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Efficient Methods for Volumetric Illumination
Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Modern imaging modalities can generate three-dimensional datasets with a very high detail level. To transfer all the information to the user in an efficient way there is a need for three-dimensional visualization. In order to enhance the diagnostic capabilities the utilized methods must supply the user with fast renderings that are easy to interpret correctly.

It can thus be a challenge to visualize a three-dimensional dataset in a way that allows the user to perceive depth and shapes. A number of stereoscopic solutions are available on the market but it is in many situations more practical and less expensive to use ordinary two-dimensional displays. Incorporation of advanced illumination can, however, improve the perception of depth in a rendering of a volume. Cast shadows provide the user with clues of distances and object hierarchy. Simulating realistic light conditions is, however, complex and it can be difficult to reach interactive frame rates. Approximations and clever implementations are consequently required.

This thesis presents efficient methods for calculation of illumination with the objective of providing the user with high spatial and shape perception. Two main types of light conditions, a single point light source and omni-directional illumination, are considered. Global transport of light is efficiently estimated using local piecewise integration which allows a graceful speed up compared to brute force techniques. Ambient light conditions are calculated by integrating the incident light along rays within a local neighborhood around each point in the volume.

Furthermore, an approach that allows the user to highlight different tissues, using luminous materials, is also available in this thesis. A multiresolution data structure is employed in all the presented methods in order to support evaluation of illumination for large scale data at interactive frame rates.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press , 2011. , 59 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1406
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-71460ISBN: 978-91-7393-041-3 (print)OAI: oai:DiVA.org:liu-71460DiVA: diva2:449126
Public defence
2011-11-25, Wrannesalen, Center for Medical Image Science and Visualization, Campus US, Linköpings universitet, Linköping, 13:00 (English)
Opponent
Supervisors
Available from: 2011-10-19 Created: 2011-10-19 Last updated: 2015-09-22Bibliographically approved
List of papers
1. Efficient Ambient and Emissive Tissue Illumination using Local Occlusion in Multiresolution Volume Rendering
Open this publication in new window or tab >>Efficient Ambient and Emissive Tissue Illumination using Local Occlusion in Multiresolution Volume Rendering
2007 (English)In: Volume Graphics 2007 Eurographics / IEEE VGTC Symposium Proceedings Sixth International Symposium on Volume Graphics, IEEE , 2007, 1-8 p.Conference paper, Published paper (Refereed)
Abstract [en]

This paper introduces a novel technique to compute illumination for Direct Volume Rendering. By adding shadow effects to volume rendered images, the perception of shapes and tissue properties can be significantly improved and it has the potential to increase the diagnostic value of medical volume rendering. The integrated intensity of incident light for a voxel is computed using a local approximation of the ambient occlusion, thus avoiding the rendering of tissues with very low illumination. Luminous tissue effects are also introduced to enhance the illumination model, controlled through an emissive component in the transfer function. This effect allows the user to highlight specific structures and can give a better understanding of tissue density. Multiresolution volume management and GPU-based computation is used to significantly speed-up the calculations and to support large data sets. The scheme yields interactive frame rates for incrementally refined ambient and emissive illumination for arbitrary transfer function changes.

Place, publisher, year, edition, pages
IEEE, 2007
Series
IEEE Transactions on Visualization and Computer Graphics, ISSN 1077-2626
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-40012 (URN)10.2312/VG/VG07/001-008 (DOI)52036 (Local ID)52036 (Archive number)52036 (OAI)
Conference
Volume Graphics 2007 Eurographics / IEEE VGTC Symposium Proceedings Sixth International Symposium on Volume Graphics, The Czech Technical University, Prague, Czech Republic, September 03–04
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2015-09-22Bibliographically approved
2. Interactive Global Light Propagation in Direct Volume Rendering using Local Piecewise Integration
Open this publication in new window or tab >>Interactive Global Light Propagation in Direct Volume Rendering using Local Piecewise Integration
2008 (English)In: Volume and Point-Based Graphics 2008, Eurographics / IEEE VGTC Symposium Proceedings Seventh International Symposium on Volume Graphics, Eurographics Association , 2008, 105-112 p.Conference paper, Published paper (Refereed)
Abstract [en]

A novel technique for efficient computation of global light propagation in interactive DVR is presented in this paper. The approach is based on a combination of local shadows from the vicinity of each voxel with global shadows calculated at high resolution but stored in a sparser grid. The resulting intensities are then used as the initial illumination for an additional pass that computes first order scattering effects. The method captures global shadowing effects with enhanced shadows of near structures. A GPU framework is used to evaluate the illumination updates at interactive frame rates, using incremental refinements of the in-scattered light. 

Place, publisher, year, edition, pages
Eurographics Association, 2008
Keyword
Volume Visualization
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-43971 (URN)10.2312/VG/VG-PBG08/105-112 (DOI)75259 (Local ID)75259 (Archive number)75259 (OAI)
Conference
Volume and Point-Based Graphics 2008, Eurographics / IEEE VGTC Symposium Proceedings Seventh International Symposium on Volume Graphics Fifth Symposium on Point-Based Graphics, Los Angeles, California, USA August 10 – 11
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2015-09-22Bibliographically approved
3. Local Ambient Occlusion in Direct Volume Rendering
Open this publication in new window or tab >>Local Ambient Occlusion in Direct Volume Rendering
2010 (English)In: IEEE Transactions on Visualization and Computer Graphics, ISSN 1077-2626, E-ISSN 1941-0506, Vol. 16, no 4, 548-559 p.Article in journal (Refereed) Published
Abstract [en]

This paper presents a novel technique to efficiently compute illumination for Direct Volume Rendering using a local approximation of ambient occlusion to integrate the intensity of incident light for each voxel. An advantage with this local approach is that fully shadowed regions are avoided, a desirable feature in many applications of volume rendering such as medical visualization. Additional transfer function interactions are also presented, for instance, to highlight specific structures with luminous tissue effects and create an improved context for semitransparent tissues with a separate absorption control for the illumination settings. Multiresolution volume management and GPU-based computation are used to accelerate the calculations and support large data sets. The scheme yields interactive frame rates with an adaptive sampling approach for incrementally refined illumination under arbitrary transfer function changes. The illumination effects can give a better understanding of the shape and density of tissues and so has the potential to increase the diagnostic value of medical volume rendering. Since the proposed method is gradient-free, it is especially beneficial at the borders of clip planes, where gradients are undefined, and for noisy data sets.

Place, publisher, year, edition, pages
IEEE, 2010
Keyword
Local illumination, volumetric ambient occlusion, volume rendering, medical visualization, emissive tissues, shading, shadowing
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-56687 (URN)10.1109/TVCG.2009.45 (DOI)000277650300003 ()
Note
©2009 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE. Frida Hernell, Patric Ljung and Anders Ynnerman, Local Ambient Occlusion in Direct Volume Rendering, 2010, IEEE TRANSACTIONS ON VISUALIZATION AND COMPUTER GRAPHICS, (16), 4, 548-559. http://dx.doi.org/10.1109/TVCG.2009.45 Available from: 2010-05-31 Created: 2010-05-31 Last updated: 2017-12-12Bibliographically approved
4. Concurrent Volume Visualization of Real-Time fMRI
Open this publication in new window or tab >>Concurrent Volume Visualization of Real-Time fMRI
Show others...
2010 (English)In: Proceedings of the 8th IEEE/EG International Symposium on Volume Graphics / [ed] Ruediger Westermann and Gordon Kindlmann, Goslar, Germany: Eurographics - European Association for Computer Graphics, 2010, 53-60 p.Conference paper, Published paper (Refereed)
Abstract [en]

We present a novel approach to interactive and concurrent volume visualization of functional Magnetic Resonance Imaging (fMRI). While the patient is in the scanner, data is extracted in real-time using state-of-the-art signal processing techniques. The fMRI signal is treated as light emission when rendering a patient-specific high resolution reference MRI volume, obtained at the beginning of the experiment. As a result, the brain glows and emits light from active regions. The low resolution fMRI signal is thus effectively fused with the reference brain with the current transfer function settings yielding an effective focus and context visualization. The delay from a change in the fMRI signal to the visualization is approximately 2 seconds. The advantage of our method over standard 2D slice based methods is shown in a user study. We demonstrate our technique through experiments providing interactive visualization to the fMRI operator and also to the test subject in the scanner through a head mounted display.

Place, publisher, year, edition, pages
Goslar, Germany: Eurographics - European Association for Computer Graphics, 2010
Series
Eurographics/IEEE VGTC Symposium on Volume Graphics, ISSN 1727-8376 ; VG10
Keyword
fMRI, Direct volume rendering, Local ambient occlusion, Real-time, Biofeedback
National Category
Medical Image Processing
Identifiers
urn:nbn:se:liu:diva-58060 (URN)10.2312/VG/VG10/053-060 (DOI)978-3-905674-23-1 (ISBN)
Conference
8th IEEE/EG International Symposium on Volume Graphics, Norrköping, Sweden, 2-3 May, 2010
Projects
CADICS
Available from: 2010-07-27 Created: 2010-07-27 Last updated: 2015-11-04Bibliographically approved

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