59,256 research outputs found
Balanced data assimilation for highly-oscillatory mechanical systems
Data assimilation algorithms are used to estimate the states of a dynamical
system using partial and noisy observations. The ensemble Kalman filter has
become a popular data assimilation scheme due to its simplicity and robustness
for a wide range of application areas. Nevertheless, the ensemble Kalman filter
also has limitations due to its inherent Gaussian and linearity assumptions.
These limitations can manifest themselves in dynamically inconsistent state
estimates. We investigate this issue in this paper for highly oscillatory
Hamiltonian systems with a dynamical behavior which satisfies certain balance
relations. We first demonstrate that the standard ensemble Kalman filter can
lead to estimates which do not satisfy those balance relations, ultimately
leading to filter divergence. We also propose two remedies for this phenomenon
in terms of blended time-stepping schemes and ensemble-based penalty methods.
The effect of these modifications to the standard ensemble Kalman filter are
discussed and demonstrated numerically for two model scenarios. First, we
consider balanced motion for highly oscillatory Hamiltonian systems and,
second, we investigate thermally embedded highly oscillatory Hamiltonian
systems. The first scenario is relevant for applications from meteorology while
the second scenario is relevant for applications of data assimilation to
molecular dynamics
Online Video Deblurring via Dynamic Temporal Blending Network
State-of-the-art video deblurring methods are capable of removing non-uniform
blur caused by unwanted camera shake and/or object motion in dynamic scenes.
However, most existing methods are based on batch processing and thus need
access to all recorded frames, rendering them computationally demanding and
time consuming and thus limiting their practical use. In contrast, we propose
an online (sequential) video deblurring method based on a spatio-temporal
recurrent network that allows for real-time performance. In particular, we
introduce a novel architecture which extends the receptive field while keeping
the overall size of the network small to enable fast execution. In doing so,
our network is able to remove even large blur caused by strong camera shake
and/or fast moving objects. Furthermore, we propose a novel network layer that
enforces temporal consistency between consecutive frames by dynamic temporal
blending which compares and adaptively (at test time) shares features obtained
at different time steps. We show the superiority of the proposed method in an
extensive experimental evaluation.Comment: 10 page
Real Time Animation of Virtual Humans: A Trade-off Between Naturalness and Control
Virtual humans are employed in many interactive applications using 3D virtual environments, including (serious) games. The motion of such virtual humans should look realistic (or ânaturalâ) and allow interaction with the surroundings and other (virtual) humans. Current animation techniques differ in the trade-off they offer between motion naturalness and the control that can be exerted over the motion. We show mechanisms to parametrize, combine (on different body parts) and concatenate motions generated by different animation techniques. We discuss several aspects of motion naturalness and show how it can be evaluated. We conclude by showing the promise of combinations of different animation paradigms to enhance both naturalness and control
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
Text-based Editing of Talking-head Video
Editing talking-head video to change the speech content or to remove filler words is challenging. We propose a novel method to edit talking-head video based on its transcript to produce a realistic output video in which the dialogue of the speaker has been modified, while maintaining a seamless audio-visual flow (i.e. no jump cuts). Our method automatically annotates an input talking-head video with phonemes, visemes, 3D face pose and geometry, reflectance, expression and scene illumination per frame. To edit a video, the user has to only edit the transcript, and an optimization strategy then chooses segments of the input corpus as base material. The annotated parameters corresponding to the selected segments are seamlessly stitched together and used to produce an intermediate video representation in which the lower half of the face is rendered with a parametric face model. Finally, a recurrent video generation network transforms this representation to a photorealistic video that matches the edited transcript. We demonstrate a large variety of edits, such as the addition, removal, and alteration of words, as well as convincing language translation and full sentence synthesis
Nonlinear dance motion analysis and motion editing using Hilbert-Huang transform
Human motions (especially dance motions) are very noisy, and it is hard to
analyze and edit the motions. To resolve this problem, we propose a new method
to decompose and modify the motions using the Hilbert-Huang transform (HHT).
First, HHT decomposes a chromatic signal into "monochromatic" signals that are
the so-called Intrinsic Mode Functions (IMFs) using an Empirical Mode
Decomposition (EMD) [6]. After applying the Hilbert Transform to each IMF, the
instantaneous frequencies of the "monochromatic" signals can be obtained. The
HHT has the advantage to analyze non-stationary and nonlinear signals such as
human-joint-motions over FFT or Wavelet transform.
In the present paper, we propose a new framework to analyze and extract some
new features from a famous Japanese threesome pop singer group called
"Perfume", and compare it with Waltz and Salsa dance. Using the EMD, their
dance motions can be decomposed into motion (choreographic) primitives or IMFs.
Therefore we can scale, combine, subtract, exchange, and modify those IMFs, and
can blend them into new dance motions self-consistently. Our analysis and
framework can lead to a motion editing and blending method to create a new
dance motion from different dance motions.Comment: 6 pages, 10 figures, Computer Graphics International 2017, Conference
short pape
Virtual Exploration of Underwater Archaeological Sites : Visualization and Interaction in Mixed Reality Environments
This paper describes the ongoing developments in Photogrammetry and Mixed Reality for the Venus European project (Virtual ExploratioN of Underwater Sites, http://www.venus-project.eu). The main goal of the project is to provide archaeologists and the general public with virtual and augmented reality tools for exploring and studying deep underwater archaeological sites out of reach of divers. These sites have to be reconstructed in terms of environment (seabed) and content (artifacts) by performing bathymetric and photogrammetric surveys on the real site and matching points between geolocalized pictures. The base idea behind using Mixed Reality techniques is to offer archaeologists and general public new insights on the reconstructed archaeological sites allowing archaeologists to study directly from within the virtual site and allowing the general public to immersively explore a realistic reconstruction of the sites. Both activities are based on the same VR engine but drastically differ in the way they present information. General public activities emphasize the visually and auditory realistic aspect of the reconstruction while archaeologists activities emphasize functional aspects focused on the cargo study rather than realism which leads to the development of two parallel VR demonstrators. This paper will focus on several key points developed for the reconstruction process as well as both VR demonstrators (archaeological and general public) issues. The ?rst developed key point concerns the densi?cation of seabed points obtained through photogrammetry in order to obtain high quality terrain reproduction. The second point concerns the development of the Virtual and Augmented Reality (VR/AR) demonstrators for archaeologists designed to exploit the results of the photogrammetric reconstruction. And the third point concerns the development of the VR demonstrator for general public aimed at creating awareness of both the artifacts that were found and of the process with which they were discovered by recreating the dive process from ship to seabed
Blending in Gravitational Microlensing Experiments: Source Confusion And Related Systematics
Gravitational microlensing surveys target very dense stellar fields in the
local group. As a consequence the microlensed source stars are often blended
with nearby unresolved stars. The presence of `blending' is a cause of major
uncertainty when determining the lensing properties of events towards the
Galactic centre. After demonstrating empirical cases of blending we utilize
Monte Carlo simulations to probe the effects of blending. We generate
artificial microlensing events using an HST luminosity function convolved to
typical ground-based seeing, adopting a range of values for the stellar density
and seeing. We find that a significant fraction of bright events are blended,
contrary to the oft-quoted assumption that bright events should be free from
blending. We probe the effect that this erroneous assumption has on both the
observed event timescale distribution and the optical depth, using realistic
detection criteria relevent to the different surveys. Importantly, under this
assumption the latter quantity appears to be reasonably unaffected across our
adopted values for seeing and density. The timescale distribution is however
biased towards smaller values, even for the least dense fields. The dominant
source of blending is from lensing of faint source stars, rather than lensing
of bright source stars blended with nearby fainter stars. We also explore other
issues, such as the centroid motion of blended events and the phenomena of
`negative' blending. Furthermore, we breifly note that blending can affect the
determination of the centre of the red clump giant region from an observed
luminosity function. This has implications for a variety of studies, e.g.
mapping extinction towards the bulge and attempts to constrain the parameters
of the Galactic bar through red clump giant number counts. (Abridged)Comment: 18 pages, 10 figures. MNRAS (in press
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