Mise en correspondance de partitions en vue du suivi d'objets

Cristina Gomila
Abstract : In the field of multimedia applications, the incoming standards promote the creation of new ways of communication, access and manipulation of audiovisual information that go far beyond the plain compression obtained by the preceding coding norms. Among the new functionalities, it is expected that the user will be allowed to access the image content by editing and manipulating the objects of interest. Nevertheless, standards are restricted to object representation and coding, leaving opened a large field of development concerning the problem of object extraction and tracking when they move along a video sequence. In a first step, we have proceeded to the study and fine tuning of widespread applicated algorithms for image filtering and segmentation, being these tools at the basis of all contentbased image and video analysis systems. More particularly, we have focused on a novel class of morphological filters known as levelings, as well as on a variant of the segmentation algorithms based on the constrained ooding of a gradient image. Segmentation techniques aim at yielding a partition image as close as possible to the one produced by the human eye, with a view to the later object recognition. Nevertheless, in most cases this last task needs human interaction. However, when we would like to retrieve an object from large collection of images, or when we would like to track an object through a long sequence, the surveillance of each image becomes infeasible. To face these situations, the development of matching algorithms able to propagate the information through a series of images become essential, human interaction being limited to a initialization step. Going from still images to sequences, the core of this thesis is devoted to the study of the partition matching problem. The method we have developed, named Joint Segmentation and Matching technique (JSM), can be defined as being of hybrid nature. It combines classical algorithms of graph matching with new editing techniques based on the hierarchy of partitions resulting from morphological segmentation. This mix provides a very robust algorithm, in spite of the instability classically associated to the segmentation processes. The result of segmenting two images can strongly differ if the segmentation process produces a single partition image, however we have shown that results are much more stable when producing a hierarchy of nested partitions, in which all contours are present and ranked through a weighted value. The JSM technique is considered a very promising approach according to the obtained results. Being flexible and powerful, it allows the recognition of an object when it reappears after occlusion thanks to the management of a memory graph. Although we have particularly focused our interest on the tracking problem, the developed algorithms can be extended to a large field of applications, being specially suited to perform object retrieval from image or video sequences databases. Finally, in the framework of the European project M4M (MPEG f(o)ur mobiles), we have focused on the development and implementation of a real-time demonstrator for detecting, segmenting and tracking the speaker in videophone sequences. In the view of this application, the real-time constraint has become the greatest challenge to overcome, forcing us to simplify and optimize our algorithms. The main interest in terms of new services is twofold : on one hand the automatic segmentation of the speaker permits the object-based coding, reducing the bitrate without loss of quality on the regions of interest ; on the other hand, it allows the user to edit the sequences by changing the scene composition, for example by introducing a new background, or grouping several speakers in a virtual meeting room.
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Cristina Gomila. Mise en correspondance de partitions en vue du suivi d'objets. Mathematics [math]. École Nationale Supérieure des Mines de Paris, 2001. English. ⟨pastel-00003272⟩

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