94,292 research outputs found
Automated Video Analysis of Animal Movements Using Gabor Orientation Filters
To quantify locomotory behavior, tools for determining the location and shape of an animal’s body are a first requirement. Video recording is a convenient technology to store raw movement data, but extracting body coordinates from video recordings is a nontrivial task. The algorithm described in this paper solves this task for videos of leeches or other quasi-linear animals in a manner inspired by the mammalian visual processing system: the video frames are fed through a bank of Gabor filters, which locally detect segments of the animal at a particular orientation. The algorithm assumes that the image location with maximal filter output lies on the animal’s body and traces its shape out in both directions from there. The algorithm successfully extracted location and shape information from video clips of swimming leeches, as well as from still photographs of swimming and crawling snakes. A Matlab implementation with a graphical user interface is available online, and should make this algorithm conveniently usable in many other contexts
A spectral optical flow method for determining velocities from digital imagery
We present a method for determining surface flows from solar images based
upon optical flow techniques. We apply the method to sets of images obtained by
a variety of solar imagers to assess its performance. The {\tt opflow3d}
procedure is shown to extract accurate velocity estimates when provided perfect
test data and quickly generates results consistent with completely distinct
methods when applied on global scales. We also validate it in detail by
comparing it to an established method when applied to high-resolution datasets
and find that it provides comparable results without the need to tune, filter
or otherwise preprocess the images before its application.Comment: 12 pages, 5 figures. Submitted to Earth Science Informatic
Effects of Lens Motion and Uneven Magnification on Image Spectra
Counter to intuition, the images of an extended galaxy lensed by a moving
galaxy cluster should have slightly different spectra in any metric gravity
theory. This is mainly for two reasons. One relies on the gravitational
potential of a moving lens being time-dependent (the
, ). The other is due to uneven
magnification across the extended, rotating source (the
, ). The time delay between
the images can also cause their redshifts to differ because of cosmological
expansion. This Differential Expansion Effect is likely to be small. Using a
simple model, we derive these effects from first principles.
One application would be to the Bullet Cluster, whose large tangential
velocity may be inconsistent with the paradigm. This velocity can
be estimated with complicated hydrodynamic models. Uncertainties with such
models can be avoided using the MCE. We argue that the MCE should be observable
with ALMA.
However, such measurements can be corrupted by the DME if typical spiral
galaxies are used as sources. Fortunately, we find that if detailed spectral
line profiles were available, then the DME and MCE could be distinguished. It
might also be feasible to calculate how much the DME should affect the mean
redshift of each image. Resolved observations of the source would be required
to do this accurately.
The DME is of order the source angular size divided by the Einstein radius
times the redshift variation across the source. Thus, it mostly affects nearly
edge-on spiral galaxies in certain orientations. This suggests that observers
should reduce the DME by careful choice of target, a possibility we discuss in
some detail.Comment: 15 pages, 8 figures, 2 tables. This is the peer-reviewed version
which has been accepted for publication in Monthly Notices of the Royal
Astronomical Societ
The Potential-Density Phase Shift Method for Determining the Corotation Radii in Spiral and Barred Galaxies
We have developed a new method for determining the corotation radii of
density waves in disk galaxies, which makes use of the radial distribution of
an azimuthal phase shift between the potential and density wave patterns. The
approach originated from improved theoretical understandings of the relation
between the morphology and kinematics of galaxies, and on the dynamical
interaction between density waves and the basic-state disk stars which results
in the secular evolution of disk galaxies. In this paper, we present the
rationales behind the method, and the first application of it to several
representative barred and grand-design spiral galaxies, using near-infrared
images to trace the mass distributions, as well as to calculate the potential
distributions used in the phase shift calculations. We compare our results with
those from other existing methods for locating the corotations, and show that
the new method both confirms the previously-established trends of bar-length
dependence on galaxy morphological types, as well as provides new insights into
the possible extent of bars in disk galaxies. Application of the method to a
larger sample and the preliminary analysis of which show that the phase shift
method is likely to be a generally-applicable, accurate, and essentially
model-independent method for determining the pattern speeds and corotation
radii of single or nested density wave patterns in galaxies. Other implications
of this work are: most of the nearby bright disk galaxies appear to possess
quasi-stationary spiral modes; that these density wave modes and the associated
basic state of the galactic disk slowly transform over time; and that
self-consistent N-particle systems contain physics not revealed by the passive
orbit analysis approaches.Comment: 48 pages, 16 figures. Accepted for publication in the Astronomical
Journa
Optical flow: a curve evolution approach
©1995 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or distribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE. This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.DOI: 10.1109/ICIP.1995.537569Presented at the 1995 International Conference on Image Processing, October 23-26, 1995, Washington, DC, USA.A novel approach for the computation of optical flow based on an L 1 type minimization is presented. It is shown that the approach has inherent advantages since it does not smooth the flow-velocity across the edges and hence preserves edge information. A numerical approach based on computation of evolving curves is proposed for computing the optical flow field and results of experiments are presented
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