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10th pacific conference on computer graphics and applications

作者： Wang, Y Samaras, D SUNY Stony Brook Dept Comp Sci Stony Brook NY 11794 USA

ISBN: (纸本)0769517854

We present a new method for the detection and estimation of multiple directional illuminants, using a single image of any object with known geometry and Lambertian reflectance. We use the resulting highly accurate estimates to modify virtually the illumination and geometry of a real scene and produce correctly illuminated Mixed Reality images. Our method obviates the need to modify the imaged scene by inserting calibration objects of any particular geometry, relying instead on partial knowledge of the geometry of the scene. Thus, the recovered multiple illuminants can be used both for image-based rendering and for shape reconstruction. Our method combines information both from the shading of the object and from shadows cast on the scene by the object. Initially we use a method based on shadows and a method based on shading independently. The shadow based method utilizes brightness variation inside the shadows cast by the object, whereas the shading based method utilizes brightness variation on the directly illuminated portions of the object. We demonstrate how the two sources of information complement each other in a number of occasions. We then describe an approach that integrates the two methods, with results superior to those obtained if the two methods are used separately. The resulting illumination information can be used (i) to render synthetic objects in a real photograph with correct illumination effects, and (ii) to virtually re-light the scene.

关键词： Brightness Calibration Geometry Layout Light sources Lighting Object detection Reflectivity Rendering (computer graphics) Virtual reality

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Physically Based Video Editing

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computer graphics FORUM 2016年第7期35卷 421-429页

作者： Bazin, J-C. Pluss (Kuster), C. Yu, G. Martin, T. Jacobson, A. Gross, M. ETH Zurich Switzerland Nanyang Technol Univ Singapore Singapore Columbia Univ New York NY 10027 USA Univ Toronto Toronto ON Canada

Convincing manipulation of objects in live action videos is a difficult and often tedious task. Skilled video editors achieve this with the help of modern professional tools, but complex motions might still lack physical realism since existing tools do not consider the laws of physics. On the other hand, physically based simulation promises a high degree of realism, but typically creates a virtual 3D scene animation rather than returning an edited version of an input live action video. We propose a framework that combines video editing and physics-based simulation. Our tool assists unskilled users in editing an input image or video while respecting the laws of physics and also leveraging the image content. We first fit a physically based simulation that approximates the object's motion in the input video. We then allow the user to edit the physical parameters of the object, generating a new physical behavior for it. The core of our work is the formulation of an image-aware constraint within physics simulations. This constraint manifests as external control forces to guide the object in a way that encourages proper texturing at every frame, yet producing physically plausible motions. We demonstrate the generality of our method on a variety of physical interactions: rigid motion, multi-body collisions, clothes and elastic bodies.

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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Interactive Design and Preview of Colored Snapshots of Indoor Scenes

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computer graphics FORUM 2020年第7期39卷 543-552页

作者： Fu, Qiang Yan, Hai Fu, Hongbo Li, Xueming Beijing Univ Posts & Telecommun Sch Digital Media & Design Arts Beijing Peoples R China City Univ Hong Kong Sch Creat Media Hong Kong Peoples R China

This paper presents an interactive system for quickly designing and previewing colored snapshots of indoor scenes. Different from high-quality 3D indoor scene rendering, which often takes several minutes to render a moderately complicated scene under a specific color theme with high-performance computing devices, our system aims at improving the effectiveness of color theme design of indoor scenes and employs an image colorization approach to efficiently obtain high-resolution snapshots with editable colors. Given several pre-rendered, multi-layer, gray images of the same indoor scene snapshot, our system is designed to colorize and merge them into a single colored snapshot. Our system also assists users in assigning colors to certain objects/components and infers more harmonious colors for the unassigned objects based on pre-collected priors to guide the colorization. The quickly generated snapshots of indoor scenes provide previews of interior design schemes with different color themes, making it easy to determine the personalized design of indoor scenes. To demonstrate the usability and effectiveness of this system, we present a series of experimental results on indoor scenes of different types, and compare our method with a state-of-the-art method for indoor scene material and color suggestion and offline/online rendering software packages.

关键词： CCS Concepts • Applied computing $Ar computer‐aided design • Computing methodologies $Ar graphics systems and interfaces Rendering

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Automatic Modeling of Urban Facades from Raw LiDAR Point Data

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computer graphics FORUM 2016年第7期35卷 269-278页

作者： Wang, J. Xu, Y. Remil, O. Xie, X. Ye, N. Yi, C. Wei, M. Nanjing Univ Aeronaut & Astronaut Nanjing Jiangsu Peoples R China HeFei Univ Technol Hefei Peoples R China

Modeling of urban facades from raw LiDAR point data remains active due to its challenging nature. In this paper, we propose an automatic yet robust 3D modeling approach for urban facades with raw LiDAR point clouds. The key observation is that building facades often exhibit repetitions and regularities. We hereby formulate repetition detection as an energy optimization problem with a global energy function balancing geometric errors, regularity and complexity of facade structures. As a result, repetitive structures are extracted robustly even in the presence of noise and missing data. By registering repetitive structures, missing regions are completed and thus the associated point data of structures are well consolidated. Subsequently, we detect the potential design intents (i.e., geometric constraints) within structures and perform constrained fitting to obtain the precise structure models. Furthermore, we apply structure alignment optimization to enforce position regularities and employ repetitions to infer missing structures. We demonstrate how the quality of raw LiDAR data can be improved by exploiting data redundancy, and discovering high level structural information (regularity and symmetry). We evaluate our modeling method on a variety of raw LiDAR scans to verify its robustness and effectiveness.

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

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Shape and Pose Estimation for Closely Interacting Persons Using Multi-view Images

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computer graphics FORUM 2018年第7期37卷 361-371页

作者： Li, Kun Jiao, Nianhong Liu, Yebin Wang, Yangang Yang, Jingyu Tianjin Univ Sch Comp Sci & Technol Tianjin 300350 Peoples R China Tsinghua Univ Dept Automat Beijing 100084 Peoples R China Southeast Univ Sch Automat Nanjing 210096 Jiangsu Peoples R China Tianjin Univ Sch Elect & Informat Engn Tianjin 300072 Peoples R China

Multi-person pose and shape estimation is very challenging, especially when the persons have close interactions. Existing methods only work well when people are well spaced out in the captured images. However, close interaction among people is very common in real life, which is more challenge due to complex articulation, frequent occlusion and inherent ambiguities. We present a fully-automatic markerless motion capture method to simultaneously estimate 3D poses and shapes of closely interacting people from multi-view sequences. We first predict the 2D joints for each person in an image, and then design a spatio-temporal tracker for multi-person pose tracking based on multi-view videos. Finally, we estimate 3D poses and shapes of all the persons with multi-view constraints using a skinned multi-person linear model (SMPL). Experimental results demonstrate that our method achieves fast but accurate pose and shape estimation results for multi-person close interaction cases. Compared with existing methods, our method does not need pre-segmentation for each person and manual intervention, which greatly reduces the complexity of the system including time complexity and system processing complexity.

关键词： Categories and Subject Descriptors (according to ACM CCS): I.4.8 [computer graphics]: Scene Analysis—Shape Motion

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Re-Compositable Panoramic Selfie with Robust Multi-Frame Segmentation and Stitching

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computer graphics FORUM 2016年第7期35卷 227-236页

作者： Li, Kai Wang, Jue Liu, Yebin Xu, Li Dai, Qionghai Shanghai Univ Sch Commun & Informat Engn Shanghai 200041 Peoples R China Tsinghua Univ Dept Automat Beijing Peoples R China Adobe Res Basel Switzerland SenseTime Grp Ltd Hong Kong Hong Kong Peoples R China

It is a challenging task for ordinary users to capture selfies with a good scene composition, given the limited freedom to position the camera. Creative hardware (e.g., selfie sticks) and software (e.g., panoramic selfie apps) solutions have been proposed to extend the background coverage of a selife, but to achieve a perfect composition on the spot when the selfie is captured remains to be difficult. In this paper, we propose a system that allows the user to shoot a selfie video by rotating the body first, then produce a final panoramic selfie image with user-guided scene composition as postprocessing. Our key technical contribution is a fully automatic, robust multi-frame segmentation and stitching framework that is tailored towards the special characteristics of selfie images. We analyze the sparse feature points and employ a spatial-temporal optimization for bilayer feature segmentation, which leads to more reliable background alignment than previous image stitching techniques. The sparse classification is then propagated to all pixels to create dense foreground masks for person-background composition. Finally, based on a user-selected foreground position, our system uses content-preserving warping to produce a panoramic seflie with minimal distortion to the face region. Experimental results show that our approach can reliably generate high quality panoramic selfies, while a simple combination of previous image stitching and segmentation approaches often fails.

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

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Reconstructing 3D Shape, Albedo and Illumination from a Single Face Image

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computer graphics FORUM 2008年第7期27卷 1729-1736页

作者： Wang, S. F. Lai, S. H. Natl Tsing Hua Univ Dept Comp Sci Hsinchu Taiwan

The morphable model has been employed to efficiently describe 3D face shape and the associated albedo with a reduced set of basis vectors. The spherical harmonics (SH) model provides a compact basis to well approximate the image appearance of a Lambertian object under different illumination conditions. Recently, the SH and morphable models have been integrated for 3D face shape reconstruction. However, the reconstructed 3D shape is either inconsistent with the SH bases or obtained just from landmarks only. In this work, we propose a geometrically consistent algorithm to reconstruct the 3D face shape and the associated albedo from a single face image iteratively by combining the morphable model and the SH model. There constructed 3D face geometry can uniquely determine the SH bases, therefore the optimal 3D face model can be obtained by minimizing the error between the input face image and a linear combination of the associated SH bases. In this way, we are able to preserve the consistency between the 3D geometry and the SH model, thus refining the 3D shape reconstruction recursively. Furthermore, we present a novel approach to recover the illumination condition from the estimated weighting vector for the SH bases in a constrained optimization formulation independent of the 3D geometry. Experimental results show the effectiveness and accuracy of the proposed face reconstruction and illumination estimation algorithm under different face poses and multiple-light-source illumination conditions.

关键词： I.3.7 [computer graphics]: Virtual reality

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Dataflow specification for system level synthesis of 3D graphics applications

Dataflow specification for system level synthesis of 3D grap...

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Asia and South pacific Design Automation conference (ASP-DAC 2001)

作者： Park, C Kim, S Ha, S Seoul Natl Univ Seoul 151742 South Korea

ISBN: (纸本)0780366336

3D graphics is becoming an important application area together with multimedia applications. The dynamic behavior of 3D graphics application brings new challenges for system level specification and synthesis methodologies. Although existing dataflow models are successfully used for DSP system design, they are not sufficient to deal with 3D graphics algorithms since they lack in global state management and dynamic behavior handling, In this paper, we propose an extended synchronous piggybacked dataflow model with dynamic constructs for representing 3D graphics algorithm. We also present implementation techniques for software and hardware synthesis from the specification. With a simple 3D graphics pipeline, we show the novelty and usefulness of the proposed specification model.

关键词： Application software computer graphics computer science Digital signal processing Electronic mail Formal specifications Hardware Pipelines Power system modeling System-level design

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Multi-functional visualization system for structure analysis

Multi-functional visualization system for structure analysis

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5th pacific conference on computer graphics and applications (pacific graphics 97)

作者： Tao, H Tadamura, K Nakamae, E Industrial Research Cent of Hiroshima Prefecture Kure Japan

ISBN: (纸本)0818680288

For displaying structure analysis data on demand, we propose a multi-franctional visualization system with a sophisticated graphical laser interface (GUI) that reflects the observer's intention interactively and is adapted to further extension. In this system, the analysis results can be expressed in various ways by interactive operations: corresponding to the user's tentative demands, plural physical quantities are displayed on the same screen simultaneously, for transient phenomena animation is available, and distributed vectors and multi-layer scalar data can be observed in stereo vision. By employing the proposed system structure analysts can easily grasp intuitively inter-object and intra-object relationships, complicated deformations, and changes of physical quantities through time in the objects.

关键词： Interactive computer systems

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Multiresolution constraints for designing subdivision surfaces via local smoothing 7

Multiresolution constraints for designing subdivision surfac...

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7th pacific conference on computer graphics and applications, pacific graphics 1999

作者： Takahashi, Shigeo Computer Center Gunma University 1-5-1 Tenjin-cho Kiryu Gunma376-8515 Japan

ISBN: (纸本)0769502938

Subdivision surfaces provide an efficient means of representing surfaces of arbitrary topological type. In recent years, multiresolution modeling with variational smoothing has played an important role in controlling such surfaces. This paper presents a new model of multiresolution constraints that can be applied to subdivision surfaces. The advantage of this model is that different geometric constraints can be imposed on the surfaces at different resolution levels. The model employs the wavelet-based framework of Lounsbery, et al. (1997), to represent the subdivision surfaces in a hierarchical fashion. In the proposed framework, local smooth filtering is used to obtain the optimal surface shape at each resolution level. Controlling the number of iterations for the local smoothing operations allows us to modify the smoothness of the subdivision surfaces even when the same set of constraints is given. Several design examples are included to demonstrate the capability of this model. © 1999 IEEE.

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