607 research outputs found
Interactive multiview video system with low decoding complexity
Research in multimedia is always investigating new ways of improving the immersive experience of the users. One current solution consists in designing systems which offer a high level of interactivity, such as multiview content navigation where the point of view can be changed while watching at a video sequence (e.g., free viewpoint television, gaming, etc.). The coding algorithm designed for the transmission of such media streams must be adapted to these novel decoder needs. However, video plus depth data transmission is usually performed by considering the information flows as two sequences encoded with MVC schemes. Whereas it achieves good compression performance, this coding approach is not appropriate for interactive applications since the decoding of a frame often requires the prior transmission and decoding of several reference frames. Moreover, the techniques recently developed to improve interactivity are generally implemented at the decoder, whose computational complexity requirements are augmented. In this paper, we propose a novel coding scheme for video plus depth sequences that is adapted to user navigation; contrarily to several common approaches, the additional complexity is added on the encoder side so that the decoder stays simple. We further propose to limit the additional bandwidth imposed by interactivity requirements by designing a rate allocation algorithm that builds on a model of the user behavior. A first version of our novel coding architecture is evaluated in terms of rate-distortion performance, where it is shown to offer a high interactivity at a reasonable bandwidth cost
Optimized Data Representation for Interactive Multiview Navigation
In contrary to traditional media streaming services where a unique media
content is delivered to different users, interactive multiview navigation
applications enable users to choose their own viewpoints and freely navigate in
a 3-D scene. The interactivity brings new challenges in addition to the
classical rate-distortion trade-off, which considers only the compression
performance and viewing quality. On the one hand, interactivity necessitates
sufficient viewpoints for richer navigation; on the other hand, it requires to
provide low bandwidth and delay costs for smooth navigation during view
transitions. In this paper, we formally describe the novel trade-offs posed by
the navigation interactivity and classical rate-distortion criterion. Based on
an original formulation, we look for the optimal design of the data
representation by introducing novel rate and distortion models and practical
solving algorithms. Experiments show that the proposed data representation
method outperforms the baseline solution by providing lower resource
consumptions and higher visual quality in all navigation configurations, which
certainly confirms the potential of the proposed data representation in
practical interactive navigation systems
Multi-View Video Packet Scheduling
In multiview applications, multiple cameras acquire the same scene from
different viewpoints and generally produce correlated video streams. This
results in large amounts of highly redundant data. In order to save resources,
it is critical to handle properly this correlation during encoding and
transmission of the multiview data. In this work, we propose a
correlation-aware packet scheduling algorithm for multi-camera networks, where
information from all cameras are transmitted over a bottleneck channel to
clients that reconstruct the multiview images. The scheduling algorithm relies
on a new rate-distortion model that captures the importance of each view in the
scene reconstruction. We propose a problem formulation for the optimization of
the packet scheduling policies, which adapt to variations in the scene content.
Then, we design a low complexity scheduling algorithm based on a trellis search
that selects the subset of candidate packets to be transmitted towards
effective multiview reconstruction at clients. Extensive simulation results
confirm the gain of our scheduling algorithm when inter-source correlation
information is used in the scheduler, compared to scheduling policies with no
information about the correlation or non-adaptive scheduling policies. We
finally show that increasing the optimization horizon in the packet scheduling
algorithm improves the transmission performance, especially in scenarios where
the level of correlation rapidly varies with time
Loss-resilient Coding of Texture and Depth for Free-viewpoint Video Conferencing
Free-viewpoint video conferencing allows a participant to observe the remote
3D scene from any freely chosen viewpoint. An intermediate virtual viewpoint
image is commonly synthesized using two pairs of transmitted texture and depth
maps from two neighboring captured viewpoints via depth-image-based rendering
(DIBR). To maintain high quality of synthesized images, it is imperative to
contain the adverse effects of network packet losses that may arise during
texture and depth video transmission. Towards this end, we develop an
integrated approach that exploits the representation redundancy inherent in the
multiple streamed videos a voxel in the 3D scene visible to two captured views
is sampled and coded twice in the two views. In particular, at the receiver we
first develop an error concealment strategy that adaptively blends
corresponding pixels in the two captured views during DIBR, so that pixels from
the more reliable transmitted view are weighted more heavily. We then couple it
with a sender-side optimization of reference picture selection (RPS) during
real-time video coding, so that blocks containing samples of voxels that are
visible in both views are more error-resiliently coded in one view only, given
adaptive blending will erase errors in the other view. Further, synthesized
view distortion sensitivities to texture versus depth errors are analyzed, so
that relative importance of texture and depth code blocks can be computed for
system-wide RPS optimization. Experimental results show that the proposed
scheme can outperform the use of a traditional feedback channel by up to 0.82
dB on average at 8% packet loss rate, and by as much as 3 dB for particular
frames
Rate-Distortion Analysis of Multiview Coding in a DIBR Framework
Depth image based rendering techniques for multiview applications have been
recently introduced for efficient view generation at arbitrary camera
positions. Encoding rate control has thus to consider both texture and depth
data. Due to different structures of depth and texture images and their
different roles on the rendered views, distributing the available bit budget
between them however requires a careful analysis. Information loss due to
texture coding affects the value of pixels in synthesized views while errors in
depth information lead to shift in objects or unexpected patterns at their
boundaries. In this paper, we address the problem of efficient bit allocation
between textures and depth data of multiview video sequences. We adopt a
rate-distortion framework based on a simplified model of depth and texture
images. Our model preserves the main features of depth and texture images.
Unlike most recent solutions, our method permits to avoid rendering at encoding
time for distortion estimation so that the encoding complexity is not
augmented. In addition to this, our model is independent of the underlying
inpainting method that is used at decoder. Experiments confirm our theoretical
results and the efficiency of our rate allocation strategy
3D video coding and transmission
The capture, transmission, and display of
3D content has gained a lot of attention in the last few
years. 3D multimedia content is no longer con fined to
cinema theatres but is being transmitted using stereoscopic
video over satellite, shared on Blu-RayTMdisks,
or sent over Internet technologies. Stereoscopic displays
are needed at the receiving end and the viewer needs to
wear special glasses to present the two versions of the
video to the human vision system that then generates
the 3D illusion. To be more e ffective and improve the
immersive experience, more views are acquired from a
larger number of cameras and presented on di fferent displays,
such as autostereoscopic and light field displays.
These multiple views, combined with depth data, also
allow enhanced user experiences and new forms of interaction
with the 3D content from virtual viewpoints.
This type of audiovisual information is represented by a
huge amount of data that needs to be compressed and
transmitted over bandwidth-limited channels. Part of
the COST Action IC1105 \3D Content Creation, Coding
and Transmission over Future Media Networks" (3DConTourNet)
focuses on this research challenge.peer-reviewe
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