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Author

Charles Goepfert

Other affiliations: École centrale de Lyon
Bio: Charles Goepfert is an academic researcher from University of Lyon. The author has contributed to research in topics: Digital image processing & Inverse problem. The author has an hindex of 3, co-authored 3 publications receiving 271 citations. Previous affiliations of Charles Goepfert include École centrale de Lyon.

Papers
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Journal ArticleDOI
TL;DR: In this article, the authors proposed a microparticle localization scheme in digital holography based on the inverse-problems approach, which yields the optimal particle set that best models the observed hologram image and resolves this global optimization problem by conventional particle detection followed by a local refinement for each particle.
Abstract: We propose a microparticle localization scheme in digital holography Most conventional digital holography methods are based on Fresnel transform and present several problems such as twin-image noise, border effects, and other effects To avoid these difficulties, we propose an inverse-problem approach, which yields the optimal particle set that best models the observed hologram image We resolve this global optimization problem by conventional particle detection followed by a local refinement for each particle Results for both simulated and real digital holograms show strong improvement in the localization of the particles, particularly along the depth dimension In our simulations, the position precision is > or =1 microm rms Our results also show that the localization precision does not deteriorate for particles near the edge of the field of view

157 citations

Journal ArticleDOI
TL;DR: This work proposes a microparticle detection scheme in digital holography by considering the camera as a truncated version of a wider sensor, and estimates the optimal particles set that best models the observed hologram image.
Abstract: We propose a microparticle detection scheme in digital holography. In our inverse problem approach, we estimate the optimal particles set that best models the observed hologram image. Such a method can deal with data that have missing pixels. By considering the camera as a truncated version of a wider sensor, it becomes possible to detect particles even out of the camera field of view. We tested the performance of our algorithm against simulated and experimental data for diluted particle conditions. With real data, our algorithm can detect particles far from the detector edges in a working area as large as 16 times the camera field of view. A study based on simulated data shows that, compared with classical methods, our algorithm greatly improves the precision of the estimated particle positions and radii. This precision does not depend on the particle's size or location (i.e., whether inside or outside the detector field of view).

86 citations

Journal ArticleDOI
TL;DR: In this article, a facility inspired by Hwang and Eaton (2004a, b) for generating a homogeneous isotropic turbulence was built, the objective being to study evaporating droplets in the presence of turbulence.
Abstract: A facility inspired by Hwang and Eaton (2004a, b) for generating a homogeneous isotropic turbulence was built, the objective being to study evaporating droplets in the presence of turbulence. Turbulence was produced by the mixing of six synthetic jets, in ambient atmosphere. Combined PIV and LDA techniques were used to measure the statistical turbulence properties. The turbulence produced was found to be homogeneous isotropic with a small mean flow within a domain having an average size of 50 mm × 50 mm × 50 mm. The rms fluctuations were of the order of 0.9 m/s, corresponding to a Taylor Reynolds number of 240 and an integral length scale of about 40 mm. This apparatus proved to be well suited to the study of the evaporation of droplets in a controlled turbulence field.

49 citations


Cited by
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Journal ArticleDOI
TL;DR: The preferential concentration of inertial particles in turbulent flows has been extensively investigated since the 1960s as discussed by the authors, and the main mathematical analysis techniques which have been developed and implemented up to now to diagnose and characterize the clustering properties of dispersed particles.

260 citations

PatentDOI
TL;DR: In this article, a method and system for performing three-dimensional holographic microscopy of an optically trapped structure is presented, which uses an inverted optical microscope, a laser source which generates a trapping laser beam wherein the laser beam is focused by an objective lens into a plurality of optical traps.
Abstract: A method and system for performing three-dimensional holographic microscopy of an optically trapped structure. The method and system use an inverted optical microscope, a laser source which generates a trapping laser beam wherein the laser beam is focused by an objective lens into a plurality of optical traps. The method and system also use a collimated laser at an imaging wavelength to illuminate the structure created by the optical traps. Imaging light scattered by the optically tapped structure forms holograms that are imaged by a video camera and analyzed by optical formalisms to determine light field to reconstruct 3-D images for analysis and evaluation.

181 citations

Journal ArticleDOI
TL;DR: This Letter suggests the use of a sparsity-promoting prior, verified in many inline holography applications, and presents a simple iterative algorithm for 3D object reconstruction under sparsity and positivity constraints.
Abstract: Inline digital holograms are classically reconstructed using linear operators to model diffraction. It has long been recognized that such reconstruction operators do not invert the hologram formation operator. Classical linear reconstructions yield images with artifacts such as distortions near the field-of-view boundaries or twin images. When objects located at different depths are reconstructed from a hologram, in-focus and out-of-focus images of all objects superimpose upon each other. Additional processing, such as maximum-of-focus detection, is thus unavoidable for any successful use of the reconstructed volume. In this Letter, we consider inverting the hologram formation model in a Bayesian framework. We suggest the use of a sparsity-promoting prior, verified in many inline holography applications, and present a simple iterative algorithm for 3D object reconstruction under sparsity and positivity constraints. Preliminary results with both simulated and experimental holograms are highly promising.

163 citations

Journal ArticleDOI
TL;DR: The influence of experimental parameters on the classical hologram reconstruction methods is assessed, offering guidelines for optimal image rendering regarding the hologram recording conditions.
Abstract: Holographic rendering of off-axis intensity digital holograms is discussed. A review of some of the main numerical processing methods, based either on the Fourier transform interpretation of the propagation integral or on its linear system counterpart, is reported. Less common methods such as adjustable magnification reconstruction schemes and Fresnelet decomposition are presented and applied to the digital treatment of off-axis holograms. The influence of experimental parameters on the classical hologram reconstruction methods is assessed, offering guidelines for optimal image rendering regarding the hologram recording conditions.

127 citations

Journal ArticleDOI
TL;DR: The orthogonal matching pursuit (OMP) algorithm as discussed by the authors is an algorithm to solve sparse approximation problems and it has been applied to solve ill-posed inverse problems in general and in particular for two deconvolution examples from mass spectrometry and digital holography.
Abstract: The orthogonal matching pursuit (OMP) is an algorithm to solve sparse approximation problems. Sufficient conditions for exact recovery are known with and without noise. In this paper we investigate the applicability of the OMP for the solution of ill-posed inverse problems in general and in particular for two deconvolution examples from mass spectrometry and digital holography respectively. In sparse approximation problems one often has to deal with the problem of redundancy of a dictionary, i.e. the atoms are not linearly independent. However, one expects them to be approximatively orthogonal and this is quantified by the so-called incoherence. This idea cannot be transfered to ill-posed inverse problems since here the atoms are typically far from orthogonal: The ill-posedness of the operator causes that the correlation of two distinct atoms probably gets huge, i.e. that two atoms can look much alike. Therefore one needs conditions which take the structure of the problem into account and work without the concept of coherence. In this paper we develop results for exact recovery of the support of noisy signals. In the two examples in mass spectrometry and digital holography we show that our results lead to practically relevant estimates such that one may check a priori if the experimental setup guarantees exact deconvolution with OMP. Especially in the example from digital holography our analysis may be regarded as a first step to calculate the resolution power of droplet holography.

93 citations