment indication fields (GIF), we can enforce an implicit covering relationship between the signed distance fields (SDF) of different layers to avoid self-intersections among different garment surfaces and the human body. Experiments demonstrate the strength of our proposed LGN framework in generating multi-layer garments as compared to state-of-the-art methods. To the best of our knowledge, LGN is the first research work to generate intersection-free multiple layers of garments on the human body from a single image.
[Paper Download] [Supplement] Alakh Aggarwal, Jikai Wang, Steven Hogue, Saifeng Ni, Madhukar Budagavi, Xiaohu Guo. (2022) "Layered-Garment Net: Generating Multiple Implicit Garment Layers from a Single Image." in Proceedings of The 16th Asian Conference on Computer Vision (ACCV), pp. 3000-3017, Macau, China, December 2022.
[Source Code]

GPU-based Supervoxel Segmentation for 3D Point Clouds
Abstract: Point cloud processing has received more attention in recent years. Due to the huge amount of data, using supervoxels to pre-segment the points can improve the performance of point cloud processing tasks. There are some supervoxel algorithms generating high-quality results, but their low efficiency hinders the wide application in point cloud processing tasks. In this paper, we try to strike a good balance between the quality and efficiency of point cloud over-segmentation. We propose an algorithm suitable for GPU acceleration, which can generate supervoxel with high efficiency. The algorithm is a seed-based segmentation method, and we carefully design two stages: the clustering stage and optimization stage, each of which can be executed in parallel on the GPU. In the first stage, the algorithm generates an initial segmentation based on well designed energy functions, and the second stage further improves the result by minimizing the segmentation energy. Our method generates good segmentation results and achieves the fastest processing speed compared with the existing methods. We evaluate the supervoxels on three public datasets. Experiments show that our algorithm can generate high-quality segmentation for various point cloud data with high efficiency, which is important for advancing the application of point cloud supervoxels in subsequent processing.
[Paper Download] Xiao Dong, Yanyang Xiao, Zhonggui Chen, Junfeng Yao, Xiaohu Guo. (2022) "GPU-based Supervoxel Segmentation for 3D Point Clouds", in Computer Aided Geometric Design
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FACIAL: Synthesizing Dynamic Talking Face With Implicit Attribute Learning
Abstract: We propose a talking face generation method that takes an audio signal as input and a short target video clip as reference, and synthesizes a photo-realistic video of the target face with natural lip motions, head poses, and eye blinks that are in-sync with the input audio signal. We note that the synthetic face attributes include not only explicit ones such as lip motions that have high correlations with speech, but also implicit ones such as head poses and eye blinks that have only weak correlation with the input audio. To model such complicated relationships among different face attributes with input audio, we propose a FACe Implicit Attribute Learning Generative Adversarial Network (FACIAL-GAN), which integrates the phonetics-aware, context-aware, and identity-aware information to synthesize the 3D face animation with realistic motions of lips, head poses, and eye blinks. Then, our Rendering-to-Video network takes the rendered face images and the attention map of eye blinks as input to generate the photo-realistic output video frames. Experimental results and user studies show our method can generate realistic talking face videos with not only synchronized lip motions, but also natural head movements and eye blinks, with better qualities than the results of state-of-the-art methods.
[Paper Download] [Supplement] Chenxu Zhang, Yifan Zhao, Yifei Huang, Ming Zeng, Saifeng Ni, Madhukar Budagavi, Xiaohu Guo. (2021) "FACIAL: Synthesizing Dynamic Talking Face with Implicit Attribute Learning." Proceedings of IEEE/CVF International Conference on Computer Vision (ICCV), pp.3867-3876.
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GPU-based Supervoxel Generation with a Novel Anisotropic Metric
Abstract: Video over-segmentation into supervoxels is an important pre-processing technique for many computer vision tasks. Videos are an order of magnitude larger than images. Most existing methods for generating supervovels are either memoryor time-inefficient, which limits their application in subsequent video processing tasks. In this paper, we present an anisotropic supervoxel method, which is memory-efficient and can be executed on the graphics processing unit (GPU). Therefore, our algorithm achieves good balance among segmentation quality, memory usage and processing time. In order to provide accurate segmentation for moving objects in video, we use the optical flow information to design a brand new non-Euclidean metric to calculate the anisotropic distances between seeds and voxels. To efficiently compute the anisotropic metric, we adjust the classic jump flooding algorithm (which is designed for parallel execution on the GPU) to generate anisotropic Voronoi tessellation in the combined color and spatio-temporal space. We evaluate our method and the representative supervoxel algorithms for their capability on segmentation performance, computation speed and memory efficiency. We also apply supervoxel results to the application of foreground propagation in videos to test the performance on solving practical problems. Experiments show that our algorithm is much faster than the existing methods, and achieves good balance on segmentation quality and efficiency.
[Paper Download] [Supplement] Xiao Dong, Zhonggui Chen, Yong-Jin Liu, Junfeng Yao, Xiaohu Guo. (2021) "GPU-based Supervoxel Generation with a Novel Anisotropic Metric", in IEEE Transactions on Image Processing, Vol. 30, pp. 8847-8860. DOI: 10.1109/TIP.2021.3120878.  
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Medial Elastics: Efficient and Collision-ready Deformation via Medial Axis Transform
Abstract: We propose a framework for the interactive simulation of nonlinear deformable objects. The primary feature of our system is the seamless integration of deformable simulation and collision culling, which are often independently handled in existing animation systems. The bridge connecting them is the medial axis transform or MAT, a high-fidelity volumetric approximation of complex 3D shapes. From the physics simulation perspective, MAT leads to an expressive and compact reduced nonlinear model. We employ a semi-reduced projective dynamics formulation, which well captures high-frequency local deformations of high-resolution models while retaining a low computation cost. Our key observation is that the most compelling (nonlinear) deformable effects are enabled by the local constraints projection, which should not be aggressively reduced, and only apply model reduction at the global stage. From the collision detection/culling perspective, MAT is geometrically versatile using linear-interpolated spheres (i.e. the so-called medial primitives) to approximate the boundary of the input model. The intersection test between two medial primitives is formulated as a quadratically constrained quadratic program problem. We give an algorithm to solve this problem exactly, which returns the deepest penetration between a pair of intersecting medial primitives. When coupled with spatial hashing, collision (including self-collision) can be efficiently identified on the GPU within few milliseconds even for massive simulations. We have tested our system on a variety of geometrically complex and high-resolution deformable objects, and our system produces convincing animations with all the collisions/self-collisions well handled at an interactive rate.
[Paper Download] Lei Lan, Ran Luo, Marco Fratarcangeli, Weiwei Xu, Huamin Wang, Xiaohu Guo, Junfeng Yao, Yin Yang. (2020) "Medial Elastics: Efficient and Collision-ready Deformation via Medial Axis Transform." ACM Transactions on Graphics  39(3): Article No.20. DOI: 10.1145/3384515
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Plane-Based Optimization of Geometry and Texture for RGB-D Reconstruction of Indoor Scenes
Abstract: We present a novel approach to reconstruct RGB-D indoor scene with plane primitives. Our approach takes as input a RGB-D sequence and a dense coarse mesh reconstructed by some 3D reconstruction method on the sequence, and generate a lightweight, low-polygonal mesh with clear face textures and sharp features without losing geometry details from the original scene. To achieve this, we firstly partition the input mesh with plane primitives, simplify it into a lightweight mesh next, then optimize plane parameters, camera poses and texture colors to maximize the photometric consistency across frames, and finally optimize mesh geometry to maximize consistency between geometry and planes. Compared to existing planar reconstruction methods which only cover large planar regions in the scene, our method builds the entire scene by adaptive planes without losing geometry details and preserves sharp features in the final mesh. We demonstrate the effectiveness of our approach by applying it onto several RGB-D scans and comparing it to other state-of-the-art reconstruction methods.
[Paper Download] Chao Wang, Xiaohu Guo. (2018) "Plane-Based Optimization of Geometry and Texture for RGB-D Reconstruction of Indoor Scenes." Proceedings of 2018 International Conference on 3D Vision (3DV 2018)  pp. 533-541. DOI: 10.1109/3DV.2018.00067
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Superpixel Generation by Agglomerative Clustering with Quadratic Error Minimization
Abstract: Superpixel segmentation is a popular image preprocessing technique in many computer vision applications. In this paper we present a novel superpixel generation algorithm by agglomerative clustering with quadratic error minimization. We use a quadratic error metric (QEM) to measure the difference of spatial compactness and color homogeneity between superpixels. Based on the quadratic function, we propose a bottom-up greedy clustering algorithm to obtain higher quality superpixel segmentation. There are two steps in our algorithm: merging and swapping. First, we calculate the merging cost of two superpixels and iteratively merge the pair with the minimum cost until the termination condition is satisfied. Then, we optimize the boundary of superpixels by swapping pixels according to their swapping cost to improve the compactness. Due to the quadratic nature of the energy function, each of these atomic operations has only O(1) time complexity. We compare the new method with other state-of-the-art superpixel generation algorithms on two datasets, and our algorithm demonstrates superior performance.
[Paper Download] Xiao Dong, Zhonggui Chen, Junfeng Yao, Xiaohu Guo. (2019) "Superpixel Generation by Agglomerative Clustering with Quadratic Error Minimization." Computer Graphics Forum  38(1): 405-416. DOI: 10.1111/cgf.13538
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Surface Approximation via Asymptotic Optimal Geometric Partition
Abstract: In this paper, we present a novel method on surface partition from the perspective of approximation theory. Different from previous shape proxies, the ellipsoidal variance proxy is proposed to penalize the partition results falling into disconnected parts. On its support, the Principle Component Analysis (PCA) based energy is developed for asymptotic cluster aspect ratio and size control. We provide the theoretical explanation on how the minimization of the PCA-based energy leads to the optimal asymptotic behavior for approximation. Moreover, we show the partitions on densely sampled triangular meshes converge to the theoretic expectations. To evaluate the effectiveness of surface approximation, polygonal/triangular surface remeshing results are generated. The experimental results demonstrate the high approximation quality of our method.
[Paper Download] [Supplement] Yiqi Cai, Xiaohu Guo, Yang Liu, Wenping Wang, Weihua Mao, Zichun Zhong. (2017) "Surface Approximation via Asymptotic Optimal Geometric Partition." IEEE Transactions on Visualization and Computer Graphics  23(12): 2613-2626. DOI: 10.1109/TVCG.2016.2623779
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Anisotropic Superpixel Generation Based on Mahalanobis Distance
Abstract: Superpixels have been widely used as a preprocessing step in various computer vision tasks. Spatial compactness and color homogeneity are the two key factors determining the quality of the superpixel representation. In this paper, these two objectives are considered separately and anisotropic superpixels are generated to better adapt to local image content. We develop a unimodular Gaussian generative model to guide the color homogeneity within a superpixel by learning local pixel color variations. It turns out maximizing the log-likelihood of our generative model is equivalent to solving a Centroidal Voronoi Tessellation (CVT) problem. Moreover, we provide the theoretical guarantee that the CVT result is invariant to affine illumination change, which makes our anisotropic superpixel generation algorithm well suited for image/video analysis in varying illumination environment. The effectiveness of our method in image/video superpixel generation is demonstrated through the comparison with other state-of-the-art methods.
[Paper Download] [Supplement] Yiqi Cai, Xiaohu Guo. (2016) "Anisotropic Superpixel Generation Based on Mahalanobis Distance." Computer Graphics Forum  35(7): 199-207. DOI: 10.1111/cgf.13017
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Q-MAT: Computing Medial Axis Transform Using Quadratic Error Minimization
Abstract: The medial axis transform (MAT) is an important shape representation for shape approximation, shape recognition, and shape retrieval. Despite years of research, there is still a lack of effective methods for efficient, robust and accurate computation of the MAT. We present an efficient method, called Q-MAT, that uses quadratic error minimization to compute a structurally simple, geometrically accurate, and compact representation of the MAT. We introduce a new error metric for approximation and a new quantitative characterization of unstable branches of the MAT, and integrate them in an extension of the well-known quadric error metric (QEM) framework for mesh decimation. Q-MAT is fast, removes insignificant unstable branches effectively, and produces a simple and accurate piecewise linear approximation of the MAT. The method is thoroughly validated and compared with existing methods for MAT computation.
[Paper Download] Pan Li, Bin Wang, Feng Sun, Xiaohu Guo, Caiming Zhang, Wenping Wang. (2015) "Q-MAT: Computing Medial Axis Transform Using Quadratic Error Minimization." ACM Transactions on Graphics  35(1): Article No.8. DOI: 10.1145/2753755
[Executable] [Source Code]

Point-Based Manifold Harmonics
Abstract: This paper proposes an algorithm to build a set of orthogonal Point-Based Manifold Harmonic Bases (PB-MHB) for spectral analysis over point-sampled manifold surfaces. To ensure that PB-MHB are orthogonal to each other, it is necessary to have symmetrizable discrete Laplace-Beltrami Operator (LBO) over the surfaces. Existing converging discrete LBO for point clouds, as proposed by Belkin et al [1], is not guaranteed to be symmetrizable. We build a new point-wisely discrete LBO over the point-sampled surface that is guaranteed to be symmetrizable, and prove its convergence. By solving the eigen problem related to the new operator, we define a set of orthogonal bases over the point cloud. Experiments show that the new operator is converging better than other symmetrizable discrete Laplacian operators (such as graph Laplacian) defined on point-sampled surfaces, and can provide orthogonal bases for further spectral geometric analysis and processing tasks.
[Paper Download] Yang Liu, Balakrishnan Prabhakaran, and Xiaohu Guo. (2012) "Point-Based Manifold Harmonics." IEEE Transactions on Visualization and Computer Graphics  18(10): 1693-1703. DOI: 10.1109/TVCG.2011.152
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GPU-Assisted Computation of Centroidal Voronoi Tessellation
Abstract: Centroidal Voronoi tessellations (CVT) are widely used in computational science and engineering. The most commonly used method is Lloyd’s method, and recently the L-BFGS method is shown to be faster than Lloyd’s method for computing the CVT. However, these methods run on the CPU and are still too slow for many practical applications. We present techniques to implement these methods on the GPU for computing the CVT on 2D planes and on surfaces, and demonstrate significant speedup of these GPU-based methods over their CPU counterparts. For CVT computation on a surface, we use a geometry image stored in the GPU to represent the surface for computing the Voronoi diagram on it. In our implementation a new technique is proposed for parallel regional reduction on the GPU for evaluating integrals over Voronoi cells.
[Paper Download] Guodong Rong, Yang Liu, Wenping Wang, Xiaotian Yin, Xianfeng Gu, and Xiaohu Guo. (2010) "GPU-Assisted Computation of Centroidal Voronoi Tessellation." IEEE Transactions on Visualization and Computer Graphics  17(3): 345-356. DOI: 10.1109/TVCG.2010.53
[Source Code for 2D CVT] [Source Code for Surface CVT]