Tag Propagation Approaches within Speaking Face Graphs for Multimodal Person Discovery

International audienceThe indexing of broadcast TV archives is a current problem in multimedia research. As the size of these databases grows continuously, meaningful features are needed to describe and connect their elements efficiently, such as the identification of speaking faces. In this context, this paper focuses on two approaches for unsupervised person discovery. Initial tagging of speaking faces is provided by an OCR-based method, and these tags propagate through a graph model based on audiovisual relations between speaking faces. Two propagation methods are proposed, one based on random walks and the other based on a hierarchical approach. To better evaluate their performances, these methods were compared with two graph clustering baselines. We also study the impact of different modality fusions on the graph-based tag propagation scenario. From a quantitative analysis, we observed that the graph propagation techniques always outperform the baselines. Among all compared strategies, the methods based on hierarchical propagation with late fusion and random walk with score-fusion obtained the highest MAP values. Finally, even though these two methods produce highly equivalent results according to Kappa coefficient, the random walk method performs better according to a paired t-test, and the computing time for the hierarchical propagation is more than 4 times lower than the one for the random walk propagation

Evaluation of morphological hierarchies for supervised segmentation

International audienceWe propose a quantitative evaluation of morphological hierarchies (quasi-flat zones, constraint connectivity, watersheds, observation scale) in a novel framework based on the marked segmentation problem. We created a set of automatically generated markers for the one object image datasets of Grabcut and Weizmann. In order to evaluate the hierarchies , we applied the same segmentation strategy by combining several parameters and markers. Our results, which shows important differences among the considered hierarchies, give clues to understand the behaviour of each method in order to choose the best one for a given application. The code and the marker datasets are available online

Combining convolutional side-outputs for road image segmentation

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Evaluation of morphological hierarchies for supervised video segmentation

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Stochastic hierarchical watershed cut based on disturbed topographical surface

International audienceIn this article we present a hierarchical stochastic image segmentation approach. This approach is based on a framework of edge-weighted graph for minimum spanning forest hierarchy. Image regions, that are represented by trees in a forest, can be merged according to a certain rule in order to create a single tree that represents segments hierarchically. In this article, we propose to add a uniform random noise into the edge-weighted graph and then we build the hierarchy with several realizations of independent segmentations. At the end, we combine all the hierarchical segmentations into a single one. As we show in this article, adding noise into the edge weights improves the segmentation precision of larger image regions and for F-Measure of objects and parts

A novel method for temporal graph classification based on transitive reduction

International audienceDomains such as bio-informatics, social network analysis, and computer vision, describe relations between entities and cannot be interpreted as vectors or fixed grids, instead, they are naturally represented by graphs. Often this kind of data evolves over time in a dynamic world, respecting a temporal order being known as temporal graphs. The latter became a challenge since subgraph patterns are very difficult to find and the distance between those patterns may change irregularly over time. While state-of-the-art methods are primarily designed for static graphs and may not capture temporal information, recent works have proposed mapping temporal graphs to static graphs to allow for the use of conventional static kernels and graph neural approaches. In this study, we compare the transitive reduction impact on these mappings in terms of accuracy and computational efficiency across different classification tasks. Furthermore, we introduce a novel mapping method using a transitive reduction approach that outperforms existing techniques in terms of classification accuracy. Our experimental results demonstrate the effectiveness of the proposed mapping method in improving the accuracy of supervised classification for temporal graphs while maintaining reasonable computational efficiency

Tag Propagation Approaches within Speaking Face Graphs for Multimodal Person Discovery

International audienceThe indexing of broadcast TV archives is a current problem in multimedia research. As the size of these databases grows continuously, meaningful features are needed to describe and connect their elements efficiently, such as the identification of speaking faces. In this context, this paper focuses on two approaches for unsupervised person discovery. Initial tagging of speaking faces is provided by an OCR-based method, and these tags propagate through a graph model based on audiovisual relations between speaking faces. Two propagation methods are proposed, one based on random walks and the other based on a hierarchical approach. To better evaluate their performances, these methods were compared with two graph clustering baselines. We also study the impact of different modality fusions on the graph-based tag propagation scenario. From a quantitative analysis, we observed that the graph propagation techniques always outperform the baselines. Among all compared strategies, the methods based on hierarchical propagation with late fusion and random walk with score-fusion obtained the highest MAP values. Finally, even though these two methods produce highly equivalent results according to Kappa coefficient, the random walk method performs better according to a paired t-test, and the computing time for the hierarchical propagation is more than 4 times lower than the one for the random walk propagation

Efficient algorithms for hierarchical graph-based segmentation relying on the Felzenszwalb-Huttenlocher dissimilarity

International audienceHierarchical image segmentation provides a region-oriented scale-space, {\em i.e.}, a set of image segmentations at different detail levels in which the segmentations at finer levels are nested with respect to those at coarser levels. However, most image segmentation algorithms, among which a graph-based image segmentation method relying on a region merging criterion was proposed by Felzenszwalb-Huttenlocher in 2004, do not lead to a hierarchy. In order to cope with a demand for hierarchical segmentation, Guimar\~aes {\em et al.} proposed in 2012 a method for hierarchizing the popular Felzenszwalb-Huttenlocher method, without providing an algorithm to compute the proposed hierarchy. This article is devoted to provide a series of algorithms to compute the result of this hierarchical graph-based image segmentation method efficiently, based mainly on two ideas: optimal dissimilarity measuring and incremental update of the hierarchical structure. Experiments show that, for an image of size 321 $\times$ 481 pixels, the most efficient algorithm produces the result in half a second whereas the most naive one requires more than four hours