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  • 101.
    Museth, Ken
    et al.
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    W Lo, M
    Barr, A
    Semi-immersive space mission design and visualization2001In: IEEE Visualization 01,2001, 2001, p. 501-Conference paper (Refereed)
  • 102.
    Museth, Ken
    et al.
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Whitaker, Ross
    Breen, David
    Editing Geometric Models2003In: Geometric Level Set Methods in Imaging, Vision and Graphics / [ed] Stanley Osher; Nikos Paragios, New York: Springer Verlag , 2003, p. -510Chapter in book (Other academic)
    Abstract [en]

       Level set methods are emerging techniques for representing, deforming, and recovering structures in an arbitrary dimension across different fields (mathematics, fluid dynamics, graphics, imaging, vision, etc.). Advances in numerical analysis have led to computationally efficient tools for computing and analyzing interface motion within level set frameworks in a host of application settings. This authoritative edited survey provides readers with the state-of-the-art in applying level set techniques in the imaging, vision, and graphics domains, presenting thematically grouped chapters contributed by leading experts from both industry and academia. The work bridges the theoretical foundations of level set methods with the latest significant applications. It will assist readers with both the technical aspects of the field as well as its practical ramifications for areas like medical imaging, computer animation, film restoration, video surveillance, visual inspection, and a range of scientific and engineering disciplines. Topics and features: * Covers comprehensively the applications of imaging, vision, & graphics * Includes a helpful introductory survey chapter on level set methods * Provides a complete overview of concepts and advanced technologies in the field * Describes leading-edge research, providing insight into a variety of potential avenues for problem solving * Supplies numerous implementations, examples, and relevant and useful experimental results This essential resource carefully integrates the theoretical foundations of level set methods with their actual performance capabilities. Its clarity of organization and approach makes the book accessible for researchers and professionals working in the areas of vision, graphics, image processing, robotics, mathematics, and computational geometry

  • 103. Nakaguchi, T
    et al.
    Okui, M
    Tsumura, N
    Museth, Ken
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Miyake, Y
    Segmentation of Pancreas from CT images Using Multiple Level Sets for Preoperative Simulation System2006In: IEICE Technical Committee on Medical Imaging,2006, 2006Conference paper (Refereed)
  • 104.
    Nguyen, Hoang
    et al.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Evangelista, Gianpaolo
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    A continuous wavelet-Galerkin method for the linear wave equation2007In: SIAM Journal on Scientific Computing, ISSN 1064-8275, E-ISSN 1095-7197Article in journal (Other academic)
    Abstract [en]

    We consider the continuous space-time Galerkin method for the linear second-order wave equation proposed by French and Peterson in 1996. A bottleneck for this approach is how to solve the discrete problems effectively. In this paper, we tackle this bottleneck by essentially employing wavelet bases in space. We show how to decouple the corresponding linear system and we prove that the resulting subsystems can be uniformly preconditioned by simple diagonal preconditioners, leading to efficient iterative solutions.

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    FULLTEXT01
  • 105.
    Nielsen, M.B.
    et al.
    University of Århus, Arhus, Denmark.
    Museth, Ken
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Dynamic tubular grid: An efficient data structure and algorithms for high resolution level sets2006In: Journal of Scientific Computing, ISSN 0885-7474, E-ISSN 1573-7691, Vol. 26, no 3, p. 261-299Article in journal (Refereed)
    Abstract [en]

    Level set methods [Osher and Sethian. Fronts propagating with curvature-dependent speed: algorithms based on Hamilton-Jacobi formulations. J. Comput. Phys. 79 (1988) 12] have proved very successful for interface tracking in many different areas of computational science. However, current level set methods are limited by a poor balance between computational efficiency and storage requirements. Tree-based methods have relatively slow access times, whereas narrow band schemes lead to very large memory footprints for high resolution interfaces. In this paper we present a level set scheme for which both computational complexity and storage requirements scale with the size of the interface. Our novel level set data structure and algorithms are fast, cache efficient and allow for a very low memory footprint when representing high resolution level sets. We use a time-dependent and interface adapting grid dubbed the "Dynamic Tubular Grid" or DT-Grid. Additionally, it has been optimized for advanced finite difference schemes currently employed in accurate level set computations. As a key feature of the DT-Grid, the associated interface propagations are not limited to any computational box and can expand freely. We present several numerical evaluations, including a level set simulation on a grid with an effective resolution of 10243. © 2006 Springer Science+Business Media, Inc.

  • 106.
    Nielsen, Michael B.
    et al.
    University of Århus, Denmark.
    Nilsson, Ola
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Söderström, Andreas
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Museth, Ken
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Out-of-core and compressed level set methods2007In: ACM Transactions on Graphics, ISSN 0730-0301, E-ISSN 1557-7368, Vol. 26, no 4, p. 16-Article in journal (Refereed)
    Abstract [en]

    This article presents a generic framework for the representation and deformation of level set surfaces at extreme resolutions. The framework is composed of two modules that each utilize optimized and application specific algorithms: 1) A fast out-of-core data management scheme that allows for resolutions of the deforming geometry limited only by the available disk space as opposed to memory, and 2) compact and fast compression strategies that reduce both offline storage requirements and online memory footprints during simulation. Out-of-core and compression techniques have been applied to a wide range of computer graphics problems in recent years, but this article is the first to apply it in the context of level set and fluid simulations. Our framework is generic and flexible in the sense that the two modules can transparently be integrated, separately or in any combination, into existing level set and fluid simulation software based on recently proposed narrow band data structures like the DT-Grid of Nielsen and Museth [2006] and the H-RLE of Houston et al. [2006]. The framework can be applied to narrow band signed distances, fluid velocities, scalar fields, particle properties as well as standard graphics attributes like colors, texture coordinates, normals, displacements etc. In fact, our framework is applicable to a large body of computer graphics problems that involve sequential or random access to very large co-dimension one (level set) and zero (e.g. fluid) data sets. We demonstrate this with several applications, including fluid simulations interacting with large boundaries (? 15003), surface deformations (? 20483), the solution of partial differential equations on large surfaces (˜40963) and mesh-to-level set scan conversions of resolutions up to ? 350003 (7 billion voxels in the narrow band). Our out-of-core framework is shown to be several times faster than current state-of-the-art level set data structures relying on OS paging. In particular we show sustained throughput (grid points/sec) for gigabyte sized level sets as high as 65% of state-of-the-art throughput for in-core simulations. We also demonstrate that our compression techniques out-perform state-of-the-art compression algorithms for narrow bands. © 2007 ACM.

  • 107. Nielsen, Michael
    et al.
    Nilsson, Ola
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Söderström, Andreas
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Museth, Ken
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Virtually Infinite Resolution Deformable Surfaces2006In: ACM SIGGRAPH ¿06 Sketches Applications,2006, 2006Conference paper (Refereed)
  • 108.
    Nilsson, Ola
    et al.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Breen, David
    Drexel University.
    Museth, Ken
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Surface Reconstruction Via Contour Metamorphosis: An Eulerian Approach With Lagrangian Particle Tracking2005In: IEEE Visualization 05,2005, IEEE , 2005, p. 407-414Conference paper (Refereed)
    Abstract [en]

    We present a robust method for 3D reconstruction of closed surfaces from sparsely sampled parallel contours. A solution to this problem is especially important for medical segmentation, where manual contouring of 2D imaging scans is still extensively used. Our proposed method is based on a morphing process applied to neighboring contours that sweeps out a 3D surface. Our method is guaranteed to produce closed surfaces that exactly pass through the input contours, regardless of the topology of the reconstruction.

    Our general approach consecutively morphs between sets of input contours using an Eulerian formulation (i.e. fixed grid) augmented with Lagrangian particles (i.e. interface tracking). This is numerically accomplished by propagating the input contours as 2D level sets with carefully constructed continuous speed functions. Specifically this involves particle advection to estimate distances between the contours, monotonicity constrained spline interpolation to compute continuous speed functions without overshooting, and stateof- the-art numerical techniques for solving the level set equations. We demonstrate the robustness of our method on a variety of medical, topographic and synthetic data sets.

  • 109.
    Nilsson, Ola
    et al.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Reimers, Martin
    Department of Informatics, University of Oslo/Centre of Mathematics for Applications, University of Oslo.
    Museth, Ken
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Brun, Anders
    Centre for Image Analysis, Swedish University of Agricultural Sciences.
    Efficient computations of geodesic distanceManuscript (preprint) (Other academic)
    Abstract [en]

    We present a novel way to efficiently compute anisotropic distances over a tessellated domain in two dimensions. The method is based on an integral formulation of distance and entails solving a dynamic programming problem. We also present an intuitive geometric construction that is used to characterize dierent types of boundary conditions and show how they aect the resulting distance function in our and competing work.

    The included benchmark study shows that our method provides signicantly better results in anisotropic regions and is faster than a current stat-of-the-art solver. Additionally, our method is straightforward to code; the test implementation is less than 150 lines of C++ code.

  • 110.
    Nilsson, Ola
    et al.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Söderström, Andreas
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology, Digital Media.
    Euclidian Distance Transform Algorithms: A comparative study2007Report (Other academic)
    Abstract [en]

    We compare the most frequently used algorithms for computing distance transforms in terms of speed, scalability and accuracy. The algorithms we consider are: partial differential equation based distancing methods of different finite difference accuracy, fast marching methods and fast sweeping methods. Our results show clearly that all the first order algorithms perform similarly in terms of accuracy and that the only major difference is efficiency. In parallel with the revision of the preprint we find that the newly proposed O(N) quantized fast marching algorithm in practice does not scale linearly.

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    FULLTEXT01
  • 111.
    Nyström, Daniel
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    A Micro-Scale View on Color Reproduction2008In: CGIV 2008/MCS'08 4th European Conference on Colour in Graphics, Imaging, and Vision and 10th International Symposium on Multispectral Colour Science, Springfield, VA, USA: The Society for Imaging Science and Technology, 2008, p. 542-Conference paper (Refereed)
    Abstract [en]

    Modeling color print reproduction is difficult, mainly because of light scattering, causing optical dot gain. Most available models are based on macroscopic color measurements, the average value over an area that is large relative to the halftone dot size. The aim of this study is to go beyond the macroscopic approach, to study color print reproduction on a micro-scale level. An experimental imaging system, combining the accuracy of color measurement instruments with a high spatial resolution, opens up new possibilities to study and model color print reproduction. The main focus is to study how the reflectance values of the printed dots and the paper between them vary with the dot area fraction. A previously proposed expansion of the Murray-Davies model is further developed to handle color prints, predicting tristimulus values. The color of the halftone dots and the paper between them is derived from 3D color histograms in CIEXYZ color space. The prediction errors of the model were found to be equivalent, or better, to that of the Yule-Nielsen model using an optimal n-factor. However, unlike Yule-Nielsen, the expanded Murray-Davies model takes into account the varying reflectance of the ink and paper, and preserves the linear additivity of reflectance, thus providing a better physical description of optical dot gain in color reproduction.

  • 112. Order onlineBuy this publication >>
    Nyström, Daniel
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Colorimetric and Multispectral Image Acquisition2006Licentiate thesis, monograph (Other academic)
    Abstract [en]

    The trichromatic principle of representing color has for a long time been dominating in color imaging. The reason is the trichromatic nature of human color vision, but as the characteristics of typical color imaging devices are different from those of human eyes, there is a need to go beyond the trichromatic approach. The interest for multi-channel imaging, i.e. increasing the number of color channels, has made it an active research topic with a substantial potential of application.

    To achieve consistent color imaging, one needs to map the imaging-device data to the device-independent colorimetric representations CIEXYZ or CIELAB, the key concept of color management. As the color coordinates depend not only on the reflective spectrum of the object but also on the spectral properties of the illuminant, the colorimetric representation suffers from metamerism, i.e. objects of the same color under a specific illumination may appear different when they are illuminated by other light sources. Furthermore, when the sensitivities of the imaging device differ from the CIE color matching functions, two spectra that appear different for human observers may result in identical device response. On contrary, in multispectral imaging, color is represented by the object’s physical characteristics namely the spectrum which is illuminant independent. With multispectral imaging, different spectra are readily distinguishable, no matter they are metameric or not. The spectrum can then be transformed to any color space and be rendered under any illumination.

    The focus of the thesis is high quality image-acquisition in colorimetric and multispectral formats. The image acquisition system used is an experimental system with great flexibility in illumination and image acquisition setup. Besides the conventional trichromatic RGB filters, the system also provides the possibility of acquiring multi-channel images, using 7 narrowband filters. A thorough calibration and characterization of all the components involved in the image acquisition system is carried out. The spectral sensitivity of the CCD camera, which can not be derived by direct measurements, is estimated using least squares regression, optimizing the camera response to measured spectral reflectance of carefully selected color samples.

    To derive mappings to colorimetric and multispectral representations, two conceptually different approaches are used. In the model-based approach, the physical model describing the image acquisition process is inverted, to reconstruct spectral reflectance from the recorded device response. In the empirical approach, the characteristics of the individual components are ignored, and the functions are derived by relating the device response for a set of test colors to the corresponding colorimetric and spectral measurements, using linear and polynomial least squares regression.

    The results indicate that for trichromatic imaging, accurate colorimetric mappings can be derived by the empirical approach, using polynomial regression to CIEXYZ and CIELAB. Because of the media-dependency, the characterization functions should be derived for each combination of media and colorants. However, accurate spectral data reconstruction requires for multi-channel imaging, using the model-based approach. Moreover, the model-based approach is general, since it is based on the spectral characteristics of the image acquisition system, rather than the characteristics of a set of color samples.

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    FULLTEXT01
  • 113.
    Nyström, Daniel
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Colorimetric and Multispectral Image Acquisition Using Model-based and Empirical Device Characterization2007In: Image Analysis: 15th Scandinavian Conference, SCIA 2007, Aalborg, Denmark, June 10-14, 2007 / [ed] Bjarne Kjær Ersbøll, Kim Steenstrup Pedersen, Springer Berlin/Heidelberg, 2007, p. 798-807Conference paper (Refereed)
    Abstract [en]

    The focus of the study is high quality image acquisition in colorimetric and multispectral formats. The aim is to combine the spatial resolution of digital images with the spectral resolution of color measurement instruments, to allow for accurate colorimetric and spectral measurements in each pixel of the acquired images. An experimental image acquisition system is used, which besides trichromatic RGB filters also provides the possibility of acquiring multi-channel images, using a set of narrowband filters. To derive mappings to colorimetric and multispectral representations, two conceptually different approaches are used. In the model-based characterization, the physical model describing the image acquisition process is inverted, to reconstruct spectral reflectance from the recorded device response. In the empirical characterization, the characteristics of the individual components are ignored, and the functions are derived by relating the device response for a set of test colors to the corresponding colorimetric and spectral measurements, using linear and polynomial least squares regression. The results indicate that for trichromatic imaging, accurate colorimetric mappings can be derived by the empirical approach, using polynomial regression to CIEXYZ and CIELAB. However, accurate spectral reconstructions requires for multi-channel imaging, with the best results obtained using the model-based approach.

  • 114. Order onlineBuy this publication >>
    Nyström, Daniel
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    High Resolution Analysis of Halftone Prints: A Colorimetric and Multispectral Study2009Doctoral thesis, monograph (Other academic)
    Abstract [en]

    To reproduce color images in print, the continuous tone image is first transformed into a binary halftone image, producing various colors by discrete dots with varying area coverage. In halftone prints on paper, physical and optical dot gains generally occur, making the print look darker than expected, and making the modeling of halftone color reproduction a challenge. Most available models are based on macroscopic color measurements, averaging the reflectance over an area that is large in relation to the halftone dots. The aim of this study is to go beyond the macroscopic approach, and study halftone color reproduction on a micro-scale level, using high resolution images of halftone prints. An experimental imaging system, combining the accuracy of color measurement instruments with a high spatial resolution, opens up new possibilities to study and analyze halftone color prints.

    The experimental image acquisition offers a great flexibility in the image acquisition setup. Besides trichromatic RGB filters, the system is also equipped with a set of 7 narrowband filters, for multi-channel images. A thorough calibration and characterization of all the components in the imaging system is described. The spectral sensitivity of the CCD camera, which can not be derived by direct measurements, is estimated using least squares regression. To reconstruct spectral reflectance and colorimetric values from the device response, two conceptually different approaches are used. In the model-based characterization, the physical model describing the image acquisition process is inverted, to reconstruct spectral reflectance from the recorded device response. In the empirical characterization, the characteristics of the individual components are ignored, and the functions are derived by relating the device response for a set of test colors to the corresponding colorimetric and spectral measurements, using linear and polynomial least squares regression techniques.

    Micro-scale images, referring to images whose resolution is high in relation to the resolution of the halftone, allow for measurements of the individual halftone dots, as well as the paper between them. To capture the characteristics of large populations of halftone dots, reflectance histograms are computed as well as 3D histograms in CIEXYZ color space. The micro-scale measurements reveal that the reflectance for the halftone dots, as well as the paper between the dots, is not constant, but varies with the dot area coverage. By incorporating the varying micro-reflectance in an expanded Murray-Davies model, the nonlinearity caused by optical dot gain can be accounted for without applying the nonphysical exponentiation of the reflectance values, as in the commonly used Yule-Nielsen model.

    Due to their different intrinsic nature, physical and optical dot gains need to be treated separately when modeling the outcome of halftone prints. However, in measurements of reflection colors, physical and optical dot gains always co-exist, making the separation a difficult task. Different methods to separate the physical and optical dot gain are evaluated, using spectral reflectance measurements, transmission scans and micro-scale images. Further, the relation between the physical dot gain and the halftone dot size is investigated, demonstrated with FM halftones of various print resolutions. The physical dot gain exhibits a clear correlation with the dot size and the dot gain increase is proportional to the increase in print resolution. The experimental observations are followed by discussions and a theoretical explanation.

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    FULLTEXT02
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    COVER01
  • 115.
    Nyström, Daniel
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Micro-scale characteristics of color prints2007In: Symposium on Image Analysis,2007, 2007, p. 33-36Conference paper (Other academic)
  • 116.
    Nyström, Daniel
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Reconstructing Spectral and Colorimetric Data Using Trichromatic and Multi-channel Imaging2007In: 9th International Symposium on Multispectral Color Science and Application, Springfield, VA, USA: The Society for Imaging Science and Technology, 2007, p. 45-52Conference paper (Refereed)
    Abstract [en]

    The aim of the study is to reconstruct spectral and colorimetric data, using trichromatic and multi-channel imaging. An experimental image acquisition system is used, which besides trichromatic RGB filters also provides the possibility of acquiring multi-channel images, using 7 narrowband filters. To derive mappings to colorimetric and multispectral representations, two conceptually different approaches are used. In the model-based approach, the physical model describing the image acquisition process is inverted, to reconstruct spectral reflectance from the recorded device response. A priori knowledge on the smooth nature of spectral reflectances is utilized, by representing the reconstructed spectra as linear combinations of basis functions, using Fourier basis and a database of real reflectance spectra. In the empirical approach, the characteristics of the individual components are ignored, and the functions are derived by relating the device response for a set of training colors to the corresponding colorimetric and spectral measurements. Beside colorimetric regression, mapping device values directly to CIEXYZ and CIELAB, experiments are also made on reconstructing spectral reflectance, using least squares regression techniques.

    The results indicate that for trichromatic imaging, accurate colorimetric mappings can be derived by the empirical approach, using polynomial regression to CIEXYZ and CIELAB. Because of the media-dependency, the characterization functions must be derived for each combination of media and colorants. However, accurate spectral reconstructions require for multi-channel imaging, using model-based device characterization. Moreover, the model-based approach is general, since it is based on the spectral characteristics of the image acquisition system, rather than the characteristics of a set of color samples.

  • 117.
    Nyström, Daniel
    et al.
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Kruse, Björn
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Colorimetric Device Characterization for Accurate Color Image Acquisition2007In: Advances in Printing and Media Technology, Vol. 36: iarigai / [ed] N. Enlund, Zagreb: Acta Graphic Publishers , 2007, p. 349-360Conference paper (Refereed)
  • 118.
    Nyström, Daniel
    et al.
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Kruse, Björn
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    High resolution properties of color prints2005In: Bijing International Conference on Imaging,2005, Beijing, China: Science Press , 2005, p. 242-243Conference paper (Other academic)
  • 119.
    Nyström, Daniel
    et al.
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Kruse, Björn
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Yang, Li
    Dept. of Chemical Engineering Karlastad University.
    A Micro-scale study of optical dot gain in color halftone2007In: Advances in Printing and Media Technology, Vol. 34: iarigai / [ed] N. Enlund & M. Lovrecek, Zagreb: Acta Graphic Publishers , 2007, p. 171-179Conference paper (Refereed)
  • 120.
    Nyström, Daniel
    et al.
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Yang, Li
    Physical and Optical Dot Gain: Separation and Relation to Print Resolution2009In: Advances in Printing and Media Technology, Vol. 36: iarigai / [ed] N. Enlund & M. Lovrecek, Zagreb: International Association of Research Organizations for the Information, Media and Graphic Arts Industries , 2009, p. 337-344Conference paper (Refereed)
  • 121.
    Olsson, Björn
    et al.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Ynnerman, Anders
    Linköping University, Department of Science and Technology, Visual Information Technology and Applications (VITA). Linköping University, The Institute of Technology.
    Lenz, Reiner
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Computing synthetic satellite images from weather prediction data2004In: Proceedings of SPIE - IS and T Electronic Imaging, VIsualization and Data Analysis / [ed] Robert F. Erbacher; Philip C. Chen; Jonathan C. Roberts; Matti T. Gr÷hn; Katy B÷rner, 2004, p. 296-304Conference paper (Other academic)
    Abstract [en]

    Satellite images are important sources of information for meteorologists to predict rapid weather changes, for example storms, now and in the near-future (Nowcasting). It is not possible to use traditional numerical weather forecasts for this purpose since these are computed with a time-lag of several hours. This means that the most recent weather changes are not taken into account. This paper presents a method to compute synthetic satellite images from simulated forecast files. The cloud information in numerical forecast data sets is of much more interest if it can be visualized with a well-known representation like the satellite image. The proposed method uses artificial neural network technology to construct a model which is trained with data from numerical forecasts and classified satellite data captured at the same points in time. The cloud cover parameters in the forecast data set are tied to the cloud classification in the satellite image using a point-to-point representation. The results show that this is a useful method to compute synthetic satellite images. The level of detail in the resulting images is lower than in a real satellite image, but detailed enough to provide information about the principal features of the cloud cover.

  • 122.
    Olsson, Björn
    et al.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Ynnerman, Anders
    Linköping University, Department of Science and Technology, Visual Information Technology and Applications (VITA). Linköping University, The Institute of Technology.
    Lenz, Reiner
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Eigenskies: a method of visualizing weather prediction data2003In: Proceedings of SPIE - IS&T Electronic Imaging, Visualization and Data Analysis / [ed] Robert F. Erbacher; Philip C. Chen; Jonathan C. Roberts; Matti T. Groehn; Katy Boerner, 2003Conference paper (Other academic)
    Abstract [en]

    Visualizing a weather prediction data set by actually synthesizing an image of the sky is a difficult problem. In this paper we present a method for synthesizing realistic sky images from weather prediction and climate prediction data. Images of the sky are combined with a number of weather parameters (like pressure and temperature) to train an artificial neural network (ANN) to predict the appearance of the sky from certain weather parameters. Hourly measurements from a period of eight months are used. The principal component analysis (PCA) method is used to decompose images of the sky into their eigen components -- the eigenskies. In this way the image information is compressed into a small number of coefficients while still preserving the main information in the image. This means that the fine details of the cloud cover cannot be synthesized using this method. The PCA coefficients together with measured weather parameters at the same time form a data point that is used to train the ANN. The results show that the method gives adequate results and although some discrepancies exist, the main appearance is correct. It is possible to distinguish between different types of weather. A rainy day looks rainy and a sunny day looks sunny.

  • 123.
    Olsson, Björn
    et al.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Ynnerman, Anders
    Linköping University, Department of Science and Technology, Visual Information Technology and Applications (VITA). Linköping University, The Institute of Technology.
    Lenz, Reiner
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    SkyVis, an Application of MATLAB in Meteorological Visualization2003In: Proceedings of Nordic Matlab Conference 2003, 2003, p. 295-300Conference paper (Other academic)
    Abstract [en]

    We present a work in progress, Sky Vis, which makes it possible to synthesize realistic images of the sky using data from weather parameter data sets. A neural-network-based model is trained to predict the appearance of the sky from a weather parameter vector. Hourly measurements of weather parameters (like temperature and pressure) and corresponding images are used as training data. The images are decomposed into their eigen components using the principal component analysis (PCA) method. The image information is thus represented using a small number of coefficients. The results show that the main appearance is correct and that it is possible to distinguish between different types of weather. A limitation is that the method is not able to synthesize images with cloud details. This method is in contrast to many previous methods able to synthesize a sky image which varies with the current weather situation.

  • 124.
    Olsson, Björn
    et al.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Ynnerman, Anders
    Linköping University, Department of Science and Technology, Visual Information Technology and Applications (VITA). Linköping University, The Institute of Technology.
    Lenz, Reiner
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Visualizing weather with synthetic high-dynamic range images2004In: Proceedings of SPIE-IS&T Electronic Imaging, Visualization and Data Analysis / [ed] Robert F. Erbacher; Philip C. Chen; Jonathan C. Roberts; Matti T. Gr÷hn; Katy B÷rner, 2004, p. 107-116Conference paper (Other academic)
    Abstract [en]

    The appearance of the sky has a fundamental effect on the way human beings perceive an environment. This paper presents a method to compute synthetic high-dynamic-range fisheye images from weather parameter data sets. These images can then be used in global-illumination systems (e. g. Radiance) to define the lighting conditions at an arbitrary weather state. Applications of this technology can be found in flight simulators and in architectural visualization. The method combines artificial neural networks and principal component analysis to associate the appearance of the sky with the state of a weather parameter vector. A model is trained with examples of sky images and weather data from a period of seven months. This model is then used to generate artificial sky images corresponding to a specific weather parameter vector. This is a novel method which contrary to many previous methods is able to synthesize a sky image which varies with the current weather state. The results show that, although it is not possible to represent the cloud details, it is possible to distinguish between different weather states.

  • 125.
    Raspaud, Martin
    et al.
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Evangelista, Gianpaolo
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Binaural partial tracking2008In: Proc. of Digital Audio Effects Conf. (DAFx'08), Helsinki, Finland: DAFx , 2008, p. 123-128Conference paper (Refereed)
    Abstract [en]

    Partial tracking in sinusoidal models have been studied for over twenty years now, and have been enhanced, making it precise and useful to analyse noiseless harmonic sounds. However, such tools have always been used in a monophonic (single channel) context. A method is thus proposed to adapt the partial tracking to the case of binaural signals. This gives a tool to perform spectral analysis of such signals, keeping relevant information from both left and right channels. Moreover, azimuth (position in the horizontal plane) information for each partial is gained using interaural cues, such as interaural time differences (ITDs) and interaural level differences (ILDs). The azimuth information can then be used as an attribute or as a constraint in the binaural partial tracking algorithm. Finally, some classification results using the azimuth of partials are presented.

  • 126.
    Raspaud, Martin
    et al.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology, Digital Media.
    Viste, Harald
    Widex AS.
    Evangelista, Gianpaolo
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology, Digital Media.
    Binaural Source Localization by Joint Estimation of ILD and ITD2010In: IEEE TRANSACTIONS ON AUDIO SPEECH AND LANGUAGE PROCESSING, ISSN 1558-7916, Vol. 18, no 1, p. 68-77Article in journal (Refereed)
    Abstract [en]

    In this paper, we propose a binaural source localization method based on interaural time differences (ITDs) and interaural level differences (ILDs). The two cues, computed from a two-channel time-frequency representation, are combined in order to estimate the azimuth of sources in binaural recording. We introduce an individual parametric model for the ITD and ILD, and an average parametric model that sets us free from measurements of the subjects HRIRs for sound localization. We conduct several experiments to validate the proposed approach and show that it compares favorably with available techniques.

  • 127. Reuterswärd, Kjell
    et al.
    Flynn, J
    Roble, D
    Museth, Ken
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Model Flowing: Capturing and tracking of deformable geometry2005In: ACM SIGGRAPH 05, Sketches Applications,2005, 2005Conference paper (Refereed)
  • 128.
    Solli, Martin
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Color Image Retrieval with Bags-of-Emotions2009In: Proceedings of SSBA 2009, Symposium on image analysis, 2009 / [ed] Josef Bigun, Antanas Verikas, Halmstad, Sweden: Halmstad University , 2009, p. 37-40Conference paper (Other academic)
  • 129.
    Solli, Martin
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Spectral Measurements on Printed Substrates with a Consumer Digital Camera2005In: Printing Future Days 2005, 1st International IARIAGI Student Conference on Print and Media Technology, Chemnitz, Germany, 2005, p. 106-113Conference paper (Other academic)
  • 130. Order onlineBuy this publication >>
    Solli, Martin
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology, Digital Media.
    Topics in Content Based Image Retrieval: Fonts and Color Emotions2009Licentiate thesis, monograph (Other academic)
    Abstract [en]

    Two novel contributions to Content Based Image Retrieval are presented and discussed. The first is a search engine for font recognition. The intended usage is the search in very large font databases. The input to the search engine is an image of a text line, and the output is the name of the font used when printing the text. After pre-processing and segmentation of the input image, a local approach is used, where features are calculated for individual characters. The method is based on eigenimages calculated from edge filtered character images, which enables compact feature vectors that can be computed rapidly. A system for visualizing the entire font database is also proposed. Applying geometry preserving linear- and non-linear manifold learning methods, the structure of the high-dimensional feature space is mapped to a two-dimensional representation, which can be reorganized into a grid-based display. The performance of the search engine and the visualization tool is illustrated with a large database containing more than 2700 fonts.

    The second contribution is the inclusion of color-based emotion-related properties in image retrieval. The color emotion metric used is derived from psychophysical experiments and uses three scales: activity, weight and heat. It was originally designed for single-color combinations and later extended to include pairs of colors. A modified approach for statistical analysis of color emotions in images, involving transformations of ordinary RGB-histograms, is used for image classification and retrieval. The methods are very fast in feature extraction, and descriptor vectors are very short. This is essential in our application where the intended use is the search in huge image databases containing millions or billions of images. The proposed method is evaluated in psychophysical experiments, using both category scaling and interval scaling. The results show that people in general perceive color emotions for multi-colored images in similar ways, and that observer judgments correlate with derived values.

    Both the font search engine and the emotion based retrieval system are implemented in publicly available search engines. User statistics gathered during a period of 20 respectively 14 months are presented and discussed.

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  • 131.
    Solli, Martin
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology, Digital Media.
    Andersson, Mattias
    Digital Printing Center, Mid Sweden University.
    Kruse, Björn
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology, Digital Media.
    Lenz, Reiner
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology, Digital Media.
    Digital Camera Characterization for Color Measurements2005In: 2005 Beijing International Conference on Imaging: Technology and Applications for the 21st Century, 2005 / [ed] Peijie Xia, Zhiying Qi, Guiping Niu, Li Zhang, Yunxia Zhou, Science Press , 2005, p. 278-279Conference paper (Other academic)
  • 132.
    Solli, Martin
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology, Digital Media.
    Andersson, Mattias
    Digital Printing Center, Mid Sweden University.
    Lenz, Reiner
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology, Digital Media.
    Kruse, Björn
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology, Digital Media.
    Color measurements with a consumer digital camera using spectral estimation techniques2005In: 14th Scandinavian Conference on Image Analysis, SCIA 2005 / [ed] Heikki Kalviainen, Jussi Parkkinen, Arto Kaarna, Heidelberg, Germany: Springer Verlag , 2005, , p. 10p. 105-114Conference paper (Refereed)
    Abstract [en]

    The use of spectrophotometers for color measurements on printed substrates is widely spread among paper producers as well as within the printing industry. Spectrophotometer measurements are precise, but time-consuming procedures and faster methods are desirable. The rapid development of digital cameras has opened the possibility to use consumer digital cameras as substitutes for spectrophotometers for certain applications such as production control. Two methods for estimating the reflectance properties of objects from camera RGB measurements using linear estimation techniques combined with linear and non-linear constraints are presented. In the experiments, we have investigated if these techniques can be used to measure the reflectance properties of flat objects such as printed pages of paper. Reflectances were converted to CIELAB color values, and the minimization of color errors were evaluated with CIE color difference formulas. Our experiments show that a consumer digital camera can be used as a fast and inexpensive alternative to spectrophotometers for color measurements on printed substrates.

  • 133.
    Solli, Martin
    et al.
    Linköping University, Department of Science and Technology. Linköping University, Department of Science and Technology, Digital Media.
    Lenz, Reiner
    Linköping University, Department of Science and Technology. Linköping University, Department of Science and Technology, Digital Media.
    Color Based Bags-of-Emotions2009In: CAIP, Computer Analysis of Images and Patterns / [ed] Xiaoyi Jiang, Nicolai Petkov, Berlin / Heidelberg: Springer , 2009, p. 573-580Conference paper (Refereed)
    Abstract [en]

    In this paper we describe how to include high level semantic information, such as aesthetics and emotions, into Content Based Image Retrieval. We present a color-based emotion-related image descriptor that can be used for describing the emotional content of images. The color emotion metric used is derived from psychophysical experiments and based on three variables: activity, weight and heat. It was originally designed for single-colors, but recent research has shown that the same emotion estimates can be applied in the retrieval of multi-colored images. Here we describe a new approach, based on the assumption that perceived color emotions in images are mainly affected by homogenous regions, defined by the emotion metric, and transitions between regions. RGB coordinates are converted to emotion coordinates, and for each emotion channel, statistical measurements of gradient magnitudes within a stack of low-pass filtered images are used for finding interest points corresponding to homogeneous regions and transitions between regions. Emotion characteristics are derived for patches surrounding each interest point, and saved in a bag-of-emotions, that, for instance, can be used for retrieving images based on emotional content.

  • 134.
    Solli, Martin
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology, Digital Media.
    Lenz, Reiner
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology, Digital Media.
    Color Emotions for Image Classification and Retrieval2008In: Proc. IS&Ts 4th European Conference on Colour in Graphics, Imaging, and Vision, CGIV 2008, 7003 Kilworth Lane, Springfield, VA 22151 USA: Society for Imaging Science and Technology , 2008, , p. 367-371Conference paper (Refereed)
    Abstract [en]

    Many content-based image retrieval systems are not takinginto account high level semantic information. In this paperwe describe our attempts to include color-based emotion-relatedproperties of images in the search. We show that using coloremotion metrics in content-based image retrieval leads to interestingmethods for image retrieval and classification based onsemantic concepts. The color emotion metric used is derivedfrom psychophysical experiments and uses three scales: activity,weight and heat. It was originally designed for single-colorcombinations and later extended to include pairs of colors. Weshow that a modified approach for statistical analysis of coloremotions in images, involving transformations of ordinary RGBhistograms,provides a useful tool for image classification andretrieval. The methods used are both very fast in feature extraction,and descriptor vectors are very short. This is essential inour application where we intend to use it for searching huge imagedatabases containing millions or billions of images.

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  • 135.
    Solli, Martin
    et al.
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Lenz, Reiner
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Color Harmony for Image Indexing2009In: 2009 IEEE 12th International Conference on Computer Vision Workshops, ICCV Workshops, IEEE , 2009, p. 1885-1892Conference paper (Refereed)
    Abstract [en]

    A predictive model for estimating the perceived harmony of ordinary multi-colored images is proposed and evaluated. The model is based on earlier research concerning two-color harmonies. Color regions of images are extracted using mean shift segmentation. Global and local harmony scores are derived for two-color combinations included in different subsets of all segmented regions. Statistical measurements of the obtained harmony scores are used for predicting the perceived overall harmony. The model is validated in a psychophysical experiment, where human observers are judging images on a harmony scale. The findings show that humans do perceive harmony in multi-colored images in similar ways, and that the proposed model results in useful predictions of harmony. The model can be applied in automatic labeling or classification of images.

  • 136.
    Solli, Martin
    et al.
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Lenz, Reiner
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Color Semantics for Image Indexing2010In: CGIV 2010/MCS'10 5th European Conference on Colour in Graphics, Imaging, and Vision and 12th International Symposium on Multispectral Colour Science / [ed] Jussi Parkkinen, Timo Jääskeläinen, Theo Gevers, Alain Trémeau, Springfield, USA: The Society for Imaging Science and Technology, 2010, p. 353-358Conference paper (Refereed)
    Abstract [en]

    We propose a color-based image descriptor that can be used for image indexing based on high-level semantic concepts. The descriptor is based on Kobayashi's Color Image Scale, which is a system that includes 130 basic colors combined in 1170 three-color combinations. Each combination is labeled with one of 180 high-level semantic concepts, like "elegant", "romantic", "provocative", etc. Moreover, words are located in a two-dimensional semantic space, and arranged into groups based on perceived similarity. From a modified approach for statistical analysis of images, involving transformations of ordinary RGB-histograms, a semantic image descriptor is derived, containing semantic information about both color combinations and single colors in the image. We show how the descriptor can be translated into different levels of semantic information, and used in indexing of multi-colored images. Intended applications are, for instance, image labeling and retrieval.

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  • 137.
    Solli, Martin
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology, Digital Media.
    Lenz, Reiner
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology, Digital Media.
    Emotional Satisfaction in Color Image Retrieval2008In: SSBA 2008, Symposium on Image Analysis, 2008, Lund, Sweden: Lund University , 2008, p. 7-10Conference paper (Other academic)
  • 138.
    Solli, Martin
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology, Digital Media.
    Lenz, Reiner
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology, Digital Media.
    FyFont: Find-your-Font in Large Font Databases2007In: Scandinavian Conference on Image Analysis, SCIA 2007 / [ed] Bjarne Kjær Ersbøll, Kim Steenstrup Pedersen, Berlin: Springer , 2007, , p. 432-441p. 432-441Conference paper (Refereed)
    Abstract [en]

    A search engine for font recognition in very large font data-bases is presented and evaluated. The search engine analyzes an image of a text line, and responds with the name of the font used when writing the text. After segmenting the input image into single characters, the recognition is mainly based on eigenimages calculated from edge filtered character images. We evaluate the system with printed and scanned text lines and character images. The database used contains 2763 different fonts from the English alphabet. Our evaluation shows that for 99.8 % of the queries, the correct font name is one of the five best matches. Apart from finding fonts in large databases, the search engine can also be used as a pre-processor for Optical Character Recognition.

  • 139.
    Solli, Martin
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology, Digital Media.
    Lenz, Reiner
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology, Digital Media.
    How to find the font name for this title2007In: SSBA 2007, Symposium on Image Analysis, 2007 / [ed] Magnus Borga, Anders Brun, Michael Felsberg, Linköping, Sweden: Linköping University , 2007, p. 37-40Conference paper (Other academic)
  • 140.
    Solli, Martin
    et al.
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Lenz, Reiner
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Visualization of large font databases2009In: Advances in Printing and Media Technology Vol. XXXVI: Proceedings of the 36th International Research Conference of iarigai / [ed] Nils Enlund, Mladen Lovrecek, Darmstadt, Germany: iarigai , 2009, p. 67-74Conference paper (Refereed)
    Abstract [en]

    We describe a novel system for interaction with large font databases. The system is an efficient tool for browsing in large font databases and as such it can be used by people in the Graphic Arts industry. The proposed approach is based on shape descriptors developed for visual characterization of character images rendered from different fonts. Here the descriptors are used in a visualization of a large font database containing more than 2700 fonts. By applying geometry preserving linear- and non-linear manifold learning methods, in combination with a refinement process, character images of different fonts are organized on a two-dimensional grid, where fonts are positioned based on visual similarity.

  • 141.
    Söderström, Andreas
    et al.
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Museth, Ken
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Non-reflective boundary conditions for incompressible free surface fluids in SIGGRAPH 2009: Talks, SIGGRAPH 09, vol , issue , pp2009In: SIGGRAPH 2009: Talks, SIGGRAPH 09, New York: ACM , 2009Conference paper (Refereed)
    Abstract [en]

    We have developed a novel approach to open-boundaries for fluid animations. More specifically we present a highly efficient energy absorbing boundary condition for the incompressible Navier-Stokes equations in the prescence of a free surface. Our work extends and adapts a Perfectly Matched Layer (PML) approach [Berenger 1994; Johnson 2007], recently developed for the Navier-Stokes equations, to free surfaces in the context fluid animations. We show how our PML boundary condition is able to effectively eliminate reflections generated by the presence of solid boundaries in the simulation domain, and that our method is far superior to simpler approaches for reducing wave reflection. Furthermore, we have adapted our theoretical PML model to work with the Stable-Fluids Eulerian Navier-Stokes solver commonly used in computer graphics. Finally, we show that the cost of deploying our method in terms of memory and additional computations is small, and for a given quality significantly less than other known methods.

  • 142.
    Tran, Linh Viet
    et al.
    Ericsson Vietnam, Daeha Business Center, Hanoi, Vietnam.
    Lenz, Reiner
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Kernel density estimators for hue based image retrieval2005In: Journal of Imaging Science And Technology, ISSN 8750-9237, Vol. 49, no 2, p. 185-188Article in journal (Refereed)
    Abstract [en]

    Color is widely used for content-based image retrieval. In these applications the color properties of an image are characterized by the probability distribution of the colors in the image. These probability distributions are very often estimated by histograms although the histograms have many drawbacks compared to other estimators such as kernel density methods. In this article we investigate whether using kernel density estimators instead of histograms could give better retrieval results based on hue descriptors of color images. In this article we introduce the Fourier series coefficients as descriptors of hue distributions. We argue that under certain conditions these coefficients are optimal in a least squared error sense. We will also apply Parseval formula to compute the similarity of two distributions directly from these Fourier coefficients. Our experiments show that this modification of the kernel based similarity estimation has better retrieval performance than the histogram methods and we will also show that the method is insensitive to parameter changes as long as they are selected in a reasonable range. © 2005, IS&T - The Society for Imaging Science and Technology.

  • 143. Tran, L.V.
    et al.
    Lenz, Reiner
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Characterization of color distributions with histograms and kernel density estimators2003Conference paper (Other academic)
    Abstract [en]

    Color is widely used for content-based image retrieval. In these applications the color properties of an image are characterized by the probability distribution of the colors in the image. These probability distributions are very often estimated by histograms although the histograms have many drawbacks compared to other estimators such as kernel density methods. In this paper we investigate whether using kernel density estimators instead of histograms could give better descriptors of color images. Experiments using these descriptors to estimate the parameters of the underlying color distribution and in color based image retrieval (CBIR) applications were carried out in which the MPEG71 database of 5466 color images with 50 standard queries are used as the benchmark. Noisy images are also generated and put into the CBIR application to test the robustness of the descriptors against the noise. The results of our experiments show that good density estimators are not necessarily good descriptors for CBIR applications. We found that the histograms perform better than kernel based methods when used as descriptors for CBIR applications. In the second part of the paper, optimal values of important parameters in the construction of these descriptors, particularly the smoothing parameters or the bandwidth of the estimators, are discussed. Our experiments show that using over-smoothed bandwidth gives better retrieval performance.

  • 144. Tran, L.V.
    et al.
    Lenz, Reiner
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Geometric invariance in describing color features2003Conference paper (Other academic)
    Abstract [en]

    We present a projective geometry framework for color invariants using the Extended Dichromatic Reflection Model, in which more realistic and complicated illuminations are considered. Many assumptions which have been used by other methods are relaxed in our framework. Specifically some of the proposed invariants do not require any additional assumption except the ones assumed by the Extended Dichromatic Reflection Model. By putting the color invariance into the projective geometry framework, we can generate different types of invariants and clarify the assumptions under which they are valid. Experiments are presented that illustrate the results derived within our framework.

  • 145. Tran, L.V.
    et al.
    Lenz, Reiner
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Spaces of probability distributions and their applications to color based image database search2001Conference paper (Other academic)
    Abstract [en]

    We present a framework to compute the distance between color distributions based on differential geometry. We investigate more detailed the case when color distributions are described as linear combinations of a set of pre-computed basic functions. Experiments in our color based image retrieval system, which were done on 1000 images from Corel image database, show the advantage of our method based on the new distance measure and color descriptor.

  • 146.
    Tran Viet, Linh
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Lenz, Reiner
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Compact colour descriptors for colour-based image retrieval2005In: Signal Processing, ISSN 0165-1684, E-ISSN 1872-7557, Vol. 85, no 2, p. 233-246Article in journal (Refereed)
    Abstract [en]

    In many colour-based image retrieval systems the colour properties of an image are described by its colour histogram. Histogram-based search is, however, often inefficient for large histogram sizes. Therefore we introduce several new, Karhunen-Loève transform (KLT)-based methods that provide efficient representations of colour histograms and differences between two colour histograms. The methods are based on the following two observations, Ordinary KLT considers colour histograms as signals and uses the Euclidian distance for optimization, KLT with generalized colour distance measures that take into account both the statistical properties of the image database and the properties of the underlying colour space should improve the retrieval performance. Image retrieval applications compare similarities between different images. Relevant for the decision is only the local structure of the image space around the current query image since the task is to find those images in the database that are most similar to this given query image. Therefore only the local topology of the feature space is of interest and compression methods should preserve this local topology as much as possible. It is therefore more important to have a good representation of the differences between features of similar images than good representations of the features of the images themselves. The optimization should therefore be based on minimizing the approximation error in the space of local histogram differences instead of the space of colour histograms. In this paper we report the results of our experiments that are done on three image databases containing more than 130,000 images. Both objective and subjective ground truth queries are used in order to evaluate the proposed methods and to compare them with other existing methods. The results from our experiments show that compression methods based on a combination of the two observations described above provide new, powerful and efficient retrieval algorithms for colour-based image retrieval. © 2004 Elsevier B.V. All rights reserved.

  • 147.
    Tran Viet, Linh
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Lenz, Reiner
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Efficient descriptors of hue distributions from kernel density estimators and Fourier transforms2004In: 2nd European Conference on Color in Graphics, Imaging and Vision,2004, Springfield, VA, USA: IST: The Society for Imaging Science and Technology , 2004, p. 151-Conference paper (Refereed)
  • 148.
    Trnka, Jiri
    et al.
    Linköping University, Department of Computer and Information Science, GIS - Geographical Information Science Group. Linköping University, The Institute of Technology.
    Lundberg, Jonas
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Jungert, Erland
    Linköping University, Department of Computer and Information Science, GIS - Geographical Information Science Group. Linköping University, The Institute of Technology.
    A Model-Based Simulation Approach to Study Role Improvisation of a Command Staff2009In: IEEE transactions on systems, man and cybernetics. Part A. Systems and humans, ISSN 1083-4427, E-ISSN 1558-2426Article in journal (Other academic)
    Abstract [en]

    This research gives attention to role improvisation in command and controlteams designated for crisis and disaster response operations in aninternational context. The paper reports a study, which had the goal todevelop, on the bases of real response operations, a role-playing simulationto explore and study role improvisation in highly realistic situations. Thestudy was based on a single-case, the command staff of the SwedishResponse Team. The objective of the study was achieved by (a) identifyingcritical areas concerning role improvisation of the command staff, (b)proposing a model-based simulation design that incorporates these areas,and (c) preparing and executing a role-playing simulation based on thisdesign. The critical areas were identified from two previous responseoperations. The analysis utilized a phenomenological approach, and wasbased on twenty-two interviews and three workshops. The identified critical areas were integrated in the simulation design by means of the initial set-up,scenario stimuli, and interactions with the simulation staff. This was basedon a synthesis of the models of command and control and responseoperations, scenario and tasks, simulation approach and manipulation of theimprovisation variables. The developed simulation was a scenario-basedreal-time role-playing simulation with a progressively unfolding scenario.The scenario was based on events taking place during the 2007 Californiawildfires. The simulation was evaluated by assessing the subjective realism.The paper reports experience from designing and conducting the roleplayingsimulation. It identifies demands and requirements, which have tobe met in order to simulate highly realistic situations. It also demonstrateshow, on the bases of real response operations, such simulations can bedesigned. Lastly, it also identifies areas that require attention in order o usethe role-playing simulations to explore and study role improvisation.

  • 149. Whitaker, Ross
    et al.
    Breen, David
    Museth, Ken
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Segmentation of Biological Volume Datasets Using a Level Set framework2001In: Volume Graphics / [ed] Min Chen, Arie E. Kaufman, Roni Yagel, Vienna: Springer , 2001, p. 249-263Chapter in book (Other academic)
  • 150. Whitaker, Ross
    et al.
    Breen, David
    Museth, Ken
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Soni, N
    A framework for Level Set segmentation of volumetric datasets2001In: IEEE Volume Graphics 01,2001, 2001, p. 159-Conference paper (Refereed)
    Abstract [en]

    This paper presents a framework for extracting surface models from a broad variety of volumetric datasets. These datasets are produced from standard 3D imaging devices, and are all noisy samplings of complex biological structures with boundaries that have low and often varying contrasts. The level set segmentation method, which is well documented in the literature, creates a new volume from the input data by solving an initial-value partial differential equation (PDE) with user-defined feature-extracting terms. Given the local/global nature of these terms, proper initialization of the level set algorithm is extremely important. Thus, level set deformations alone are not sufficient, they must be combined with powerful initialization techniques in order to produce successful segmentations. Our level set segmentation approach consists of defining a set of suitable pre-processing techniques for initialization and selecting /tuning different feature-extracting terms in the level set algorithm. This collection of techniques forms a toolkit that can be applied, under the guidance of a user, to segment a variety of volumetric data. Users can combine these methods in different ways and thereby access a wide range of functionalities, several of which are described in this paper and demonstrated on noisy volume data.

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