The Experts below are selected from a list of 5157 Experts worldwide ranked by ideXlab platform
Antonio-josé Sánchez-salmerón - One of the best experts on this subject based on the ideXlab platform.
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Efficient Lens Distortion Correction for Decoupling in Calibration of Wide Angle Lens Cameras
IEEE Sensors Journal, 2013Co-Authors: Carlos Ricolfe-viala, Antonio-josé Sánchez-salmerón, Angel ValeraAbstract:In photogrammetry applications, camera parameters must be as accurate as possible to avoid deviations in measurements from images. Errors increase if wide angle Lens cameras are used. Moreover, the coupling between intrinsic and extrinsic camera parameters and the Lens Distortion model influences the result of the calibration process notably. This paper proposes a method for calibrating wide angle Lens cameras, which takes into account the existing hard coupling. The proposed method obtains stable results, which do not depend on how the image Lens Distortion is corrected.
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Using the camera pin-hole model restrictions to calibrate the Lens Distortion model
Optics & Laser Technology, 2011Co-Authors: Carlos Ricolfe-viala, Antonio-josé Sánchez-salmerónAbstract:Abstract Camera calibration required the computation of camera pin-hole and Lens Distortion models. The Lens Distortion is estimated alone or together with the pin-hole model, by using some existing Lens Distortion non-metric or self-calibration methods. If both models are computed together, then the models are adjusted to training data, but not to real camera. This is because both pin-hole and Lens Distortion models are coupled. If they are computed separately, difficulties arise since calibration of Lens Distortion alone is an unstable process. To improve existing camera calibration methods, this paper proposes a metric calibration method to compute Lens Distortion separately from the pin-hole model. This method is solved under stable conditions, independently of the computed Lens Distortion model, since pin-hole and Distortion models are computed separately. Images of a planar template are used. First, using distorted control points extracted from images, a set of undistorted points which fits in the pin-hole model are computed. Second, with distorted and undistorted control points, Lens Distortion is calibrated by using a metric calibration process.
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Lens Distortion models evaluation
Applied optics, 2010Co-Authors: Carlos Ricolfe-viala, Antonio-josé Sánchez-salmerónAbstract:Many Lens Distortion models exist with several variations, and each Distortion model is calibrated by using a different technique. If someone wants to correct Lens Distortion, choosing the right model could represent a very difficult task. Calibration depends on the chosen model, and some methods have unstable results. Normally, the Distortion model containing radial, tangential, and prism Distortion is used, but it does not represent high Distortion accurately. The aim of this paper is to compare different Lens Distortion models to define the one that obtains better results under some conditions and to explore if some model can represent high and low Distortion adequately. Also, we propose a calibration technique to calibrate several models under stable conditions. Since performance is hard conditioned with the calibration technique, the metric Lens Distortion calibration method is used to calibrate all the evaluated models.
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Robust metric calibration of non-linear camera Lens Distortion
Pattern Recognition, 2010Co-Authors: Carlos Ricolfe-viala, Antonio-josé Sánchez-salmerónAbstract:Camera Lens Distortion is crucial to obtain the best performance cameral model. Up to now, different techniques exist, which try to minimize the calibration error using different Lens Distortion models or computing them in different ways. Some compute Lens Distortion camera parameters in the camera calibration process together with the intrinsic and extrinsic ones. Others isolate the Lens Distortion calibration without using any template and basing the calibration on the deformation in the image of some features of the objects in the scene, like straight lines or circles. These Lens Distortion techniques which do not use any calibration template can be unstable if a complete camera Lens Distortion model is computed. They are named non-metric calibration or self-calibration methods. Traditionally a camera has been always best calibrated if metric calibration is done instead of self-calibration. This paper proposes a metric calibration technique which computes the camera Lens Distortion isolated from the camera calibration process under stable conditions, independently of the computed Lens Distortion model or the number of parameters. To make it easier to resolve, this metric technique uses the same calibration template that will be used afterwards for the calibration process. Therefore, the best performance of the camera Lens Distortion calibration process is achieved, which is transferred directly to the camera calibration process.
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Correcting non-linear Lens Distortion in cameras without using a model
Optics & Laser Technology, 2010Co-Authors: Carlos Ricolfe-viala, Antonio-josé Sánchez-salmerónAbstract:Abstract Camera Lens Distortion calibration is the first step in resolving any metric application with a camera. To date, Lens Distortion was corrected using some existing Lens Distortion non-metric or self-calibration methods. Using a Lens Distortion model means defining a global rule to correct the entire image. This global rule does not take into account particular Lens Distortion effects not represented by the model. Moreover, to calibrate the model, only some features of the scene such as straight lines, circles or vanishing points are used. Since only the feature of the scene used to calibrate the model is guaranteed by the Distortion rectification, it is certain that the model will not be precise. The result is an approximation of the real image Distortion. To improve the Lens Distortion rectification, a method without using a model is proposed. Using a set of control points distributed across the entire image, they are corrected to assure all the restrictions of the scene. With both sets of points, the points detected in the image and the undistorted ones, image local transformations are defined considering only nearby control points. Rather than calibrating a global model, local functions are characterized. The Distortion correction is defined by a rectification surface composed of local surface patches each influenced by nearby control points. This method is more sensitive to local deformations and allows the image to be corrected in accordance with its Distortion.
Daniel Santana-cedrés - One of the best experts on this subject based on the ideXlab platform.
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Estimation of the Lens Distortion Model by Minimizing a Line Reprojection Error
IEEE Sensors Journal, 2017Co-Authors: Daniel Santana-cedrés, Luis Gomez, Miguel Alemán-flores, Agustín Salgado, Julio Esclarín, Luis Mazorra, Luis ÁlvarezAbstract:Most techniques for camera calibration that use planar calibration patterns require the computation of a Lens Distortion model and a homography. Both are simultaneously refined using a bundle adjustment that minimizes the reprojection error of a collection of points when projected from the scene onto the camera sensor. These points are usually the corners of the rectangles of a calibration pattern. However, if the Lens shows a significant Distortion, the location and matching of the corners can be difficult and inaccurate. To cope with this problem, instead of point correspondences, we propose to use line correspondences to compute the reprojection error. We have designed a fully automatic algorithm to estimate the Lens Distortion model and the homography by computing line correspondences and minimizing the line reprojection error. In the experimental setup, we focus on the analysis of the quality of the obtained Lens Distortion model. We present some experiments that show that the proposed method outperforms the results obtained by standard methods to compute Lens Distortion models based on line rectification.
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Line detection in images showing significant Lens Distortion and application to Distortion correction
Pattern Recognition Letters, 2014Co-Authors: Miguel Alemán-flores, Luis Gomez, Luis Álvarez, Daniel Santana-cedrésAbstract:Lines are one of the basic primitives used by the perceptual system to analyze and interpret a scene. Therefore, line detection is a very important issue for the robustness and flexibility of Computer Vision systems. However, in the case of images showing a significant Lens Distortion, standard line detection methods fail because lines are not straight. In this paper we present a new technique to deal with this problem: we propose to extend the usual Hough representation by introducing a new parameter which corresponds to the Lens Distortion, in such a way that the search space is a three-dimensional space, which includes orientation, distance to the origin and also Distortion. Using the collection of distorted lines which have been recovered, we are able to estimate the Lens Distortion, remove it and create a new Distortion-free image by using a two-parameter Lens Distortion model. We present some experiments in a variety of images which show the ability of the proposed approach to extract lines in images showing a significant Lens Distortion.
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CIARP (1) - Wide-Angle Lens Distortion Correction Using Division Models
Progress in Pattern Recognition Image Analysis Computer Vision and Applications, 2013Co-Authors: Miguel Alemán-flores, Luis Gomez, Luis Álvarez, Daniel Santana-cedrésAbstract:In this paper we propose a new method to automatically correct wide-angle Lens Distortion from the distorted lines generated by the projection on the image of 3D straight lines. We have to deal with two major problems: on the one hand, wide-angle Lenses produce a strong Distortion, which makes the detection of distorted lines a particularly difficult task. On the other hand, the usual single parameter polynomial Lens Distortion models is not able to manage such a strong Distortion. We propose an extension of the Hough transform by adding a Distortion parameter to detect the distorted lines, and division Lens Distortion models to manage wide-angle Lens Distortion. We present some experiments on synthetic and real images to show the ability of the proposed approach to automatically correct this type of Distortion. A comparison with a state-of-the-art method is also included to show the benefits of our method.
Luis Álvarez - One of the best experts on this subject based on the ideXlab platform.
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Estimation of the Lens Distortion Model by Minimizing a Line Reprojection Error
IEEE Sensors Journal, 2017Co-Authors: Daniel Santana-cedrés, Luis Gomez, Miguel Alemán-flores, Agustín Salgado, Julio Esclarín, Luis Mazorra, Luis ÁlvarezAbstract:Most techniques for camera calibration that use planar calibration patterns require the computation of a Lens Distortion model and a homography. Both are simultaneously refined using a bundle adjustment that minimizes the reprojection error of a collection of points when projected from the scene onto the camera sensor. These points are usually the corners of the rectangles of a calibration pattern. However, if the Lens shows a significant Distortion, the location and matching of the corners can be difficult and inaccurate. To cope with this problem, instead of point correspondences, we propose to use line correspondences to compute the reprojection error. We have designed a fully automatic algorithm to estimate the Lens Distortion model and the homography by computing line correspondences and minimizing the line reprojection error. In the experimental setup, we focus on the analysis of the quality of the obtained Lens Distortion model. We present some experiments that show that the proposed method outperforms the results obtained by standard methods to compute Lens Distortion models based on line rectification.
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Line detection in images showing significant Lens Distortion and application to Distortion correction
Pattern Recognition Letters, 2014Co-Authors: Miguel Alemán-flores, Luis Gomez, Luis Álvarez, Daniel Santana-cedrésAbstract:Lines are one of the basic primitives used by the perceptual system to analyze and interpret a scene. Therefore, line detection is a very important issue for the robustness and flexibility of Computer Vision systems. However, in the case of images showing a significant Lens Distortion, standard line detection methods fail because lines are not straight. In this paper we present a new technique to deal with this problem: we propose to extend the usual Hough representation by introducing a new parameter which corresponds to the Lens Distortion, in such a way that the search space is a three-dimensional space, which includes orientation, distance to the origin and also Distortion. Using the collection of distorted lines which have been recovered, we are able to estimate the Lens Distortion, remove it and create a new Distortion-free image by using a two-parameter Lens Distortion model. We present some experiments in a variety of images which show the ability of the proposed approach to extract lines in images showing a significant Lens Distortion.
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wide angle Lens Distortion correction using division models
Iberoamerican Congress on Pattern Recognition, 2013Co-Authors: Miguel Alemanflores, Luis Gomez, Luis Álvarez, Daniel SantanacedresAbstract:In this paper we propose a new method to automatically correct wide-angle Lens Distortion from the distorted lines generated by the projection on the image of 3D straight lines. We have to deal with two major problems: on the one hand, wide-angle Lenses produce a strong Distortion, which makes the detection of distorted lines a particularly difficult task. On the other hand, the usual single parameter polynomial Lens Distortion models is not able to manage such a strong Distortion. We propose an extension of the Hough transform by adding a Distortion parameter to detect the distorted lines, and division Lens Distortion models to manage wide-angle Lens Distortion. We present some experiments on synthetic and real images to show the ability of the proposed approach to automatically correct this type of Distortion. A comparison with a state-of-the-art method is also included to show the benefits of our method.
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CIARP (1) - Wide-Angle Lens Distortion Correction Using Division Models
Progress in Pattern Recognition Image Analysis Computer Vision and Applications, 2013Co-Authors: Miguel Alemán-flores, Luis Gomez, Luis Álvarez, Daniel Santana-cedrésAbstract:In this paper we propose a new method to automatically correct wide-angle Lens Distortion from the distorted lines generated by the projection on the image of 3D straight lines. We have to deal with two major problems: on the one hand, wide-angle Lenses produce a strong Distortion, which makes the detection of distorted lines a particularly difficult task. On the other hand, the usual single parameter polynomial Lens Distortion models is not able to manage such a strong Distortion. We propose an extension of the Hough transform by adding a Distortion parameter to detect the distorted lines, and division Lens Distortion models to manage wide-angle Lens Distortion. We present some experiments on synthetic and real images to show the ability of the proposed approach to automatically correct this type of Distortion. A comparison with a state-of-the-art method is also included to show the benefits of our method.
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Zoom Dependent Lens Distortion Mathematical Models
Journal of Mathematical Imaging and Vision, 2012Co-Authors: Luis Álvarez, Luis Gomez, Pedro HenriquezAbstract:We propose new mathematical models to study the variation of Lens Distortion models when modifying zoom setting in the case of zoom Lenses. The new models are based on a polynomial approximation to account for the variation of the radial Distortion parameters through the range of zoom Lens settings and, on the minimization of a global error energy measuring the distance between sequences of distorted aligned points and straight lines after Lens Distortion correction. To validate the performance of the method we present experimental results on calibration pattern images and on sport event scenarios using broadcast video cameras. We obtain, experimentally, that using just a second order polynomial approximation of Lens Distortion parameter zoom variation, the quality of Lens Distortion correction is as good as the one obtained individually frame by frame using independent Lens Distortion model for each frame.
Carlos Ricolfe-viala - One of the best experts on this subject based on the ideXlab platform.
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Efficient Lens Distortion Correction for Decoupling in Calibration of Wide Angle Lens Cameras
IEEE Sensors Journal, 2013Co-Authors: Carlos Ricolfe-viala, Antonio-josé Sánchez-salmerón, Angel ValeraAbstract:In photogrammetry applications, camera parameters must be as accurate as possible to avoid deviations in measurements from images. Errors increase if wide angle Lens cameras are used. Moreover, the coupling between intrinsic and extrinsic camera parameters and the Lens Distortion model influences the result of the calibration process notably. This paper proposes a method for calibrating wide angle Lens cameras, which takes into account the existing hard coupling. The proposed method obtains stable results, which do not depend on how the image Lens Distortion is corrected.
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Using the camera pin-hole model restrictions to calibrate the Lens Distortion model
Optics & Laser Technology, 2011Co-Authors: Carlos Ricolfe-viala, Antonio-josé Sánchez-salmerónAbstract:Abstract Camera calibration required the computation of camera pin-hole and Lens Distortion models. The Lens Distortion is estimated alone or together with the pin-hole model, by using some existing Lens Distortion non-metric or self-calibration methods. If both models are computed together, then the models are adjusted to training data, but not to real camera. This is because both pin-hole and Lens Distortion models are coupled. If they are computed separately, difficulties arise since calibration of Lens Distortion alone is an unstable process. To improve existing camera calibration methods, this paper proposes a metric calibration method to compute Lens Distortion separately from the pin-hole model. This method is solved under stable conditions, independently of the computed Lens Distortion model, since pin-hole and Distortion models are computed separately. Images of a planar template are used. First, using distorted control points extracted from images, a set of undistorted points which fits in the pin-hole model are computed. Second, with distorted and undistorted control points, Lens Distortion is calibrated by using a metric calibration process.
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Lens Distortion models evaluation
Applied optics, 2010Co-Authors: Carlos Ricolfe-viala, Antonio-josé Sánchez-salmerónAbstract:Many Lens Distortion models exist with several variations, and each Distortion model is calibrated by using a different technique. If someone wants to correct Lens Distortion, choosing the right model could represent a very difficult task. Calibration depends on the chosen model, and some methods have unstable results. Normally, the Distortion model containing radial, tangential, and prism Distortion is used, but it does not represent high Distortion accurately. The aim of this paper is to compare different Lens Distortion models to define the one that obtains better results under some conditions and to explore if some model can represent high and low Distortion adequately. Also, we propose a calibration technique to calibrate several models under stable conditions. Since performance is hard conditioned with the calibration technique, the metric Lens Distortion calibration method is used to calibrate all the evaluated models.
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Robust metric calibration of non-linear camera Lens Distortion
Pattern Recognition, 2010Co-Authors: Carlos Ricolfe-viala, Antonio-josé Sánchez-salmerónAbstract:Camera Lens Distortion is crucial to obtain the best performance cameral model. Up to now, different techniques exist, which try to minimize the calibration error using different Lens Distortion models or computing them in different ways. Some compute Lens Distortion camera parameters in the camera calibration process together with the intrinsic and extrinsic ones. Others isolate the Lens Distortion calibration without using any template and basing the calibration on the deformation in the image of some features of the objects in the scene, like straight lines or circles. These Lens Distortion techniques which do not use any calibration template can be unstable if a complete camera Lens Distortion model is computed. They are named non-metric calibration or self-calibration methods. Traditionally a camera has been always best calibrated if metric calibration is done instead of self-calibration. This paper proposes a metric calibration technique which computes the camera Lens Distortion isolated from the camera calibration process under stable conditions, independently of the computed Lens Distortion model or the number of parameters. To make it easier to resolve, this metric technique uses the same calibration template that will be used afterwards for the calibration process. Therefore, the best performance of the camera Lens Distortion calibration process is achieved, which is transferred directly to the camera calibration process.
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Correcting non-linear Lens Distortion in cameras without using a model
Optics & Laser Technology, 2010Co-Authors: Carlos Ricolfe-viala, Antonio-josé Sánchez-salmerónAbstract:Abstract Camera Lens Distortion calibration is the first step in resolving any metric application with a camera. To date, Lens Distortion was corrected using some existing Lens Distortion non-metric or self-calibration methods. Using a Lens Distortion model means defining a global rule to correct the entire image. This global rule does not take into account particular Lens Distortion effects not represented by the model. Moreover, to calibrate the model, only some features of the scene such as straight lines, circles or vanishing points are used. Since only the feature of the scene used to calibrate the model is guaranteed by the Distortion rectification, it is certain that the model will not be precise. The result is an approximation of the real image Distortion. To improve the Lens Distortion rectification, a method without using a model is proposed. Using a set of control points distributed across the entire image, they are corrected to assure all the restrictions of the scene. With both sets of points, the points detected in the image and the undistorted ones, image local transformations are defined considering only nearby control points. Rather than calibrating a global model, local functions are characterized. The Distortion correction is defined by a rectification surface composed of local surface patches each influenced by nearby control points. This method is more sensitive to local deformations and allows the image to be corrected in accordance with its Distortion.
Luis Gomez - One of the best experts on this subject based on the ideXlab platform.
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Estimation of the Lens Distortion Model by Minimizing a Line Reprojection Error
IEEE Sensors Journal, 2017Co-Authors: Daniel Santana-cedrés, Luis Gomez, Miguel Alemán-flores, Agustín Salgado, Julio Esclarín, Luis Mazorra, Luis ÁlvarezAbstract:Most techniques for camera calibration that use planar calibration patterns require the computation of a Lens Distortion model and a homography. Both are simultaneously refined using a bundle adjustment that minimizes the reprojection error of a collection of points when projected from the scene onto the camera sensor. These points are usually the corners of the rectangles of a calibration pattern. However, if the Lens shows a significant Distortion, the location and matching of the corners can be difficult and inaccurate. To cope with this problem, instead of point correspondences, we propose to use line correspondences to compute the reprojection error. We have designed a fully automatic algorithm to estimate the Lens Distortion model and the homography by computing line correspondences and minimizing the line reprojection error. In the experimental setup, we focus on the analysis of the quality of the obtained Lens Distortion model. We present some experiments that show that the proposed method outperforms the results obtained by standard methods to compute Lens Distortion models based on line rectification.
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Line detection in images showing significant Lens Distortion and application to Distortion correction
Pattern Recognition Letters, 2014Co-Authors: Miguel Alemán-flores, Luis Gomez, Luis Álvarez, Daniel Santana-cedrésAbstract:Lines are one of the basic primitives used by the perceptual system to analyze and interpret a scene. Therefore, line detection is a very important issue for the robustness and flexibility of Computer Vision systems. However, in the case of images showing a significant Lens Distortion, standard line detection methods fail because lines are not straight. In this paper we present a new technique to deal with this problem: we propose to extend the usual Hough representation by introducing a new parameter which corresponds to the Lens Distortion, in such a way that the search space is a three-dimensional space, which includes orientation, distance to the origin and also Distortion. Using the collection of distorted lines which have been recovered, we are able to estimate the Lens Distortion, remove it and create a new Distortion-free image by using a two-parameter Lens Distortion model. We present some experiments in a variety of images which show the ability of the proposed approach to extract lines in images showing a significant Lens Distortion.
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wide angle Lens Distortion correction using division models
Iberoamerican Congress on Pattern Recognition, 2013Co-Authors: Miguel Alemanflores, Luis Gomez, Luis Álvarez, Daniel SantanacedresAbstract:In this paper we propose a new method to automatically correct wide-angle Lens Distortion from the distorted lines generated by the projection on the image of 3D straight lines. We have to deal with two major problems: on the one hand, wide-angle Lenses produce a strong Distortion, which makes the detection of distorted lines a particularly difficult task. On the other hand, the usual single parameter polynomial Lens Distortion models is not able to manage such a strong Distortion. We propose an extension of the Hough transform by adding a Distortion parameter to detect the distorted lines, and division Lens Distortion models to manage wide-angle Lens Distortion. We present some experiments on synthetic and real images to show the ability of the proposed approach to automatically correct this type of Distortion. A comparison with a state-of-the-art method is also included to show the benefits of our method.
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CIARP (1) - Wide-Angle Lens Distortion Correction Using Division Models
Progress in Pattern Recognition Image Analysis Computer Vision and Applications, 2013Co-Authors: Miguel Alemán-flores, Luis Gomez, Luis Álvarez, Daniel Santana-cedrésAbstract:In this paper we propose a new method to automatically correct wide-angle Lens Distortion from the distorted lines generated by the projection on the image of 3D straight lines. We have to deal with two major problems: on the one hand, wide-angle Lenses produce a strong Distortion, which makes the detection of distorted lines a particularly difficult task. On the other hand, the usual single parameter polynomial Lens Distortion models is not able to manage such a strong Distortion. We propose an extension of the Hough transform by adding a Distortion parameter to detect the distorted lines, and division Lens Distortion models to manage wide-angle Lens Distortion. We present some experiments on synthetic and real images to show the ability of the proposed approach to automatically correct this type of Distortion. A comparison with a state-of-the-art method is also included to show the benefits of our method.
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Zoom Dependent Lens Distortion Mathematical Models
Journal of Mathematical Imaging and Vision, 2012Co-Authors: Luis Álvarez, Luis Gomez, Pedro HenriquezAbstract:We propose new mathematical models to study the variation of Lens Distortion models when modifying zoom setting in the case of zoom Lenses. The new models are based on a polynomial approximation to account for the variation of the radial Distortion parameters through the range of zoom Lens settings and, on the minimization of a global error energy measuring the distance between sequences of distorted aligned points and straight lines after Lens Distortion correction. To validate the performance of the method we present experimental results on calibration pattern images and on sport event scenarios using broadcast video cameras. We obtain, experimentally, that using just a second order polynomial approximation of Lens Distortion parameter zoom variation, the quality of Lens Distortion correction is as good as the one obtained individually frame by frame using independent Lens Distortion model for each frame.
