Browsing by Author "Zhang, Xiaopeng"

Now showing 1 - 6 of 6
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    Customized Summarizations of Visual Data Collections
    (© 2021 Eurographics ‐ The European Association for Computer Graphics and John Wiley & Sons Ltd, 2021) Yuan, Mengke; Ghanem, Bernard; Yan, Dong‐Ming; Wu, Baoyuan; Zhang, Xiaopeng; Wonka, Peter; Benes, Bedrich and Hauser, Helwig
    We propose a framework to generate customized summarizations of visual data collections, such as collections of images, materials, 3D shapes, and 3D scenes. We assume that the elements in the visual data collections can be mapped to a set of vectors in a feature space, in which a fitness score for each element can be defined, and we pose the problem of customized summarizations as selecting a subset of these elements. We first describe the design choices a user should be able to specify for modeling customized summarizations and propose a corresponding user interface. We then formulate the problem as a constrained optimization problem with binary variables and propose a practical and fast algorithm based on the alternating direction method of multipliers (ADMM). Our results show that our problem formulation enables a wide variety of customized summarizations, and that our solver is both significantly faster than state‐of‐the‐art commercial integer programming solvers and produces better solutions than fast relaxation‐based solvers.
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    Deep Deformation Detail Synthesis for Thin Shell Models
    (The Eurographics Association and John Wiley & Sons Ltd., 2023) Chen, Lan; Gao, Lin; Yang, Jie; Xu, Shibiao; Ye, Juntao; Zhang, Xiaopeng; Lai, Yu-Kun; Memari, Pooran; Solomon, Justin
    In physics-based cloth animation, rich folds and detailed wrinkles are achieved at the cost of expensive computational resources and huge labor tuning. Data-driven techniques make efforts to reduce the computation significantly by utilizing a preprocessed database. One type of methods relies on human poses to synthesize fitted garments, but these methods cannot be applied to general cloth animations. Another type of methods adds details to the coarse meshes obtained through simulation, which does not have such restrictions. However, existing works usually utilize coordinate-based representations which cannot cope with large-scale deformation, and requires dense vertex correspondences between coarse and fine meshes. Moreover, as such methods only add details, they require coarse meshes to be sufficiently close to fine meshes, which can be either impossible, or require unrealistic constraints to be applied when generating fine meshes. To address these challenges, we develop a temporally and spatially as-consistent-as-possible deformation representation (named TS-ACAP) and design a DeformTransformer network to learn the mapping from low-resolution meshes to ones with fine details. This TS-ACAP representation is designed to ensure both spatial and temporal consistency for sequential large-scale deformations from cloth animations. With this TS-ACAP representation, our DeformTransformer network first utilizes two mesh-based encoders to extract the coarse and fine features using shared convolutional kernels, respectively. To transduct the coarse features to the fine ones, we leverage the spatial and temporal Transformer network that consists of vertex-level and frame-level attention mechanisms to ensure detail enhancement and temporal coherence of the prediction. Experimental results show that our method is able to produce reliable and realistic animations in various datasets at high frame rates with superior detail synthesis abilities compared to existing methods.
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    Feature Curve Network Extraction via Quadric Surface Fitting
    (The Eurographics Association, 2019) Zhengda, Lu; Guo, Jianwei; Xiao, Jun; Wang, Ying; Zhang, Xiaopeng; Yan, Dong-Ming; Lee, Jehee and Theobalt, Christian and Wetzstein, Gordon
    Feature curves on 3D shapes provide a high dimensional representation of the geometry and reveal their underlying structure. In this paper, we present an automatic approach for extracting complete feature curve networks from 3D models, as well as generating a high-quality patch layout. Starting from an initial collection of noisy and fragmented feature curves, we first filter non-salient or noisy feature curves by utilizing a quadric surface fitting technique. We then handle the curve intersections and curve missing by conducting a feature extension step to form a closed feature curve network. Finally, we generate a patch layout to reveal a highly structured representation of the input surfaces. Experimental results demonstrate that our algorithm is robust for extracting complete feature curve networks from complex input meshes and achieves superior quality patch layouts compared with the state-of-the-art approaches.
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    Learning Scene Illumination by Pairwise Photos from Rear and Front Mobile Cameras
    (The Eurographics Association and John Wiley & Sons Ltd., 2018) Cheng, Dachuan; Shi, Jian; Chen, Yanyun; Deng, Xiaoming; Zhang, Xiaopeng; Fu, Hongbo and Ghosh, Abhijeet and Kopf, Johannes
    Illumination estimation is an essential problem in computer vision, graphics and augmented reality. In this paper, we propose a learning based method to recover low-frequency scene illumination represented as spherical harmonic (SH) functions by pairwise photos from rear and front cameras on mobile devices. An end-to-end deep convolutional neural network (CNN) structure is designed to process images on symmetric views and predict SH coefficients. We introduce a novel Render Loss to improve the rendering quality of the predicted illumination. A high quality high dynamic range (HDR) panoramic image dataset was developed for training and evaluation. Experiments show that our model produces visually and quantitatively superior results compared to the state-of-the-arts. Moreover, our method is practical for mobile-based applications.
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    Tree Branch Level of Detail Models for Forest Navigation
    (© 2017 The Eurographics Association and John Wiley & Sons Ltd., 2017) Zhang, Xiaopeng; Bao, Guanbo; Meng, Weiliang; Jaeger, Marc; Li, Hongjun; Deussen, Oliver; Chen, Baoquan; Chen, Min and Zhang, Hao (Richard)
    We present a level of detail (LOD) method designed for tree branches. It can be combined with methods for processing tree foliage to facilitate navigation through large virtual forests. Starting from a skeletal representation of a tree, we fit polygon meshes of various densities to the skeleton while the mesh density is adjusted according to the required visual fidelity. For distant models, these branch meshes are gradually replaced with semi‐transparent lines until the tree recedes to a few lines. Construction of these complete LOD models is guided by error metrics to ensure smooth transitions between adjacent LOD models. We then present an instancing technique for discrete LOD branch models, consisting of polygon meshes plus semi‐transparent lines. Line models with different transparencies are instanced on the GPU by merging multiple tree samples into a single model. Our technique reduces the number of draw calls in GPU and increases rendering performance. Our experiments demonstrate that large‐scale forest scenes can be rendered with excellent detail and shadows in real time.We present a level of detail (LOD) method designed for tree branches. It can be combined with methods for processing tree foliage to facilitate navigation through large virtual forests. Starting from a skeletal representation of a tree, we fit polygon meshes of various densities to the skeleton while the mesh density is adjusted according to the required visual fidelity. For distant models, these branch meshes are gradually replaced with semi‐transparent lines until the tree recedes to a few lines. Construction of these complete LOD models is guided by error metrics to ensure smooth transitions between adjacent LOD models. We then present an instancing technique for discrete LOD branch models, consisting of polygon meshes plus semi‐transparent lines.
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    Tree Growth Modelling Constrained by Growth Equations
    (© 2018 The Eurographics Association and John Wiley & Sons Ltd., 2018) Yi, Lei; Li, Hongjun; Guo, Jianwei; Deussen, Oliver; Zhang, Xiaopeng; Chen, Min and Benes, Bedrich
    Modelling and simulation of tree growth that is faithful to the living environment and numerically consistent to botanic knowledge are important topics for realistic modelling in computer graphics. The realism factors concerned include the effects of complex environment on tree growth and the reliability of the simulation in botanical research, such as horticulture and agriculture. This paper proposes a new approach, namely, integrated growth modelling, to model virtual trees and simulate their growth by enforcing constraints of environmental resources and tree morphological properties. Morphological properties are integrated into a growth equation with different parameters specified in the simulation, including its sensitivity to light, allocation and usage of received resources and effects on its environment. The growth equation guarantees that the simulation procedure numerically matches the natural growth phenomenon of trees. With this technique, the growth procedures of diverse and realistic trees can also be modelled in different environments, such as resource competition among multiple trees.Modelling and simulation of tree growth that is faithful to the living environment and numerically consistent to botanic knowledge are important topics for realistic modelling in computer graphics. The realism factors concerned include the effects of complex environment on tree growth and the reliability of the simulation in botanical research, such as horticulture and agriculture. This paper proposes a new approach, namely, integrated growth modelling, to model virtual trees and simulate their growth by enforcing constraints of environmental resources and tree morphological properties. Morphological properties are integrated into a growth equation with different parameters specified in the simulation, including its sensitivity to light, allocation and usage of received resources and effects on its environment. The growth equation guarantees that the simulation procedure numerically matches the natural growth phenomenon of trees.