K.T. Choi

The University of Hong Kong, Hong Kong, Hong Kong

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Publications (5)0 Total impact

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    K.T. Choi, S.C. Chan, T.S. Ng
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    ABSTRACT: In this paper, a new perceptual based rate control algorithm for MPEG-2 is presented. The algorithm first determines the target bit count for each frame using simple statistical models. Precise bit allocation is used to adjust the macroblock quantization scale factors to meet the given bit count, with the uniform visual fidelity as the primary objective. Since the buffer is very stable, it is less sensitive to transmission delay. Experimental results showed that it gave better visual quality and less buffer variations as compared to the TM5 rate control scheme
    Circuits and Systems, 1998. ISCAS '98. Proceedings of the 1998 IEEE International Symposium on; 01/1998
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    K.T. Choi, S.C. Chan, T.S. Ng
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    ABSTRACT: Transform coding often leads to artifacts called blocking when the image or video is compressed to low bit-rate. In this paper, a new post-processing scheme using selective low-pass filtering and fuzzy-based enhancement is proposed. The merit of the scheme is that it can remove most of the blocking artifacts found in image or video coding while preserving most of the fine details. Simulation results demonstrated that the proposed algorithm can significantly improve the visual quality of the decoded image
    Circuits and Systems, 1997. ISCAS '97., Proceedings of 1997 IEEE International Symposium on; 07/1997
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    K.T. Choi, S.C. Chan, T.S. Ng
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    ABSTRACT: Motion estimation using block matching algorithms (BMA) is frequently used to reduced the temporal redundancy found in video coding. The performance of the mean squared error (MSE) is usually better than the mean absolute difference (MAD). However, the computational complexity is higher due to the squaring operations. In this paper, we propose a multiple candidates approach to shorten the gap between the two methods with slight increase in computational complexity. Application of the proposed algorithm to subband motion estimation is studied and simulation results demonstrate that great improvement in performance can be obtained with similar computational complexity as the MAD measure
    Signal Processing, 1996., 3rd International Conference on; 11/1996
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    K.T. Choi, S.C. Chan, T.S. Ng
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    ABSTRACT: In this paper we present a fast algorithm to reduce the computational complexity of block motion estimation. The reduction is obtained from the use of a new hexagonal subsampling pattern and the domain decimation method introduced by Cheng and Chan (see Proc. IEEE ICASSP, vol.4, p.2313, 1996). The multiple candidates search method is also introduced to improve the robustness of the algorithm. Computer simulation shows that the performance is very close to that of the full search
    Image Processing, 1996. Proceedings., International Conference on; 10/1996
  • K. T. Choi, S. C. Chan, T. S. Ng
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    ABSTRACT: Transform coding often leads to artifacts called blocking when the image or videci is compressed to low bit-rate. In this paper, a new post-processing scheme using selective low-pass filtering and fuzzy- based enhancement is proposed. The merit of the scheme is that it can remove most of the blocking artifacts found in image or video coding while preserving most of the fine details. Simulation results demonstrated that the proposed algorithm can significantly improve the visual quality of the decoded image. I. 1NTRODUCTIC)N Transform coding using the Discrete Cosine Transform (DCT) is the most popular approach for image compression. However, it often Yeads to artifacts called blocking when the image or video is compressed to low bit-rate. This artifact can be reduced by proper selecting the quantization step sizes in the coder andor by post-processing the decoded image. Blocking artifact originates from the block: based nature of transform coding. Since the image is divided into square blocks and each block is ccided and quantized individually, there will be noticeable discontinuity between adjacent blocks when the picture is encoded at low bit-rate. Since blocking is a high frequency artifacts, low-pass filtering can be used to reduce its effect. However, simple low-pass filtering usually leads to over-smoothing of the high frequency components found in edges and textures. Previous research on post-processing using space- variant filters (l) was done by smoothing of the edges and by estimating the edge irlfonnation in the compressed image data (2). This is a rather difficult in low bit-rate coding since the actual edge information will be severely distorted. Other approach based on iterative method has also been proposed. In (3), the image is reconstructed using the method of projections onto convex sets (POCS) (3) where a number of constrains on the coded images such quantization step- size are used together with low-pass filtering to remove the blocking artifacts.