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Variable temporal-length 3-D discrete cosine.transform coding

IEEE TRANSACTIONS ON IMAGE PROCESSING 1997年第5期6卷 758-763页

作者： Chan, YL Siu, WC Dept. of Electron. Eng. Hong Kong Polytech. Univ. Kowloon

Three-dimensional discrete cosine transform (3-D DCT) coding has the advantage of reducing the interframe redundancy among a number of consecutive frames, while the motion compensation technique can only reduce the redundancy of at most two frames. However, the performance of the 3-D DCT coding will be degraded for complex scenes with a greater amount of motion. This paper presents a 3-D DCT coding with a variable temporal length that is determined by the scene change detector. Our idea is to let the motion activity in each block be very low, while the efficiency of the 3-D DCT coding could be increased. Experimental results show that this technique is indeed very efficient. The present approach has substantial improvement over the conventional fixed-length 3 D DCT coding and is also better than that of the Moving Picture Expert Group (MPEG) coding.

关键词： .transform coding image sequence shown in Fig coder motion activity DCT coding MCTC technique

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Wavelet-based very low bit-rate video coding using image warping and overlapped block motion compensation

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IEE PROCEEDINGS-VISION IMAGE AND SIGNAL PROCESSING 2001年第2期148卷 93-101页

作者： Heising, G Marpe, D Cycon, HL Petukhov, AP Heinrich Hertz Inst Commun Technol Image Proc Dept Berlin Germany Fachhsch Tech & Wirtschaft Berlin Germany Univ S Carolina Dept Math Columbia SC 29208 USA

The authors present an algorithm for very low bit-rate video coding that combines new ideas in motion estimation, wavelet filter design, and wavelet-based coding techniques. A new motion compensation technique using image warping and overlapped block motion compensation is proposed to reduce temporal redundancies in a given image sequence. This combined motion model has the advantage of representing more complex motion than simple block matching schemes. To further improve the quality of the temporal prediction, an adaptive grid with variable density according to the varying motion activity of a given scene is generated. An adaptively switched high-quality texture interpolation is employed to cope with the problem of fractional displacements in such a way that both objective and subjective reconstruction quality is improved. Spatial decorrelation of the motion compensated residual images is performed using an one-parametric family of biorthogonal infinite impulse response (IIR) wavelet filters coupled with the highly efficient pre-coding scheme of 'partitioning, aggregation and conditional coding' (PACC). Experimental results demonstrate significant improvements in objective quality of 1.0-2.3 dB PSNR in comparison to the H.263+ test model TMN10 using advanced coding options. In addition, the authors' intracoding method provides a performance gain of 0.5 dB PSNR on the average for a test suite of various still images when compared to the emerging still image coding standard JPEG-2000.

关键词： .transform coding compensation image warping motion discontinuities motion vector block motion OBMC warping model

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DC coefficient restoration technique and its application to image coding

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IEE PROCEEDINGS-VISION IMAGE AND SIGNAL PROCESSING 2002年第5期149卷 272-282页

作者： Tse, FW Cham, WK Liu, JZ Chinese Univ Hong Kong Dept Elect Engn Hong Kong Hong Kong Peoples R China

In the traditional approach of block transform image coding, a large number of bits are allocated to the DC coefficients. A technique called DC coefficient restoration (DCCR) has been proposed to further improve the compression ability of block transform image coding by not transmitting the DC coefficients but estimating them from the transmitted AC coefficients. Images thus generated, however, have inherent errors that degrade the image visual quality. In the paper, a global estimation DCCR scheme is proposed that can eliminate the inherent errors. The scheme estimates all the DC coefficients of the blocks simultaneously by minimising the sum of the energy of all the edge difference vectors of the image. The performance of the global estimation DCCR is evaluated using a mathematical model and experiments. Fast algorithms are also developed for efficient implementation of the proposed scheme.

关键词： .transform coding image coding DPCM MED criterion JPEG image transform coefficients unitary Block transform quantisation AC coefficients quantised DC coefficients global estimation

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Adaptive MLP post-processing for block-based coded images

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IEE PROCEEDINGS-VISION IMAGE AND SIGNAL PROCESSING 2000年第5期147卷 463-473页

作者： Huang, YL Chang, RF Natl Chung Cheng Univ Dept Comp Sci & Informat Engn Chiayi 62107 Taiwan

Block-based image coding techniques are widely used for encoding images and videos. However. many annoying artefacts appear when an image is encoded at low bit rates. In these artefacts, the blocking effects are very obvious to human vision. Thus, an efficient blocking effect reduction scheme is essential for preserving the visual quality of decompressed images. A new adaptive post-processing algorithm is proposed to reduce the blocking artefacts of block-based coded images by using neural network techniques in the spatial domain. The algorithm combines a variance-based classifier and multilayer perceptrons to improve the performance of post-processing. In the proposed algorithm, the blocking and ringing effects in a reconstructed image are diminished without blurring of the edges, and the detailed region in the image is also enhanced. Comparison results between the proposed algorithm and other algorithms are made with several Joint photographic Experts Group and vector quantisation decompressed images. In the simulations, the results of reconstructed images with improvements in both visual quality and PSNR are shown. It is found that the proposed algorithm is an effective post-processing algorithm for block-based image coding at low bit rates.

关键词： .transform coding video compression image coding bit rates MLP decompressed reconstructed images coded images blocking effects

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Optimized nonorthogonal transforms for image compression

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IEEE TRANSACTIONS ON IMAGE PROCESSING 1997年第4期6卷 507-522页

作者： Guleryuz, OG Orchard, MT PRINCETON UNIV DEPT ELECT & COMP ENGNPRINCETONNJ 08544

The.transform coding of images is analyzed from a common standpoint in order to generate a framework for the design of optimal transforms. It is argued that all transform coders are alike in the way they manipulate the data structure formed by transform coefficients. A general energy compaction measure is proposed to generate optimized transforms with desirable characteristics particularly suited to the simple.transform coding operation of scalar quantization and entropy coding, It is shown that the optimal linear decoder (inverse transform) must be an optimal linear estimator, independent of the structure of the transform generating the coefficients, A formulation that sequentially optimizes the transforms is presented, and design equations and algorithms for its computation provided, The properties of the resulting transform systems are investigated, In particular, it is shown that the resulting basis are nonorthogonal and complete, producing energy compaction optimized, decorrelated transform coefficients, Quantization issues related to nonorthogonal expansion coefficients are addressed with a simple, efficient algorithm, Tao implementations are discussed, and image coding examples are given, It is shown that the proposed design framework results in systems with superior energy compaction properties and excellent coding results.

关键词： .transform coding perfect existing methods image coding completeness imposed decorrelated class of images transform-reconstruction

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