Refereed conference proceedings

1. Incremental spherical linear interpolation
   Authors: Barrera, T.(1); Hast, A.; Bengtsson, E.
   (1) Barrera Kristiansen AB, Uppsala
   Conference: SIGRAD 2004: Special theme - Environmental visualization, Linköping electronic conference proceedings, vol 13, pp.7-10
   Editor: Seipel, S.
   Publisher: Linköping University Electronic Press
   Abstract: Animation is often done by setting up a sequence of key orientations, represented by quaternions. The in between orientations are obtained by spherical linear interpolation (SLERP) of the quaternions, which then can be used to rotate the objects. However, SLERP involves the computation of trigonometric functions, which are computationally expensive. Since it is often required that the angle between each quaternion should be the same, we propose that incremental SLERP is used instead. In this paper we demonstrate five different methods for incremental SLERP, whereof one is new, and their pros and cons are discussed.

2. Fast intensity distribution functions for soft and hard edged spotlights
   Authors: Hast, A.; Barrera, T.(1); Bengtsson, E.
   (1) Barrera Kristiansen AB, Uppsala
   Conference: International Conference in Central Europe on Computer Graphics, Visualization and Computer Vision, (WSCG 2004), Proc., pp.95-99
   Abstract: The purpose of this paper is twofold: to propose two fast distribution functions for spotlights and to use terminology used in stage lighting to model these luminaries. In OpenGL and other API's the original Warn model is used where the light distribution is computed using a power function. In professional modeling tools, a linear or a cubic function is often used. We propose the use of two different quadratic functions instead that will make the computation involved faster than using the power function or a cubic function. Moreover it will be more flexible than using a linear function. These functions can be used to model both hard and soft edged spotlights

3. Improved diffuse anisotropic shading
   Authors: Hast, A.; Wesslén, D. (1); Seipel, S.
   (1) Dept. of Mathematics, Natural Sciences, and Computing, University College of Gävle
   Conference: SIGRAD 2004: Special theme - Environmental visualization, Linköping electronic conference proceedings, vol 13, pp. 57-58
   Editor: Seipel, S.
   Publisher: Linköping university electronic press
   Abstract: Cloth, hair, brushed metal, and other surfaces with small, regular surface features exhibit anisotropic reflectance properties for which common isotropic shading methods are not suited. Shading of such materials is often implemented by computing the normal giving the maximum light contribution instead of solving the integral that is the sum of all reflected light. In this paper we show that this integral can be simplified if the direction to the viewer and fibre geometry is not taken into account. Still, this will give a more accurate result than the very rough simplification of using the maximum contribution. This computation is simple for diffuse light. However, the specular light still needs some more elaboration to work.

4. Development of a virtual laboratory system for science education and the study of collaborative action
   Authors: Jensen, N. (1); Seipel, S.; von Voigt, G. (1); Raasch, S. (1); Olbrich, S. (1); Nejdl W. (1)
   (1) University of Hannover, Germany
   Conference: World Conference on Educational Multimedia, Hypermedia & Telecommunications (AACE ED Media Conference) 2004
   Abstract: The paper specifies the development of a toolkit to run synthetic science laboratories. The aim was to facilitate collaborative experimenting for problem-based learning in a virtual lab. The goal was to demonstrate virtual experimenting by use of interactive 3D visualization and simulation. Technology was developed over six years and in part designed in explicit accordance to didactic models. For tests, we built a virtual lab that comprised media tools and complex computer simulations, and we evaluated it with promising results. Students used data from meteorology and experimented together. Generally, they enjoyed using the system and collaborated in a motivated way. We identified which tools they preferred. The paper indicates ways to improve the design of virtual labs by use of our toolkit.

5. Segmentation and separation of point like fluorescent markers in digital images
   Authors: Karlsson, P.; Lindblad, J.
   Conference: IEEE International Symposium on Biomedical Imaging (ISBI 2004), Proc., pp. 1291-1294
   Publisher: Mira Digital Publishing
   Abstract: We present a method for accurate segmentation of point like signals from fluorescent markers, in digital microscopic images with subcellular resolution. The method is able to segment and separate clustered signals, which facilitates accurate dot counting. The method performance is evaluated using synthetic images, that are modeled after real digital microscopy images of cells. The results show that the method is able to detect point like fluorescent signals as accurately as a manual operator.

6. Real-time rendering of accumulated snow
   Authors: Ohlsson, P.; Seipel, S.
   Conference: SIGRAD 2004: Special theme - Environmental visualization, Linköping electronic conference proceedings, vol 13, pp. 25-32
   Editor: Seipel, S.
   Publisher: Linköping University Electronic Press
   Abstract: This paper presents a method of computing snow accumulation as a per pixel effect while rendering the scene. The method is similar to the shadow mapping method for shadow calculations. A depth buffer is used to find out how much snow a particular surface should receive. The amount of snow is then modified depending on the slope of the surface. To render the snow in a convincing way 3D noise is utilized for the lighting of the snow surface.

7. 2D grey-level skeleton computation: A discrete 3D approach
   Authors: Sanniti di Baja, G. (1); Nyström, I.
   (1) Istituto di Cibernetica, National Research Council of Italy (CNR) Napoli, Italy
   Conference: International Conference on Pattern Recognition (ICPR 2004), Proc., vol III, pp. 526-529
   Editors: Kittler, J.; Petrou, M.; Nixon, M.
   Publisher: IEEE Computer Society
   Abstract: A discrete 3D binary approach to compute the skeleton in 2D grey-level images is presented. The 2D grey-level input image is converted to a 3D binary image and the top surface of the foreground is identified. This discrete surface then undergoes skeletonization. The obtained 3D curve skeleton is pruned, before being projected back to a 2D grey-level image. This is suitably post-processed, since the projection may cause spurious loops and thickening. This algorithm can find applications in optical character recognition and document analysis or in other situations where shape analysis by skeletons is desired. An important property of the suggested method is that no hard segmentation into foreground and background is needed prior to the skeletonization.

8. Using grey-level and shape information for decomposing proteins in 3D images
   Authors: Sintorn, I.; Mata, S. (1)
   (1) Dept. of Computer Science, Statistics and Telematics, Rey Juan Carlos University, Móstoles-Madrid, Spain
   Conference: IEEE International Symposium on Biomedical Imaging (ISBI 2004), Proc., pp. 800-803
   Publisher: Mira Digital Publishing
   Abstract: An image analysis method for decomposing 3D objects using a combination of grey-level and shape is presented. The method consists of two major parts: seeding based on grey-level information and growth from the seeds based on shape information. The growth is performed in two steps in order to prevent seeds located in peripheral or protruding parts of the object from growing into other parts. The method was developed to decompose 3D reconstructions of proteins into their structural subunits. The proteins are imaged with SET (Sidec Electron Tomography) at a resolution of approximately 2nm, and delineated from the background by thresholding prior to application of our decomposition method. Decomposition can be a useful tool in the second step of the segmentation process to help distinguish between true protein molecules and other objects. It can also be useful for analyzing and visualizing interactions between proteins.

9. Defuzzification of discrete objects by optimizing area and perimeter similarity
   Authors: Sladoje, N.; Lindblad, J.; Nyström, I.
   Conference: International Conference on Pattern Recognition (ICPR 2004), Proc., vol III, pp. 455-458
   Editors: Kittler, J.; Petrou, M.; Nixon, M.
   Publisher: IEEE Computer Society
   Abstract: We present a defuzzification method which produces a crisp digital object starting from a fuzzy digital one, while keeping selected properties of them as similar as possible. Our main focus is on defuzzification based on the invariance of perimeter and area measures while taking into account with the membership values. We perform a similarity optimization procedure using on a region growing approach to obtain a crisp object with the desired properties.

10. Surface skeletons in grids with non-cubic voxels
    Author: Strand, R.
    Conference: International Conference on Pattern Recognition (ICPR 2004), Proc., vol I, pp. 548-551
    Editors: Kittler, J.; Petrou, M.; Nixon, M.
    Publisher: IEEE Computer Society
    Abstract: An algorithm for computing surface skeletons on the face-centered cubic (fcc) grid and the body-centered cubic (bcc) grid is presented. The fcc grid and the bcc grid are three-dimensional grids where the voxels are rhombic dodecahedra and truncated octahedra, respectively. The DT is used to generate the set of centres of maximal balls (CMBs) which will be ``anchor points'' when constructing the skeleton. Simple points are used in order to make the skeleton topologically correct and CMBs to produce a fully reversible skeleton. Using only simple points and the CMBs generates a skeleton with a lot of branches. By using a set of additional conditions for removal and preservation of gridpoints, most of these branches are merged into surfaces. For comparison, the algorithm is also implemented for the cubic grid.

11. Fast surface rendering for interactive medical image segmentation with haptic feedback
    Authors: Vidholm, E.; Agmund, J.
    Conference: SIGRAD 2004: Special theme - Environmental visualization, Linköping electronic conference proceedings, vol 13, pp. 33-39
    Editor: Seipel, S.
    Publisher: Linköping University Electronic Press
    Abstract: In this work, we present a haptic-enabled application for interactive editing in medical image segmentation. We use a fast surface rendering algorithm to display the different segmented objects, and we apply a proxy-based volume haptics algorithm to be able to touch and edit these objects at interactive rates. As an application example, we show how the system can be used to initialize a fast marching segmentation algorithm for extracting the liver in magnetic resonance (MR) images and then edit the result if it is incorrect.

12. Haptic guided seeding of MRA images for semi-automatic segmentation
    Authors: Vidholm, E.; Tizon, X.; Nyström, I.; Bengtsson, E.
    Conference: IEEE International Symposium on Biomedical Imaging (ISBI 2004), Proc., pp. 288-291
    Publisher: Mira digital Publishing
    Abstract: We investigate how stereo graphics and haptics can be combined to facilitate the seeding procedure in semi-automatic segmentation of magnetic resonance angiography (MRA) images. Real-time volume rendering using maximum intensity projections (MIPs) has been implemented together with a haptic rendering method that provides force feedback based on local gradients and intensity values. This combination allows a user to trace vessels in the image, and to place seed-points directly in the 3D data set. Seed-regions are propagated from the seed-points according to an algorithm that favors bright voxels. An experienced user have tested the interface on whole-body MRA images with promising results.

13. GPU-assisted Surface Reconstruction and Motion Analysis from Range Scanner Data
    Authors: Wesslén, D. (1); Seipel, S.
    (1) Dept. of Mathematics, Natural Sciences, and Computing, University College of Gävle
    Conference: SIGRAD 2004: Special theme - Environmental visualization, Linköping electronic conference proceedings, vol 13, pp. 51-52
    Editor: Seipel, S.
    Publisher: Linköping University Electronic Press
    Abstract: We present a method for rapid GPU-assisted surface reconstruction from range scanner data producing meshes suitable for visualization and analysis of very slow-moving objects from multiple scans of the same area.
    Comment:Short paper.

14. The virtual forest
    Authors: Wesslén, D. (1); Seipel, S.
    (1) Dept. of Mathematics, Natural Sciences, and Computing, University College of Gävle
    Conference: SIGRAD 2004: Special theme - Environmental visualization, Linköping electronic conference proceedings, vol 13, pp. 61
    Editor: Seipel, S.
    Publisher: Linköping University Electronic Press
    Comment:Poster

15. Collaborative 3D visualizations of geo-spatial information for command and control
    Authors:Winkler Pettersson, L. (1); Seipel, S.
    (1) Dept. of Information Technology, UU
    Conference: SIGRAD 2004: Special theme - Environmental visualization, Linköping electronic conference proceedings, vol 13, pp. 41-47
    Editor: Seipel, S.
    Publisher: Linköping university electronic press
    Abstract: We present a prototype command and control system that is based on view-dependent co-located visualizations of geographically related data. It runs on a 3D display environment, in which several users can interact with view consistent visualizations of information. The display system projects four independent stereoscopic image pairs at full resolution upon a custom designed optical screen. It uses head tracking for up to four individual observers to generate distortion free imagery that is rendered on a PC based rendering cluster. We describe the technical platform and system configuration and introduce our unified software architecture that allows integrating multiple rendering processes with head tracking for multiple viewers. We then present results of our current visualization application in the field of military command and control. The command and control system renders view consistent geographical information in a stereoscopic 3D view whereby command and control symbols are presented in a viewpoint adapted way. We summarize our experiences with this new environment and discuss technical soundness and performance.

16. In situ tomographic display for interactive data visualization
    Authors: Winkler Pettersson, L. (1); Wesslén, D. (2); Seipel, S.
    (1) Dept. of Information Technology, UU
    (2) Dept. of Mathematics, Natural Sciences, and Computing, University College of Gävle
    Conference: Third Nordic conference on Human-computer interaction, Proc., pp. 93-96
    Publisher: ACM Press, New York
    Abstract: With tomographic in situ visualization we present a novel approach to interactive data visualization and exploration. This visualization concept is useful for presentation of spatially co-located information that is normally not visible to the human's eye. The tomographic in situ display allows for interactive cutting through data in space by using a spatially tracked and calibrated display. In this paper we describe the technical apparatus of our prototype and describe an application for the tomographic in situ visualization in the field of indoor climate studies.

17. Modeling image processing tasks as flexible workflows for improved quality of service
    Authors: Zdravkovic, J.(1); Åhlén, J.
    (1) Dept. of Computer Science, Royal Institute of Technology, Stockholm
    Conference: IADIS International Conference on Applied Computing, Proc., pp. 363-370
    Abstract: Processing of nontrivial images is a difficult task performed throughout a set of ordered steps. Besides the basic functionality that a process must satisfy, quality of service goals are to be met. Images should be processed within a certain time and a certain quality should be attained. To manage image-processing tasks in the optimal way, the process goals must be defined explicitly and their fulfillment has to be controlled. Modeling image-processing tasks with workflows would enable control of the fulfillment of goals. In addition, by introducing flexible semantics in the workflow, the process could be executed along optimal execution alternatives. In this paper, we propose an approach to model the class of image processing tasks with workflows that would, based on the extended semantics, allow for flexibility in the process execution toward optimal goals fulfillment.

18. Supercover of non-square and non-cubic grids
    Authors: Linh, T. K. (1); Imiya, A (1); Strand, R.; Borgefors, G.
    (1) Chiba University, Japan
    Conference: 10th International Workshop on Combinatorial Image Analysis, Proc., pp. 88-97
    Editors: Klette, R.; Zunic, J.
    Publisher: Springer-Verlag, Lecture Notes in Computer Science Vol. 3322
    Abstract: We define algebraic discrete geometry of hexagonal- and rhombic-dodecahedral- grids on a plane in a space, respectively. Since, a hexagon and a rhombic-dodecahedron are elements for tilling on a plane and in a space, respectively, a hexagon and a rhombic-dodecahedron are suitable as elements of discrete objects on a plane and in a space, respectively. For the description of linear objects in a discrete space, algebraic discrete geometry provides a unified treatment employing double Diophantus equations. In this paper, we introduce supercove for the hexagonal- and rhombic-dodecahedral- grid-systems on a plane and in a space, respectively.