179 research outputs found
DOPE: Distributed Optimization for Pairwise Energies
We formulate an Alternating Direction Method of Mul-tipliers (ADMM) that
systematically distributes the computations of any technique for optimizing
pairwise functions, including non-submodular potentials. Such discrete
functions are very useful in segmentation and a breadth of other vision
problems. Our method decomposes the problem into a large set of small
sub-problems, each involving a sub-region of the image domain, which can be
solved in parallel. We achieve consistency between the sub-problems through a
novel constraint that can be used for a large class of pair-wise functions. We
give an iterative numerical solution that alternates between solving the
sub-problems and updating consistency variables, until convergence. We report
comprehensive experiments, which demonstrate the benefit of our general
distributed solution in the case of the popular serial algorithm of Boykov and
Kolmogorov (BK algorithm) and, also, in the context of non-submodular
functions.Comment: Accepted at CVPR 201
Multi texture analysis of colorectal cancer continuum using multispectral imagery
Purpose
This paper proposes to characterize the continuum of colorectal cancer (CRC) using multiple texture features extracted from multispectral optical microscopy images. Three types of pathological tissues (PT) are considered: benign hyperplasia, intraepithelial neoplasia and carcinoma.
Materials and Methods
In the proposed approach, the region of interest containing PT is first extracted from multispectral
images using active contour segmentation. This region is then encoded using texture features based on the Laplacian-of-Gaussian (LoG) filter, discrete wavelets (DW) and gray level co-occurrence matrices (GLCM). To assess the significance of textural differences between PT types, a statistical analysis based on the Kruskal-Wallis test is performed. The usefulness of texture features is then evaluated quantitatively in terms of their ability to predict PT types using various classifier models.
Results
Preliminary results show significant texture differences between PT types, for all texture features (p-value < 0.01). Individually, GLCM texture features outperform LoG and DW features in terms of PT type prediction. However, a higher performance can be achieved by combining all texture features, resulting in a mean classification accuracy of 98.92%, sensitivity of 98.12%, and specificity of 99.67%.
Conclusions
These results demonstrate the efficiency and effectiveness of combining multiple texture features for characterizing the continuum of CRC and discriminating between pathological tissues in multispectral images
Constrained Deep Networks: Lagrangian Optimization via Log-Barrier Extensions
This study investigates the optimization aspects of imposing hard inequality
constraints on the outputs of CNNs. In the context of deep networks,
constraints are commonly handled with penalties for their simplicity, and
despite their well-known limitations. Lagrangian-dual optimization has been
largely avoided, except for a few recent works, mainly due to the computational
complexity and stability/convergence issues caused by alternating explicit dual
updates/projections and stochastic optimization. Several studies showed that,
surprisingly for deep CNNs, the theoretical and practical advantages of
Lagrangian optimization over penalties do not materialize in practice. We
propose log-barrier extensions, which approximate Lagrangian optimization of
constrained-CNN problems with a sequence of unconstrained losses. Unlike
standard interior-point and log-barrier methods, our formulation does not need
an initial feasible solution. Furthermore, we provide a new technical result,
which shows that the proposed extensions yield an upper bound on the duality
gap. This generalizes the duality-gap result of standard log-barriers, yielding
sub-optimality certificates for feasible solutions. While sub-optimality is not
guaranteed for non-convex problems, our result shows that log-barrier
extensions are a principled way to approximate Lagrangian optimization for
constrained CNNs via implicit dual variables. We report comprehensive weakly
supervised segmentation experiments, with various constraints, showing that our
formulation outperforms substantially the existing constrained-CNN methods,
both in terms of accuracy, constraint satisfaction and training stability, more
so when dealing with a large number of constraints
HyperDense-Net: A hyper-densely connected CNN for multi-modal image segmentation
Recently, dense connections have attracted substantial attention in computer
vision because they facilitate gradient flow and implicit deep supervision
during training. Particularly, DenseNet, which connects each layer to every
other layer in a feed-forward fashion, has shown impressive performances in
natural image classification tasks. We propose HyperDenseNet, a 3D fully
convolutional neural network that extends the definition of dense connectivity
to multi-modal segmentation problems. Each imaging modality has a path, and
dense connections occur not only between the pairs of layers within the same
path, but also between those across different paths. This contrasts with the
existing multi-modal CNN approaches, in which modeling several modalities
relies entirely on a single joint layer (or level of abstraction) for fusion,
typically either at the input or at the output of the network. Therefore, the
proposed network has total freedom to learn more complex combinations between
the modalities, within and in-between all the levels of abstraction, which
increases significantly the learning representation. We report extensive
evaluations over two different and highly competitive multi-modal brain tissue
segmentation challenges, iSEG 2017 and MRBrainS 2013, with the former focusing
on 6-month infant data and the latter on adult images. HyperDenseNet yielded
significant improvements over many state-of-the-art segmentation networks,
ranking at the top on both benchmarks. We further provide a comprehensive
experimental analysis of features re-use, which confirms the importance of
hyper-dense connections in multi-modal representation learning. Our code is
publicly available at https://www.github.com/josedolz/HyperDenseNet.Comment: Paper accepted at IEEE TMI in October 2018. Last version of this
paper updates the reference to the IEEE TMI paper which compares the
submissions to the iSEG 2017 MICCAI Challeng
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