Christophe Ducottet's research while affiliated with French National Centre for Scientific Research and other places

Publications (72)

Article
Full-text available
In situ transmission electron microscopy (TEM) studies of dynamic events produce large quantities of data especially under the form of images. In the important case of heterogeneous catalysis, environmental TEM (ETEM) under gas and temperature allows to follow a large population of supported nanoparticles (NPs) evolving under reactive conditions. I...
Chapter
Faster R-CNN has become a standard model in deep-learning based object detection. However, in many cases, few annotations are available for images in the application domain referred as the target domain whereas full annotations are available for closely related public or synthetic datasets referred as source domains. Thus, a domain adaptation is ne...
Article
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Most recent methods of image augmentation and prediction are building upon the deep learning paradigm. A careful preparation of the image dataset and the choice of a suitable network architecture are crucial steps to assess the desired image features and, thence, achieve accurate predictions. We first propose to help the learning process by adding...
Article
Sediment transport in mountain and gravel-bed-rivers is characterized by bedload transport of a wide range of grain sizes. When the bed is moving, dynamic void openings permit downward infiltration of the smaller particles. This process, termed here ‘kinetic sieving’, has been studied in industrial contexts, but more rarely in fluvial sediment tran...
Preprint
Full-text available
True contact between randomly rough solids consists of myriad individual micro-junctions. While their total area controls the adhesive friction force of the interface, other macroscopic features, including viscoelastic friction, wear, stiffness and electric resistance, also strongly depend on the size and shape of individual micro-junctions. Here w...
Article
Full-text available
True contact between randomly rough solids consists of myriad individual microjunctions. While their total area controls the adhesive friction force of the interface, other macroscopic features, including viscoelastic friction, wear, stiffness, and electric resistance, also strongly depend on the size and shape of individual microjunctions. We show...
Article
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Multi-object tracking is a difficult problem underlying many computer vision applications. In this work, we focus on bedload sediment transport experiments in a turbulent flow were sediments are represented by small spherical calibrated glass beads. The aim is to track all beads over long time sequences to obtain sediment velocities and concentrati...
Poster
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Sediment transport in rivers and mountain streams remains poorly understood partly due to the polydispersity of particles and resulting segregation. Experiments in the tilted, narrow, glass-sided channel, at Irstea in Grenoble, France, were carried out to study bedload transport of bimodal bead mixtures. The behavior of the beads is recorded throug...
Article
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Significance We investigate the origin of static friction, the threshold force at which a frictional interface starts to slide. For rough contacts involving rubber or human skin, we show that the real contact area, to which static friction is proportional, significantly decreases under increasing shear, well before the onset of sliding. For those s...
Preprint
Symmetry is one of the significant visual properties inside an image plane, to identify the geometrically balanced structures through the real-world objects. Existing symmetry detection methods rely on descriptors of the local image features and their neighborhood behavior, resulting incomplete symmetrical axis candidates to discover mirror similar...
Conference Paper
Full-text available
The proposed algorithm detects globally the symmetry axes inside an image plane. The main steps are as follows: We firstly extract edge features using Log-Gabor filters with different scales and orientations. Afterwards, we use the edge characteristics associated with the textural and color information as symmetrical weights for voting triangulatio...
Conference Paper
Full-text available
Symmetry is one of the significant visual properties inside an image plane, to identify the geometrically balanced structures through real-world objects. Existing symmetry detection methods rely on descriptors of the local image features and their neighborhood behavior, resulting incomplete symmetrical axis candidates to discover the mirror similar...
Conference Paper
Full-text available
Symmetry is an important composition feature by investigating similar sides inside an image plane. It has a crucial effect to recognize man-made or nature objects within the universe. Recent symmetry detection approaches used a smoothing kernel over different voting maps in the polar coordinate system to detect symmetry peaks, which split the regio...
Conference Paper
Full-text available
In recent years, there has been renewed interest in bilateral symmetry detection in images. It consists in detecting the main bilateral symmetry axis inside artificial or natural images. State-of-the-art methods combine feature point detection, pairwise comparison and voting in Hough-like space. In spite of their good performance, they fail to give...
Article
Recent advances in image classification mostly rely on the use of powerful local features combined with an adapted image representation. Although Convolutional Neural Network (CNN) features learned from ImageNet were shown to be generic and very efficient, they still lack of flexibility to take into account variations in the spatial layout of visua...
Conference Paper
Full-text available
Multi-object tracking is a difficult problem, but in recent years, particle filter-based object trackers (or Sequential Monte Carlo Estimation based trackers) have proven to be very effective. This method consists of a dynamic model for prediction and an observation model to evaluate the likelihood of a predicted state (Doucet et al. 2001). In othe...
Conference Paper
Full-text available
Bedload transport is the sediment load transported in contact with the bed of a river channel. Empirical relations are often used to predict sediment transport rates. However, as rivers are highly variable (e.g. geometries, flow rates), these predictions usually lack accuracy. Consequently, a more detailed comprehension of the physical processes is...
Conference Paper
Bedload, the part of sediment transport remaining in contact with the bed has been mainly investigated from a fluid perspective. Bedload should also be considered from a granular point of view, and take into account the grain-grain interactions. This paper focuses on particle tracking velocimetry algorithms to better understand bedload transport at...
Article
In the context of category level scene classification, the bag-of-visual-words model (BoVW) is widely used for image representation. This model is appearance based and does not contain any information regarding the arrangement of the visual words in the 2D image space. To overcome this problem, recent approaches try to capture information about eit...
Article
With multimedia information retrieval, combining different modalities - text, image, audio or video provides additional information and generally improves the overall system performance. For this purpose, the linear combination method is presented as simple, flexible and effective. However, it requires to choose the weight assigned to each modality...
Article
The Spatial Pyramid Matching approach has become very popular to model images as sets of local bag-ofwords. The image comparison is then done region-by-region with an intersection kernel. Despite its success, this model presents some limitations: the grid partitioning is predefined and identical for all images and the matching is sensitive to intra...
Conference Paper
Full-text available
Color description is a challenging task because of large variations in RGB values which occur due to scene accidental events, such as shadows, shading, specularities, illuminant color changes, and changes in viewing geometry. Traditionally, this challenge has been addressed by capturing the variations in physics-based models, and deriving invariant...
Conference Paper
Full-text available
This paper presents a novel approach to incorporate spatial information in the bag-ofvisual- words model for category level and scene classification. In the traditional bag-ofvisual- words model, feature vectors are histograms of visual words. This representation is appearance based and does not contain any information regarding the arrangement of...
Article
Résumé. Avec le développement du numérique, des quantités très importantes de documents composés de texte et d'images sont échangés, ce qui nécessite le développement de modèles permettant d'exploiter efficacement ces informations multimédias. Dans le contexte de la recherche d'information, un modèle possible consiste à représenter séparément les i...
Article
Full-text available
Bedload sediment transport of two-size coarse spherical particle mixtures in a turbulent supercritical flow was analyzed with image and particle tracking velocimetry algorithms in a two-dimensional flume. The image processing procedure is entirely presented. Experimental results, including the size, the position, the trajectory, the state of moveme...
Article
This paper focuses on non-linear pattern matching transforms based on mathematical morphology for gray level image processing. Our contribution is on two fronts. First, we unify the existing and a priori unconnected approaches to this problem by establishing their theoretical links with topology. Setting them within the same context allows to highl...
Conference Paper
Full-text available
Image representation using bag of visual words approach is commonly used in image classification. Features are extracted from images and clustered into a visual vocabulary. Images can then be represented as a normalized histogram of visual words similarly to textual documents represented as a weighted vector of terms. As a result, text categorizati...
Article
Full-text available
Aluminum sheet is currently used for body panels on a number of mass-produced vehicles, in particular for closure panels. AA5xxx alloys always contain coarse inter-metallic particles (Al(x)(Fe,Mn)(y)Si, Mg(2)Si) after casting. In the present work inter-metallic particle break-up during hot reversible rolling of AA5182 alloy sheets has been analyzed...
Conference Paper
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As an alternative to vector representations, a recent trend in image classification suggests to integrate additional structural information in the description of images in order to enhance classification accuracy. Rather than being represented in a p-dimensional space, images can typically be encoded in the form of strings, trees or graphs and are...
Article
L'holographie numérique en ligne est une technique prometteuse dans le domaine de la visualisation quantitative des écoulements. Elle permet notamment de mesurer et de positionner en 3D des petits objets à partir de l'acquisition d'une seule image et avec un montage expérimental très simple. Le traitement numérique des images-hologramme corresponda...
Conference Paper
Full-text available
This paper reports our multimedia information retrieval experiments carried out for the ImageCLEF track 2009. In 2008, we proposed a multimedia document model defined as a vector of textual and visual terms weighted using a tf.idf approch [5]. For our second participation, our goal was to improve this previous model in the following ways: 1) use of...
Article
Full-text available
Nous présentons dans cet article un modèle de représentation de documents multimédia combinant des informations textuelles et des descripteurs visuels. Le texte et l'image composant un document sont chacun décrits par un vecteur de poids $tf.idf$ en suivant une approche "sac-de-mots". Le modèle utilisé permet d'effectuer des requêtes multimédia pou...
Article
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The problem of 3D shape characterisation has been intensively studied lately, because computing power is greatly increasing and image acquisition is more efficient, with new real 3D image acquisition methods like microtomography. The material studied in this work is a 5xxx aluminium alloy. It contains intermetallic particles which control both form...
Conference Paper
Full-text available
This paper reports our multimedia information retrieval experiments carried out for the ImageCLEF track (ImageCLEFwiki[10]). We propose a new multimedia model combining textual and/or visual information which enables to perform textual, visual, or multimedia queries. We experiment the model on ImageCLEF data and we compare the results obtained usin...
Article
Full-text available
In-line holography is a 3D imaging technique which has been used for many years, especially in experimental fluid mechanics for the 3D localization and sizing of micro-particles from the acquisition of a single 2D image (hologram). This technique is easily usable in an industrial environment thanks to its simple setup. We have recently presented an...
Article
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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. A unifying description of existing digital suppression methods is given in...
Article
Full-text available
The potential of in-line digital holography to locate and measure the size of particles distributed throughout a volume (in one shot) has been established. These measurements are fundamental for the study of particle trajectories in fluid flow. The most important issues in digital holography today are poor depth positioning accuracy, transverse fie...
Article
The goal of this paper is to describe a methodology for characterizing 3D complex shapes using morphological features. First, we provide 3D morphological measurements for understanding complex shapes. Second, we explain the analysis method based on principal component analysis. We illustrate our approach on populations of intermetallic particles of...
Article
Bed load transport is a longstanding problem despite its major implication in river morphodynamics. The physical processes ruling coarse-particle/fluid systems are indeed poorly known, impairing our ability to compute local and even bulk quantities such as the sediment flux in rivers.We present an experimental study of a two-size mixture of coarse...
Article
Full-text available
Determination of horizontal velocity fields on the solar surface is crucial for understanding the dynamics of structures like mesogranulation or supergranulation or simply the distribution of magnetic fields. We pursue here the development of a method called CST for coherent structure tracking, which determines the horizontal motion of granules in...
Article
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RESUME : Le but de cet article est de décrire une méthodologie pour caractériser par des mesures morphologiques des formes complexes tridimensionnelles. Dans un premier temps, nous proposons de paramètres morphologiques 3D pour expliciter la nature complexe de forme. Ensuite nous expliquons la méthode d'analyse des données utilisée basée sur l'anal...
Article
Full-text available
A method to analyze bed load with image processing was developed. The motion of coarse spherical particles on a mobile bed entrained by a shallow turbulent flow down a steep channel was filmed with a high-speed camera. The water free surface and the particle positions were detected combining classical image processing algorithms. We developed a par...
Article
Full-text available
Digital holography, which consists of both acquiring the hologram image in a digital camera and numerically reconstructing the information, offers new and faster ways to make the most of a hologram. We describe a new method to determine the rough size of particles in an in-line hologram. This method relies on a property that is specific to interfer...
Article
Full-text available
In-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...
Article
Full-text available
Substantial variations in the particle flux are commonly observed in field measurements on gravel-bed rivers and in laboratory experiments mimicking river behavior on a smaller scale. These fluctuations can be explained by the natural variability of sediment supply and hydraulic conditions. We conducted laboratory experiments of particle transport...
Article
The numerical reconstruction of an in-line digital hologram is a critical point in digital holographic particle image velocimetry. In particular, the shape of the axial profile of the reconstructed particles plays an important role in depth recovery. We show that this profile presents some oscillations when reconstructing by convolution with the Fr...
Article
First, we present a wavelet-based algorithm for edge detection and characterization, which is an adaptation of Mallat and Hwang's method. This algorithm relies on a modelization of contours as smoothed singularities of three particular types (transitions, peaks and lines). On the one hand, it allows to detect and locate edges at an adapted scale. O...
Article
Digital holography is used to extend 2D Particle Image Velocimetry to volumic field measurements thanks to the use of correlation. The flow seeded with particles is analyzed from two successive holograms recorded by in-line holography directly on a numerical sensor. The holograms are then processed in order to extract the 3D displacements. The prin...
Article
Les travaux présentés dans ce mémoire se répartissent en deux principaux thèmes : l'analyse de singularités par ondelettes et le traitement numérique d'hologrammes. Pour effectuer des mesures sur les images il peut être utile de rechercher des formes particulières ou des primitives élémentaires telles que des points, des contours, les droites,... E...
Article
Full-text available
Dans cette communication, nous présentons deux nouvelles transformées de mise en correspondance de formes (pattern matching) dans les images à niveaux de gris. Elles se basent sur le principe du palpage mécanique et sont définies dans le contexte de la morphologie mathématique. La première transformée permet de localiser dans une image toutes les i...
Conference Paper
A new device named GDS has been designed to measure with image analysis every few seconds the Grain size distribution and the Solid Discharge of natural particles downstream of an experimental mobile bed flume. The range of medium diameters of the particles has for the moment been restricted from about 2 to 20 mm. This device was successfully teste...
Article
Transfer of sediments from hillslope to channel is controlled by the building up of mor- phodynamic structures at different space and timescales (e.g. antidunes, step-pool sys- tem, alternate bars, braiding). One fundamental process allowing or enhancing those structures is grain size sorting. Bed-load experiments with non-uniform material are ofte...
Article
We present a new scheme for feature points detection on a grey level image. Its principle is the study of the gradient phase signal along object edges and the characterization of the behavior across scales of the wavelet coefficients of this signal. The features points are determined as transition points of this signal. In the second part, we study...
Article
We propose a method based on the study of wavelet transform modulus maxima to characterize signal or image edges from smoothed singularities. This characterization is used to extract robust feature points from object edges. They are tracked along an image sequence to study the motion of unrigid objects. Practical results of edge characterization an...
Conference Paper
Le problème traité dans cet article concerne la mesure de déformations locales d'interfaces d'objets déformables en vue d'étudier leur dynamique. Les objets considérés peuvent être des solides déformables ou des fluides, qui ne disposent pas obligatoirement de frontières nettement définies sur toute leur périphérie, et dont les images sont éventuel...

Citations

... For instance, AI-enabled nanoparticle synthesis platforms and nanoparticle delivery systems (AI-assisted algorithms) have been adopted to optimize the synthesis and delivery of magnetic nanoparticles for anticancer drug delivery, respectively. It uses machine learning, deep learning, and computer vision techniques to predict the optimal parameters for nanoparticle synthesis that accurately target the nanoparticles to the desired cells [258,259]. Furthermore, AI-assisted algorithms have also been employed to track the magnetic nanoparticles and monitor the toxicity of the drug during delivery to provide insights into cancer progression and identify potential therapeutic strategies [260]. It uses natural language processing, deep learning, and computer vision techniques to accurately detect the nanoparticles at the specified locations (tumor sites) and assess the levels of toxicity of the drug, respectively. ...
... In fact, meaningful results were obtained just with U-Net both in liquid and gas phases, and under temperature changes, surpassing the former traditional and unsupervised approaches. [174][175][176] In any case, it is clear that ML has much more to say in in situ EM, and it will surely explode as soon as the in situ machinery becomes a much wider standard within the community. For instance, we envision the use of CS to reduce the required frame rate, similarly to CS-tomography, further allowing the chemical and physical tracking of beam-sensitive materials. ...
... To address the issue of missing inter-slice information and bridge the gap further between 2D and 3D strategies, a distance transform was applied to the initial volume before slicing. This approach, introduced in [15], allows to enhance 2D images by adding geodesic information in non-textured areas. The ADS-net, trained on augmented 2D images by 3D geodesic information, can be considered somehow as a 2.5D network. ...
... Then we investigated the problem from a domain adaptive perspective to assess the ability of object detector trained on a chairlift to CHAPTER 2. STATE OF THE ART perform well on new unseen chairlift [37]. While in [38] we opted to exploit the geometrical constraint by guiding shallow and deep classifiers using binary masks representing the safety bar, then we proposed a solution to boost the generalizability of the deeper classifier. In the later sections of this chapter, we present an overview of the available literature on each of these aspects. ...
... Furthermore, SCL [30] learns more discriminative representations by interacting different losses and training strategy. Recently, Alqasir et al. indicated that adapting the region proposal sub-network in Faster R-CNN is crucial [31]. Existing works strive into diminishing the domain gap in both global feature (or image) level and local feature (or instance) level. ...
... Although dilation/contraction processes were not studied in our experiments, the decrease in porosity may suggest that contraction of the bed is likely the only process that occurred. As explained by Frey et al. (2020), a moving bedload layer creates space for particles to infiltrate and, therefore, decreasing the porosity. However, we believe that the rising limb of the hydrograph of short time-to-peak floods might cause dilation during under-threshold flows. ...
... The corresponding roughness parameters are = 1.180 mm, = 2.25 mm −2 and = 0.0419 mm. Let us now discuss the physical relevance of such a coarse optimal resolution, based on the Power Spectrum Density (PSD) of the same rough topography given in Fig. S1 of Sahli et al. (2019). The PSD has a plateau at large scales followed by a power law at smaller scales. ...
... The opacity of the intruder among transparent beads combined with the high frequency recording allowed us to follow the position of the large particle frame by frame. A Particle Tracking Velocimetry (PTV) algorithm developped by Lafaye de Micheaux et al. (2018) was used. This algorithm relies on two steps. ...
... Thus, its detection is challenging. Since the proposed algorithm detects symmetry axes as primary lines, we compare the proposed algorithm with the existing methods [8,9,14,33] Fig. 10: Detection results of symmetry axes. The ground-truth axes are in red, the detection results of Loy and Eklundh [33] are in green, and those of the proposed algorithm are in yellow. ...
... Marcelo et al. [29] outperformed other competitors in the 2017 competition with a registration technique that registered the collection of original points to their mirror-reflected counterparts. Methods based on image gradient [30] or important edges also achieved robust symmetry axes extraction [31][32][33]. ...