Proceedings of 32nd IEEE Conference on Decision and Control
In this paper we generalize a technique for eliminating the drift from the description of a contr... more In this paper we generalize a technique for eliminating the drift from the description of a control system on a matrix Lie group with left-invariant vector fields. A diffeomorphism of the state space together with an affine input transformation are used in order to put the system into an equivalent left-invariant driftfree form. Techniques developed for steering drift-free control systems may then be applied. We apply this method to the Lie group of the rigid rotations SO(3) as in the authors' previous work [6], and to a new example, the rigid motions SE(3).
The paper focuses on the problem of explicitly generating open loop strategies for steering contr... more The paper focuses on the problem of explicitly generating open loop strategies for steering control systems with left-invariant vector fields on the Lie group of rigid rotations SO(3). Both systems with and without drift are considered as well as systems with three, two or one input(s). For each of these cases, if possible, we present a constructive solution to the steering problem. The most interesting cases are those of systems with drift and either only or two inputs. Having two inputs gives us the freedom to choose the steering time. In the case of only one input our algorithm will drive the system to the desired orientation in a finite time. There are, however, limitations on the choice of the arrival time. Simulations have been developed and the results animated on a Silicon Graphics Iris workstation. In particular, video-taped animation of the algorithms mentioned above will be presented at the conference.
Proceedings. First International Symposium on 3D Data Processing Visualization and Transmission
In many applications surfaces containing a large number of primitives occur. Geometry compression... more In many applications surfaces containing a large number of primitives occur. Geometry compression reduces storage space and transmission time for such models. A special case is given by polygonal isosurfaces generated from gridded volume data. However, most current state-of-the-art geometry compression systems do not capitalize on the structure that is characteristic of such isosurfaces, namely that the surfaces are defined by a set of vertices on edges of the grid. We propose a compression method for isosurfaces that is designed to exploit this feature. We tested our method for several isosurfaces from a CT scan of a human head. For this data set our coder outperformed state-of-the-art geometry compression methods by a factor of 2.2 to 2.8 in terms of compression ratio.
2013 IEEE 15th International Workshop on Multimedia Signal Processing (MMSP), 2013
ABSTRACT In this paper we present a technique for the rendering of directional sources by means o... more ABSTRACT In this paper we present a technique for the rendering of directional sources by means of loudspeaker arrays. The proposed methodology is based on a decomposition of the sound field in terms of plane waves. Within this framework the directivity of the source is naturally included in the rendering problem, therefore accommodating the directivity into the picture becomes much simpler. For this purpose, the loudspeaker array is subdivided into overlapping sub-arrays, each generating a plane wave component. The individual plane waves are then weighed by the desired directivity pattern. Simulations and experimental results show that the proposed technique is able to reproduce the sound field of directional sources with an improved accuracy with respect to existing techniques.
2013 IEEE International Conference on Acoustics, Speech and Signal Processing, 2013
In this paper we propose a methodology for the localization of virtual acoustic sources for sound... more In this paper we propose a methodology for the localization of virtual acoustic sources for sound field rendering applications. After the reconstruction of the sound field in the listening area by means of circular harmonic decomposition, the virtual source location is found through the Hough transform. We prove the accuracy of the proposed methodology by comparing the source locations estimates with those of a subjective test campaign.
2000 10th European Signal Processing Conference, 2000
In this paper we propose a 3D reconstruction technique based on the analysis of the extremal boun... more In this paper we propose a 3D reconstruction technique based on the analysis of the extremal boundaries of the imaged surface. The method correctly determines the correspondences between apparent (viewer-dependent) contours and accurately determines location, orientation and curvature of the surface in the proximity of the apparent rims.
2009 IEEE International Conference on Acoustics, Speech and Signal Processing, 2009
In this paper we present a novel hierarchical and scalable three-stage algorithm to effectively p... more In this paper we present a novel hierarchical and scalable three-stage algorithm to effectively perform musical audio semantic segmentation. In the first stage, the energy spectrum of the entire audio track is analyzed to find significant energy textures that may characterize different semantic segments; in the second and third stages, tonal and timbric features are used to refine the segmentation by moving or deleting segment boundaries. Experimental results on a set of 58 songs show that our algorithm is able to attain good semantic segmentation just after the first step, with a precision of 64% and a recall of 96%. After second step the precision increases to 79%; the best precision result is obtained after the third step, where a value of 85% is reached. In this step the minimum average recall value of 92% is obtained.
2004 12th European Signal Processing Conference, 2004
In this paper we discuss the how to best handle motion vectors in spatially scalable wavelet-base... more In this paper we discuss the how to best handle motion vectors in spatially scalable wavelet-based video decoders. Motion vectors with full resolution are normally included in the bit-steams relative to spatially scaled version of a video sequence. When a low-resolution version of the original sequence is received, the decoder must scale the motion vectors accordingly. We will show that the motion vector scaling (truncation) is not the best solution and that better results can be obtained by interpolating the subsampled sequence to full resolution using of the wavelet synthesis low-pass filter. We illustrate the results of experiments carried out with an in-band wavelet-based fully scalable coder that performs spatial analysis, followed by temporal filtering. Emphasis is given to the computation of the Overcomplete DWT in the spatially scalable scenario.
2012 Proceedings of the 20th European Signal Processing Conference (EUSIPCO), 2012
Music Information Retrieval systems are often based on the analysis of a large number of low-leve... more Music Information Retrieval systems are often based on the analysis of a large number of low-level audio features. When dealing with problems of musical genre description and visualization, however, it would be desirable to work with a very limited number of highly informative and discriminant macro-descriptors. In this paper we focus on a specific class of training-based descriptors, which are obtained as the log-likelihood of a Gaussian Mixture Model trained with short musical excerpts that selectively exhibit a certain semantic homogeneity. As these descriptors are critically dependent on the training sets, we approach the problem of how to automatically generate suitable training sets and optimize the associated macro-features in terms of discriminant power and informative impact. We then show the application of a set of three identified macro-features to genre visualization, tracking and classification.
In this paper we present a simple yet effective method for estimating the geometry of an acoustic... more 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.
1996 8th European Signal Processing Conference (EUSIPCO 1996), 1996
Signal decimation aimed at optimal spectral packing has a variety of applications in areas rangin... more Signal decimation aimed at optimal spectral packing has a variety of applications in areas ranging from array processing to image processing. In this article we propose and discuss a new method for determining decimation grid and prefilter that best fit the spectral extension of any 2D signal defined on an arbitrary sampling lattice. The method has been implemented and tested on digital images in order to evaluate quality degradation due to optimal spectral truncation.
In this paper we propose a novel system for indoor video surveillance. Our system, starting from ... more In this paper we propose a novel system for indoor video surveillance. Our system, starting from a sequence of images, is able to detect and track moving objects even in the presence of significant variations of scene illumination. After a first analysis and clustering of the luminance time changes, a classification algorithm based on a fuzzy logic approach is used to identify moving regions that really represent unexpected objects moving in the scene, while discarding reflections and luminance profile changes due to illumination variations. One key feature of our system is its modest computation complexity, which allows it to operate in real-time on a standard PC platform. The real-time implementation of the system has been tested on a wide variety of situations, proving its effectiveness and robustness.
IEEE/ACM Transactions on Audio, Speech, and Language Processing, 2014
Estimating the geometric and reflective properties of the environment is important for a wide ran... more Estimating the geometric and reflective properties of the environment is important for a wide range of applications of space-time audio processing, from acoustic scene analysis to room equalization and spatial audio rendering. In this manuscript, we propose a methodology for frequency-subband in-situ estimation of the reflection coefficients of planar surfaces. This is a rather challenging task, as the reflection coefficients depend on the frequency and the angle of incidence and their estimate is highly sensitive to background noise and interfering sources. Our method is based on the assumption that we know the geometry of the reflectors; the position and the radiation pattern of the source; the position and the spatial response of the array. Applying beamforming algorithms on a single set of measured sensor data, we estimate the angular distribution of the acoustic energy (angular pseudospectrum) that impinges on a microphone array. We then apply a two-step iterative estimation technique based on an Expectation-Maximization (EM) algorithm. The first step estimates the scaling factors. The second one infers the reflection coefficients from the scaling factors. Under the assumption of additive white Gaussian noise, we finally determine the reflection coefficients with a Maximum Likelihood (ML) estimation method. The effectiveness and the accuracy of the proposed technique are assessed through experiments based on measured data.
IEEE Transactions on Circuits and Systems I: Regular Papers, 2016
A large class of transcendental equations involving exponentials can be made explicit using the L... more A large class of transcendental equations involving exponentials can be made explicit using the Lambert W function. In the last fifteen years, this powerful mathematical tool has been extensively used to find closed-form expressions for currents or voltages in circuits containing diodes. Until now almost all the studies about the W function in circuit analysis concern the Kirchhoff (K) domain, while only few works in the literature describe explicit models for diode circuits in the Wave Digital (WD) domain. However explicit models of NonLinear Elements (NLEs) in the WD domain are particularly desirable, especially in order to avoid the use of iterative algorithms. This paper explores the range of action of the W function in the WD domain; it describes a procedure to search for explicit wave mappings, for both one-port and multi-port NLEs containing diodes. WD models, describing an arbitrary number of different parallel and anti-parallel diodes, a transformerless ring modulator and some BJT amplifier configurations, are derived. In particular, an extended version of the BJT Ebers-Moll model, suitable for implementing feedback between terminals, is introduced.
2015 IEEE Workshop on Applications of Signal Processing to Audio and Acoustics (WASPAA), 2015
This paper proposes a methodology for the accurate visualization of acoustic reflections in a roo... more This paper proposes a methodology for the accurate visualization of acoustic reflections in a room from acoustic measurements by a spherical microphone array. The goal is to provide insight on the relationship between architectural and acoustic features. This task requires high-resolution acoustic images. In this contribution, we achieve this goal by introducing two main modifications of existing approaches. At first, we adopt an explicit model that takes into account the scattering due to the rigid spherical surface where the microphone capsules are hosted. Then, we obtain an estimate of the acoustic power coming from a grid of directions using a spectral analysis approach based on the matching of array data covariance matrix. We conclude this manuscript by showing applications of the devised methodology in real world cases.
Proceedings. International Conference on Image Processing
Abstract We propose a novel system for indoor video surveillance. It is able to detect and track ... more Abstract We propose a novel system for indoor video surveillance. It is able to detect and track moving objects even in the presence of significant variations of scene illumination. After a preliminary analysis and clustering of temporal changes in the video sequence, the algorithm performs a classification based on fuzzy logic, aimed at identifying moving regions that really correspond to unexpected objects in the scene. The proposed approach tends to discard shadows, reflections and luminance profile changes due to illumination variations. ...
Proceedings of 32nd IEEE Conference on Decision and Control
In this paper we generalize a technique for eliminating the drift from the description of a contr... more In this paper we generalize a technique for eliminating the drift from the description of a control system on a matrix Lie group with left-invariant vector fields. A diffeomorphism of the state space together with an affine input transformation are used in order to put the system into an equivalent left-invariant driftfree form. Techniques developed for steering drift-free control systems may then be applied. We apply this method to the Lie group of the rigid rotations SO(3) as in the authors' previous work [6], and to a new example, the rigid motions SE(3).
The paper focuses on the problem of explicitly generating open loop strategies for steering contr... more The paper focuses on the problem of explicitly generating open loop strategies for steering control systems with left-invariant vector fields on the Lie group of rigid rotations SO(3). Both systems with and without drift are considered as well as systems with three, two or one input(s). For each of these cases, if possible, we present a constructive solution to the steering problem. The most interesting cases are those of systems with drift and either only or two inputs. Having two inputs gives us the freedom to choose the steering time. In the case of only one input our algorithm will drive the system to the desired orientation in a finite time. There are, however, limitations on the choice of the arrival time. Simulations have been developed and the results animated on a Silicon Graphics Iris workstation. In particular, video-taped animation of the algorithms mentioned above will be presented at the conference.
Proceedings. First International Symposium on 3D Data Processing Visualization and Transmission
In many applications surfaces containing a large number of primitives occur. Geometry compression... more In many applications surfaces containing a large number of primitives occur. Geometry compression reduces storage space and transmission time for such models. A special case is given by polygonal isosurfaces generated from gridded volume data. However, most current state-of-the-art geometry compression systems do not capitalize on the structure that is characteristic of such isosurfaces, namely that the surfaces are defined by a set of vertices on edges of the grid. We propose a compression method for isosurfaces that is designed to exploit this feature. We tested our method for several isosurfaces from a CT scan of a human head. For this data set our coder outperformed state-of-the-art geometry compression methods by a factor of 2.2 to 2.8 in terms of compression ratio.
2013 IEEE 15th International Workshop on Multimedia Signal Processing (MMSP), 2013
ABSTRACT In this paper we present a technique for the rendering of directional sources by means o... more ABSTRACT In this paper we present a technique for the rendering of directional sources by means of loudspeaker arrays. The proposed methodology is based on a decomposition of the sound field in terms of plane waves. Within this framework the directivity of the source is naturally included in the rendering problem, therefore accommodating the directivity into the picture becomes much simpler. For this purpose, the loudspeaker array is subdivided into overlapping sub-arrays, each generating a plane wave component. The individual plane waves are then weighed by the desired directivity pattern. Simulations and experimental results show that the proposed technique is able to reproduce the sound field of directional sources with an improved accuracy with respect to existing techniques.
2013 IEEE International Conference on Acoustics, Speech and Signal Processing, 2013
In this paper we propose a methodology for the localization of virtual acoustic sources for sound... more In this paper we propose a methodology for the localization of virtual acoustic sources for sound field rendering applications. After the reconstruction of the sound field in the listening area by means of circular harmonic decomposition, the virtual source location is found through the Hough transform. We prove the accuracy of the proposed methodology by comparing the source locations estimates with those of a subjective test campaign.
2000 10th European Signal Processing Conference, 2000
In this paper we propose a 3D reconstruction technique based on the analysis of the extremal boun... more In this paper we propose a 3D reconstruction technique based on the analysis of the extremal boundaries of the imaged surface. The method correctly determines the correspondences between apparent (viewer-dependent) contours and accurately determines location, orientation and curvature of the surface in the proximity of the apparent rims.
2009 IEEE International Conference on Acoustics, Speech and Signal Processing, 2009
In this paper we present a novel hierarchical and scalable three-stage algorithm to effectively p... more In this paper we present a novel hierarchical and scalable three-stage algorithm to effectively perform musical audio semantic segmentation. In the first stage, the energy spectrum of the entire audio track is analyzed to find significant energy textures that may characterize different semantic segments; in the second and third stages, tonal and timbric features are used to refine the segmentation by moving or deleting segment boundaries. Experimental results on a set of 58 songs show that our algorithm is able to attain good semantic segmentation just after the first step, with a precision of 64% and a recall of 96%. After second step the precision increases to 79%; the best precision result is obtained after the third step, where a value of 85% is reached. In this step the minimum average recall value of 92% is obtained.
2004 12th European Signal Processing Conference, 2004
In this paper we discuss the how to best handle motion vectors in spatially scalable wavelet-base... more In this paper we discuss the how to best handle motion vectors in spatially scalable wavelet-based video decoders. Motion vectors with full resolution are normally included in the bit-steams relative to spatially scaled version of a video sequence. When a low-resolution version of the original sequence is received, the decoder must scale the motion vectors accordingly. We will show that the motion vector scaling (truncation) is not the best solution and that better results can be obtained by interpolating the subsampled sequence to full resolution using of the wavelet synthesis low-pass filter. We illustrate the results of experiments carried out with an in-band wavelet-based fully scalable coder that performs spatial analysis, followed by temporal filtering. Emphasis is given to the computation of the Overcomplete DWT in the spatially scalable scenario.
2012 Proceedings of the 20th European Signal Processing Conference (EUSIPCO), 2012
Music Information Retrieval systems are often based on the analysis of a large number of low-leve... more Music Information Retrieval systems are often based on the analysis of a large number of low-level audio features. When dealing with problems of musical genre description and visualization, however, it would be desirable to work with a very limited number of highly informative and discriminant macro-descriptors. In this paper we focus on a specific class of training-based descriptors, which are obtained as the log-likelihood of a Gaussian Mixture Model trained with short musical excerpts that selectively exhibit a certain semantic homogeneity. As these descriptors are critically dependent on the training sets, we approach the problem of how to automatically generate suitable training sets and optimize the associated macro-features in terms of discriminant power and informative impact. We then show the application of a set of three identified macro-features to genre visualization, tracking and classification.
In this paper we present a simple yet effective method for estimating the geometry of an acoustic... more 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.
1996 8th European Signal Processing Conference (EUSIPCO 1996), 1996
Signal decimation aimed at optimal spectral packing has a variety of applications in areas rangin... more Signal decimation aimed at optimal spectral packing has a variety of applications in areas ranging from array processing to image processing. In this article we propose and discuss a new method for determining decimation grid and prefilter that best fit the spectral extension of any 2D signal defined on an arbitrary sampling lattice. The method has been implemented and tested on digital images in order to evaluate quality degradation due to optimal spectral truncation.
In this paper we propose a novel system for indoor video surveillance. Our system, starting from ... more In this paper we propose a novel system for indoor video surveillance. Our system, starting from a sequence of images, is able to detect and track moving objects even in the presence of significant variations of scene illumination. After a first analysis and clustering of the luminance time changes, a classification algorithm based on a fuzzy logic approach is used to identify moving regions that really represent unexpected objects moving in the scene, while discarding reflections and luminance profile changes due to illumination variations. One key feature of our system is its modest computation complexity, which allows it to operate in real-time on a standard PC platform. The real-time implementation of the system has been tested on a wide variety of situations, proving its effectiveness and robustness.
IEEE/ACM Transactions on Audio, Speech, and Language Processing, 2014
Estimating the geometric and reflective properties of the environment is important for a wide ran... more Estimating the geometric and reflective properties of the environment is important for a wide range of applications of space-time audio processing, from acoustic scene analysis to room equalization and spatial audio rendering. In this manuscript, we propose a methodology for frequency-subband in-situ estimation of the reflection coefficients of planar surfaces. This is a rather challenging task, as the reflection coefficients depend on the frequency and the angle of incidence and their estimate is highly sensitive to background noise and interfering sources. Our method is based on the assumption that we know the geometry of the reflectors; the position and the radiation pattern of the source; the position and the spatial response of the array. Applying beamforming algorithms on a single set of measured sensor data, we estimate the angular distribution of the acoustic energy (angular pseudospectrum) that impinges on a microphone array. We then apply a two-step iterative estimation technique based on an Expectation-Maximization (EM) algorithm. The first step estimates the scaling factors. The second one infers the reflection coefficients from the scaling factors. Under the assumption of additive white Gaussian noise, we finally determine the reflection coefficients with a Maximum Likelihood (ML) estimation method. The effectiveness and the accuracy of the proposed technique are assessed through experiments based on measured data.
IEEE Transactions on Circuits and Systems I: Regular Papers, 2016
A large class of transcendental equations involving exponentials can be made explicit using the L... more A large class of transcendental equations involving exponentials can be made explicit using the Lambert W function. In the last fifteen years, this powerful mathematical tool has been extensively used to find closed-form expressions for currents or voltages in circuits containing diodes. Until now almost all the studies about the W function in circuit analysis concern the Kirchhoff (K) domain, while only few works in the literature describe explicit models for diode circuits in the Wave Digital (WD) domain. However explicit models of NonLinear Elements (NLEs) in the WD domain are particularly desirable, especially in order to avoid the use of iterative algorithms. This paper explores the range of action of the W function in the WD domain; it describes a procedure to search for explicit wave mappings, for both one-port and multi-port NLEs containing diodes. WD models, describing an arbitrary number of different parallel and anti-parallel diodes, a transformerless ring modulator and some BJT amplifier configurations, are derived. In particular, an extended version of the BJT Ebers-Moll model, suitable for implementing feedback between terminals, is introduced.
2015 IEEE Workshop on Applications of Signal Processing to Audio and Acoustics (WASPAA), 2015
This paper proposes a methodology for the accurate visualization of acoustic reflections in a roo... more This paper proposes a methodology for the accurate visualization of acoustic reflections in a room from acoustic measurements by a spherical microphone array. The goal is to provide insight on the relationship between architectural and acoustic features. This task requires high-resolution acoustic images. In this contribution, we achieve this goal by introducing two main modifications of existing approaches. At first, we adopt an explicit model that takes into account the scattering due to the rigid spherical surface where the microphone capsules are hosted. Then, we obtain an estimate of the acoustic power coming from a grid of directions using a spectral analysis approach based on the matching of array data covariance matrix. We conclude this manuscript by showing applications of the devised methodology in real world cases.
Proceedings. International Conference on Image Processing
Abstract We propose a novel system for indoor video surveillance. It is able to detect and track ... more Abstract We propose a novel system for indoor video surveillance. It is able to detect and track moving objects even in the presence of significant variations of scene illumination. After a preliminary analysis and clustering of temporal changes in the video sequence, the algorithm performs a classification based on fuzzy logic, aimed at identifying moving regions that really correspond to unexpected objects in the scene. The proposed approach tends to discard shadows, reflections and luminance profile changes due to illumination variations. ...
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