3,299 research outputs found
Regularized Newton Methods for X-ray Phase Contrast and General Imaging Problems
Like many other advanced imaging methods, x-ray phase contrast imaging and
tomography require mathematical inversion of the observed data to obtain
real-space information. While an accurate forward model describing the
generally nonlinear image formation from a given object to the observations is
often available, explicit inversion formulas are typically not known. Moreover,
the measured data might be insufficient for stable image reconstruction, in
which case it has to be complemented by suitable a priori information. In this
work, regularized Newton methods are presented as a general framework for the
solution of such ill-posed nonlinear imaging problems. For a proof of
principle, the approach is applied to x-ray phase contrast imaging in the
near-field propagation regime. Simultaneous recovery of the phase- and
amplitude from a single near-field diffraction pattern without homogeneity
constraints is demonstrated for the first time. The presented methods further
permit all-at-once phase contrast tomography, i.e. simultaneous phase retrieval
and tomographic inversion. We demonstrate the potential of this approach by
three-dimensional imaging of a colloidal crystal at 95 nm isotropic resolution.Comment: (C)2016 Optical Society of America. One print or electronic copy may
be made for personal use only. Systematic reproduction and distribution,
duplication of any material in this paper for a fee or for commercial
purposes, or modifications of the content of this paper are prohibite
High-Performance Multi-Mode Ptychography Reconstruction on Distributed GPUs
Ptychography is an emerging imaging technique that is able to provide
wavelength-limited spatial resolution from specimen with extended lateral
dimensions. As a scanning microscopy method, a typical two-dimensional image
requires a number of data frames. As a diffraction-based imaging technique, the
real-space image has to be recovered through iterative reconstruction
algorithms. Due to these two inherent aspects, a ptychographic reconstruction
is generally a computation-intensive and time-consuming process, which limits
the throughput of this method. We report an accelerated version of the
multi-mode difference map algorithm for ptychography reconstruction using
multiple distributed GPUs. This approach leverages available scientific
computing packages in Python, including mpi4py and PyCUDA, with the core
computation functions implemented in CUDA C. We find that interestingly even
with MPI collective communications, the weak scaling in the number of GPU nodes
can still remain nearly constant. Most importantly, for realistic diffraction
measurements, we observe a speedup ranging from a factor of to
depending on the data size, which reduces the reconstruction time remarkably
from hours to typically about 1 minute and is thus critical for real-time data
processing and visualization.Comment: work presented in NYSDS 201
Ptychographic hyperspectral spectromicroscopy with an extreme ultraviolet high harmonic comb
We demonstrate a new scheme of spectromicroscopy in the extreme ultraviolet
(EUV) spectral range, where the spectral response of the sample at different
wavelengths is imaged simultaneously. It is enabled by applying ptychographical
information multiplexing (PIM) to a tabletop EUV source based on high harmonic
generation, where four spectrally narrow harmonics near 30 nm form a spectral
comb structure. Extending PIM from previously demonstrated visible wavelengths
to the EUV/X-ray wavelengths promises much higher spatial resolution and more
powerful spectral contrast mechanism, making PIM an attractive
spectromicroscopy method in both the microscopy and the spectroscopy aspects.
Besides the sample, the multicolor EUV beam is also imaged in situ, making our
method a powerful beam characterization technique. No hardware is used to
separate or narrow down the wavelengths, leading to efficient use of the EUV
radiation
Compensation for the setup instability in ptychographic imaging
The high-frequency vibration of the imaging system degrades the quality of
the reconstruction of ptychography by acting as a low-pass filter on ideal
diffraction patterns. In this study, we demonstrate that by subtracting the
deliberately blurred diffraction patterns from the recorded patterns and adding
the properly amplified subtraction to the original data, the high-frequency
components lost by the vibration of the setup can be recovered, and thus the
image quality can be distinctly improved. Because no prior knowledge regarding
the vibrating properties of the imaging system is needed, the proposed method
is general and simple and has applications in several research fields.Comment: 13pages, 10figure
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