21,723 research outputs found
Focal-plane wavefront sensing with high-order adaptive optics systems
We investigate methods to calibrate the non-common path aberrations at an
adaptive optics system having a wavefront-correcting device working at an
extremely high resolution (larger than 150x150). We use focal-plane images
collected successively, the corresponding phase-diversity information and
numerically efficient algorithms to calculate the required wavefront updates.
The wavefront correction is applied iteratively until the algorithms converge.
Different approaches are studied. In addition of the standard Gerchberg-Saxton
algorithm, we test the extension of the Fast & Furious algorithm that uses
three images and creates an estimate of the pupil amplitudes. We also test
recently proposed phase-retrieval methods based on convex optimisation. The
results indicate that in the framework we consider, the calibration task is
easiest with algorithms similar to the Fast & Furious.Comment: 11 pages, 7 figures, published in SPIE proceeding
Solving ptychography with a convex relaxation
Ptychography is a powerful computational imaging technique that transforms a
collection of low-resolution images into a high-resolution sample
reconstruction. Unfortunately, algorithms that are currently used to solve this
reconstruction problem lack stability, robustness, and theoretical guarantees.
Recently, convex optimization algorithms have improved the accuracy and
reliability of several related reconstruction efforts. This paper proposes a
convex formulation of the ptychography problem. This formulation has no local
minima, it can be solved using a wide range of algorithms, it can incorporate
appropriate noise models, and it can include multiple a priori constraints. The
paper considers a specific algorithm, based on low-rank factorization, whose
runtime and memory usage are near-linear in the size of the output image.
Experiments demonstrate that this approach offers a 25% lower background
variance on average than alternating projections, the current standard
algorithm for ptychographic reconstruction.Comment: 8 pages, 8 figure
Phase Retrieval with Application to Optical Imaging
This review article provides a contemporary overview of phase retrieval in
optical imaging, linking the relevant optical physics to the information
processing methods and algorithms. Its purpose is to describe the current state
of the art in this area, identify challenges, and suggest vision and areas
where signal processing methods can have a large impact on optical imaging and
on the world of imaging at large, with applications in a variety of fields
ranging from biology and chemistry to physics and engineering
Computer Aided ECG Analysis - State of the Art and Upcoming Challenges
In this paper we present current achievements in computer aided ECG analysis
and their applicability in real world medical diagnosis process. Most of the
current work is covering problems of removing noise, detecting heartbeats and
rhythm-based analysis. There are some advancements in particular ECG segments
detection and beat classifications but with limited evaluations and without
clinical approvals. This paper presents state of the art advancements in those
areas till present day. Besides this short computer science and signal
processing literature review, paper covers future challenges regarding the ECG
signal morphology analysis deriving from the medical literature review. Paper
is concluded with identified gaps in current advancements and testing, upcoming
challenges for future research and a bullseye test is suggested for morphology
analysis evaluation.Comment: 7 pages, 3 figures, IEEE EUROCON 2013 International conference on
computer as a tool, 1-4 July 2013, Zagreb, Croati
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