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Английские материалы
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Lew Stelmach, Wa James Tam, Dan Meegan, and Andrй Vincent Stereo Image Quality: Effects of Mixed Spatio-Temporal Resolution
Abstract—We explored the response of the human visual system to mixed-resolution stereo video-sequences, in which one eye view was spatially or temporally low-pass filtered. It was expected that perceived quality, depth, and sharpness would be relatively unaffected by low-pass filtering, compared to the case where both eyes viewed a filtered image. Subjects viewed two 10-second stereo video-sequences, in which the right-eye frames were filtered vertically (V) and horizontally (H) at 1 2 H, 1 2 V, 1 4 H, 1 4 V, 1 2 H 1 2 V, 1 2 H 1 4 V, 1 4 H 1 2 V, and 1 4 H 1 4 V resolution. Temporal filtering was implemented for a subset of these conditions at 1 2 temporal resolution, or with drop-andrepeat frames. Subjects rated the overall quality, sharpness, and overall sensation of depth. It was found that spatial filtering produced acceptable results: the overall sensation of depth was unaffected by low-pass filtering, while ratings of quality and of sharpness were strongly weighted towards the eye with the greater spatial resolution. By comparison, temporal filtering produced unacceptable results: field averaging and drop-and-repeat frame conditions yielded images with poor quality and sharpness, even though perceived depth was relatively unaffected. We conclude that spatial filtering of one channel of a stereo video-sequence may be an effective means of reducing transmission bandwidth.
RAR  214кбайт
Yuzo Senda Approximate Criteria for the MPEG-2 Motion Estimation
Abstract—This paper proposes three kinds of approximate criteria for the MPEG-2 motion estimation. They are based on the behavior of motion-compensated prediction, which uses a kind of averaging. A simplified motion estimation method is derived as a result of applying the criteria to the MPEG-2 Test Model motion estimator. The Test Model motion estimator consists of three steps: 1) finding full-pel motion vectors; 2) refining the vectors to half-pel accuracy; and 3) evaluating either the interpolative or the dual-prime prediction mode, which is a combination of the vectors. Since the second and the third steps require a huge number of data transfers, the circuit size of the steps becomes comparable to that of the first step. The simplified method solves this problem while keeping practically equivalent performance. In the second and the third steps, the simplified method reduces the number of necessary computations to less than 1%, and that of data transfers to less than 8% of the Test Model motion estimator. Even though the simplified method only modifies the second and third steps, the number of total data transfers, including those for the first step, is also reduced to 27% in main profile or 20% in simple profile.
RAR  176кбайт
K. T. Tan and Mohammed Ghanbari A Multi-Metric Objective Picture-Quality Measurement Model for MPEG video
Abstract—Different coding schemes introduce different artifacts to the decoded pictures, making it difficult to design an objective quality model capable of measuring all of them. A feasible approach is to design a picture-quality model for each kind of known distortion, and combine the results from the models according to the perceptual impact of each type of impairment. In this letter, a multi-metric model comprising of a perceptual model and a blockiness detector is proposed, designed for MPEG video. Very high correlation between the objective scores from the model and the subjective assessment results has been achieved.
RAR  112кбайт
Christian J. van den Branden Lambrecht, Daniele M. Costantini, Giovanni L. Sicuranza, and Murat Kunt Quality Assessment of Motion Rendition in Video Coding
Abstract—This paper addresses the issue of test and quality assessment of motion rendition in digital video coding. Motion estimation and compensation are critical modules in video coders, as they are the most demanding resources and largely account for the visual quality of the resulting compressed stream. The testing of such modules is thus very important. A computational metric, based on a spatiotemporal model of the human visual system and of human motion sensing, is proposed and used to evaluate MPEG-2 compressed video. The metric is able to assess the quality of motion rendition and exhibits a good correlation with subjective data.
RAR  335кбайт
Wilfried Philips Comparison of Techniques for Intra-Frame Coding of Arbitrarily Shaped Video Object Boundary Blocks
Abstract— This paper presents experimental results that demonstrate that the weakly separable polynomial orthonormal transform outperforms the shape adaptive discrete cosine transform (SADCT) and the recently introduced improved SADCT with .dc correction at the expense of a nonprohibitive increase in the number of computations. Some other improvements to SADCT-like schemes are also suggested.
RAR  75кбайт
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  495кбайт
Gregory J. Conklin and Sheila S. Hemami A Comparison of Temporal Scalability Techniques
Abstract—A temporally scalable video coding algorithm allows extraction of video of multiple frame rates from a single coded stream. In recent years, several video coding techniques have been proposed that provide temporal scalability using subband coding, both without and with motion compensation. With a two-band subband decomposition applied hierarchically, frame rates halve after each filtering operation. Alternatively, motion-compensated prediction (as used in MPEG) can provide temporal scalability and the same frame rates as temporal subband coding through strategic placement of reference frames and selective decoding of frames. This paper compares three temporal coding techniques with respect to providing temporal scalability: temporal subband coding (TSB), motion-compensated temporal subband coding (MC-TSB), and motion compensated prediction (MCP). Predicted rate-distortion performances at full- and lower frame rates and experimental quantitative and visual performances from coding several video sequences are compared. The comparison is explicitly for temporal coding when the dimensionality of the subsequent source coding is held constant; any spatial or higher dimensional source coding can follow. In theory and in practice, MCP and MC-TSB always outperform TSB. For high-bit-rate full-frame-rate video, the performances of MCP and MC-TSB are approximately equivalent. However, to provide temporal scalability, MCP clearly provides the best performance in terms of visual quality, quantitative quality, and bit rate of the lower frame-rate video.
RAR  524кбайт
Zixiang Xiong, Kannan Ramchandran, Michael T. Orchard, and Ya-Qin Zhang A Comparative Study of DCT- and Wavelet-Based Image Coding
Abstract—We undertake a study of the performance difference of the discrete cosine transform (DCT) and the wavelet transform for both image and video coding, while comparing other aspects of the coding system on an equal footing based on the state-of-theart coding techniques. Our studies reveal that, for still images, the wavelet transform outperforms the DCT typically by the order of about 1 dB in peak signal-to-noise ratio. For video coding, the advantage of wavelet schemes is less obvious. We believe that the image and video compression algorithm should be addressed from the overall system viewpoint: quantization, entropy coding, and the complex interplay among elements of the coding system are more important than spending all the efforts on optimizing the transform.
RAR  66кбайт
Wenwu Zhu, Yao Wang, and Qin-Fan Zhu Second-Order Derivative-Based Smoothness Measure for Error Concealment in DCT-Based Codecs
Abstract—In this paper, we study the recovery of lost or erroneous transform coefficients in image and video communication systems employing discrete cosine transform (DCT)-based codecs. Previously, we have developed a technique that exploits the smoothness property of image signals and recovers the damaged blocks by maximizing a smoothness measure. There, the firstorder derivative was used as the smoothness measure, which can lead to the blurring of sharp edges. In order to alleviate this problem, we propose to use second-order derivatives as the smoothness measure. Our simulation results show that a weighted combination of the quadratic variation and the Laplacian operator can significantly reduce the blurring across the edges while enforcing smoothness along the edges.
RAR  183кбайт
Dzung T. Hoang, Philip M. Long, and Jeffrey Scott Vitter 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. Minimizing a combination of rate and distortion yields further improvements. Although these explicit-minimization schemes are computationally intensive, they provide invaluable insight which we use to develop practical algorithms. We show that minimizing a simple heuristic function of the prediction error and the motion vector code length results in rate–distortion performance comparable to explicit-minimization schemes while being computationally feasible. Experimental results are provided for coders that operate within the H.261 standard.
RAR  474кбайт

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