16,657 research outputs found
Localizing Region-Based Active Contours
©2008 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/TIP.2008.2004611In this paper, we propose a natural framework that allows any region-based segmentation energy to be re-formulated in a local way. We consider local rather than global image statistics and evolve a contour based on local information. Localized contours are capable of segmenting objects with heterogeneous feature profiles that would be difficult to capture correctly using a standard global method. The presented technique is versatile enough to be used with any global region-based active contour energy and instill in it the benefits of localization. We describe this framework and demonstrate the localization of three well-known energies in order to illustrate how our framework can be applied to any energy. We then compare each localized energy to its global counterpart to show the improvements that can be achieved. Next, an in-depth study of the behaviors of these energies in response to the degree of localization is given. Finally, we show results on challenging images to illustrate the robust and accurate segmentations that are possible with this new class of active contour models
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Shape-driven segmentation of the arterial wall in intravascular ultrasound images
Segmentation of arterial wall boundaries from intravascular images is an important problem for many applications in the study of plaque characteristics, mechanical properties of the arterial wall, its 3D reconstruction,
and its measurements such as lumen size, lumen radius, and wall radius. We present a shape-driven approach to segmentation of the arterial wall from intravascular ultrasound images in the rectangular domain. In a properly built
shape space using training data, we constrain the lumen and media-adventitia contours to a smooth, closed geometry, which increases the segmentation quality without any tradeoff with a regularizer term. In addition to a shape prior,
we utilize an intensity prior through a non-parametric probability density based image energy, with global image measurements rather than pointwise measurements used in previous methods. Furthermore, a detection step is included to address the challenges introduced to the segmentation process by side branches and calcifications. All these features greatly enhance our segmentation method. The tests of our algorithm on a large dataset demonstrate the effectiveness of our approach
Automated detection of extended sources in radio maps: progress from the SCORPIO survey
Automated source extraction and parameterization represents a crucial
challenge for the next-generation radio interferometer surveys, such as those
performed with the Square Kilometre Array (SKA) and its precursors. In this
paper we present a new algorithm, dubbed CAESAR (Compact And Extended Source
Automated Recognition), to detect and parametrize extended sources in radio
interferometric maps. It is based on a pre-filtering stage, allowing image
denoising, compact source suppression and enhancement of diffuse emission,
followed by an adaptive superpixel clustering stage for final source
segmentation. A parameterization stage provides source flux information and a
wide range of morphology estimators for post-processing analysis. We developed
CAESAR in a modular software library, including also different methods for
local background estimation and image filtering, along with alternative
algorithms for both compact and diffuse source extraction. The method was
applied to real radio continuum data collected at the Australian Telescope
Compact Array (ATCA) within the SCORPIO project, a pathfinder of the ASKAP-EMU
survey. The source reconstruction capabilities were studied over different test
fields in the presence of compact sources, imaging artefacts and diffuse
emission from the Galactic plane and compared with existing algorithms. When
compared to a human-driven analysis, the designed algorithm was found capable
of detecting known target sources and regions of diffuse emission,
outperforming alternative approaches over the considered fields.Comment: 15 pages, 9 figure
Shape-driven segmentation of the arterial wall in intravascular ultrasound images
Segmentation of arterial wall boundaries from intravascular images is an important problem for many applications in the study of plaque characteristics, mechanical properties of the arterial wall, its 3D reconstruction,
and its measurements such as lumen size, lumen radius, and wall radius. We present a shape-driven approach to segmentation of the arterial wall from intravascular ultrasound images in the rectangular domain. In a properly built
shape space using training data, we constrain the lumen and media-adventitia contours to a smooth, closed geometry, which increases the segmentation quality without any tradeoff with a regularizer term. In addition to a shape prior,
we utilize an intensity prior through a non-parametric probability density based image energy, with global image measurements rather than pointwise measurements used in previous methods. Furthermore, a detection step is included to address the challenges introduced to the segmentation process by side branches and calcifications. All these features greatly enhance our segmentation method. The tests of our algorithm on a large dataset demonstrate the effectiveness of our approach
Magneto-Centrifugal Launching of Jets from Accretion Disks. II: Inner Disk-Driven Winds
We follow numerically the time evolution of axisymmetric outflows driven
magneto-centrifugally from the inner portion of accretion disks, from their
launching surface to large, observable distances. Special attention is paid to
the collimation of part of the outflow into a dense, narrow jet around the
rotation axis, after a steady state has been reached. For parameters typical of
T Tauri stars, we define a fiducial ``jet'' as outlined by the contour of
constant density at 10^4 cm^{-3}. We find that the jet, so defined, appears
nearly cylindrical well above the disk, in agreement with previous asymptotic
analyses. Closer to the equatorial plane, the density contour can either bulge
outwards or pinch inwards, depending on the conditions at the launching
surface, particularly the mass flux distribution. We find that even though a
dense, jet-like feature is always formed around the axis, there is no guarantee
that the high-density axial jet would dominate the more tenuous, wide-angle
part of the wind. Specifically, on the 100 AU scale, resolvable by HST and
ground-based adaptive optics for nearby T Tauri winds, the fraction of the wind
mass flux enclosed by the fiducial jet can vary substantially, again depending
on the launching conditions. We show two examples in which the fraction is ~20%
and ~45%. These dependences may provide a way to constrain the conditions at
the launching surface, which are poorly known at present.Comment: 11 pages, 6 figures. Accepted for publication in ApJ, scheduled for
vol. 595, October 1, 200
Interactive image segmentation based on level sets of probabilities
In this paper, we present a robust and accurate algorithm for interactive image segmentation. The level set method is clearly advantageous for image objects with a complex topology and fragmented appearance. Our method integrates discriminative classification models and distance transforms with the level set method to avoid local minima and better snap to true object boundaries. The level set function approximates a transformed version of pixelwise posterior probabilities of being part of a target object. The evolution of its zero level set is driven by three force terms, region force, edge field force, and curvature force. These forces are based on a probabilistic classifier and an unsigned distance transform of salient edges. We further propose a technique that improves the performance of both the probabilistic classifier and the level set method over multiple passes. It makes the final object segmentation less sensitive to user interactions. Experiments and comparisons demonstrate the effectiveness of our method. © 2012 IEEE.published_or_final_versio
Inside-Out Planet Formation. V. Structure of the Inner Disk as Implied by the MRI
The large population of Earth to super-Earth sized planets found very close
to their host stars has motivated consideration of formation
models. In particular, Inside-Out Planet Formation is a scenario in which
planets coalesce sequentially in the disk, at the local gas pressure maximum
near the inner boundary of the dead zone. The pressure maximum arises from a
decline in viscosity, going from the active innermost disk (where thermal
ionization of alkalis yields high viscosities via the magneto-rotational
instability (MRI)) to the adjacent dead zone (where the MRI is quenched).
Previous studies of the pressure maximum, based on -disk models, have
assumed ad hoc values for the viscosity parameter in the active zone,
ignoring the detailed physics of the MRI. Here we explicitly couple the MRI
criteria to the -disk equations, to find steady-state (constant
accretion rate) solutions for the disk structure. We consider the effects of
both Ohmic and ambipolar resistivities, and find solutions for a range of disk
accretion rates ( = - /yr),
stellar masses ( = 0.1 - 1 ), and fiducial values of
the -MRI -viscosity in the dead zone ( - ). We find that: (1) A midplane pressure maximum forms
radially the inner boundary of the dead zone; (2) Hall resistivity
dominates near the midplane in the inner disk, which may explain why close-in
planets do form in 50% of systems; (3) X-ray ionization can be
competitive with thermal ionization in the inner disk, because of the low
surface density there in steady-state; and (4) our inner disk solutions are
viscously unstable to surface density perturbations.Comment: 34 pages, 28 figures, 3 appendices. Accepted by the Astrophysical
Journa
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