Английские материалы
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| Авторы |
Название статьи |
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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
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| 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
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| 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
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| 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
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| 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
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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 495кбайт
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| 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
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| 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
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| 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
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| 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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