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Scale-aware Structure-Preserving Texture Filtering

computer graphics FORUM 2016年第7期35卷 77-86页

作者： Jeon, Junho Lee, Hyunjoon Kang, Henry Lee, Seungyong POSTECH Dept Comp Sci & Engn Pohang South Korea Univ Missouri Dept Math & Comp Sci St Louis MO 63121 USA

this paper presents a novel method to enhance the performance of structure-preserving image and texture filtering. With conventional edge-aware filters, it is often challenging to handle images of high complexity where features of multiple scales coexist. In particular, it is not always easy to find the right balance between removing unimportant details and protecting important features when they come in multiple sizes, shapes, and contrasts. Unlike previous approaches, we address this issue from the perspective of adaptive kernel scales. Relying on patch-based statistics, our method identifies texture from structure and also finds an optimal per-pixel smoothing scale. We show that the proposed mechanism helps achieve enhanced image/ texture filtering performance in terms of protecting the prominent geometric structures in the image, such as edges and corners, and keeping them sharp even after significant smoothing of the original signal.

关键词： Categories and Subject Descriptors (according to ACM CCS) I.4.3 [Image Processing and computer Vision]: Enhancement&mdash Smoothing

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Facial Feature Exaggeration According to Social Psychology of Face Perception

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computer graphics FORUM 2016年第7期35卷 391-399页

作者： Tian, Lihui Xiao, Shuangjiu Shanghai Jiao Tong Univ Shanghai 200030 Peoples R China

We propose a personality trait exaggeration system emphasizing the impression of human face in images, based on multi-level features learning and exaggeration. these features are called Personality Trait Model(PTM). Abstract level of PTM is social psychology trait of face perception such as amiable, mean, cute and so on. Concrete level of PTM is shape feature and texture feature. A training phase is presented to learn multi-level features of faces from different images. Statistical survey is taken to label sample images with people's first impressions. From images with the same labels, we capture not only shape features but also texture features to enhance exaggeration effect. Texture feature is expressed by matrix to reflect depth of facial organs, wrinkles and so on. In application phase, original images will be exaggerated using PTM iteratively. And exaggeration rate for each iteration is constrained to keep likeness with the original face. Experimental results demonstrate that our system can emphasize chosen social psychology traits effectively.

关键词： Categories and Subject Descriptors (according to ACM CCS) I.3.3 [computer graphics]: Picture/Image Generation&mdash

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An Efficient Structure-Aware Bilateral Texture Filtering for Image Smoothing

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computer graphics FORUM 2016年第7期35卷 57-66页

作者： Lin, Ting-Hao Way, Der-Lor Shih, Zen-Chung Tai, Wen-Kai Chang, Chin-Chen Natl Chiao Tung Univ Hsinchu Taiwan Taipei Natl Univ Arts Taipei Taiwan Natl Taiwan Univ Sci & Technol Taipei Taiwan Natl United Univ Miaoli Taiwan

Photos contain well-structured and plentiful visual information. Edges are active and expressive stimuli for human visual perception. However, it is hard to separate structure from details because edge strength and object scale are entirely different concepts. this paper proposes a structure-aware bilateral texture algorithm to remove texture patterns and preserve structures. Our proposed method is simple and fast, as well as effective in removing textures. Instead of patch shift, smaller patches represent pixels located at structure edges, and original patches represent the texture regions. Specifically, this paper also improves joint bilateral filter to preserve small structures. Moreover, a windowed inherent variation is adapted to distinguish textures and structures for detecting structure edges. Finally, the proposed method produces excellent experimental results. these results are compared to some results of previous studies. Besides, structure-preserving filtering is a critical operation in many image processing applications. Our proposed filter is also demonstrated in many attractive applications, such as seam carving, detail enhancement, artistic rendering, etc.

关键词： IMAGE processing IMAGING systems TEXTURE mapping CONTENT filters (computer science) computer graphics

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Minimal Sampling for Effective Acquisition of Anisotropic BRDFs

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computer graphics FORUM 2016年第7期35卷 299-309页

作者： Vavra, R. Filip, J. CAS Inst Informat Theory & Automat Prague Czech Republic

BRDFs are commonly used for material appearance representation in applications ranging from gaming and the movie industry, to product design and specification. Most applications rely on isotropic BRDFs due to their better availability as a result of their easier acquisition process. On the other hand, anisotropic BRDF due to their structure-dependent anisotropic highlights, are more challenging to measure and process. this paper thus leverages the measurement process of anisotropic BRDF by representing such BRDF by the collection of isotropic BRDFs. Our method relies on an anisotropic BRDF database decomposition into training isotropic slices forming a linear basis, where appropriate sparse samples are identified using numerical optimization. When an unknown anisotropic BRDF is measured, these samples are repeatably captured in a small set of azimuthal directions. All collected samples are then used for an entire measured BRDF reconstruction from a linear isotropic basis. Typically, below 100 samples are sufficient for the capturing of main visual features of complex anisotropic materials, and we provide a minimal directional samples to be regularly measured at each sample rotation. We conclude, that even simple setups relying on five bidirectional samples (maximum of five stationary sensors/lights) in combination with eight rotations (rotation stage for specimen) can yield a promising reconstruction of anisotropic behavior. Next, we outline extension of the proposed approach to adaptive sampling of anisotropic BRDF to gain even better performance. Finally, we show that our method allows using standard geometries, including industrial multi-angle reflectometers, for the fast measurement of anisotropic BRDFs.

关键词： Categories and Subject Descriptors (according to ACM CCS) I.3.7 [computer graphics]: three-Dimensional graphics and Realism&mdash Color shading shadowing and texture I.4.1 [computer graphics]: Digitization and Image Capture&mdash Reflectance

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Decoupled Space and Time Sampling of Motion and Defocus Blur for Unified Rendering of Transparent and Opaque Objects

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computer graphics FORUM 2016年第7期35卷 441-450页

作者： Widmer, S. Wodniok, D. thul, D. Guthe, S. Goesele, M. Tech Univ Darmstadt Grad Sch Computat Engn Darmstadt Germany Tech Univ Darmstadt Darmstadt Germany

We propose a unified rendering approach that jointly handles motion and defocus blur for transparent and opaque objects at interactive frame rates. Our key idea is to create a sampled representation of all parts of the scene geometry that are potentially visible at any point in time for the duration of a frame in an initial rasterization step. We store the resulting temporally-varying fragments (t-fragments) in a bounding volume hierarchy which is rebuild every frame using a fast spatial median construction algorithm. this makes our approach suitable for interactive applications with dynamic scenes and animations. Next, we perform spatial sampling to determine all t-fragments that intersect with a specific viewing ray at any point in time. Viewing rays are sampled according to the lens uv-sampling for depth-of-field effects. In a final temporal sampling step, we evaluate the predetermined viewing ray/t-fragment intersections for one or multiple points in time. this allows us to incorporate all standard shading effects including transparency. We describe the overall framework, present our GPU implementation, and evaluate our rendering approach with respect to scalability, quality, and performance.

关键词： Categories and Subject Descriptors (according to ACM CCS) I.3.6 [computer graphics]: Methodology and Techniques&mdash graphics data structures and data types I.3.7 [computer graphics]: three-Dimensional graphics and Realism&mdash Raytracing

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Geometrically Based Linear Iterative Clustering for Quantitative Feature Correspondence

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computer graphics FORUM 2016年第7期35卷 1-10页

作者： Yan, Qingan Yang, Long Liang, Chao Liu, Huajun Hu, Ruimin Xiao, Chunxia Wuhan Univ Sch Comp Wuhan 430072 Peoples R China Wuhan Univ State Key Lab Software Engn Wuhan 430072 Peoples R China

A major challenge in feature matching is the lack of objective criteria to determine corresponding points. Recent methods find match candidates first by exploring the proximity in descriptor space, and then rely on a ratio-test strategy to determine final correspondences. However, these measurements are heuristic and subjectively excludes massive true positive correspondences that should be matched. In this paper, we propose a novel feature matching algorithm for image collections, which is capable of providing quantitative depiction to the plausibility of feature matches. We achieve this by exploring the epipolar consistency between feature points and their potential correspondences, and reformulate feature matching as an optimization problem in which the overall geometric inconsistency across the entire image set ought to be minimized. We derive the solution of the optimization problem in a simple linear iterative manner, where a k-means-type approach is designed to automatically generate consistent feature clusters. Experiments show that our method produces precise correspondences on a variety of image sets and retrieves many matches that are subjectively rejected by recent methods. We also demonstrate the usefulness of the framework in structure from motion task for denser point cloud reconstruction.

关键词： Categories and Subject Descriptors (according to ACM CCS) I.3.m [computer graphics]: Computational photography&mdash I.4.0 [computer graphics]: General&mdash I.4.7 [computer graphics]: Feature Measurement&mdash

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Harmonic Functions for Rotational Symmetry Vector Fields

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computer graphics FORUM 2016年第7期35卷 507-516页

作者： Shen, Zhongwei Fang, Xianzhong Liu, Xinguo Bao, Hujun Huang, Jin Zhejiang Univ State Key Lab CAD&CG Hangzhou Zhejiang Peoples R China

Representing rotational symmetry vector as a set of vectors is not suitable for design due to lacking of a consistent ordering for measurement. In this paper we introduce a spectral method to find rotation invariant harmonic functions for symmetry vector field design. this method is developed for 3D vector fields, but it is applicable in 2D. Given the finite symmetry group G of a symmetry vector field v(x) on a 3D domain Omega, we formulate the harmonic function h (s) as a stationary point of group G. Using the real spherical harmonic (SH) bases, we showed the coefficients of the harmonic functions are an eigenvector of the SH rotation matrices corresponding to group G. Instead of solving eigen problems to obtain the eigenvector, we developed a forward constructive method based on orthogonal group theory. the harmonic function found by our method is not only invariant under G, but also expressive and can distinguish different rotations with respect to G. At last, we demonstrate some vector field design results with tetrahedron-symmetry, cube-symmetry and dodecahedron-symmetry groups.

关键词： Categories and Subject Descriptors (according to ACM CCS) I.3.5 [computer graphics]: Computational Geometry and Object Modeling&mdash Geometric algorithms

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Proxy-guided Image-based Rendering for Mobile Devices

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computer graphics FORUM 2016年第7期35卷 353-362页

作者： Reinert, Bernhard Kopf, Johannes Ritschel, Tobias Cuervo, Eduardo Chu, David Seidel, Hans-Peter MPI Informat Saarbrucken Germany Microsoft Res Redmond WA USA UCL London WC1E 6BT England Facebook Menlo Pk CA USA Google Mountain View CA USA

VR headsets and hand-held devices are not powerful enough to render complex scenes in real-time. A server can take on the rendering task, but network latency prohibits a good user experience. We present a new image-based rendering (IBR) architecture for masking the latency. It runs in real-time even on very weak mobile devices, supports modern game engine graphics, and maintains high visual quality even for large view displacements. We propose a novel server-side dual-view representation that leverages an optimally-placed extra view and depth peeling to provide the client with coverage for filling disocclusion holes. this representation is directly rendered in a novel wide-angle projection with favorable directional parameterization. A new client-side IBR algorithm uses a pre-transmitted level-of-detail proxy with an encaging simplification and depth-carving to maintain highly complex geometric detail. We demonstrate our approach with typical VR/mobile gaming applications running on mobile hardware. Our technique compares favorably to competing approaches according to perceptual and numerical comparisons.

关键词： IMAGING systems IMAGE analysis IMAGE processing VIRTUAL reality computer simulation PARAMETERIZATION

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Piecewise smooth reconstruction of normal vector field on digital data

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computer graphics FORUM 2016年第7期35卷 157-167页

作者： Coeurjolly, David Foare, Marion Gueth, Pierre Lachaud, Jacques-Olivier Univ Lyon CNRS LIRIS UMR 5205 F-69622 Lyon France Univ Savoie Mont Blanc UMR 5127 CNRS Lab Math Chambery France

We propose a novel method to regularize a normal vector field defined on a digital surface (boundary of a set of voxels). When the digital surface is a digitization of a piecewise smooth manifold, our method localizes sharp features (edges) while regularizing the input normal vector field at the same time. It relies on the optimisation of a variant of the Ambrosio-Tortorelli functional, originally defined for denoising and contour extraction in image processing [AT90]. We reformulate this functional to digital surface processing thanks to discrete calculus operators. Experiments show that the output normal field is very robust to digitization artifacts or noise, and also fairly independent of the sampling resolution. the method allows the user to choose independently the amount of smoothing and the length of the set of discontinuities. Sharp and vanishing features are correctly delineated even on extremely damaged data. Finally, our method can be used to enhance considerably the output of state-of-the-art normal field estimators like Voronoi Covariance Measure [MOG11] or Randomized Hough Transform [BM12].

关键词： Categories and Subject Descriptors (according to ACM CCS) [computer graphics]: Modeling - Digital Geometry Processing&mdash Modeling - Shape Analysis

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Temporally Coherent and Artistically Intended Stylization of Feature Lines Extracted from 3D Models

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computer graphics FORUM 2016年第7期35卷 137-146页

作者： Cardona, L. Saito, S. Tokyo Inst Technol Tokyo Japan

In this paper, we propose a method to maintain the temporal coherence of stylized feature lines extracted from 3D models and preserve an artistically intended stylization provided by the user. We formally define the problem of combining spatio-temporal continuity and artistic intention as a weighted energy minimization problem of competing constraints. the proposed method updates the style properties to provide real-time smooth transitions from current to goal stylization, by assuring first- and second-order temporal continuity, as well as spatial continuity along each stroke. the proposed weighting scheme guarantees that the stylization of strokes maintains motion coherence with respect to the apparent motion of the underlying surface in consecutive frames. this weighting scheme emphasizes temporal continuity for small apparent motions where the human vision system is able to keep track of the scene, and prioritizes the artistic intention for large apparent motions where temporal coherence is not expected. the proposed method produces temporally coherent and visually pleasing animations without the flickering artifacts of previous methods, while also maintaining the artistic intention of a goal stylization provided by the user.

关键词： Categories and Subject Descriptors (according to ACM CCS) I.3.3 [computer graphics]: Picture/Image Generation&mdash Line and curve generation

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