Shape from Stereo Using Fine Correlation: Method and Error Analysis

We are considering the problem of recovering the three-dimensional geometry of a scene from binocular stereo disparity. Once a dense disparity map has been computed from a stereo pair of images, one often needs to calculate some local differential properties of the corresponding 3-D surface such as orientation or curvatures. The usual approach is to build a 3-D reconstruction of the surface(s) from which all shape properties will then be derived without ever going back to the original images. In this paper, we depart from this paradigm and propose to use the images directly to compute the shape properties. We thus propose a new method, called \emph{fine correlation}, extending the classical correlation method to estimate accurately both the disparity and its derivatives directly from the image data. We then relate those derivatives to differential properties of the surface such as orientation and curvatures. We present the results of the reconstruction and of the estimation of the surface orientation and curvatures on some stereo pairs of real images. The performance and accuracy of both classical and fine correlation are analysed using synthetic images. By modeling the correlation error distribution as a mixture of Gaussian, we can compute the intrinsic accuracy of each method and the proportion of false matches, depending on the local disparity slope. The results show that the accuracy is almost constant with respect to slope using fine correlation, whereas it increases dramatically using classical correlation

Automatic calibration and removal of distortion from scenes of structured environments

International audienceMost algorithms in 3D computer vision rely on the pinhole camera model because of its simplicity, whereas video optics, especially low-cost wide-angle lens, generate a lot of nonlinear distortion which can be critical. To find the distortion parameters of a camera, we use the following fundamental property: a camera follows the pinhole model if and only if the projection of every line in space onto the camera is a line. Consequently, if we find the transformation on the video image so that every line in space is viewed in the transformed image as a line, then we know how to remove the distortion from the image. The algorithm consists of first doing edge extraction on a possibly distorted video sequence, then doing polygonal approximation with a large tolerance on these edges to extract possible lines from the sequence, and then finding the parameters of our distortion model that best transform these edges to segments. Results are presented on real video images, compared with distortion calibration obtained by a full camera calibration method which uses a calibration grid

Event related potentials elicited by violations of auditory regularities in patients with impaired consciousness.

International audienceImproving our ability to detect conscious processing in non communicating patients remains a major goal of clinical cognitive neurosciences. In this perspective, several functional brain imaging tools are currently under development. Bedside cognitive event-related potentials (ERPs) derived from the EEG signal are a good candidate to explore consciousness in these patients because: (1) they have an optimal time resolution within the millisecond range able to monitor the stream of consciousness, (2) they are fully non-invasive and relatively cheap, (3) they can be recorded continuously on dedicated individual systems to monitor consciousness and to communicate with patients, (4) and they can be used to enrich patients' autonomy through brain-computer interfaces. We recently designed an original auditory rule extraction ERP test that evaluates cerebral responses to violations of temporal regularities that are either local in time or global across several seconds. Local violations led to an early response in auditory cortex, independent of attention or the presence of a concurrent visual task, while global violations led to a late and spatially distributed response that was only present when subjects were attentive and aware of the violations. In the present work, we report the results of this test in 65 successive recordings obtained at bedside from 49 non-communicating patients affected with various acute or chronic neurological disorders. At the individual level, we confirm the high specificity of the 'global effect': only conscious patients presented this proposed neural signature of conscious processing. Here, we also describe in details the respective neural responses elicited by violations of local and global auditory regularities, and we report two additional ERP effects related to stimuli expectancy and to task learning, and we discuss their relations to consciousness

Survival and consciousness recovery are better in the minimally conscious state than in the vegetative state

BACKGROUND The prognosis value of early clinical diagnosis of consciousness impairment is documented by an extremely limited number of studies, whereas it may convey important information to guide medical decisions. OBJECTIVE We aimed at determining if patients diagnosed at an early stage (<90 days after brain injury) as being in the minimally conscious state (MCS) have a better prognosis than patients in the vegetative state/Unresponsive Wakefulness syndrome (VS/UWS), independent of care limitations or withdrawal decisions. METHODS Patients hospitalized in ICUs of the Pitié-Salpêtrière Hospital (Paris, France) from November 2008 to January 2011 were included and evaluated behaviourally with standardized assessment and with the Coma Recovery Scale-Revised as being either in the VS/UWS or in the MCS. They were then prospectively followed until 1July 2011 to evaluate their outcome with the GOSE. We compared survival function and outcomes of these two groups. RESULTS Both survival function and outcomes, including consciousness recovery, were significantly better in the MCS group. This difference of outcome still holds when considering only patients still alive at the end of the study. CONCLUSIONS Early accurate clinical diagnosis of VS/UWS or MCS conveys a strong prognostic value of survival and of consciousness recovery

EUROfusion Integrated Modelling (EU-IM) capabilities and selected physics applications

International audienceRecent developments and achievements of the EUROfusion Code Development for Integrated Modelling project (WPCD), which aim is to provide a validated integrated modelling suite for the simulation and prediction of complete plasma discharges in any tokamak, are presented. WPCD develops generic complex integrated simulations, workflows, for physics applications, using the standardized European Integrated Modelling (EU-IM) framework. Selected physics applications of EU-IM workflows are illustrated in this paper

Recherche de signes de conscience chez des malades non communicants : une approche clinique et électrophysiologique

Understanding the neurophysiological mechanisms and neural bases of consciousness is a major scientific and medical challenge. To do this, one has to distinguish neural mechanisms of conscious state from those subserving conscious access to a given mental state (that is awareness). Experimental data having contrasted conscious / non conscious state (coma, sleep, sedation) on the one hand, and conscious/ unconscious processing of a very same stimulus on the other hand are in favour of the implication of a network of lateral and medial frontal and parietal areas in both conscious state and conscious access. The comparison of conscious/ non conscious state is unfortunately limited by arousal difference between these two states. So, we endeavoured to overcome this problem by exploring two categories of patients with a same level of arousal but a different state of awareness: unaware awaked patients (vegetative state) versus awaked and minimally conscious patients (minimally conscious state). Our results obtained by using high-density auditory event related potentials argue in favour of the implication of the very same network of frontal and parietal areas than the one described above in both conscious state and conscious access to a given information. This network activation is associated with the emergence of a P300b wave, on event related potentials, which seems to be a very specific marker of consciousness. Our work also give us the opportunity to discover a potential new marker of consciousness, namely the contingent negative variation (CNV).Comprendre les mécanismes neurophysiologiques et les bases neurales de la conscience est un défi médico-scientifique majeur. A cette fin, il faut opérer une distinction entre les mécanismes neuraux des états de conscience, et ceux qui sous-tendent l'accès conscient à un contenu mental particulier (ou la prise de conscience). Les données expérimentales ayant contrasté état conscient/ état non conscient (coma, sommeil, sédation) d'une part, et perception consciente/inconsciente d'un même stimulus d'autre part, sont en faveur de l'implication d'un réseau d'aires cérébrales fronto-pariétales à la fois dans l'état et dans l'accès conscient à une information donnée. La comparaison état conscient/ état non conscient est malheureusement limitée par les différences de vigilance existant entre ces états. Nous avons cherché à contourner ce problème en nous focalisant sur deux populations de malades présentant un niveau de vigilance proche mais différant sous l'angle de l'état de conscience : patients éveillés, non conscients (état végétatif) versus patients éveillés et minimalement conscients (état de conscience minimale). Nos résultats, obtenus en utilisant les potentiels évoqués auditifs cognitifs à haute densité spatiale, sont en faveur de l'implication du même réseau d'aires cérébrales fronto-pariétales que celui mentionné ci-dessus, à la fois dans l'état et l'accès conscient. L'activation de ce réseau est contemporaine de l'apparition d'une P300b en potentiels évoqués qui semble constituer un marqueur très spécifique de conscience. Notre travail nous a permis également d'identifier un possible nouveau marqueur de la conscience qu'est la variation contingente négative (CNV)

Awareness assessment in disorders of consciousness patients : a clinical and electrophysiological approach

Comprendre les mécanismes neurophysiologiques et les bases neurales de la conscience est un défi médico-scientifique majeur. A cette fin, il faut opérer une distinction entre les mécanismes neuraux des états de conscience, et ceux qui sous-tendent l'accès conscient à un contenu mental particulier (ou la prise de conscience). Les données expérimentales ayant contrasté état conscient/ état non conscient (coma, sommeil, sédation) d'une part, et perception consciente/inconsciente d'un même stimulus d'autre part, sont en faveur de l'implication d'un réseau d'aires cérébrales fronto-pariétales à la fois dans l'état et dans l'accès conscient à une information donnée. La comparaison état conscient/ état non conscient est malheureusement limitée par les différences de vigilance existant entre ces états. Nous avons cherché à contourner ce problème en nous focalisant sur deux populations de malades présentant un niveau de vigilance proche mais différant sous l'angle de l'état de conscience : patients éveillés, non conscients (état végétatif) versus patients éveillés et minimalement conscients (état de conscience minimale). Nos résultats, obtenus en utilisant les potentiels évoqués auditifs cognitifs à haute densité spatiale, sont en faveur de l'implication du même réseau d'aires cérébrales fronto-pariétales que celui mentionné ci-dessus, à la fois dans l'état et l'accès conscient. L'activation de ce réseau est contemporaine de l'apparition d'une P300b en potentiels évoqués qui semble constituer un marqueur très spécifique de conscience. Notre travail nous a permis également d'identifier un possible nouveau marqueur de la conscience qu'est la variation contingente négative (CNV).Understanding the neurophysiological mechanisms and neural bases of consciousness is a major scientific and medical challenge. To do this, one has to distinguish neural mechanisms of conscious state from those subserving conscious access to a given mental state (that is awareness). Experimental data having contrasted conscious / non conscious state (coma, sleep, sedation) on the one hand, and conscious/ unconscious processing of a very same stimulus on the other hand are in favour of the implication of a network of lateral and medial frontal and parietal areas in both conscious state and conscious access. The comparison of conscious/ non conscious state is unfortunately limited by arousal difference between these two states. So, we endeavoured to overcome this problem by exploring two categories of patients with a same level of arousal but a different state of awareness: unaware awaked patients (vegetative state) versus awaked and minimally conscious patients (minimally conscious state). Our results obtained by using high-density auditory event related potentials argue in favour of the implication of the very same network of frontal and parietal areas than the one described above in both conscious state and conscious access to a given information. This network activation is associated with the emergence of a P300b wave, on event related potentials, which seems to be a very specific marker of consciousness. Our work also give us the opportunity to discover a potential new marker of consciousness, namely the contingent negative variation (CNV)

Straight Lines Have to Be Straight -- Automatic Calibration and Removal of Distortion from Scenes of Structured Environments

Most algorithms in 3D computer vision rely on the pinhole camera model because of its simplicity, whereas video optics, especially low-cost wide-angle or fish-eye lenses, generate a lot of non-linear distortion which can be critical. To find the distortion parameters of a camera, we use the following fundamental property: a camera follows the pinhole model if and only if the projection of every line in space onto the camera is a line. Consequently, if we find the transformation on the video image so that every line in space is viewed in the transformed image as a line, then we know how to remove the distortion from the image. The algorithm consists of first doing edge extraction on a possibly distorted video sequence, then doing polygonal approximation with a large tolerance on these edges to extract possible lines from the sequence, and then finding the parameters of our distortion model that best transform these edges to segments. Results are presented on real video images, compared with distortion calibration obtained by a full camera calibration method which uses a calibration grid

Contributions à la synthèse de nouvelles vues à partir de photographies

Nous nous sommes intéressés à la synthèse de nouvelles vues réalistes d'une scène décrite par un ensemble restreint de photographies, ce qui nous a conduit au développement d'une chaîne de traitement complète et originale. Cette chaîne de traitement a été construite autour d'un moteur de rendu appliquant la technique du "placage de texture dépendant du point de vue" à une représentation géométrique simple de la scène décomposée en couches, le réalisme des images synthétisées étant alors maximal malgré la simplicité des données utilisées. Ensuite nous avons étudié la correction de certaines erreurs de rendu dues au placage de texture et avons proposé une procédure géométriquement valide pour supprimer les erreurs dites de "ghosting". Enfin nous avons cherché à estimer automatiquement les masques binaires associés aux couches 3D de la scène grâce à une nouvelle approche de segmentation par "graph-cut" faisant entre autre appel à une certaine connaissance géométrique (planar-key).We were interested in the synthesis of realistic novel views of a scene described by a limited number of photographs. This lead us to design a complete and genuine processing pipeline. This pipeline is based on a rendering engine applying the 'view-dependent texture mapping' technique to a simple geometric representation of a scene decomposed into layers. The realism of the generated images is consequently optimal despite the simplicity of the input data. We also studied the correction of some rendering errors caused by texture mapping and we suggested a geometrically valid procedure to correct the so-called 'ghosting artefacts'. Finally we investigated the automatic estimation of the binary masks associated with the 3D layers of the scene and we designed a new segmentation approach using 'graph-cuts' and, among others, a particular geometric knowledge (planar-key).NICE-BU Sciences (060882101) / SudocSudocFranceF