5,147 research outputs found
Geometric robustness of deep networks: analysis and improvement
Deep convolutional neural networks have been shown to be vulnerable to
arbitrary geometric transformations. However, there is no systematic method to
measure the invariance properties of deep networks to such transformations. We
propose ManiFool as a simple yet scalable algorithm to measure the invariance
of deep networks. In particular, our algorithm measures the robustness of deep
networks to geometric transformations in a worst-case regime as they can be
problematic for sensitive applications. Our extensive experimental results show
that ManiFool can be used to measure the invariance of fairly complex networks
on high dimensional datasets and these values can be used for analyzing the
reasons for it. Furthermore, we build on Manifool to propose a new adversarial
training scheme and we show its effectiveness on improving the invariance
properties of deep neural networks
Geometric and photometric affine invariant image registration
This thesis aims to present a solution to the correspondence problem for the registration
of wide-baseline images taken from uncalibrated cameras. We propose an affine
invariant descriptor that combines the geometry and photometry of the scene to find
correspondences between both views. The geometric affine invariant component of the
descriptor is based on the affine arc-length metric, whereas the photometry is analysed
by invariant colour moments. A graph structure represents the spatial distribution of the
primitive features; i.e. nodes correspond to detected high-curvature points, whereas arcs
represent connectivities by extracted contours. After matching, we refine the search for
correspondences by using a maximum likelihood robust algorithm. We have evaluated
the system over synthetic and real data. The method is endemic to propagation of errors
introduced by approximations in the system.BAE SystemsSelex Sensors and Airborne System
Heterotic Coset Models and (0,2) String Vacua
A Lagrangian definition of a large family of (0,2) supersymmetric conformal
field theories may be made by an appropriate gauge invariant combination of a
gauged Wess-Zumino-Witten model, right-moving supersymmetry fermions, and
left-moving current algebra fermions. Throughout this paper, use is made of the
interplay between field theoretic and algebraic techniques (together with
supersymmetry) which is facilitated by such a definition. These heterotic coset
models are thus studied in some detail, with particular attention paid to the
(0,2) analogue of the N=2 minimal models, which coincide with the `monopole'
theory of Giddings, Polchinski and Strominger. A family of modular invariant
partition functions for these (0,2) minimal models is presented. Some examples
of N=1 supersymmetric four dimensional string theories with gauge groups E_6 X
G and SO(10) X G are presented, using these minimal models as building blocks.
The factor G represents various enhanced symmetry groups made up of products of
SU(2) and U(1).Comment: 53 pages, harvmac (Corrections made to spectra of E_6 examples. Other
minor changes.
Part-to-whole Registration of Histology and MRI using Shape Elements
Image registration between histology and magnetic resonance imaging (MRI) is
a challenging task due to differences in structural content and contrast. Too
thick and wide specimens cannot be processed all at once and must be cut into
smaller pieces. This dramatically increases the complexity of the problem,
since each piece should be individually and manually pre-aligned. To the best
of our knowledge, no automatic method can reliably locate such piece of tissue
within its respective whole in the MRI slice, and align it without any prior
information. We propose here a novel automatic approach to the joint problem of
multimodal registration between histology and MRI, when only a fraction of
tissue is available from histology. The approach relies on the representation
of images using their level lines so as to reach contrast invariance. Shape
elements obtained via the extraction of bitangents are encoded in a
projective-invariant manner, which permits the identification of common pieces
of curves between two images. We evaluated the approach on human brain
histology and compared resulting alignments against manually annotated ground
truths. Considering the complexity of the brain folding patterns, preliminary
results are promising and suggest the use of characteristic and meaningful
shape elements for improved robustness and efficiency.Comment: Paper accepted at ICCV Workshop (Bio-Image Computing
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