Local greyvalue invariants for image retrieval

Abstract | This paper addresses the problem of retrieving images from large image databases. The method is based on local greyvalue invariants which are computed at automatically detected interest points. Avoting algorithm and semi-local constraints make retrieval possible. Indexing allows for e cient retrieval from a database of more than 1000 images. Experimental results show correct retrieval in the case of partial visibility, similarity transformations, extraneous features, and small perspective deformations

Arc and path consistency revisited

Journal ArticleMackworth and Freuder have analyzed the time complexity of several constraint satisfaction algorithms [4]. We present here new algorithms for arc and path consistency and show that the arc consistency algorithm is optimal in time complexity and of the same order space complexity as the earlier algorithms. A refined solution for the path consistency problem is proposed. However, the space complexity of the path consistency algorithm makes it practicable only for small problems. These algorithms are the result of the synthesis techniques used in ALICE (a general constraint satisfaction system) and local consistency methods

Loose but Normal: A Semantic Association Study

An abnormal facilitation of the spreading activation within semantic networks is thought to underlie schizophrenics' remote associations and referential ideas. In normal subjects, elevated magical ideation (MI) has also been associated with a style of thinking similar to that of schizotypal subjects. We thus wondered whether normal subjects with a higher MI score would judge "loose associations” as being more closely related than do subjects with a lower MI score. In two experiments, we investigated whether judgments of the semantic distance between stimulus words varied as a function of MI. In the first experiment, random word pairs of two word classes, animals and fruits, were presented. Subjects had to judge the semantic distance between word pairs. In the second experiment, sets of three words were presented, consisting of a pair of indirectly related, or unrelated nouns plus a third noun. Subjects had to judge the semantic distance of the third noun to the word pair. The results of both experiments showed that higher MI subjects considered unrelated words as more closely associated than did lower MI subjects. We conjecture that for normal subjects high on MI "loose associations” may not be loose after all. We also note that the tendency to link uncommon, nonobvious, percepts may not only be the basis of paranormal and paranoid ideas of reference, but also a prerequisite of creative thinkin

Indexation et appariement d'images par modèle de mélange gaussien des couleurs

- Nous proposons d'approximer la distribution de certains descripteurs d'image, comme la couleur ou la couleur associée à une information de gradient, par d'une part des histogrammes et d'autre part un mélange de gaussiennes. La dimension de cette dernière signature étant choisie automatiquement par des critères statistiques, le gain sur la taille de l'index est souvent important. Concernant la qualité de l'appariement, les histogrammes semblent plus performants

Optimal 3D Sensor Placement to Obtain Accurate 3D Point Positions

International audience3D measurements can be achieved from several views using the principle of optical triangulation. This paper deals with the problem of where to place cameras in order to obtain a minimal error in the detection. We pose the problem in terms of an optimization design, dividing this in two main components: 1) an analytical part dedicated to the analysis of error propagation from which a criterion is derivated, 2) an heuristical part which is going to minimize this criterion. In this way, the approach consists of an uncertainty analysis applied to the reconstruction process from which a covariance matrix is computed. This matrix represents the uncertainty of the detection from which the criteria is derived. Thus, a multicellular genetic algorithm is implemented in order to minimize the criterion. Graphical examples are provided to illustrate the effectiveness and efficiency of the solution

Gaussian Mixture Densities for Indexing of Localized Objects in a Video Sequence

The appearance of non-rigid objects in a video stream is highly variable and therefore makes the identification of similar objects very complex. Furthermore, the indexing process of all detected objects is a very challengin- g problem when all appearances of an object would be stored: The database produced would become so large that searching would be intractable. In this paper we present a framework for object-based indexing which on one side increases the robustness of existing feature detectors used for object recognition and on the other side reduces the size of the database. The temporal variation of features of a tracked object in the video-shot is modeled by a mixture of Gaussians. Given a tracked object, this consists in separating the feature distribution into homogeneous clusters. Each cluster corresponds to a stable view of the tracked object. We put in competitions seven different Gaussian models and the number of Gaussian components varies up to four. The EM algorithm is applied to estimate the parameters of the mixture of Gaussians where the number of its components and the Gaussian model are a priori fixed. The choice of the best structure of the data (model and number of Gaussians) is realized by different criteria: BIC, ICL and NEC. The training of the system is done on a set of different tracked objects and the Gaussian mixture classifier is used to recognize new occurrences of objects. Experiments on a video base of twelve different objects are conducted and eight color features are tested. A comparison in the performance of the proposed system and the temporal feature method is analyzed and reported

Indexation et appariement d'images par modèle de mélange gaussien des couleurs

Nous proposons d'indexer un objet, ou partie d'image, par le paramètre d'un mélange gaussien qui approxime la distribution des couleurs, le nombre de classes étant choisi automatiquement par des critères bayésiens. Tout objet requête sera alors apparié à l'objet indexé le plus vraisemblable parmi tous les objets indexés de la base d'apprentissage. Cette technique est ensuite comparée à celle de l'indexation par histogrammes utilisant la dissimilarité du chi-deux pour apparier. L'avantage des mélanges gaussiens repose principalement sur un gain important de la taille de l'index par rapport aux histogrammes surtout lorsque la dimension augmente, tout en gardant une qualité d'appariement du même ordre

Fast and Realistic Image Synthesis for Telemanipulation Purposes

International audienceWe describe here a method to build fast and realistic synthetic images, which does not require a tedious a priori modeling of the scene to be displayed. We only use photos or videos of a real scene taken from some viewpoints, which in some way we 'wrap' to get new (synthetic) images of the same scene. This way, we can virtually see and move inside the 3d scene. The process consists of two steps: we first need to registrate the so-called reference views, using computer vision techniques. Then we just project the obtained model onto the plane of a virtual camera; this last step is fast and gives realistic results, allowing to use the method for instance to simulate the environment of a tele-operated device. 1 Introduction Synthetic images have proven useful for telemanipulation: synthesizing the environment of the operated device is needed for visualization, simulation, and better remote positioning

Fusion of 3D B-Spline Surface Patches Reconstructed from Image Sequences

International audienceThis paper considers the problem of merging a set of distinct three dimensional B-spline surface patches, which are reconstructed from observations of the motion of occluding contours in image sequences. We propose an original method of fusing these partially overlapping patches in order to obtain a whole surface. This approach is based on a triangular mesh and surface interpolation through regularized uniform bicubic B-spline surface patches. Experimental results are presented for both synthetic and real data