Coding local and global binary visual features extracted from video sequences

Binary local features represent an effective alternative to real-valued descriptors, leading to comparable results for many visual analysis tasks, while being characterized by significantly lower computational complexity and memory requirements. When dealing with large collections, a more compact representation based on global features is often preferred, which can be obtained from local features by means of, e.g., the Bag-of-Visual-Word (BoVW) model. Several applications, including for example visual sensor networks and mobile augmented reality, require visual features to be transmitted over a bandwidth-limited network, thus calling for coding techniques that aim at reducing the required bit budget, while attaining a target level of efficiency. In this paper we investigate a coding scheme tailored to both local and global binary features, which aims at exploiting both spatial and temporal redundancy by means of intra- and inter-frame coding. In this respect, the proposed coding scheme can be conveniently adopted to support the Analyze-Then-Compress (ATC) paradigm. That is, visual features are extracted from the acquired content, encoded at remote nodes, and finally transmitted to a central controller that performs visual analysis. This is in contrast with the traditional approach, in which visual content is acquired at a node, compressed and then sent to a central unit for further processing, according to the Compress-Then-Analyze (CTA) paradigm. In this paper we experimentally compare ATC and CTA by means of rate-efficiency curves in the context of two different visual analysis tasks: homography estimation and content-based retrieval. Our results show that the novel ATC paradigm based on the proposed coding primitives can be competitive with CTA, especially in bandwidth limited scenarios.Comment: submitted to IEEE Transactions on Image Processin

Source localization and denoising: a perspective from the TDOA space

In this manuscript, we formulate the problem of denoising Time Differences of Arrival (TDOAs) in the TDOA space, i.e. the Euclidean space spanned by TDOA measurements. The method consists of pre-processing the TDOAs with the purpose of reducing the measurement noise. The complete set of TDOAs (i.e., TDOAs computed at all microphone pairs) is known to form a redundant set, which lies on a linear subspace in the TDOA space. Noise, however, prevents TDOAs from lying exactly on this subspace. We therefore show that TDOA denoising can be seen as a projection operation that suppresses the component of the noise that is orthogonal to that linear subspace. We then generalize the projection operator also to the cases where the set of TDOAs is incomplete. We analytically show that this operator improves the localization accuracy, and we further confirm that via simulation.Comment: 25 pages, 9 figure

Dictionary-based Equivalent Source Method for Near-Field Acoustic Holography

In this paper, we propose a modification of the standard Equivalent Source Method (ESM) for Near-Field Acoustic Holography (NAH). As in EMS, we aim at modeling the acoustic pressure radiated from a vibrating object, and its surface velocity, as the joint effect of a set of equivalent sources located within or close to the object itself. The estimation of the equivalent source strengths (weigths) comes from the solution of a highly ill-conditioned problem. Rather than solving this problem in the least-squares sense, we exploit the 3D model of the vibrating object, along with a rough estimate of its physical parameters, to restrict the space of the solutions. More specifically, we make use of Finite Element Analysis for populating a compressed dictionary of possible equivalent source weights. NAH is then approached by seeking a sparse linear combination of the entries of the dictionary. Experiments carried on a public database prove the effectiveness of the proposed technique, especially when the number of available microphones is limited, and in the presence of a significant level of measurement noise

Localization of planar acoustic reflectors from the combination of linear estimates

In this paper we present a simple yet effective method for estimating the geometry of an acoustic enclosure in three-dimensions. By capturing the acoustic impulse responses using a microphone array and a loudspeaker at different spatial locations we transform the localization of planar reflectors into the estimation of multiple linear reflectors. By decomposing the microphone array into co-planar sub-arrays the line parameters of the reflectors lying on the corresponding planes can be inferred using a geometric constraint. By intersecting these lines the actual lying plane of each reflector can be estimated. The proposed method is evaluated using a three-dimensional microphone array in a real conference room

A Geometrical-Statistical Approach to Outlier Removal for TDOA Measurements

The curse of outlier measurements in estimation problems is a well-known issue in a variety of fields. Therefore, outlier removal procedures, which enables the identification of spurious measurements within a set, have been developed for many different scenarios and applications. In this paper, we propose a statistically motivated outlier removal algorithm for time differences of arrival (TDOAs), or equivalently range differences (RD), acquired at sensor arrays. The method exploits the TDOA-space formalism and works by only knowing relative sensor positions. As the proposed method is completely independent from the application for which measurements are used, it can be reliably used to identify outliers within a set of TDOA/RD measurements in different fields (e.g., acoustic source localization, sensor synchronization, radar, remote sensing, etc.). The proposed outlier removal algorithm is validated by means of synthetic simulations and real experiments

Enabling visual analysis in wireless sensor networks

This demo showcases some of the results obtained by the GreenEyes project, whose main objective is to enable visual analysis on resource-constrained multimedia sensor networks. The demo features a multi-hop visual sensor network operated by BeagleBones Linux computers with IEEE 802.15.4 communication capabilities, and capable of recognizing and tracking objects according to two different visual paradigms. In the traditional compress-then-analyze (CTA) paradigm, JPEG compressed images are transmitted through the network from a camera node to a central controller, where the analysis takes place. In the alternative analyze-then-compress (ATC) paradigm, the camera node extracts and compresses local binary visual features from the acquired images (either locally or in a distributed fashion) and transmits them to the central controller, where they are used to perform object recognition/tracking. We show that, in a bandwidth constrained scenario, the latter paradigm allows to reach better results in terms of application frame rates, still ensuring excellent analysis performance

MANIFESTAÇÕES SOCIAIS E NOVAS MÍDIAS: a construção de uma cultura contra-hegemônica

O artigo analisa algumas manifestações sociais que surgiram pelo mundo a partir de 2008, em especial no Egito, na Espanha, nos EUA, no Chile e no Brasil. O nosso interesse está no impacto, nessas manifestações, do uso das redes sociais, já razoavelmente inseridas num contexto de intensa mediação na comunicação entre manifestantes e na opinião pública em geral. Analisamos dois aspectos: o impacto na organização desses movimentos e o uso cada vez mais central das imagens como forma de comunicação. Com a preocupação de identificar pontos de novidade mais do que analisá-los profundamente, indicamos que há interessantes possibilidades de luta contra-hegemônica a partir do uso extensivo e intensivo das mídias sociais, o que se dá pela busca da democracia radical e pelo uso crítico da imagem. PALAVRAS-CHAVE: Internet. Mídias sociais. Hegemonia. Movimentos sociais. Política.SOCIAL MANIFESTATIONS AND NEW MEDIA: the construction of a counter-hegemonic culture Paulo Rodrigues Gajanigo Rogério Ferreira de Souza The article analyzes some social protests that have appeared around the world from 2008, especially in Egypt, Spain, USA, Chile and Brazil. Our interest is in the impact, on these events, of the use of social networks, already fairly inserted in a context of intense mediation in communication between protesters and public opinion in general. We analyze two aspects: the impact on the organization of these movements and more central use of images as a form of communication. With a view to identify new points, more than deeply analyze them, indicate that there are interesting possibilities for counter-hegemonic struggle from the extensive and intensive use of social media, which is given by the search for radical democracy and critical use of images. KEYWORDS: Internet. Social media. Hegemony. Social movements. Policy.MANIFESTATIONS SOCIALES ET NOUVEAUX MÉDIAS: la construction d’une culture contrehégémonique Paulo Rodrigues Gajanigo Rogério Ferreira de Souza Cet article analyse quelques manifestations sociales qui ont eu lieu dans le monde à partir de 2008, tout spécialement en Égypte, en Espagne, aux États-Unis, au Chili et au Brésil. Notre centre d’intérêt se situe au niveau de l’impact créé par l’utilisation des réseaux sociaux dans ces manifestations déjà suffisamment insérées dans un contexte d’intense médiation de ces réseaux pour la communication entre les manifestants et l’opinion publique en général. L’analyse porte sur deux aspects: l’impact au niveau de l’organisation de ces mouvements et l’utilisation chaque fois plus centrale des images comme moyen de communication. Dans l’intérêt d’identifier des éléments nouveaux plus que d’en approfondir l’analyse, nous signalons qu’il y a des possibilités intéressantes de lutte contre-hégémonique grâce à l’utilisation intensive des médias sociaux, auxquels on fait appel en vue d’une démocratie radicale et pour l’utilisation critique de l’image. MOTS-CLÉS: Internet. Médias sociaux. Hégémonie. Mouvements sociaux. Politique. Publicação Online do Caderno CRH no Scielo: http://www.scielo.br/ccrh  Publicação Online do Caderno CRH: http://www.cadernocrh.ufba.br