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Publications
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Interactive Hair Rendering and Appearance Editing under Environment Lighting
Kun Xu, Li-Qian Ma, Bo Ren, Rui Wang, Shi-Min Hu
ACM Transactions on Graphics 30(6), 173:1-173:10, 2011. (Proc. SIGGRAPH Asia 2011)
We present an interactive algorithm for hair rendering and appearance editing under complex environment lighting represented as spherical radial basis functions (SRBFs). Our main contribution is to derive a compact 1D circular Gaussian representation that can accurately model the hair scattering function introduced by [Marschner et al. 2003]. The primary benefit of this representation is that it enables us to evaluate, at run-time, closed-form integrals of the scattering function with each SRBF light, resulting in efficient computation of both single and multiple scatterings. In contrast to previous work, our algorithm computes the rendering integrals entirely on the fly and does not depend on expensive precomputation. Thus we allow the user to dynamically change the hair scattering parameters, which can vary spatially. Analyses show that our 1D circular Gaussian representation is both accurate and concise. In addition, our algorithm incorporates the eccentricity of the hair. We implement our algorithm on the GPU, achieving interactive hair rendering and simultaneous appearance editing under complex environment maps for the first time.
[project page] [ paper 1.9M ] [ pptx 34.6M 4.4M (no video) ] [supplemental 1.3M ]
[ video 53.2M ]
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Efficient Affinity-based Edit Propagation using K-D Tree
Kun Xu, Yong Li , Tao Ju, Shi-Min Hu, Tian-Qiang Liu
ACM Transactions on Graphics 28(5), 118:1-118:6, 2009. (Proc. SIGGRAPH Asia 2009)
Image/video editing by strokes has become increasingly popular due to the ease of interaction. Propagating the user inputs to the rest of the image/video, however, is often time and memory consuming especially for large data. We propose here an efficient scheme that allows affinity-based edit propagation to be computed on data containing tens of millions of pixels at interactive rate (in matter of seconds). The key in our scheme is a novel means for approximately solving the optimization problem involved in edit propagation, using adaptive clustering in a high-dimensional, affinity space. Our approximation significantly reduces the cost of existing affinity-based propagation methods while maintaining visual fidelity, and enables interactive stroke-based editing even on high resolution images and long video sequences using commodity computers.
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Edit Propagation on Bidirectional Texture Functions
Kun Xu, Jiaping Wang, Xin Tong, Shi-Min Hu, Baining Guo
Computer Graphics Forum 28(7), 1871-1877, 2009. (Proc. Pacific Graphics 2009)
We propose an efficient method for editing bidirectional texture functions (BTFs) based on edit propagation scheme. In our approach, users specify sparse edits on a certain slice of BTF. An edit propagation scheme is then applied to propagate edits to the whole BTF data. The consistency of the BTF data is maintained by propagating similar edits to points with similar underlying geometry/reflectance. For this purpose, we propose to use view independent features including normals and reflectance features reconstructed from each view to guide the propagation process. We also propose an adaptive sampling scheme for speeding up the propagation process. Since our method needn’t any accurate geometry and reflectance information, it allows users to edit complex BTFs with interactive feedback.
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Spherical Piecewise Constant Basis Functions for All-Frequency Precomputed Radiance Transfer
Kun Xu, Yun-Tao Jia, Hongbo Fu, Shi-Min Hu, Chiew-Lan Tai
IEEE Transaction on Visualization and Computer Graphics 14(2), 454-467, 2008.
This paper presents a novel basis function, called spherical piecewise constant basis function (SPCBF), for precomputed radiance transfer. SPCBFs have several desirable properties: rotatability, ability to represent all-frequency signals, and support for efficient multiple product. By partitioning the illumination sphere into a set of subregions, and associating each subregion with an SPCBF valued 1 inside the region and 0 elsewhere, we precompute the light coefficients using the resulting SPCBFs. We run-time approximate BRDF and visibility coefficients with the same set of SPCBFs through fast lookup of summed-area-table (SAT) and visibility distance table (VDT), respectively. SPCBFs enable new effects such as object rotation in all-frequency rendering of dynamic scenes and onthe-fly BRDF editing under rotating environment lighting. With graphics hardware acceleration, our method achieves real-time frame rates.
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Real-time homogeneous translucent material editing
Kun Xu, Yue Gao, Yong Li, Tao Ju, Shi-Min Hu
Computer Graphics Forum 26(3), 545-552, 2007. (Proc. EuroGraphics 2007)
This paper presents a novel method for real-time homogeneous translucent material editing under fixed illumination. We consider the complete analytic BSSRDF model proposed by Jensen et al.[JMLH01], including both multiple scattering and single scattering. Our method allows the user to adjust the analytic parameters of BSSRDF and provides high-quality, real-time rendering feedback. Inspired by recently developed Precomputed Radiance Transfer (PRT) techniques, we approximate both the multiple scattering diffuse reflectance function and the single scattering exponential attenuation function in the analytic model using basis functions, so that re-computing the outgoing radiance at each vertex as parameters change reduces to simple dot products. In addition, using a non-uniform piecewise polynomial basis, we are able to achieve smaller approximation error than using bases adopted in previous PRT-based works, such as spherical harmonics and wavelets. Using hardware acceleration, we demonstrate that our system generates images comparable to [JMLH01] at real-time frame-rates.
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Spherical Harmonics
Scaling Jiaping
Wang, Kun Xu, Kun Zhou, Stephen
Lin, Shi-Min Hu, Baining
Guo
Pacific Conference on Computer Graphics and
Applications, Oct 2006.
The Visual Computer, Volume 22, p713-720, Sept
2006.
In this
paper, we present a new SH operation, called spherical
harmonics scaling, to shrink or expand a spherical
function in frequency domain. We show that this problem can be
elegantly formulated as a linear transformation of SH projections,
which is efficient to compute and easy to implement on a GPU.
Spherical harmonics scaling is particularly useful for extrapolating
visibility and radiance functions at a sample point to points closer
to or farther from an occluder or light source. With SH scaling, we
present applications to lowfrequency shadowing for general
deformable object, and to efficient approximation of spherical
irradiance functions within a mid-range illumination
environment.
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Experiences
- Research Intern at Internet Graphics Group, Microsoft Research Asia (2004.10 - 2005.10)
- mentor: Xin Tong
- location: Beijing, P.R. China
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Awards
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Microsoft Fellowship, 2008
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Links
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