Perception-Augmenting Illumination

AT each stage of the visualization pipeline, the information is impeded by loss or by noise because of imprecise acquisition, storage limitations, and processing. Furthermore, it passes through the complex and not yet well understood pathways in the human visual system and finally to result into a mental image. Due to the noise that impedes the information in the visualization pipeline and the processes in the human visual system, the mental image and the real-world phenomenon do not match. From the aspect of physics, the input of the visual system is confined only to patterns of light. Illumination is therefore essential in 3D visualization for perception of visualized objects. In this thesis, several advancements for advanced volumetric lighting are presented. First, a novel lighting model that supports interactive light source placement and yields a high-quality soft shadowing effect, is proposed. The light transport is represented by conical functions and approximated with an incremental blurring operation of the opacity buffer during front-to-back slicing of the volume. Furthermore, a new perceptuallyfounded model for expressing shadows that gives a full control over the appearance of shadows in terms of color and opacity, is presented. Third, a systematic error in perception of surface slant is modeled. This knowledge is then applied to adjust an existing shading model in a manner that compensates for the error in perception. These new visualization methodologies are linked to the knowledge of perceptual psychology and the craft of illustrators, who experimented with visual-presentation techniques for centuries. The new methodologies are showcased on challenging acoustic modalities such as 3D medical ultrasound and sonar imaging. Related Publications This thesis is based on the following publications: (A) V. Šoltészová, D. Patel, S. Bruckner and I. Viola. A Multidirectional Occlusion Shading Model for Direct Volume Rendering. In Computer Graphics Forum (EuroVis 2010), 29(3), pages 883–891, 2010 (Level 2) (B) V. Šoltészová, D. Patel and I. Viola. Chromatic Shadows for Improved Perception. In Proceedings of Non-Photorealistic Rendering and Animation (NPAR 2011), pages 105–115, 2011 (Level 1) (C) V. Šoltészová, Ç. Turkay, M. C. Price and I. Viola. A Perceptual-Statistics Shading Model. In IEEE Transactions on Visualization and Computer Graphics (IEEE SciVis 2012), to appear, 2012 (Level 2) (D) V. Šoltészová, R. Patel, H. Hauser and I. Viola. Stylized Volume Visualization of Streamed Sonar Data. In Proceedings of Spring Conference on Computer Graphics (SCCG 2012), pages 13–20, 2012 (Level 1, invited submission of an extended version in Level 2 Computer Graphcis Forum in preparation) (E) V. Šoltészová, L. E. Sævil Helljesen, W. Wein, O. H. Gilja and I. Viola. LowestVariance Streamlines for Filtering of 3D Ultrasound. In Proceedings of Eurographics Workshop on Visual Computing In Biomedicine (EG VCBM 2012), accepted, 2012 (Level 1) The following publication is also related to this thesis: (I) Å. Birkeland, V. Šoltészová, D. Hönigmann, O. H. Gilja, Odd Helge, S. Brekke, T. Ropinski and I. Viola. The Ultrasound Visualization Pipeline. In Dagstuhl Book, to appear. (II) D. Patel, S. Bruckner, V. Šoltészová, J. M. Nordbotten. Instant Convolution Shadows for Volumetric Detail Mapping. Submitted to Transactions on Graphics. All manuscripts that constitute this thesis were written during the PhD project and the author of this thesis is also their main author. Ivan Viola, the main supervisor of this thesis, coauthored all manuscripts. Viola contributed not only by his advice and guidance, but also with an inspiration for most of the novel ideas presented in this thesis. Paper A and Paper B are coauthored by Daniel Patel who helped to maturate the novel ideas during numerous discussions and brainstormings, to collect the related works and to write the manuscript. He also implemented a tool for CIELAB–RGB color conversion. Last but not least, he was a great moral support. Paper A is also coauthored by Stefan Bruckner who provided the framework VolumeShop [10], and contributed to the implementation and to the discussions. He also helped revising the manuscript. Paper C is coauthored by Çaǧatay Turkay and Mark C. Price. Turkay contributed with advice for visual and statistical analysis that was needed for creation of the perceptual model. Price provided help during the experiment-preparation phase and later with the analysis of the collected data. Paper D is coauthored by Ruben Patel and Helwig Hauser. Ruben Patel was the collaborating scientists from the Institute of Marine Research who contributed with datasets, his feedback during the design process and with material for the introduction of the manuscript. Hauser contributed with numerous discussions and suggestions to ameliorate the text. The presentation of this paper was awarded by the 2nd best presentation award decided by the audience. The paper itself was also awarded the 2nd best paper award decided by the paper committee and the authors were invited to submit an extended version to the Computer Graphics Forum journal. Paper E is also coauthored by Linn Emilie Sævil Helljesen and Odd Helge Gilja who are the clinical partners of the IllustraSound research project. Gilja is also the co-supervisor of this thesis. Helljesen performed the evaluation and Gilja contributed with feedback and amelioration of the text. This paper is also coauthored by Wolfgang Wein who was the collaborating partner and expert on image processing. He provided his advice and contributed to the revision of the manuscript.