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Yang L.,Hong Kong UST | Tse Y.-C.,Hong Kong UST | Sander P.V.,Hong Kong UST | Lawrence J.,University of Virginia | And 3 more authors.
Proceedings of the 2011 SIGGRAPH Asia Conference, SA'11 | Year: 2011

We introduce a method for increasing the framerate of real-time rendering applications. Whereas many existing temporal upsampling strategies only reuse information from previous frames, our bidirectional technique reconstructs intermediate frames from a pair of consecutive rendered frames. This significantly improves the accuracy and efficiency of data reuse since very few pixels are simultaneously occluded in both frames. We present two versions of this basic algorithm. The first is appropriate for fill-bound scenes as it limits the number of expensive shading calculations, but involves rasterization of scene geometry at each intermediate frame. The second version, our more significant contribution, reduces both shading and geometry computations by performing reprojection using only image-based buffers. It warps and combines the adjacent rendered frames using an efficient iterative search on their stored scene depth and flow. Bidirectional reprojection introduces a small amount of lag. We perform a user study to investigate this lag, and find that its effect is minor. We demonstrate substantial performance improvements (3-4×) for a variety of applications, including vertex-bound and fill-bound scenes, multi-pass effects, and motion blur. © 2011 ACM.

Chen G.,Hong Kong UST | Sander P.V.,Hong Kong UST | Nehab D.,IMPA | Yang L.,Hong Kong UST | And 2 more authors.
ACM Transactions on Graphics | Year: 2012

We present a novel approach for real-time rendering of static 3D models front-to-back or back-to-front relative to any viewpoint outside its bounding volume. The approach renders depth-sorted triangles using a single draw-call. At run-time, we replace the traditional sorting strategy of existing algorithms with a faster triangle selection strategy. The selection process operates on an extended sequence of triangles annotated by test planes, created by our off-line preprocessing stage. Based on these test planes, a simple run-time procedure uses the given viewpoint to select a subsequence of triangles for rasterization. Selected subsequences are statically presorted by depth and contain each input triangle exactly once. Our method runs on legacy hardware and renders depth-sorted static models significantly faster than previous approaches. We conclude demonstrating the real-time rendering of order-independent transparency effects. © 2012 ACM.

Li H.,Hong Kong UST | Wei L.-Y.,Microsoft | Sander P.V.,Hong Kong UST | Fu C.-W.,Nanyang Technological University
ACM Transactions on Graphics | Year: 2010

Blue noise sampling is widely employed for a variety of imaging, geometry, and rendering applications. However, existing research so far has focused mainly on isotropic sampling, and challenges remain for the anisotropic scenario both in sample generation and quality verification. We present anisotropic blue noise sampling to address these issues. On the generation side, we extend dart throwing and relaxation, the two classical methods for isotropic blue noise sampling, for the anisotropic setting, while ensuring both high-quality results and efficient computation. On the verification side, although Fourier spectrum analysis has been one of the most powerful and widely adopted tools, so far it has been applied only to uniform isotropic samples. We introduce approaches based on warping and sphere sampling that allow us to extend Fourier spectrum analysis for adaptive and/or anisotropic samples; thus, we can detect problems in alternative anisotropic sampling techniques that were not yet found via prior verification. We present several applications of our technique, including stippling, visualization, surface texturing, and object distribution. © 2010 ACM.

Golin M.,Hong Kong UST | Zhang Y.,Hong Kong UST
IEEE Transactions on Information Theory | Year: 2010

The state-of-the-art in length-limited Huffman coding (LLHC) algorithms is the Θ (nD)-time, Θ (n)-space one of Hirschberg and Larmore, where n is the size of the code and D ≤ n is the length restriction on the codewords. This is a very clever, very problem specific, technique. This paper presents a simple dynamic-programming (DP) method that solves the problem with the same time and space bounds. The fact that there was an Θ (nD) time DP algorithm was previously known; it is a straightforward DP with the Monge property (which permits an order of magnitude speedup). It was not interesting, though, because it also required Θ (nD) space. The main result of this paper is the technique developed for reducing the space. It is quite simple and applicable to many other problems modeled by DPs with the Monge property. This is illustrated with examples from web-proxy design and wireless mobile paging. © 2006 IEEE.

Lu J.,Hong Kong UST | Lu J.,Princeton University | Sander P.V.,Hong Kong UST | Finkelstein A.,Princeton University
Proceedings of I3D 2010: The 2010 ACM SIGGRAPH Symposium on Interactive 3D Graphics and Games | Year: 2010

We introduce a real-time system that converts images, video, or 3D animation sequences to artistic renderings in various painterly styles. The algorithm, which is entirely executed on the GPU, can efficiently process 512 resolution frames containing 60,000 individual strokes at over 30 fps. In order to exploit the parallel nature of GPUs, our algorithm determines the placement of strokes entirely from local pixel neighborhood information. The strokes are rendered as point sprites with textures. Temporal coherence is achieved by treating the brush strokes as particles and moving them based on optical flow. Our system renders high quality results while allowing the user interactive control over many stylistic parameters such as stroke size, texture and density. Copyright © 2010 by the Association for Computing Machinery, Inc.

Scherzer D.,MPI Informatik | Yang L.,Hong Kong UST | Mattausch O.,Vienna University of Technology | Nehab D.,IMPA | And 3 more authors.
Computer Graphics Forum | Year: 2012

Nowadays, there is a strong trend towards rendering to higher-resolution displays and at high frame rates. This development aims at delivering more detail and better accuracy, but it also comes at a significant cost. Although graphics cards continue to evolve with an ever-increasing amount of computational power, the speed gain is easily counteracted by increasingly complex and sophisticated shading computations. For real-time applications, the direct consequence is that image resolution and temporal resolution are often the first candidates to bow to the performance constraints (e.g. although full HD is possible, PS3 and XBox often render at lower resolutions). In order to achieve high-quality rendering at a lower cost, one can exploit temporal coherence (TC). The underlying observation is that a higher resolution and frame rate do not necessarily imply a much higher workload, but a larger amount of redundancy and a higher potential for amortizing rendering over several frames. In this survey, we investigate methods that make use of this principle and provide practical and theoretical advice on how to exploit TC for performance optimization. These methods not only allow incorporating more computationally intensive shading effects into many existing applications, but also offer exciting opportunities for extending high-end graphics applications to lower-spec consumer-level hardware. To this end, we first introduce the notion and main concepts of TC, including an overview of historical methods. We then describe a general approach, image-space reprojection, with several implementation algorithms that facilitate reusing shading information across adjacent frames. We also discuss data-reuse quality and performance related to reprojection techniques. Finally, in the second half of this survey, we demonstrate various applications that exploit TC in real-time rendering. © 2012 The Eurographics Association and Blackwell Publishing Ltd.

Han S.,Hong Kong UST | Sander P.V.,Hong Kong UST
Proceedings - 20th ACM SIGGRAPH Symposium on Interactive 3D Graphics and Games, I3D 2016 | Year: 2016

We introduce an automatic approach for optimizing the triangle rendering order of animated meshes with the objective of reducing overdraw while maintaining good post-transform vertex cache efficiency. Our approach is based on prior methods designed for static meshes. We propose an algorithm that clusters the space of viewpoints and key frames. For each cluster, we generate a triangle order that exhibits satisfactory vertex cache efficiency and low overdraw. Results show that our approach significantly improves overdraw throughout the entire animation sequence while only requiring a few index buffers. We expect that this approach will be useful for games and other real-time rendering applications that involve complex shading of articulated characters. © 2016 ACM.

Goel N.,Go Vivace Inc. | Thomas S.,Johns Hopkins University | Agarwal M.,IIIT Allahabad | Akyazi P.,Bogazici University | And 9 more authors.
ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings | Year: 2010

Preparation of a lexicon for speech recognition systems can be a significant effort in languages where the written form is not exactly phonetic. On the other hand, in languages where the written form is quite phonetic, some common words are often mispronounced. In this paper, we use a combination of lexicon learning techniques to explore whether a lexicon can be learned when only a small lexicon is available for boot-strapping. We discover that for a phonetic language such as Spanish, it is possible to do that better than what is possible from generic rules or hand-crafted pronunciations. For a more complex language such as English, we find that it is still possible but with some loss of accuracy. ©2010 IEEE.

Ghoshal A.,Saarland University | Povey D.,Microsoft | Agarwal M.,IIIT Allahabad | Akyazi P.,Bogazici University | And 9 more authors.
ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings | Year: 2010

In this paper we present a novel approach for estimating feature-space maximum likelihood linear regression (fMLLR) transforms for full-covariance Gaussian models by directly maximizing the likelihood function by repeated line search in the direction of the gradient. We do this in a pre-transformed parameter space such that an approximation to the expected Hessian is proportional to the unit matrix. The proposed algorithm is as efficient or more efficient than standard approaches, and is more flexible because it can naturally be combined with sets of basis transforms and with full covariance and subspace precision and mean (SPAM) models. ©2010 IEEE.

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