Browsing by Author "Wang, Tse-Wei"

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A Parametric Window Design for OBMC with Variable Block Size Motion Estimates
(2009)
Chen, Yi-Wen
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Wang, Tse-Wei
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Tseng, Yu-Cheng
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Peng, Wen-Hsiao
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Lee, Suh-Yin
This paper addresses the problem of adapting overlapped block motion compensation (OBMC) windows for use with variable blocksize motion estimates. We tackle the problem by using a parametric window design, which expresses, based on a statistical motion model, the optimal weights as a function of the distances between the predicted pixel and its nearby block centers. The formula enables both prediction weights and prediction order to be adapted on a pixel-by-pixel basis. Extensive experiments have been conducted using JM 12.4. Compared with conventional block motion compensation, our scheme shows a bitrate saving of 18%, (5% on average) while maintaining the same or even higher PSNR (0.1 dB). It also provides a competitive advantage to variable block size motion compensation. Additionally, a hybrid of the two techniques achieves a further bitrate reduction of 13%. The result, nevertheless, provides only a lower bound on what is achievable since both motion estimation and mode decision were accomplished without considering OBMC. Further improvement is expected by incorporating iterative methods.
A rate-distortion optimization model for SVC inter-layer encoding and bitstream extraction
(2008-12-01)
Peng, Wen-Hsiao
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Zao, John K.
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Huang, Hsueh-Ting
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Wang, Tse-Wei
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Huang, Lin-Shung
The Scalable Video Coding (SVC) standard enables viewing devices to adapt their video reception using bitstream extraction. Since SVC offers spatial, temporal, and quality combined scalability, extracting proper bitstreams for different viewing devices can be a non-trivial task, and naive choices usually produce poor playback quality. In this paper, we propose a two-prong approach to achieve rate-distortion (R-D) optimal extraction of SVC bitstreams. For SVC encoding, we developed a set of adaptation rules for setting the quantization parameters and the inter-layer dependencies among the SVC coding layers. A well-adapted SVC bitstream thus produced manifests good R-D trade-offs when its scalable layers are extracted along extraction paths consisting of successive refinement steps. For extracting R-D optimized bitstreams for different viewing devices, we formalized the notion of optimal and near-optimal extraction paths and devised computationally efficient strategies to search for the extraction paths. Experiment results demonstrated that our R-D optimized adaptation schemes and extraction strategies offer significant improvement in playback picture quality among heterogeneous viewing devices. Particularly, our adaptation rules promise R-D convexity along optimal extraction paths and permit the use of steepest-descent strategy to discover the optimal/near-optimal paths. This simple search strategy performs only half of the computation necessary for an exhaustive search. (C) 2008 Elsevier Inc. All rights reserved.
Analysis of Template Matching Prediction and Its Application to Parametric Overlapped Block Motion Compensation
(2010)
Wang, Tse-Wei
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Chen, Wen
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Peng, Wen-Hsiao
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資訊工程學系
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Department of Computer Science
Template matching prediction (TMP), which estimates the motion for a target block by using its surrounding pixels, has been observed to perform efficiently in inter-frame coding. In this paper, we expose, from a more theoretical viewpoint, the factors that determine the prediction efficiency of TMP. It is shown that the motion estimate found by template matching tends to be the motion associated with the template centroid and that TMP consistently outperforms SKIP prediction, but hardly competes with block motion compensation (BMC) unless both the motion and intensity fields are less random or have high spatial correlation. We also demonstrate how template and block motion estimates can jointly be applied in a parametric overlapped block motion compensation (OBMC) framework to further improve temporal prediction. Preliminary results show that combining TMP with OBMC can yield 2-16% reductions in mean-square prediction error, as compared with the single use of OBMC. The gain is even higher (18%) when the performance is compared with that of the standard BMC.
MULTIDIMENSIONAL SVC BITSTREAM ADAPTATION AND EXTRACTION FOR RATE-DISTORTION OPTIMIZED HETEROGENEOUS MULTICASTING AND PLAYBACK
(2008)
Peng, Wen-Hsiao
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Zao, John K.
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Huang, Hsueh-Ting
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Wang, Tse-Wei
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Kuo, Lun-Chia
In this paper, we propose an optimal SVC bitstream extraction scheme that can produce scalable layer representations for different viewing devices scattered over a multicasting network with diverse link bandwidth. Our scheme can determine optimal extraction orders/paths that are implementable at different multicasting nodes by performing successive steps of multiple adaptation. In addition to this basic scheme, we also develop an unambiguous denotation for the optimal extraction paths, and an algorithm for deducing the optimal extraction paths for less capable devices through path truncation. Extensive SVC encoding and adaptation experiments have been performed using JSVM 9 and both objective quality metrics (PSNR and MSE) as well as subjective metric (VQM). The experiment results showed that our scheme works well if convexity of R-D performance is maintained throughout the SVC bitstream.
ON THE ANALYSIS AND DESIGN OF MOTION SAMPLING STRUCTURE FOR ADVANCED MOTION-COMPENSATED PREDICTION
(2010)
Tseng, Yu-Chen
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Wu, Chung-Hao
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Chen, Yi-Wen
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Wang, Tse-Wei
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Peng, Wen-Hsiao
This paper addresses the problem of improving motion sampling efficiency for motion-compensated prediction (MCP). We provide a theoretical framework for analyzing the effect of motion sampling structure on MCP efficiency. It is shown that the sampling grid induced by the quadtree partition in H.264/AVC is suboptimal. To improve sampling efficiency, we propose a new pattern, which provides sampling points at both the center and the top-left corner of a macroblcok. When contrasted with conventional NxN/2 block partition, the proposed scheme performs consistently and significantly better in subjective and objective quality.
Rate-distortion optimized SVC bitstream extraction for heterogeneous devices : A preliminary investigation
(2007)
Peng, Wen-Hsiao
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Huang, Lin-Shung
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Zao, John K.
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Lu, Jiun-Shien
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Wang, Tse-Wei
The emerging SVC standard enables partial extraction and decoding of video bitstreams, and thus allows various viewing devices to adapt their video reception and playback according to devices capability and network performance. This desirable feature, however, comes with a caveat: the parts of a bitstream needed for providing good quality playback at different devices may differ significantly depending on the visual characteristics of video programs, the quantization and dependency settings of SVC encoders as well as the display formats of viewing devices. In this paper, we present the results of our preliminary investigation on the intricate relations among these factors. We discovered a set of constraints on the setting of quantization parameters and the choices of reference layers for inter-layer dependencies that ensures good rate-distortion trade-offs and regular bitstream; extraction paths. We called these constraints, the adaptation rules for inter-layer encoding, and their resulting outputs, the well-adapted layers/bitstreams. We further discovered that bitstream extraction by different viewing devices follow predictable paths if the SVC bitstream is well-adapted and the playback process extracts a complete set of interdependent network abstraction layer (NAL) units in every refinement step. These regular extraction paths enabled us to develop an efficient bitstream extraction algorithm based on local optimization of rate-distortion ratios. The experimental results using standard testing sequences confirmed our findings.