164 research outputs found
Blind image deconvolution: nonstationary Bayesian approaches to restoring blurred photos
High quality digital images have become pervasive in modern scientific and everyday life —
in areas from photography to astronomy, CCTV, microscopy, and medical imaging. However
there are always limits to the quality of these images due to uncertainty and imprecision in the
measurement systems. Modern signal processing methods offer the promise of overcoming
some of these problems by postprocessing
these blurred and noisy images. In this thesis,
novel methods using nonstationary statistical models are developed for the removal of blurs
from out of focus and other types of degraded photographic images.
The work tackles the fundamental problem blind image deconvolution (BID); its goal is
to restore a sharp image from a blurred observation when the blur itself is completely unknown.
This is a “doubly illposed”
problem — extreme lack of information must be countered
by strong prior constraints about sensible types of solution. In this work, the hierarchical
Bayesian methodology is used as a robust and versatile framework to impart the required prior
knowledge.
The thesis is arranged in two parts. In the first part, the BID problem is reviewed, along
with techniques and models for its solution. Observation models are developed, with an
emphasis on photographic restoration, concluding with a discussion of how these are reduced
to the common linear spatially-invariant
(LSI) convolutional model. Classical methods for the
solution of illposed
problems are summarised to provide a foundation for the main theoretical
ideas that will be used under the Bayesian framework. This is followed by an indepth
review
and discussion of the various prior image and blur models appearing in the literature, and then
their applications to solving the problem with both Bayesian and nonBayesian
techniques.
The second part covers novel restoration methods, making use of the theory presented in Part I.
Firstly, two new nonstationary image models are presented. The first models local variance in
the image, and the second extends this with locally adaptive noncausal
autoregressive (AR)
texture estimation and local mean components. These models allow for recovery of image
details including edges and texture, whilst preserving smooth regions. Most existing methods
do not model the boundary conditions correctly for deblurring of natural photographs, and a
Chapter is devoted to exploring Bayesian solutions to this topic.
Due to the complexity of the models used and the problem itself, there are many challenges
which must be overcome for tractable inference. Using the new models, three different inference
strategies are investigated: firstly using the Bayesian maximum marginalised a posteriori
(MMAP) method with deterministic optimisation; proceeding with the stochastic methods
of variational Bayesian (VB) distribution approximation, and simulation of the posterior distribution
using the Gibbs sampler. Of these, we find the Gibbs sampler to be the most effective
way to deal with a variety of different types of unknown blurs. Along the way, details are given
of the numerical strategies developed to give accurate results and to accelerate performance.
Finally, the thesis demonstrates state of the art
results in blind restoration of synthetic and real
degraded images, such as recovering details in out of focus photographs
Learning by Hallucinating: Vision-Language Pre-training with Weak Supervision
Weakly-supervised vision-language (V-L) pre-training (W-VLP) aims at learning
cross-modal alignment with little or no paired data, such as aligned images and
captions. Recent W-VLP methods, which pair visual features with object tags,
help achieve performances comparable with some VLP models trained with aligned
pairs in various V-L downstream tasks. This, however, is not the case in
cross-modal retrieval (XMR). We argue that the learning of such a W-VLP model
is curbed and biased by the object tags of limited semantics.
We address the lack of paired V-L data for model supervision with a novel
Visual Vocabulary based Feature Hallucinator (WFH), which is trained via weak
supervision as a W-VLP model, not requiring images paired with captions. WFH
generates visual hallucinations from texts, which are then paired with the
originally unpaired texts, allowing more diverse interactions across
modalities.
Empirically, WFH consistently boosts the prior W-VLP works, e.g. U-VisualBERT
(U-VB), over a variety of V-L tasks, i.e. XMR, Visual Question Answering, etc.
Notably, benchmarked with recall@{1,5,10}, it consistently improves U-VB on
image-to-text and text-to-image retrieval on two popular datasets Flickr30K and
MSCOCO. Meanwhile, it gains by at least 14.5% in cross-dataset generalization
tests on these XMR tasks. Moreover, in other V-L downstream tasks considered,
our WFH models are on par with models trained with paired V-L data, revealing
the utility of unpaired data. These results demonstrate greater generalization
of the proposed W-VLP model with WFH.Comment: Accepted to WACV'23. Please find supplementary material at
https://drive.google.com/file/d/1SmCBGsUgkYLAhmK83RZqY03bq4j3214p/view?usp=sharin
TparvaDB: a database to support Theileria parva vaccine development
We describe the development of TparvaDB, a comprehensive resource to facilitate research towards development of an East Coast fever vaccine, by providing an integrated user-friendly database of all genome and related data currently available for Theileria parva. TparvaDB is based on the Generic Model Organism Database (GMOD) platform. It contains a complete reference genome sequence, Expressed Sequence Tags (ESTs), Massively Parallel Signature Sequencing (MPSS) expression tag data and related information from both public and private repositories. The Artemis annotation workbench provides online annotation functionality. TparvaDB represents a resource that will underpin and promote ongoing East Coast fever vaccine development and biological research
Premise Selection for Mathematics by Corpus Analysis and Kernel Methods
Smart premise selection is essential when using automated reasoning as a tool
for large-theory formal proof development. A good method for premise selection
in complex mathematical libraries is the application of machine learning to
large corpora of proofs. This work develops learning-based premise selection in
two ways. First, a newly available minimal dependency analysis of existing
high-level formal mathematical proofs is used to build a large knowledge base
of proof dependencies, providing precise data for ATP-based re-verification and
for training premise selection algorithms. Second, a new machine learning
algorithm for premise selection based on kernel methods is proposed and
implemented. To evaluate the impact of both techniques, a benchmark consisting
of 2078 large-theory mathematical problems is constructed,extending the older
MPTP Challenge benchmark. The combined effect of the techniques results in a
50% improvement on the benchmark over the Vampire/SInE state-of-the-art system
for automated reasoning in large theories.Comment: 26 page
Reframing Kurtz’s Painting: Colonial Legacies and Minority Rights in Ethnically Divided Societies
Minority rights constitute some of the most normatively and economically important human rights. Although the political science and legal literatures have proffered a number of constitutional and institutional design solutions to address the protection of minority rights, these solutions are characterized by a noticeable neglect of, and lack of sensitivity to, historical processes. This Article addresses that gap in the literature by developing a causal argument that explains diverging practices of minority rights protections as functions of colonial governments’ variegated institutional practices with respect to particular ethnic groups. Specifically, this Article argues that in instances where colonial governments politicize and institutionalize ethnic hegemony in the pre-independence period, an institutional legacy is created that leads to lower levels of minority rights protections. Conversely, a uniform treatment and depoliticization of ethnicity prior to independence ultimately minimizes ethnic cleavages post-independence and consequently causes higher levels of minority rights protections. Through a highly structured comparative historical analysis of Botswana and Ghana, this Article builds on a new and exciting research agenda that focuses on the role of long-term historio-structural and institutional influences on human rights performance and makes important empirical contributions by eschewing traditional methodologies that focus on single case studies that are largely descriptive in their analyses. Ultimately, this Article highlights both the strength of a historical approach to understanding current variations in minority rights protections and the varied institutional responses within a specific colonial government
Multiple light scattering in anisotropic random media
In the last decade Diffusing Wave Spectroscopy (DWS) has emerged as a
powerful tool to study turbid media. In this article we develop the formalism
to describe light diffusion in general anisotropic turbid media. We give
explicit formulas to calculate the diffusion tensor and the dynamic absorption
coefficient, measured in DWS experiments. We apply our theory to uniaxial
systems, namely nematic liquid crystals, where light is scattered from thermal
fluctuations of the local optical axis, called director. We perform a detailed
analysis of the two essential diffusion constants, parallel and perpendicular
to the director, in terms of Frank elastic constants, dielectric anisotropy,
and applied magnetic field. We also point out the relevance of our results to
different liquid crystalline systems, such as discotic nematics, smectic-A
phases, and polymer liquid crystals. Finally, we show that the dynamic
absorption coefficient is the angular average over the inverse viscosity, which
governs the dynamics of director fluctuations.Comment: 23 pages, 12 ps figures, to be published in Phys. Rev.
Rationale, design and methods of the Study of Work and Pain (SWAP): a cluster randomised controlled trial testing the addition of a vocational advice service to best current primary care for patients with musculoskeletal pain (ISRCTN 52269669)
Background
Musculoskeletal pain is a major contributor to short and long term work absence. Patients
seek care from their general practitioner (GP) and yet GPs often feel ill-equipped to deal with
work issues. Providing a vocational case management service in primary care, to support
patients with musculoskeletal problems to remain at or return to work, is one potential
solution but requires robust evaluation to test clinical and cost-effectiveness.
Methods/Design
This protocol describes a cluster randomised controlled trial, with linked qualitative
interviews, to investigate the effect of introducing a vocational advice service into general
practice, to provide a structured approach to managing work related issues in primary care
patients with musculoskeletal pain who are absent from work or struggling to remain in work.
General practices (n = 6) will be randomised to offer best current care or best current care
plus a vocational advice service. Adults of working age who are absent from or struggling to
remain in work due to a musculoskeletal pain problem will be invited to participate and 330
participants will be recruited. Data collection will be through patient completed
questionnaires at baseline, 4 and 12 months. The primary outcome is self-reported work
absence at 4 months. Incremental cost-utility analysis will be undertaken to calculate the cost
per additional QALY gained and incremental net benefits. A linked interview study will
explore the experiences of the vocational advice service from the perspectives of GPs, nurse
practitioners (NPs), patients and vocational advisors.
Discussion
This paper presents the rationale, design, and methods of the Study of Work And Pain
(SWAP) trial. The results of this trial will provide evidence to inform primary care practice
and guide the development of services to provide support for musculoskeletal pain patients
with work-related issues.
Trial registration
Current Controlled Trials ISRCTN52269669
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