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 ] [ bibtex ]

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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