Javier Sánchez

Javier Sánchez
Universidad de Las Palmas de Gran Canaria | ULPGC · Department of Computer Sciences and Systems

PhD

About

101
Publications
25,645
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1,931
Citations
Introduction
Javier Sánchez works at the Department of Computer Science in the University of Las Palmas de Gran Canaria. He works in Computer Vision and Artificial Intelligence. His main research lines are motion estimation, stereoscopic vision, 3D reconstruction and video stabilization.
Additional affiliations
January 2015 - December 2015
Ecole normale supérieure de Cachan
Position
  • Visiting researcher
October 2011 - December 2011
Ecole normale supérieure de Cachan
Position
  • Visiting researcher
July 2001 - September 2001
Education
July 1997 - December 2001
Universidad de Las Palmas de Gran Canaria
Field of study
  • Computer Science

Publications

Publications (101)
Article
Full-text available
En este documento se plantea la necesidad de colaboración entre las redes sociales y los repositorios. Ambos tienen objetivos similares pero se complementan en una serie de aspectos. Es necesario que estén dispuestos a compartir sus datos, centrándose cada uno en generar más valor a partir de la información de la que disponen.
Conference Paper
Full-text available
http://www.insticc.org/node/TechnicalProgram/visigrapp/presentationDetails/87675
Article
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This article studies the effectiveness of optical flow methods applied to short baseline image pairs under different noise levels. New metrics have been developed to analyze the results because the usual metrics are inadequate in a subpixel context. We have used the implementation of some standard optical flow methods adapted to the stereo problem....
Article
Full-text available
In this work, we propose several improvements of the inverse compositional algorithm for parametric registration. We propose an improved handling of boundary pixels, a different color handling and gradient estimation, and the possibility to skip scales in the multiscale coarse-to-fine scheme. In an experimental part, we analyze the influence of the...
Article
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In this work, we present an implementation and thorough study of the Harris corner detector. This feature detector relies on the analysis of the eigenvalues of the autocorrelation matrix. The algorithm comprises seven steps, including several measures for the classification of corners, a generic non-maximum suppression method for selecting interest...
Article
Full-text available
Video stabilization aims at removing the undesirable effects of camera motion by estimating its shake and applying a smoothing compensation. This paper proposes a unified mathematical analysis and classification of existing smoothing strategies. We assume that the apparent velocity induced by the camera is estimated as a set of global parametric mo...
Chapter
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Portable cameras record dynamic first-person video footage and these videos contain information on the motion of the individual to whom the camera is mounted, defined as ego. We address the task of discovering ego-motion from the video itself, without other external calibration information. We investigate the use of similarity transformations betwe...
Article
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This paper is devoted to a rigorous implementation and to an exhaustive comparison of video stabilization techniques. These techniques aim at removing the undesirable effects of camera shake. They first estimate a global transform from frame to frame, which can be a translation, a similarity, an affine map or a homography. This generates a signal t...
Article
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This article presents an implementation of the 'Midway Equalization' method for videos. This technique allows us to modify the image histograms so that they present similar luminances. We propose two algorithms: the first one based on histogram inversion and the second one on the sorting of images intensities. The former computes the histograms and...
Article
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We present an implementation of the inverse compositional algorithm for parametric motion estimation. It computes a global motion between two images using a non-linear least square technique. Our implementation allows computing several types of planar transformations, such as translations, similarities, affinities or homographies. The algorithm is...
Article
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The accurate preservation of motion discontinuities is a typical problem in variational optical flow methods. A widely used technique that provides good results consists in using a decreasing function for mitigating the regularization at flow edges. However, if the smoothing is not well controlled, this strategy may produce instabilities over the c...
Article
The aim of this work is to study several strategies for the preservation of flow discontinuities in variational optical flow methods. We analyze the combination of robust functionals and diffusion tensors in the smoothness assumption. Our study includes the use of tensors based on decreasing functions, which has shown to provide good results. Howev...
Technical Report
Full-text available
We analyze the discontinuity preserving problem in TV-L1 optical flow methods. This type of methods typically creates rounded effects at flow boundaries, which usually do not coincide with object contours. A simple strategy to overcome this problem consists in inhibiting the diffusion at high image gradients. In this work, we first introduce a gene...
Conference Paper
Full-text available
The use of decreasing functions, for mitigating the regulariza-tion at image contours, is typical in many recent optical flow methods. However, finding the correct parameter for getting the best of this strategy is challenging. Most of the methods use default parameters that are conservative, providing results that are not better than traditional a...
Technical Report
Full-text available
We analyse the influence of colour information in optical flow methods. Typically, most of these techniques compute their solutions using grayscale intensities due to its simplicity and faster processing, ignoring the colour features. However, the current processing systems have minimized their computational cost and, on the other hand, it is reaso...
Conference Paper
Full-text available
We propose an efficient solution for preserving the motion boundaries in variational optical flow methods. This is a key problem of recent TV-L 1 methods, which typically create rounded effects at flow edges. A simple strategy to overcome this problem consists in inhibiting the smoothing at high image gradients. However, depending on the strength o...
Article
Full-text available
En este trabajo se presenta Capaware, una plataforma de software libre para el desarrollo de aplicaciones geográficas 3D multicapa, que surge a partir de la iniciativa del Instituto Tecnológico de Canarias en colaboración con la Universidad de Las Palmas de Gran Canaria. Este entorno simplifica la creación de aplicaciones 3D sobre territorios geogr...
Article
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In this work, we describe an implementation of the variational method proposed by Brox et al. in 2004, which yields accurate optical flows with low running times. It has several benefits with respect to the method of Horn and Schunck: it is more robust to the presence of outliers, produces piecewise-smooth flow fields and can cope with constant bri...
Article
Full-text available
The seminal work of Horn and Schunck is the first variational method for optical flow estimation. It introduced a novel framework where the optical flow is computed as the solution of a minimization problem. From the assumption that pixel intensities do not change over time, the optical flow constraint equation is derived. This equation relates the...
Article
Full-text available
This article describes an implementation of the optical flow estimation method introduced by Zach, Pock and Bischof in 2007. This method is based on the minimization of a functional containing a data term using the L 1 norm and a regularization term using the total variation of the flow. The main feature of this formulation is that it allows discon...
Conference Paper
Full-text available
The aim of this work is to propose a method for computing the inverse optical flow between two frames in a sequence. We assume that the image registration has already been obtained in one direction and we need to estimate the mapping in the opposite direction. The direct and inverse mappings can easily be related through a simple warping formula, w...
Conference Paper
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The aim of this work is to propose a new method for estimating the backward flow directly from the optical flow. We assume that the optical flow has already been computed and we need to estimate the inverse mapping. This mapping is not bijective due to the presence of occlusions and disocclusions, therefore it is not possible to estimate the invers...
Conference Paper
Full-text available
The aim of this paper is to analyze the discontinuity preserving behavior of two methods in optical flow. With this objetive, we have implemented a well-known optical flow method that uses isotropic TV-L 1 regularization. For the second approach, we have modified this method, by adding a decreasing function in the regularization term, to avoid smoo...
Conference Paper
Full-text available
In this work we propose a new variational model for the consistent estimation of motion fields. The aim of this work is to develop appropriate spatio-temporal coherence models. In this sense, we propose two main contributions: a nonlinear flow constancy assumption, similar in spirit to the nonlinear brightness constancy assumption, which convenient...
Article
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We propose a novel method for real-time camera motion tracking in planar view scenarios. This method relies on the geometry of a tripod, an initial estimation of camera pose for the first video frame and a primitive tracking procedure. This process uses lines and circles as primitives, which are extracted applying classification and regression tree...
Article
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We propose four algorithms for computing the inverse optical flow between two images. We assume that the forward optical flow has already been obtained and we need to estimate the flow in the backward direction. The forward and backward flows can be related through a warping formula, which allows us to propose very efficient algorithms. These are p...
Article
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The accuracy and performance of current variational optical flow methods have considerably increased during the last years. The complexity of these techniques is high and enough care has to be taken for the implementation. The aim of this work is to present a comprehensible implementation of recent variational optical flow methods. We start with an...
Article
Full-text available
This paper describes a wildfire forecasting application based on a 3D virtual environment and a fire simulation engine. A novel open-source framework is presented for the development of 3D graphics applications over large geographic areas, offering high performance 3D visualization and powerful interaction tools for the Geographic Information Syste...
Conference Paper
Full-text available
One of the key problems in computer vision is the estimation of motion in image sequences. The apparent displacement of the pixels through the image sequence is generally called optical flow. This is a low-level task that is the base for many other high-level applications, such us stereoscopic vision and 3D scene reconstruction, object tracking, am...
Article
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In this paper we present a new method for image primitives tracking based on a CART (Classification and Regression Tree). Primitives tracking procedure uses lines and circles as primitives. We have applied the proposed method to sport event scenarios, specifically, soccer matches. We estimate CART parameters using a learning procedure based on RGB...
Conference Paper
Full-text available
This paper describes a wildfire forecasting application based on a 3D virtual environment and a fire simulation engine. A new open source framework is presented for the development of 3D graphics applications over large geographic areas offering high performance 3D visualization and powerful interaction tools for the Geographic Information Systems...
Chapter
Full-text available
Currently, meteorological satellites provide multichannel image sequences including visible, temperature and water vapor channels. Based on a variational approach, we propose mathematical models to address some of the usual challenges in satellite image analysis such as: (i) the estimation and smoothing of the cloud structures by decoupling them in...
Article
Motion estimation has many applications in fluid analysis, and a lot of work has been carried out using Particle Image Velocimetry (PIV) to capture and measure the flow motion from sequences of 2D images. Recent technological advances allow capturing 3D PIV sequences of moving particles. In the context of 3D flow motion, the assumption of incompres...
Conference Paper
Full-text available
This abstract describes the development of a wildfire forecasting plugin using Capaware. Capaware is designed as an easy to use open source framework to develop D graphics applications over large geographic areas offering high performance D visualization and powerful interaction tools for the Geographic Information Systems (GIS) community. Some oth...
Conference Paper
Full-text available
This paper describes a wildfire forecasting application based on a 3D virtual environment and a fire simulation engine. A new open source framework is presented for the development of 3D graphics applications over large geographic areas offering high performance 3D visualization and powerful interaction tools for the Geographic Information Systems...
Article
Full-text available
Canarias es una región muy sensible a los incendios forestales. Cuando surge un evento de este tipo, se impone una gestión adecuada, encaminada a minimizar los daños ocasionados y en definitiva a la rápida extinción del incendio. Sólo en Gran Canaria y Tenerife, la superficie afectada por incendios en el mes de Agosto de 2007 (aproximadamente 35.06...
Article
Full-text available
Jorge, P .A.; López, I. J.; Macías, A.; Martín, D.; Nebot, R. J.; Sabbagh, I.; Sánchez, J.; Sánchez, A .J.; Suárez, J.P. y Trujillo, A.: (2008): Entorno de desarrollo de software libre para aplicaciones geográficas 3D: GEVIEMER (Gestor Virtual de Emergencias). En: Hernández, L. y Parreño, J. M. (Eds.), Tecnologías de la Información Geográfica para...
Article
Full-text available
Currently, meteorological satellites provide multichannel image sequences including visible, temperature and water vapour channels. Based on a variational approach, we propose mathematical models to address some of the usual challenges in satellite image analysis such as: (i) the estimation of the cloud structure motion by combining information fro...
Article
Full-text available
Currently, meteorological satellites provide multichannel image sequences including visible, temperature and water vapor channels. Based on a variational approach, we propose mathematical models to address some of the usual challenges in satellite image analysis such as: (i) the estimation and smoothing of the cloud structures by decoupling them i...
Article
Full-text available
We present in this paper a variational approach to accurately estimate simultaneously the velocity field and its derivatives directly from PIV image sequences. Our method differs from other techniques that have been presented in the literature in the fact that the energy minimization used to estimate the particles motion depends on a second order T...
Article
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Traditional techniques of dense optical flow estimation do not generally yield symmetrical solutions: the results will differ if they are applied between images I 1 and I 2 or between images I 2 and I 1. In this work, we present a method to recover a dense optical flow field map from two images, while explicitely taking into account the symmetry ac...
Article
Full-text available
The aim of this work is to accurately estimate from an image the parameters of some ellipses and their relative positions with respect to a given pattern. The process is characterized because it is fully automated and is robust against image noise and occlusions. We have built a calibrator pattern with two planes each containing several ordered cir...
Conference Paper
Full-text available
One of the main technique used to recover motion analysis from two images or to register them is variational optical flow, where the pixels of one image are matched to the pixels of the second image by minimizing an energy functional. In the standard formulation of variational optical flow, the estimated motion vector field depends on the reference...
Conference Paper
Full-text available
Estimation of motion has many applications in fluid analysis. Lots of work has been carried out using Particle Image Velocimetry to design experiments which capture and measure the flow motion using 2D images. Recent technological advances allow capturing 3D PIV image sequences of moving particles. In this context, we propose a new three-dimension...
Conference Paper
Full-text available
Estimation of motion has many applications in fluid analysis. Lots of work has been carried out using Particle Image Velocimetry to design experiments which capture and measure the flow motion using 2D images. Recent technological advances allow capturing 3D PIV image sequences of moving particles. In this context, we propose a 3D motion estimation...
Conference Paper
Full-text available
The aim of this work is to propose a model for computing the optical flow in a sequence of images. We introduce a new temporal regularizer that is suitable for large displacements. We propose to decouple the spatial and temporal regularizations to avoid an incongruous formulation. For the spatial regularization we use the Nagel–Enkelmann operator a...