SUPER RESOLUTION EN HOLOGRAPHIE NUMERIQUE POUR LA RECONSTRUCTION TRIDIMENSIONNELLE HAUTE RESOLUTION D'HOLOGRAMMES

International audienceNous proposons ici un algorithme de reconstruction par approche « problèmes inverses » d'une pile d'hologrammes d'objets. Celui-ci permet d'améliorer la résolution des hologrammes, et la précision de l'estimation de la position 3D et de la taille des objets holographiés. Les bénéfices de l'approche sont démontrés au travers du traitement d'hologrammes simulés et expérimentaux

Fast and accurate 3D object recognition directly from digital holograms

International audiencePattern recognition methods can be used in the context of digital holography to perform the task of object detection, classification, and position extraction directly from the hologram rather than from the reconstructed optical field. These approaches may exploit the differences between the holographic signatures of objects coming from distinct object classes and/or different depth positions. Direct matching of diffraction patterns, however, becomes computationally intractable with increasing variability of objects due to the very high dimensionality of the dictionary of all reference diffraction patterns. We show that most of the diffraction pattern variability can be captured in a lower dimensional space. Good performance for object recognition and localization is demonstrated at a reduced computational cost using a low-dimensional dictionary. The principle of the method is illustrated on a digit recognition problem and on a video of experimental holograms of particles

Co-design of an in-line holographic microscope with enhanced axial resolution: selective filtering digital holography

International audienceCommon-path digital in-line holography is considered as a valuable 3D diagnostic techniques for a wide range of applications. This configuration is cost effective and relatively immune to variation in the experimental environment. Nevertheless, due to its common-path geometry, the signal to noise-ratio of the acquired hologram is weak as most of the detector (i.e. CCD/CMOS sensor) dynamics is occupied by the reference field signal, whose energy is orders of magnitude higher than the field scattered by the imaged object. As it is intrinsically impossible to modify the ratio of energy of reference to the object field, we propose a co-design approach (Optics/Data Processing) to tackle this issue. The reference to object field ratio is adjusted by adding a 4-f device to a conventional in-line holographic setup , making it possible to reduce the weight of the reference field while keeping the object field almost constant. Theoretical analysis of the Cràmer-Rao lower bounds of the corresponding imaging model illustrate the advantages of this approach. These lower bounds can be asymptotically reached using a parametric inverse problems reconstruction. This implementation results in a 60 % gain in axial localization accuracy (for of 100 µm diameter spherical objects) compared to a classical in-line holography setup

In-line particle holography with an astigmatic beam: set-up self-calibration using an "inverse problems" approach

11 pagesInternational audienceThe use of digital in-line holography for the characterization of confined flows in cylindrical geometry confinements (e.g. cylindrical pipe or cylindrical capillaries) is discussed. Due to cylindrical geometry of the walls, the illuminating laser wave can be strongly astigmatic, which renders the use of classical reconstruction techniques impossible. Contrary to plane wave holography set-up, the diffraction pattern of the particles strongly depends on the axial distance of the latter to the entry face of the confinement structure. To address this reconstruction issue, we propose to use an "inverse problems" approach. This approach amounts to finding the best match (least squares solution) between a diffraction pattern model and the captured hologram. For this purpose, a direct imaging model for astigmatic holograms, based on the use of transfer matrices is presented and validated by comparing experimental and simulated holograms. The accuracy of the "inverse problems" reconstruction is then used to calibrate the experimental set-up adjustable parameters. Finally, the approach is tested through experimental astigmatic hologram reconstruction, thus paving the way to its use in pipe flow studies

Numerical suppression of the twin-image in in-line holography of a volume of micro-objects

This paper was published in Measurement Science and Technology and is made available as an electronic reprint with the permission of IOP. The paper can be found at the following URL on the IOP website: http://www.iop.org/EJ/journal/MSTInternational audienceWe address the twin-image problem that arises in holography due to the lack of phase information in intensity measurements. This problem is of great importance in in-line holography where spatial elimination of the twin image cannot be carried out as in off-axis holography. A unifying description of existing digital suppression methods is given in the light of deconvolution techniques. Holograms of objects spread in 3D cannot be processed through available approaches. We suggest an iterative algorithm and demonstrate its efficacy on both simulated and real data. This method is suitable to enhance the reconstructed images from a digital hologram of small objects

Reconstruction of the rose of directions from a digital micro-hologram of fibers

International audienceDigital holography makes it possible to acquire quickly the interference patterns of objects spread in a volume. The digital processing of the fringes is still too slow to achieve on line analysis of the holograms. We describe a new approach to obtain information on the direction of illuminated objects. The key idea is to avoid reconstruction of the volume followed by classical three-dimensional image processing. The hologram is processed using a global analysis based on autocorrelation. A fundamental property of diffraction patterns leads to an estimate of the mean geometric-covariogram (MGC) of the objects projections. The rose of directions is connected with the MGC through an inverse problem. In the general case, only the 2D rose of the object projections can be reconstructed. The further assumption of unique-size objects gives access with the knowledge of this size to the 3D direction information. An iterative scheme is suggested to reconstruct the 3D rose in this special case. Results are provided on holograms of paper fibers

Inverse problem approach for particle digital holography: accurate location

International audienceOptical holography allows to record tridimensionnal informations of a scene using only one 2D sensor. Physical optics allows to analyticaly modelise hologram formation according to objects parameters (position, size, shape...). In simple objects case (e.g. spherical particles), the model is reduced to few parameters (four per particles: x,y,z,radius). Using inverse problem approach, it is possible to determine these parameters resolving a global optimization problem. This new approach is more efficient than classical method : particle parameters estimation is far more precise and it is possible to localize particles outside of the camera field of view. The presented method achieves to detect particles in an area sixteenth times wider than the CCD field of view with equal precision on both simulated and real digital holograms. Moreover strong improvements in the precision of the localization of the particles were noticed, particularly along the depth dimension

Twin-image noise reduction by phase retrieval in in-line digital holography

14 pagesInternational audienceIn-line digital holography conciles the applicative interest of a simple optical set-up with the speed, low cost and potential of digital reconstruction. We address the twin-image problem that arises in holography due to the lack of phase information in intensity measurements. This problem is of great importance in in-line holography where spatial elimination of the twin-image cannot be carried out as in off-axis holography. Applications in digital holography of particle fields greatly depend on its suppression to reach greater particle concentrations, keeping a sufficient signal to noise ratio in reconstructed images. We describe in this paper methods to improve numerically the reconstructed images by twin-image reduction. ©2005 COPYRIGHT SPI

Inline hologram reconstruction with sparsity constraints

International audienceInline 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 Bayesian framework. We suggest the use of a sparsity-promoting prior, intrinsically verified due to inline holography requirements, 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

Inverse problem approach for particle digital holography: accurate location based on local optimisation

The definitive version is available at http://www.opticsinfobase.org/abstract.cfm?URI=josaa-24-4-1164International audienceThis paper proposes a new micro-particles localization scheme in digital holography. Most conventionnal digital holography methods, are based on Fresnel transform and have several issues such as twin-image, border effects... To avoid these difficulties, we propose an inverse problem approach, which yields the optimal particles set which 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 on both simulated and real digital holograms show strong improvements in the localization of the particles, in particular along the depth dimension. In our simulations, the position precision is about or better than 1 µm rms. Our results also show that the localization precision does not deteriorate for particles near the edges of the field of view