199,320 research outputs found
Live User-guided Intrinsic Video For Static Scenes
We present a novel real-time approach for user-guided intrinsic decomposition of static scenes captured by an RGB-D sensor. In the first step, we acquire a three-dimensional representation of the scene using a dense volumetric reconstruction framework. The obtained reconstruction serves as a proxy to densely fuse reflectance estimates and to store user-provided constraints in three-dimensional space. User constraints, in the form of constant shading and reflectance strokes, can be placed directly on the real-world geometry using an intuitive touch-based interaction metaphor, or using interactive mouse strokes. Fusing the decomposition results and constraints in three-dimensional space allows for robust propagation of this information to novel views by re-projection.We leverage this information to improve on the decomposition quality of existing intrinsic video decomposition techniques by further constraining the ill-posed decomposition problem. In addition to improved decomposition quality, we show a variety of live augmented reality applications such as recoloring of objects, relighting of scenes and editing of material appearance
Statistical and systematic uncertainties in pixel-based source reconstruction algorithms for gravitational lensing
Gravitational lens modeling of spatially resolved sources is a challenging
inverse problem with many observational constraints and model parameters. We
examine established pixel-based source reconstruction algorithms for de-lensing
the source and constraining lens model parameters. Using test data for four
canonical lens configurations, we explore statistical and systematic
uncertainties associated with gridding, source regularisation, interpolation
errors, noise, and telescope pointing. Specifically, we compare two gridding
schemes in the source plane: a fully adaptive grid that follows the lens
mapping but is irregular, and an adaptive Cartesian grid. We also consider
regularisation schemes that minimise derivatives of the source (using two
finite difference methods) and introduce a scheme that minimises deviations
from an analytic source profile. Careful choice of gridding and regularisation
can reduce "discreteness noise" in the surface that is inherent in the
pixel-based methodology. With a gridded source, some degree of interpolation is
unavoidable, and errors due to interpolation need to be taken into account
(especially for high signal-to-noise data). Different realisations of the noise
and telescope pointing lead to slightly different values for lens model
parameters, and the scatter between different "observations" can be comparable
to or larger than the model uncertainties themselves. The same effects create
scatter in the lensing magnification at the level of a few percent for a peak
signal-to-noise ratio of 10, which decreases as the data quality improves.Comment: 20 pages, 18 figures, accepted to MNRAS, see
http://physics.rutgers.edu/~tagoreas/papers/ for high resolution image
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
Adaptive foveated single-pixel imaging with dynamic super-sampling
As an alternative to conventional multi-pixel cameras, single-pixel cameras
enable images to be recorded using a single detector that measures the
correlations between the scene and a set of patterns. However, to fully sample
a scene in this way requires at least the same number of correlation
measurements as there are pixels in the reconstructed image. Therefore
single-pixel imaging systems typically exhibit low frame-rates. To mitigate
this, a range of compressive sensing techniques have been developed which rely
on a priori knowledge of the scene to reconstruct images from an under-sampled
set of measurements. In this work we take a different approach and adopt a
strategy inspired by the foveated vision systems found in the animal kingdom -
a framework that exploits the spatio-temporal redundancy present in many
dynamic scenes. In our single-pixel imaging system a high-resolution foveal
region follows motion within the scene, but unlike a simple zoom, every frame
delivers new spatial information from across the entire field-of-view. Using
this approach we demonstrate a four-fold reduction in the time taken to record
the detail of rapidly evolving features, whilst simultaneously accumulating
detail of more slowly evolving regions over several consecutive frames. This
tiered super-sampling technique enables the reconstruction of video streams in
which both the resolution and the effective exposure-time spatially vary and
adapt dynamically in response to the evolution of the scene. The methods
described here can complement existing compressive sensing approaches and may
be applied to enhance a variety of computational imagers that rely on
sequential correlation measurements.Comment: 13 pages, 5 figure
Process of image super-resolution
In this paper we explain a process of super-resolution reconstruction
allowing to increase the resolution of an image.The need for high-resolution
digital images exists in diverse domains, for example the medical and spatial
domains. The obtaining of high-resolution digital images can be made at the
time of the shooting, but it is often synonymic of important costs because of
the necessary material to avoid such costs, it is known how to use methods of
super-resolution reconstruction, consisting from one or several low resolution
images to obtain a high-resolution image. The american patent US 9208537
describes such an algorithm. A zone of one low-resolution image is isolated and
categorized according to the information contained in pixels forming the
borders of the zone. The category of it zone determines the type of
interpolation used to add pixels in aforementioned zone, to increase the
neatness of the images. It is also known how to reconstruct a low-resolution
image there high-resolution image by using a model of super-resolution
reconstruction whose learning is based on networks of neurons and on image or a
picture library. The demand of chinese patent CN 107563965 and the scientist
publication "Pixel Recursive Super Resolution", R. Dahl, M. Norouzi, J. Shlens
propose such methods. The aim of this paper is to demonstrate that it is
possible to reconstruct coherent human faces from very degraded pixelated
images with a very fast algorithm, more faster than compressed sensing (CS),
easier to compute and without deep learning, so without important technology
resources, i.e. a large database of thousands training images (see
arXiv:2003.13063).
This technological breakthrough has been patented in 2018 with the demand of
French patent FR 1855485 (https://patents.google.com/patent/FR3082980A1, see
the HAL reference https://hal.archives-ouvertes.fr/hal-01875898v1).Comment: 19 pages, 10 figure
Accelerated Cardiac Diffusion Tensor Imaging Using Joint Low-Rank and Sparsity Constraints
Objective: The purpose of this manuscript is to accelerate cardiac diffusion
tensor imaging (CDTI) by integrating low-rankness and compressed sensing.
Methods: Diffusion-weighted images exhibit both transform sparsity and
low-rankness. These properties can jointly be exploited to accelerate CDTI,
especially when a phase map is applied to correct for the phase inconsistency
across diffusion directions, thereby enhancing low-rankness. The proposed
method is evaluated both ex vivo and in vivo, and is compared to methods using
either a low-rank or sparsity constraint alone. Results: Compared to using a
low-rank or sparsity constraint alone, the proposed method preserves more
accurate helix angle features, the transmural continuum across the myocardium
wall, and mean diffusivity at higher acceleration, while yielding significantly
lower bias and higher intraclass correlation coefficient. Conclusion:
Low-rankness and compressed sensing together facilitate acceleration for both
ex vivo and in vivo CDTI, improving reconstruction accuracy compared to
employing either constraint alone. Significance: Compared to previous methods
for accelerating CDTI, the proposed method has the potential to reach higher
acceleration while preserving myofiber architecture features which may allow
more spatial coverage, higher spatial resolution and shorter temporal footprint
in the future.Comment: 11 pages, 16 figures, published on IEEE Transactions on Biomedical
Engineerin
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