Chau-Wai Wong

The Hong Kong Polytechnic University, Hong Kong, Hong Kong

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Publications (4)6.84 Total impact

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    Chau-Wai Wong, Wan-Chi Siu
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    ABSTRACT: In this paper, we propose a new discrete cosine transform (DCT)-like kernel IK(5, 7, 3) and revitalize another DCT-like kernel IK(13, 17, 7) for the transform coding process of hybrid video coding. Making use one of these kernels together with the H.264/AVC kernel IK(1, 2, 1), we are able to design new multiple-kernel schemes which give better coding performance over that of the conventional approaches. All these schemes make use of the adaptive kernel mechanism at macroblock-level (MB-AKM), which requires heavy computation during the encoding process. We subsequently discovered that a rate-distortion feature extracted from a pair of kernels gives an intrinsic property that can be used to select a better kernel for a two-kernel MB-AKM system. This is a powerful tool with theoretical interest and practical uses. In order to reduce computation substantially, we make use of this tool to make an analysis and design of a frame-level adaptive kernel mechanism and come up with a simple solution that the kernel IK(1, 2, 1) be used for I-frames and P-frames and the kernel IK(5, 7, 3) be used for B-frames coding. This proposed frame-based AKM gives similar, or even better, performance as the proposed macroblock-based AKM. Furthermore, it substantially reduces computation and certainly gives a good improvement in terms of the PSNR and bitrate compared to those obtained from the H.264/AVC default scheme and other MB-AKM schemes available in the literature.
    IEEE Transactions on Circuits and Systems for Video Technology 12/2011; · 1.82 Impact Factor
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    Chau-Wai Wong, Wan-Chi Siu
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    ABSTRACT: In this paper, we present an analysis of the dyadic approximation error introduced by the integerization of transform coding in H.264/AVC-like codecs. We derive the analytical formulations for dyadic approximation error and nonorthogonality error. We further classify the dyadic approximation error into a "system error" and a "nonflat error," and proposed two models for them. We found that the "nonflat error" has a substantial impact on video quality if the number of shifting bits at decoder side (DQ_BITS) is small. We also give a theoretical justification on why scaling factors at encoder side are better to be adapted to the rescaling factors at decoder side in H.264/AVC-like codecs.
    IEEE Transactions on Image Processing 10/2011; 20(10):2780-7. · 3.20 Impact Factor
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    Chau-Wai Wong, Wan-Chi Siu
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    ABSTRACT: In a recent paper, Dong proposed a set of order-16 nonorthogonal integer cosine transforms (NICTs). They proved that the reconstruction error caused by the nonorthogonality is negligible as compared to the error caused by the quantization. However, we would like to point out three problems found in derivations and also give two comments. Nevertheless, the problems are defects only, hence do not affect the overall justifications to the proposed NICT. This letter is to enhance and clarify the proof of Dong 's work.
    IEEE Transactions on Circuits and Systems for Video Technology 01/2011; 21:1765-1767. · 1.82 Impact Factor
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    Chau-Wai Wong, Wan-Chi Siu
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    ABSTRACT: APSIPA ASC 2009: Asia-Pacific Signal and Information Processing Association, 2009 Annual Summit and Conference. 4-7 October 2009. Sapporo, Japan. Oral session: Image and Video Coding (5 October 2009). In this paper, we make use of a multiple-kernel scheme as a guide to exploit the transform kernel selection strategy of the hybrid video coding. We have found that the kernel selection tendency lies in a feature which can be extracted from a pair of kernels. We propose using the IK(1,2,1) kernel for I- and P-Frames and the IK(5,7,3) kernel for B-Frames for the H.264 Video Coding Standard. This gives a good improvement in terms of the PSNR and bitrate compared to those using a single kernel in the H.264 (JM 12.2) and the multiple-kernel schemes available in the literature. We also generalize a feature extracted from a pair of kernels to form a feature extracted from a group of many kernels. This collection of corresponding operation points forms the Macroblock-Level Kernel Galaxy (MLKG). Regarding to the robustness and ease of visualizing the performance, we also propose using the MLKG as a guide to design a single-kernel transform coding process for possible future video coding standards.