6 results
Search Results
Now showing 1 - 6 of 6
Item Geometry-aware Video Registration(The Eurographics Association, 2010) Palma, Gianpalo; Callieri, Marco; Dellepiane, Matteo; Corsini, Massimiliano; Scopigno, Roberto; Reinhard Koch and Andreas Kolb and Christof Rezk-SalamaWe present a new method for the accurate registration of video sequences of a real object over its dense triangular mesh. The goal is to obtain an accurate video-to-geometry registration to allow the bidirectional data transfer between the 3D model and the video using the perspective projection defined by the camera model. Our solution uses two different approaches: feature-based registration by KLT video tracking, and statistic-based registration by maximizing the Mutual Information (MI) between the gradient of the frame and the gradient of the rendering of the 3D model with some illumination related properties, such as surface normals and ambient occlusion. While the first approach allows a fast registration of short sequences with simple camera movements, the MI is used to correct the drift problem that KLT tracker produces over long sequences, due to the incremental tracking and the camera motion. We demonstrate, using synthetic sequences, that the alignment error obtained with our method is smaller than the one introduced by KLT, and we show the results of some interesting and challenging real sequences of objects of different sizes, acquired under different conditions.Item Principles and Practices of Robust, Photography-based Digital Imaging Techniques for Museums(The Eurographics Association, 2010) Mudge, Mark; Schroer, Carla; Earl, Graeme; Martinez, Kirk; Pagi, Hembo; Toler-Franklin, Corey; Rusinkiewicz, Szymon; Palma, Gianpaolo; Wachowiak, Melvin; Ashley, Michael; Matthews, Neffra; Noble, Tommy; Dellepiane, Matteo; Alessandro Artusi and Morwena Joly and Genevieve Lucet and Denis Pitzalis and Alejandro RibesThis full day tutorial will use lectures and demonstrations from leading researchers and museum practitioners to present the principles and practices for robust photography-based digital techniques in museum contexts. The tutorial will present many examples of existing and cutting-edge uses of photography-based imaging including Reflectance Transformation Imaging (RTI), Algorithmic Rendering (AR), camera calibration, and methods of imaged-based generation of textured 3D geometry. Leading museums are now adopting the more mature members of this family of robust digital imaging practices. These practices are part of the emerging science known as Computational Photography (CP). The imaging family's common feature is the purpose-driven selective extraction of information from sequences of standard digital photographs. The information is extracted from the photographic sequences by computer algorithms. The extracted information is then integrated into a new digital representations containing knowledge not present in the original photographs, examined either alone or sequentially. The tutorial will examine strategies that promote widespread museum adoption of empirical acquisition technologies, generate scientifically reliable digital representations that are born archival', assist this knowledge's long-term digital preservation, enable its future reuse for novel purposes, aid the physical conservation of the digitally represented museum materials, and enable public access and research.Item Removing Shadows for Color Projection Using Sun Position Estimation(The Eurographics Association, 2010) Dellepiane, Matteo; Benedetti, Luca; Scopigno, Roberto; Alessandro Artusi and Morwena Joly and Genevieve Lucet and Denis Pitzalis and Alejandro RibesThe result of an outdoors 3D scanning acquisition campaign is usually an accurate 3D model of the site, but in most of the cases the quality of the color acquired by the scanner is not satisfying. Alternative solutions, like the projection of a photographic dataset acquired in a different stage, are still dependent on the quality of the initial images. The short time for the acquisition campaigns and the weather conditions often force the shooting of images taken under a strong direct sun illumination. This generates colored models of poor quality. In this paper we present a method to estimate the sun position starting from a geo-referenced 3D model and a set of images. The sun position can enhance both the image alignment and color projection phases. Moreover, the detection and removal of the shadows from the images produces a better and more coherent color in the final 3D model. Using this kind of approach, outdoor sites can be acquired producing a high quality color information together with an accurate geometric measurement.Item Mutual Correspondences: An Hybrid Method for Image-to-geometry Registration(The Eurographics Association, 2010) Sottile, Michele; Dellepiane, Matteo; Cignoni, Paolo; Scopigno, Roberto; Enrico Puppo and Andrea Brogni and Leila De FlorianiImage registration is an important task in several applications of Computer Graphics and Computer Vision. Among the large number of proposed approaches, currently there is no solution which is automatic and robust enough to handle any general case. The most robust methods usually require a significant intervention by the user to specify many 2D-3D correspondences, while automatic techniques often rely on strong assumptions about the quality of 2D and 3D data. In this paper we present Mutual Correspondences, which is based on a minimization function which combines correspondences based and Mutual Information based approaches, and takes advantage of the strong points of both. Mutual Correspondences give the user the possibility to "guide" Mutual Information with only a few 2D- 3D correspondences. The proposed approach results in a wider convergence range and in higher registration accuracy, regardless of the quality of both the image and the 3D model. Mutual Correspondences were applied on some practical cases, where state-of-the-art approaches tended to fail, and they provided a mean to obtain accurate results. This led to a simple, robust and practical approach that can provide a way to register images in a few seconds.Item Improving 2D-3D Registration by Mutual Information using Gradient Maps(The Eurographics Association, 2010) Palma, Gianpaolo; Corsini, Massimiliano; Dellepiane, Matteo; Scopigno, Roberto; Enrico Puppo and Andrea Brogni and Leila De FlorianiIn this paper we propose an extension for the algorithms of image-to-geometry registration by Mutual Information( MI) to improve the performance and the quality of the alignment. Proposed for the registration of multi modal medical images, in the last years MI has been adapted to align a 3D model to a given image by using different renderings of the model and a gray-scale version of the input image. A key aspect is the choice of the rendering process to correlate the 3D model to the image without taking into account the texture data and the lighting conditions. Even if several rendering types for the 3D model have been analyzed, in some cases the alignment fails for two main reasons: the peculiar reflection behavior of the object that we are not able to reproduce in the rendering of the 3D model without knowing the material characteristics of the object and the lighting conditions of the acquisition environment; the characteristics of the image background, especially non uniform background, that can degrade the convergence of the registration. To improve the quality of the registration in these cases we propose to compute the MI between the gradient map of the 3D rendering and the gradient map of the image in order to maximize the shared data between them.Item Using Lego Pieces for Camera Calibration: a Preliminary Study(The Eurographics Association, 2010) Baronti, Luca; Dellepiane, Matteo; Scopigno, Roberto; H. P. A. Lensch and S. SeipelCamera calibration is an important operation for a number of applications in the field of Computer Graphics and Computer Vision. In particular, if the intrinsic parameters of the camera are known in advance, the accuracy of results is extremely improved. For this reason, several easy procedures to calibrate a camera have been proposed. The accuracy and ease-of-use of these procedures is strongly related to the needed calibration target, which is usually a single 2D printed pattern (i.e. a checkerboard). In this paper we propose the use of an alternative: a Lego structure. Lego pieces exhibit several strong-points, like the off-the-shelf availability and the geometric accuracy. Additionally, it s easy to prepare a structure and obtain the corresponding 3D model using freeware tools. Hence, we present the preliminary tests on the use of Lego structures for camera calibration. The tests have been performed on a user-friendly ad-hoc tool, which takes advantage of the peculiar features of Lego to automatically correct the positions of the 2D and 3D correspondences used for calibration. Results show that it s possible to obtain accurate results starting from a few photos, and that the entire procedure can be completed in a very short time.Camera calibration is an important operation for a number of applications in the field of Computer Graphics and Computer Vision. In particular, if the intrinsic parameters of the camera are known in advance, the accuracy of results is extremely improved. For this reason, several easy procedures to calibrate a camera have been proposed. The accuracy and ease-of-use of these procedures is strongly related to the needed calibration target, which is usually a single 2D printed pattern (i.e. a checkerboard). In this paper we propose the use of an alternative: a Lego structure. Lego pieces exhibit several strong-points, like the off-the-shelf availability and the geometric accuracy. Additionally, it s easy to prepare a structure and obtain the corresponding 3D model using freeware tools. Hence, we present the preliminary tests on the use of Lego structures for camera calibration. The tests have been performed on a user-friendly ad-hoc tool, which takes advantage of the peculiar features of Lego to automatically correct the positions of the 2D and 3D correspondences used for calibration. Results show that it s possible to obtain accurate results starting from a few photos, and that the entire procedure can be completed in a very short time.