Scattering techniques are today well controlled to characterize roughnesses of high-precision substrates and coatings, which are around a fraction of a nanometer in the optical bandwidth [1, 2, 3]. All these techniques involve a receiver, sample or beam motion so as to record the whole angular scattering pattern by reflection and transmission. However, in some situations these angular motions are penalising. This is the case when fast roughness-measurements are required (on-line measurements), or when the sample cannot be displaced (case of large pieces), or when only one scattering direction is allowed (case where the sample cannot be separated from a system) … For these reasons we recently proposed proposed [4] an alternative which consisted in using white light so as to cancel any mechanical movement in a scattering system. The resulting system is a one-angle white-light scatterometer with a reduced spatial frequency bandwidth. The principle of this white light scatterometer relies on the wavelength-angle equivalence in the spatial frequency. However additional concepts must be introduced to make the white light scattering to be proportional to roughness. Actually we have to shape the wavelength spectrum of illumination in a specific way given by theory. Two experimental techniques are presented to shape the incident spectrum. The first [4] is based on an interferential filter but suffers some disadvantages, such as the absence of tunability or retroaction. The second technique [5] involves micro-mirror or LCD matrices coupled with gratings, and offers several advantages. Fast retroaction allows to take account of a shift in the source power, and the tunability also offers the opportunity to build quasi-arbitrary filters. This last remark allows to extract a series of roughness moments (not only the roughness), so that the autocorrelation function of the topography can be reconstructed. We will discuss advantages and limits of this new technique.
In this paper, we introduce a method to stabilize the variance of decimated transforms using one
or two variance stabilizing transforms (VST). These VSTs are applied to the 3-D Meyer wavelet
pyramidal transform which is the core of the first generation 3D curvelets. This allows us to
extend these 3-D curvelets to handle Poisson noise, that we apply to the denoising of a simulated
cosmological volume.
KEYWORDS: Data modeling, Associative arrays, Convolution, Signal to noise ratio, Data analysis, Wavelets, Data processing, Matrices, Mars, Carbon dioxide
The recent development of multi-channel sensors has motivated interest in devising new methods for the
coherent processing of multivariate data. An extensive work has already been dedicated to multivariate
data processing ranging from blind source separation (BSS) to multi/hyper-spectral data restoration.
Previous work has emphasized on the fundamental role played by sparsity and morphological diversity
to enhance multichannel signal processing.
GMCA is a recent algorithm for multichannel data analysis which was used successfully in a variety of
applications including multichannel sparse decomposition, blind source separation (BSS), color image
restoration and inpainting. Inspired by GMCA, a recently introduced algorithm coined HypGMCA
is described for BSS applications in hyperspectral data processing. It assumes the collected data is a
linear instantaneous mixture of components exhibiting sparse spectral signatures as well as sparse spatial
morphologies, each in specified dictionaries of spectral and spatial waveforms. We report on numerical
experiments with synthetic data and application to real observations which demonstrate the validity of
the proposed method.
In the scope of the Fermi mission, Poisson noise removal should improve data quality and make source detection
easier. This paper presents a method for Poisson data denoising on sphere, called Multi-Scale Variance Stabilizing
Transform on Sphere (MS-VSTS). This method is based on a Variance Stabilizing Transform (VST), a transform
which aims to stabilize a Poisson data set such that each stabilized sample has an (asymptotically) constant
variance. In addition, for the VST used in the method, the transformed data are asymptotically Gaussian. Thus,
MS-VSTS consists in decomposing the data into a sparse multi-scale dictionary (wavelets, curvelets, ridgelets...),
and then applying a VST on the coefficients in order to get quasi-Gaussian stabilized coefficients. In this present
article, the used multi-scale transform is the Isotropic Undecimated Wavelet Transform. Then, hypothesis tests
are made to detect significant coefficients, and the denoised image is reconstructed with an iterative method
based on Hybrid Steepest Descent (HST). The method is tested on simulated Fermi data.
KEYWORDS: Transform theory, Wavelets, 3D image processing, Chemical species, Video, Denoising, Wavelet transforms, Neodymium, Signal to noise ratio, Data acquisition
During data acquisition, the loss of data is usual. It can be due to malfunctioning sensors of a CCD camera or
any other acquiring system, or because we can only observe a part of the system we want to analyze. This problem
has been addressed using diffusion through the use of partial differential equations in 2D and in 3D, and recently
using sparse representations in 2D in a process called inpainting which uses sparsity to get a solution (in the
masked/unknown part) which is statistically similar to the known data, in the sense of the transformations used,
so that one cannot tell the inpainted part from the real one. It can be applied on any kind of 3D data, whether
it is 3D spatial data, 2D and time (video) or 2D and wavelength (multi-spectral imaging). We present inpainting
results on 3D data using sparse representations. These representations may include the wavetet transforms, the
discrete cosine transform, and 3D curvelet transforms.
The Multi-scale Variance Stabilization Transform (MSVST) has recently been proposed for 2D Poisson data
denoising.1 In this work, we present an extension of the MSVST with the wavelet transform to multivariate
data-each pixel is vector-valued-, where the vector field dimension may be the wavelength, the energy, or the
time. Such data can be viewed naively as 3D data where the third dimension may be time, wavelength or
energy (e.g. hyperspectral imaging). But this naive analysis using a 3D MSVST would be awkward as the data
dimensions have different physical meanings. A more appropriate approach would be to use a wavelet transform,
where the time or energy scale is not connected to the spatial scale. We show that our multivalued extension of
MSVST can be used advantageously for approximately Gaussianizing and stabilizing the variance of a sequence
of independent Poisson random vectors. This approach is shown to be fast and very well adapted to extremely
low-count situations. We use a hypothesis testing framework in the wavelet domain to denoise the Gaussianized
and stabilized coefficients, and then apply an iterative reconstruction algorithm to recover the estimated vector
field of intensities underlying the Poisson data. Our approach is illustrated for the detection and characterization
of astrophysical sources of high-energy gamma rays, using realistic simulated observations. We show that the
multivariate MSVST permits efficient estimation across the time/energy dimension and immediate recovery of
spectral properties.
FMRI time course processing is traditionally performed using linear regression followed by statistical hypothesis
testing. While this analysis method is robust against noise, it relies strongly on the signal model. In this paper, we
propose a non-parametric framework that is based on two main ideas. First, we introduce a problem-specific type
of wavelet basis, for which we coin the term "activelets". The design of these wavelets is inspired by the form of
the canonical hemodynamic response function. Second, we take advantage of sparsity-pursuing search techniques
to find the most compact representation for the BOLD signal under investigation. The non-linear optimization
allows to overcome the sensitivity-specificity trade-off that limits most standard techniques. Remarkably, the
activelet framework does not require the knowledge of stimulus onset times; this property can be exploited to
answer to new questions in neuroscience.
KEYWORDS: Signal to noise ratio, Associative arrays, Denoising, Chemical species, RGB color model, Image restoration, Signal processing, Inverse problems, Data modeling, Image processing
Over the last few years, the development of multi-channel sensors motivated interest in methods for the
coherent processing of multivariate data. From blind source separation (BSS) to multi/hyper-spectral
data restoration, an extensive work has already been dedicated to multivariate data processing. Previous
work has emphasized on the fundamental role played by sparsity and morphological diversity to
enhance multichannel signal processing.
Morphological diversity has been first introduced in the mono-channel case to deal with contour/texture
extraction. The morphological diversity concept states that the data are the linear combination of several
so-called morphological components which are sparse in different incoherent representations. In
that setting, piecewise smooth features (contours) and oscillating components (textures) are separated
based on their morphological differences assuming that contours (respectively textures) are sparse in the
Curvelet representation (respectively Local Discrete Cosine representation).
In the present paper, we define a multichannel-based framework for sparse multivariate data representation.
We introduce an extension of morphological diversity to the multichannel case which boils down
to assuming that each multichannel morphological component is diversely sparse spectrally and/or spatially.
We propose the Generalized Morphological Component Analysis algorithm (GMCA) which aims
at recovering the so-called multichannel morphological components. Hereafter, we apply the GMCA
framework to two distinct multivariate inverse problems : blind source separation (BSS) and multichannel
data restoration. In the two aforementioned applications, we show that GMCA provides new and
essential insights into the use of morphological diversity and sparsity for multivariate data processing.
Further details and numerical results in multivariate image and signal processing will be given illustrating
the good performance of GMCA in those distinct applications.
This article proposes a new method for image separation into a linear combination of morphological components.
This method is applied to decompose an image into meaningful cartoon and textural layers and is used
to solve more general inverse problems such as image inpainting. For each of these components, a dictionary is
learned from a set of exemplar images. Each layer is characterized by a sparse expansion in the corresponding
dictionary. The separation inverse problem is formalized within a variational framework as the optimization of an
energy functional. The morphological component analysis algorithm allows to solve iteratively this optimization
problem under sparsity-promoting penalties. Using adapted dictionaries learned from data allows to circumvent
some difficulties faced by fixed dictionaries. Numerical results demonstrate that this adaptivity is indeed crucial
to capture complex texture patterns.
Wavelet-based methods for multiple hypothesis testing are
described and their potential for activation mapping of human
functional magnetic resonance imaging (fMRI) data is investigated.
In this approach, we emphasize convergence between methods of
wavelet thresholding or shrinkage and the problem of multiple
hypothesis testing in both classical and Bayesian contexts.
Specifically, our interest will be focused on ensuring a trade off
between type I probability error control and power dissipation. We
describe a technique for controlling the false discovery rate at
an arbitrary level of type 1 error in testing multiple wavelet
coefficients generated by a 2D discrete wavelet transform (DWT) of
spatial maps of {fMRI} time series statistics. We also describe
and apply recursive testing methods that can be used to define a
threshold unique to each level and orientation of the 2D-DWT.
Bayesian methods, incorporating a formal model for the anticipated
sparseness of wavelet coefficients representing the signal or true
image, are also tractable. These methods are comparatively
evaluated by analysis of "null" images (acquired with the subject
at rest), in which case the number of positive tests should be
exactly as predicted under the hull hypothesis, and an
experimental dataset acquired from 5 normal volunteers during an
event-related finger movement task. We show that all three
wavelet-based methods of multiple hypothesis testing have good
type 1 error control (the FDR method being most conservative) and
generate plausible brain activation maps.
Level set methods offer a powerful approach for the medical image segmentation since it can handle any of the cavities, concavities, convolution, splitting or merging. However, this method requires specifying initial curves and can only provide good results if these curves are placed near symmetrically with respect to the object boundary. Another well known segmentation technique - morphological watershed transform can segment unique boundaries from an image, but it is very sensitive to small variations of the image magnitude and consequently the number of generated regions is undesirably large and the segmented boundaries is not smooth enough. In this paper, a hybrid 3D medical image segmentation algorithm, which combines the watershed transform and level set techniques, is proposed. This hybrid algorithm resolves the weaknesses of each method. An initial partitioning of the image into primitive regions is produced by applying the watershed transform on the image gradient magnitude, then this segmentation results is treated as the initial localization of the desired contour, and used in the following level set method, which provides closed, smoothed and accurately localized contours or surfaces. Experimental results are also presented and discussed.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.