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Сжатие видео - Low Bitrate


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Dzung T. Hoang, Philip M. Long, and Jeffrey Scott Vitter, Fellow Efficient Cost Measures for Motion Estimation at Low Bit Rates
Abstract— We present and compare methods for choosing motion vectors for block-based motion-compensated video coding. The primary focus is on videophone and videoconferencing applications, where low bit rates are necessary, where motion is usually limited, and where the amount of computation is also limited. In a typical block-based motion-compensated video coding system, motion vectors are transmitted along with a lossy encoding of the residuals. As the bit rate decreases, the proportion required to transmit the motion vectors increases. We provide experimental evidence that choosing motion vectors explicitly to minimize rate (including motion vector coding), subject to implicit constraints on distortion, yields better rate–distortion tradeoffs than minimizing some measure of prediction error.
RAR  474 кбайт
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John C.-H. Ju, Yen-Kuang Chen, and S. Y. Kung A Fast Rate-Optimized Motion Estimation Algorithm for Low-Bit-Rate Video Coding
Abstract—Motion estimation is known to be the main bottleneck in real-time encoding applications, and the search for an effective motion estimation algorithm (in terms of computational complexity and compression efficiency) has been a challenging problem for years. This paper describes a new block-matching algorithm that is much faster than the full search algorithm and occasionally even produces better rate-distortion curves than the full search algorithms. We observe that a piecewise continuous motion field reduces the bit rate for differentially encoded motion vectors. Our motion estimation algorithm exploits the spatial correlations of motion vectors effectively in the sense of producing better rate-distortion curves. Furthermore, we incorporate such correlations in a multiresolution framework to reduce the computational complexity. Simulation shows that this method is successful because of the homogeneous and reliable estimation of the displacement vectors. In nine out of our ten benchmark simulations, the performance of the full search algorithm and that of our subblock multiresolution method is about the same. In one out of our ten benchmark simulations, our method has improvement.
RAR  316 кбайт
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Jorge Sastre, Antonio Ferreras, and Josй Fйlix Hernбndez-Gil Motion Vector Size-Compensation Based Method for Very Low Bit-Rate Video Coding
Abstract—In this paper, a new method to achieve better compression efficiency in low bit-rate video coding is proposed. It is based on a global bit-rate reduction at a macroblock level, optimizing the number of bits to code each macroblock as a whole by means of motion vector and headers size compensation. The selection of the best motion vector and different coding modes for each block of the current picture will be made depending not only on trying to choose the best prediction for the block, but also on the number of bits to code the associate headers, introducing some kind of penalization in the cost function. This method improves efficiency on video compression for all qualities, but especially for low-quality video coding, whose efficiency improvement can reach 17%. Its implementation is simple, and compatible with most video-compression standards (H.263, MPEG, etc.). Results of the algorithm in a state-of-the-art H.263+ codec are presented, and demonstrate that the efficiency enhancement is achieved with minimal time-processing increase, and even decrease, in some conditions.
RAR  440 кбайт
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Gopal Lakhani and Norman Zhong Derivation of Prediction Equations for Blocking Effect Reduction
Abstract—In [1], a heuristic is proposed to solve an optimization problem on reduction of blocking effects seen in low bit-rate coded images. This paper presents a novel solution to the same problem. Not only does it compute the global minimum, but its computational complexity is significantly smaller as well. The solution is stated in the form of prediction equations for computation of certain discrete cosine transform coefficients—an approach adapted by JPEG for its block-smoothing method. Experimental results show that our solution outperforms JPEG’s method.
RAR  150 кбайт
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Jorge Sastre, Antonio Ferreras, and Josй Fйlix Hernбndez-Gil Motion Vector Size-Compensation Based Method for Very Low Bit-Rate Video Coding
Abstract—In this paper, a new method to achieve better compression efficiency in low bit-rate video coding is proposed. It is based on a global bit-rate reduction at a macroblock level, optimizing the number of bits to code each macroblock as a whole by means of motion vector and headers size compensation. The selection of the best motion vector and different coding modes for each block of the current picture will be made depending not only on trying to choose the best prediction for the block, but also on the number of bits to code the associate headers, introducing some kind of penalization in the cost function. This method improves efficiency on video compression for all qualities, but especially for low-quality video coding, whose efficiency improvement can reach 17%. Its implementation is simple, and compatible with most video-compression standards (H.263, MPEG, etc.). Results of the algorithm in a state-of-the-art H.263+ codec are presented, and demonstrate that the efficiency enhancement is achieved with minimal time-processing increase, and even decrease, in some conditions.
RAR  440 кбайт
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Guoliang Fan, and Wai-Kuen Cham Model-Based Edge Reconstruction for Low Bit-Rate Wavelet-Compressed Images
Abstract—At low bit rates, wavelet-based image coding is superior to most traditional block-based methods in terms of visibility and severity of coding artifacts in coded images. However, the compressed images still suffer from obvious distortions around sharp edges, which are perceptually objectionable. In order to improve image quality for low bit-rate wavelet-based image coding, we proposed a model-based edge-reconstruction algorithm for recovering the lossy edges in coded images. Our approach applies a general model to represent varieties of edges existing in an image. Based on this model, the edge degradation process due to quantization errors of wavelet coefficients is analyzed with the characterization of two kinds of artifacts at edges.We develop two operations, model-based edge approximation and Gaussian smoothing, to reconstruct distorted edges by reducing both artifacts respectively. The proposed method is able to improve image quality in terms of both visual perception and image fidelity (peak signal-to-noise ratio) for most images coded by wavelet-based methods at low bit-rates.
RAR  346 кбайт
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Beong-Jo Kim, Zixiang Xiong, and William A. Pearlman, Fellow Low Bit-Rate Scalable Video Coding with 3-D Set Partitioning in Hierarchical Trees (3-D SPIHT)
Abstract—In this paper, we propose a low bit-rate embedded video coding scheme that utilizes a 3-D extension of the set partitioning in hierarchical trees (SPIHT) algorithm which has proved so successful in still image coding. Three-dimensional spatio-temporal orientation trees coupled with powerful SPIHT sorting and refinement renders 3-D SPIHT video coder so efficient that it provides comparable performance to H.263 objectively and subjectively when operated at the bit rates of 30 to 60 kbits/s with minimal system complexity. Extension to color-embedded video coding is accomplished without explicit bit allocation, and can be used for any color plane representation. In addition to being rate scalable, the proposed video coder allows multiresolutional scalability in encoding and decoding in both time and space from one bit stream. This added functionality along with many desirable attributes, such as full embeddedness for progressive transmission, precise rate control for constant bit-rate traffic, and lowcomplexity for possible software-only video applications, makes the proposed video coder an attractive candidate for multimedia applications.
RAR  342 кбайт
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Wee Sun Lee, Mark R. Pickering, Michael R. Frater, and John F. Arnold A Robust Codec for Transmission of Very Low Bit-Rate Video over Channels with Bursty Errors
Abstract—We describe a robust codec for the transmission of very low bit-rate video over channels with a variety of errors, including random and bursty bit errors and packet loss. The codec exploits adaptivity to give good performance with a low overhead. By only protecting macroblocks which would otherwise be poorly concealed by the decoder, the codec allows adaptive selection of the parts of video to protect. For protection, it uses multiple description codes which indirectly provide frequency-based adaptivity by protecting the more significant DCT coefficients. Simulations show significant improvements in the performance of the codec when compared to codecs which use intra macroblock updating (raster scan and random) at the same overhead. The codec is efficient in its use of bits and has good error resilience properties both objectively and subjectively over a wide range of conditions. Further, transcoding of the received bit stream to the standard H.263 syntax is relatively easy.
RAR  225 кбайт
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Detlev Marpe and Hans L. Cycon Very Low Bit-Rate Video Coding Using Wavelet-Based Techniques
Abstract—In this paper, we propose a very low bit-rate video coding scheme based on a discrete wavelet transform (DWT), block-matching motion estimation (BME), and overlapped block motion compensation (OBMC). Our approach reveals that the coding process works more efficiently if the quantized wavelet coefficients are preprocessed by a mechanism exploiting the redundancies in the wavelet subband structure. Thus, we introduce a new framework of precoding techniques based on the concepts of partitioning, aggregation, and conditional coding (PACC). Our experimental results show that our PACC coder outperforms the VM (Version 5.1) of MPEG4 both for the coding of intraframes (1–2 dB PSNR) and residual frames (up to 1.5 dB PSNR) of typical MPEG4 test sequences. The subjective quality of reconstructed video is, in general, superior to that obtained from the VM implementation. In addition, when restricted to the intraframe mode, the proposed coding algorithm produces results which are among the best reported for still image compression.
RAR  741 кбайт
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Jozsef Vass, Bing-Bing Chai, Kannappan Palaniappan, and Xinhua Zhuang Significance-Linked Connected Component Analysis for Very Low Bit-Rate Wavelet Video Coding
Abstract—In recent years, a tremendous success in wavelet image coding has been achieved. It is mainly attributed to innovative strategies for data organization and representation of wavelet-transformed images. However, there have been only a few successful attempts in wavelet video coding. The most successful is perhaps Sarnoff Corp.’s zerotree entropy (ZTE) video coder. In this paper, a novel hybrid wavelet video coding algorithm termed video significance-linked connected component analysis (VSLCCA) is developed for very low bit-rate applications. There also has been empirical evidence that wavelet transform combined with those innovative data organization and representation strategies can be an invaluable asset in very low bit-rate video coding as long as motion compensated error frames are ensured to be free of blocking effect or coherent. In the proposed VSLCCA codec, first, fine-tuned motion estimation based on the H.263 Recommendation is developed to reduce temporal redundancy, and exhaustive overlapped block motion compensation is utilized to ensure coherency in motion compensated error frames. Second, wavelet transform is applied to each coherent motion compensated error frame to attain global energy compaction. Third, significant fields of wavelettransformed error frames are organized and represented as significance-linked connected components so that both the withinsubband clustering and the cross-scale dependency are exploited. Last, the horizontal and vertical components of motion vectors are encoded separately using adaptive arithmetic coding while significant wavelet coefficients are encoded in bit-plane order by using high order Markov source modeling and adaptive arithmetic coding. Experimental results on eight standard MPEG-4 test sequences show that for intraframe coding, on average the proposed codec exceeds H.263 and ZTE in peak signal-to-noise ratio by as much as 2.07 and 1.38 dB at 28 kbits, respectively. For entire sequence coding, VSLCCA is superior to H.263 and ZTE by 0.35 and 0.71 dB on average, respectively.
RAR  894 кбайт
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Sangyoun Lee and Vijay K. Madisetti Parameter Optimization of Robust Low-Bit-Rate Video Coders
Abstract—Most standards provide a generalized syntax and semantics framework for video coders, leaving the selection and optimization of the right parameter set (and lookup tables) to the implementation. The choice of the right parameter set that is suitable for a rich enough class of input sequences is, however, quite difficult. This difficulty is particularly amplified in the lowbit- rate video coding arena, where robust parameter sets are very important. We propose that robust parameter estimation, using the Taguchi methods, when applied to low-bit-rate video coding allows effective (near optimal) performance over a wide variety of input data streams. A number of experimental results confirm the improvement (via robustness) vis-`a-vis conventional parameter estimation methods, and these methods promise a solution to the design of efficient parameter sets that support standards.
RAR  172 кбайт
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Seung Chul Yoon, Krishna Ratakonda, and Narendra Ahuja, Fellow Low Bit-Rate Video Coding with Implicit Multiscale Segmentation
Abstract— In this paper, we report on our efforts toward developing a multiscale segmentation based video compression algorithm aimed at very low bit-rate applications such as video teleconferencing and video phones.We introduce novel techniques for multiscale segmentation based motion compensation and residual coding. Our region based forward motion compensation strategy (in terms of direction of motion vector, which is from the previous frame to the current frame) regulates the size and number of regions used, by pruning a multiscale segmentation of video frames. Since regions used for motion compensation are obtained by segmenting the previously decoded frame, the shape of the regions need not be transmitted to the decoder. Furthermore, our hierarchical motion compensation strategy refines an initial region level, coarse motion field to obtain a dense motion field which provides pixel level motion vectors. The refinement procedure does not require any additional information to be transmitted. This motion compensation technique effectively addresses the problem of dealing with “holes” and “overlapping regions” which are inherent to forward motion compensation. Residual coding is performed using a novel method which exploits the fact that the energy of the residual resulting from motion compensation is concentrated in a priori predictable positions. We will show that this residual coding technique can also be extrapolated to improve the performance of coders using a block based motion compensation strategy. A fusion of these concepts leads to a gain of 2–3 dB in peak signal-to-noise ratio, apart from significant perceptual improvement, over a generic video coding algorithm using a block based motion compensation strategy (such as H.261 or H.263) for a variety of test sequences.
RAR  546 кбайт
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Wenjun Zeng, and Bede Liu, Fellow Geometric-Structure-Based Error Concealment with Novel Applications in Block-Based Low-Bit-Rate Coding
Abstract—This paper first proposes a computationally efficient spatial directional interpolation scheme, which makes use of the local geometric information extracted from the surrounding blocks. The proposed error-concealment scheme produces results that are superior to those of other approaches, in terms of both peak signal-to-noise ratio and visual quality. Then a novel approach that incorporates this directional spatial interpolation at the receiver is proposed for block-based low-bit-rate coding. The key observation is that the directional spatial interpolation at the receiver can reconstruct faithfully a large percentage of the blocks that are intentionally not sent. A rate-distortion optimal way to drop the blocks is shown. The new approach can be made compatible with standard JPEG and MPEG decoders. The blockdropping approach also has an important application for dynamic rate shaping in transmitting precompressed videos over channels of dynamic bandwidth. Experimental results show that the proposed coding and rate-shaping systems can provide significant subjective and objective gains over conventional approaches.
RAR  1344 кбайт
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Weixing Zhang and Thomas R. Fischer Comparison of Different Image Subband Coding Methods at Low Bit Rates
Abstract—Two image subband coding methods are introduced as combinations of trellis-coded quantization (TCQ) with zerotree and stack-run coding. These TCQ-based image coding algorithms are compared, at low bit rates, with the set partitioning in hierarchical trees and stack-run scalar quantization-based image coding algorithms. Direct use of TCQ with zerotree or stack-run coding methods is found to provide little or no improvement in rate-distortion performance compared to scalar quantization.
RAR  495 кбайт
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Nikolaos Doulamis, Anastasios Doulamis, Dimitrios Kalogeras, and Stefanos Kollias Low Bit-Rate Coding of Image Sequences Using Adaptive Regions of interest
Abstract— An adaptive algorithm for extracting foreground objects from background in videophone or videoconference applications is presented in this paper. The algorithm uses a neural network architecture that classifies the video frames in regionsof- interest (ROI) and non-ROI areas, also being able to automatically adapt its performance to scene changes. The algorithm is incorporated in motion-compensated discrete cosine transform (MC–DCT)-based coding schemes, allocating more bits to ROI than to non-ROI areas. Simulation results are presented, using the Claire and Trevor sequences, which show reconstructed images of better quality, as well as signal-to-noise ratio improvements of about 1.4 dB, compared to those achieved by standard MC–DCT encoders.
RAR  356 кбайт
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Dzung T. Hoang, Philip M. Long, and Jeffrey Scott Vitter, Fellow, EEE Efficient Cost Measures for Motion Estimation at Low Bit Rates
Abstract— We present and compare methods for choosing motion vectors for block-based motion-compensated video coding. The primary focus is on videophone and videoconferencing applications, where low bit rates are necessary, where motion is usually limited, and where the amount of computation is also limited. In a typical block-based motion-compensated video coding system, motion vectors are transmitted along with a lossy encoding of the residuals. As the bit rate decreases, the proportion required to transmit the motion vectors increases. We provide experimental evidence that choosing motion vectors explicitly to minimize rate (including motion vector coding), subject to implicit constraints on distortion, yields better rate–distortion tradeoffs than minimizing some measure of prediction error.
RAR  474 кбайт
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Takahiro Fukuhara, Kohtaro Asai, Tokumichi Murakami Very Low Bit-Rate Video Coding with Block Partitioning and Adaptive Selection of Two Time-Differential Frame Memories
Abstract—Recently several studies on very low bit rate video coding have been reported. One of the major goals of the studies is to improve coding performance, which gives better subjective and objective quality than conventional coding methods at the same bit rate. As the shape and structure of an object in a picture are arbitrary, the performance of traditional coding with block-based motion compensation (MC) is not satisfactory. In this paper, we present advanced MC schemes for very low bit-rate video coding. Major features of the proposed MC are blockpartitioning prediction and utilization of two time-differential reference frames. This coding scheme improves image quality around objects’ boundaries and consequently reduces prediction errors. It also works well in the case of object occlusions. The combination of the proposed MC and discrete cosine transformation (DCT) will show better performance in several test sequences than full-spec H.263.
RAR  641 кбайт
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Ralph Neff and Avideh Zakhor Very Low Bit-Rate Video Coding Based on Matching Pursuits
Abstract—We present a video compression algorithm which performs well on generic sequences at very low bit rates. This algorithm was the basis for a submission to the November 1995 MPEG-4 subjective tests. The main novelty of the algorithm is a matching-pursuit based motion residual coder. The method uses an inner-product search to decompose motion residual signals on an overcomplete dictionary of separable Gabor functions. This coding strategy allows residual bits to be concentrated in the areas where they are needed most, providing detailed reconstructions without block artifacts. Coding results from the MPEG-4 Class A compression sequences are presented and compared to H.263. We demonstrate that the matching pursuit system outperforms the H.263 standard in both peak signal-to-noise ratio (PSNR) and visual quality.
RAR  1324 кбайт
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Raj Talluri, Karen Oehler, Thomas Bannon, Jonathan D. Courtney, Arnab Das, and Judy Liao A Robust, Scalable, Object-Based Video Compression Technique for Very Low Bit-Rate Coding
Abstract—This paper describes an object-based video coding scheme (OBVC) that was proposed by Texas Instruments to the emerging ISO MPEG-4 video compression standardization effort. This technique achieves efficient compression by separating coherently moving objects from stationary background and compactly representing their shape, motion, and the content. In addition to providing improved coding efficiency at very low bit rates, the technique provides the ability to selectively encode, decode, and manipulate individual objects in a video stream. This technique supports all three MPEG-4 functionalities tested in the November 1995 tests, namely, improved coding efficiency, error resilience, and content scalability. This paper also describes the error protection and concealment schemes that enable robust transmission of compressed video over noisy communication channels such as analog phone lines and wireless links. The noise introduced by the communication channel is characterized by both burst errors and random bit errors. Applications of this object-based video coding technology include videoconferencing, video telephony, desktop multimedia, and surveillance video.
RAR  1157 кбайт
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