Graphics Lunch

Home Members Applications Projects Seminars Publications Facilities Internal Web Contact Us

Search

Graphics Lunch - 2001

Graphics Lunch is a forum for informal and formal discussions over lunch for those interested in graphics and visualization issues at Maryland. It also serves as a forum for talks from visitors to our lab about their recent research in graphics and visualization. Students and faculty can use this venue to practise and prepare for their conference papers, discuss recent and upcoming papers and conferences, or inform others about graphics and visualization news. Meetings are held on Mondays from 12:00pm to 1:30pm in the CFAR Seminar Room (AVW 4424) .

November 30, 2001 Expressive Volume Rendering

Presented By Penny Rheingans, University of Maryland Baltimore County

Comments Graphics Seminar Series

Abstract
Accurately and automatically conveying the structure of a volume model is a problem not fully solved by existing volume rendering approaches. Physics-based volume rendering approaches create images which may match the appearance of translucent materials in nature, but may not embody important structural details. Transfer function approaches allow flexible design of the volume appearance, but generally require substantial hand tuning for each new data set in order to be effective. We have introduced the volume illustration approach, combining the familiarity of a physics-based illumination model with the ability to enhance important features using non-photorealistic rendering techniques. Since features to be enhanced are defined on the basis of higher-order model characteristics rather than volume sample value, the application of volume illustration techniques requires less manual tuning than the design of a good transfer function. Volume illustration provides a flexible unified framework for enhancing structural perception of volume models through the amplification of features, the addition of illumination effects, and the application of procedural textures.
Volume illustration works on both presampled and procedurally defined volume models, enabling a range of image styles from practical technical illustrations to more abstract painterly effects. I will first present some techniques from painting and technical illustration for conveying shape and depth, particularly those relevant for translucent subjects. After that, I will describe the volume illustration approach and present some results from this new investigation.
November 2, 2001 Rendering Fast with Arbitrary Detail: Rediscovering Curved Surfaces

Presented By Subodh Kumar, Johns Hopkins University

Comments Graphics Seminar Series

Abstract
I will talk about an efficient algorithm to render spline model. This algorithm combines view-dependent uniform and adaptive tessellations of spline surfaces. The algorithm dynamically adjusts the level of detail of the triangulation at each frame. It samples each surface patch more densely in regions of high curvature and less densely in regions of low curvature. This algorithm precomputes a prioritized list of important samples on the surface. At rendering time, it adds these points in the specified order to the triangulation. Once the pre-computed points are exhausted and even more detail is re-quired on some region of the patch, additional samples, now uniformly spaced, are added to the triangulation. The algorithm works well in practice and has a low memory footprint.
September 21, 2001 Fuzzy Molecular Surfaces

Presented By Chang-Ha Lee

Abstract
The previous methods to compute smooth molecular surface assumed that each atom in a molecule has a fixed position without thermal motion or uncertainty. In real world, the position of an atom in a molecule is fuzzy because of its uncertainty in protein structure determination and thermal energy of the atom.
We propose a method to compute smooth molecular surface for atoms that are either vibrating or otherwise have uncertainty in their positions. The Gaussian distribution is used for modeling the fuzziness of each atom, and a p-probability sphere is computed for each atom with a certain confidence level. The smooth molecular surface with fuzzy atoms is computed efficiently from extended-radius p-probability spheres.
We have implemented a program for visualizing three-dimensional molecular structures including the smooth molecular surface with fuzzy atoms using multi-layered transparent surfaces, where the surface of each layer has a different confidence level and the transparency associated with the confidence level.

August 27, 2001 Warping Diffusion Tensor Images

Presented By Dongrong Xu, Johns Hopkins University

Abstract
Brain neural fiber connectivity is critical in understanding brain white matter structure and brain functions. Diffusion tensor (DT) images provide insight into the fiber connectivities. Tradtional approaches of processing DT image usually first extract the fibers in the original space into a volume of fibers and then warp different volumes into an atlas space to be registered for analysis. This actually breaks the connectivity and turns off some important graphics information. So the generated result view is a cloud without connectivity. Here in this paper, we have developed an approach that can allow us to maintain the connectivity in DT image warping so that the visulization of the connectivity will be tracked instead of a fuzzy cloud.
This DT warping method is derived from Procrustean matrix analysis, which allows to transform DT directly so that analysis can directly based on DT image itself. During the process of warping a DT image, in addition to relocating every tensor at each voxel, it is necessary to re-adjust the orientation of each tensor. Since the deformation is non-linear, this step is challenging. Compared with those existing approaches,our methods can figure out the affine transformation from its local displacement at any scale. This method thus does not need the displacement field to be everywhere small, which was an in-practical prerequirement but important in warping DT images. Therefore, our approach is more reliable and practical. The experimental results show that our new method keeps the connectivity very well.

July 30, 2001 Matching 3D Models with Shape Distributions

Presented By Thomas Baby

Comments This paper by Robert Osada, Thomas Funkhouser, Bernard Chazelle, and David Dobkin from Princeton University was presented at the Shape Modeling International, Genova, Italy in May 2001. It is available online here.

June 4, 2001 A Signal-Processing Framework for Inverse Rendering

Presented By Zhiyun Li

Comments This paper from Stanford University (work by Ravi Ramamoorthi and Pat Hanrahan) was published in SIGGRAPH 2001. The full paper is available here.

May 21, 2001 The Randomized z-Buffer Algorithm: Interactive Rendering of Highly Complex Scenes

Presented By Xuejun Hao

Comments This paper is by Michael Wand, Matthias Fischer, Ingmar Peter, Friedhelm Meyer auf der Heide, and Wolfgang Straßer, all at the University of Tuebingen, Germany. The paper was published in SIGGRAPH 2001. More information can be found here.

April 23, 2001 Differential Point Rendering

Presented By Aravind Kalaiah

Comments This is a dry run of Aravind's presentation at the Eurographics Workshop on Rendering 2001, held on the 26^th of June, 2001 in London, UK. The paper is available online here.

Abstract We present a novel point rendering primitive, called Differential Point (DP), that captures the local differential geometry in the vicinity of a sampled point. This is a more general point representation that, for the cost of a few additional bytes, packs much more information per point than the traditional point-based models. This information is used to efficiently render the surface as a collection of local neighborhoods. The advantages to this representation are manifold: (1) it delivers a significant reduction in the number of point primitives that represent a surface (2) it achieves a robust hardware accelerated per-pixel shading - even with no connectivity information (3) it offers a novel point-based simplification technique that has a convenient and intuitive interface for the user to efficiently resolve the speed versus quality tradeoff. The number of primitives being equal, DPs produce a much better quality of rendering than a pure splat-based approach. Visual appearances being similar, DPs are about two times faster and require about 75% less disk space in comparison to splatting primitives.

April 2, 2001 First Graphics Lunch at Maryland

Presented By Amitabh Varshney

Abstract This is to kick-off the Graphics Lunch at Maryland. We will be discussing the general overview and spirit of this series of lunches as well as talk about other issues of relevance to GVIL such as the state of ongoing projects and equipment acquisition. We will also plan out the shared software testbed for the lab.

Top

November 30, 2001	Expressive Volume Rendering
Presented By	Penny Rheingans, University of Maryland Baltimore County
Comments	Graphics Seminar Series
Abstract	Accurately and automatically conveying the structure of a volume model is a problem not fully solved by existing volume rendering approaches. Physics-based volume rendering approaches create images which may match the appearance of translucent materials in nature, but may not embody important structural details. Transfer function approaches allow flexible design of the volume appearance, but generally require substantial hand tuning for each new data set in order to be effective. We have introduced the volume illustration approach, combining the familiarity of a physics-based illumination model with the ability to enhance important features using non-photorealistic rendering techniques. Since features to be enhanced are defined on the basis of higher-order model characteristics rather than volume sample value, the application of volume illustration techniques requires less manual tuning than the design of a good transfer function. Volume illustration provides a flexible unified framework for enhancing structural perception of volume models through the amplification of features, the addition of illumination effects, and the application of procedural textures. Volume illustration works on both presampled and procedurally defined volume models, enabling a range of image styles from practical technical illustrations to more abstract painterly effects. I will first present some techniques from painting and technical illustration for conveying shape and depth, particularly those relevant for translucent subjects. After that, I will describe the volume illustration approach and present some results from this new investigation.
November 2, 2001	Rendering Fast with Arbitrary Detail: Rediscovering Curved Surfaces
Presented By	Subodh Kumar, Johns Hopkins University
Comments	Graphics Seminar Series
Abstract	I will talk about an efficient algorithm to render spline model. This algorithm combines view-dependent uniform and adaptive tessellations of spline surfaces. The algorithm dynamically adjusts the level of detail of the triangulation at each frame. It samples each surface patch more densely in regions of high curvature and less densely in regions of low curvature. This algorithm precomputes a prioritized list of important samples on the surface. At rendering time, it adds these points in the specified order to the triangulation. Once the pre-computed points are exhausted and even more detail is re-quired on some region of the patch, additional samples, now uniformly spaced, are added to the triangulation. The algorithm works well in practice and has a low memory footprint.
September 21, 2001	Fuzzy Molecular Surfaces
Presented By	Chang-Ha Lee
Abstract	The previous methods to compute smooth molecular surface assumed that each atom in a molecule has a fixed position without thermal motion or uncertainty. In real world, the position of an atom in a molecule is fuzzy because of its uncertainty in protein structure determination and thermal energy of the atom. We propose a method to compute smooth molecular surface for atoms that are either vibrating or otherwise have uncertainty in their positions. The Gaussian distribution is used for modeling the fuzziness of each atom, and a p-probability sphere is computed for each atom with a certain confidence level. The smooth molecular surface with fuzzy atoms is computed efficiently from extended-radius p-probability spheres. We have implemented a program for visualizing three-dimensional molecular structures including the smooth molecular surface with fuzzy atoms using multi-layered transparent surfaces, where the surface of each layer has a different confidence level and the transparency associated with the confidence level.
August 27, 2001	Warping Diffusion Tensor Images
Presented By	Dongrong Xu, Johns Hopkins University
Abstract	Brain neural fiber connectivity is critical in understanding brain white matter structure and brain functions. Diffusion tensor (DT) images provide insight into the fiber connectivities. Tradtional approaches of processing DT image usually first extract the fibers in the original space into a volume of fibers and then warp different volumes into an atlas space to be registered for analysis. This actually breaks the connectivity and turns off some important graphics information. So the generated result view is a cloud without connectivity. Here in this paper, we have developed an approach that can allow us to maintain the connectivity in DT image warping so that the visulization of the connectivity will be tracked instead of a fuzzy cloud. This DT warping method is derived from Procrustean matrix analysis, which allows to transform DT directly so that analysis can directly based on DT image itself. During the process of warping a DT image, in addition to relocating every tensor at each voxel, it is necessary to re-adjust the orientation of each tensor. Since the deformation is non-linear, this step is challenging. Compared with those existing approaches,our methods can figure out the affine transformation from its local displacement at any scale. This method thus does not need the displacement field to be everywhere small, which was an in-practical prerequirement but important in warping DT images. Therefore, our approach is more reliable and practical. The experimental results show that our new method keeps the connectivity very well.
July 30, 2001	Matching 3D Models with Shape Distributions
Presented By	Thomas Baby
Comments	This paper by Robert Osada, Thomas Funkhouser, Bernard Chazelle, and David Dobkin from Princeton University was presented at the Shape Modeling International, Genova, Italy in May 2001. It is available online here.
June 4, 2001	A Signal-Processing Framework for Inverse Rendering
Presented By	Zhiyun Li
Comments	This paper from Stanford University (work by Ravi Ramamoorthi and Pat Hanrahan) was published in SIGGRAPH 2001. The full paper is available here.
May 21, 2001	The Randomized z-Buffer Algorithm: Interactive Rendering of Highly Complex Scenes
Presented By	Xuejun Hao
Comments	This paper is by Michael Wand, Matthias Fischer, Ingmar Peter, Friedhelm Meyer auf der Heide, and Wolfgang Straßer, all at the University of Tuebingen, Germany. The paper was published in SIGGRAPH 2001. More information can be found here.
April 23, 2001	Differential Point Rendering
Presented By	Aravind Kalaiah
Comments	This is a dry run of Aravind's presentation at the Eurographics Workshop on Rendering 2001, held on the 26^th of June, 2001 in London, UK. The paper is available online here.
Abstract	We present a novel point rendering primitive, called Differential Point (DP), that captures the local differential geometry in the vicinity of a sampled point. This is a more general point representation that, for the cost of a few additional bytes, packs much more information per point than the traditional point-based models. This information is used to efficiently render the surface as a collection of local neighborhoods. The advantages to this representation are manifold: (1) it delivers a significant reduction in the number of point primitives that represent a surface (2) it achieves a robust hardware accelerated per-pixel shading - even with no connectivity information (3) it offers a novel point-based simplification technique that has a convenient and intuitive interface for the user to efficiently resolve the speed versus quality tradeoff. The number of primitives being equal, DPs produce a much better quality of rendering than a pure splat-based approach. Visual appearances being similar, DPs are about two times faster and require about 75% less disk space in comparison to splatting primitives.
April 2, 2001	First Graphics Lunch at Maryland
Presented By	Amitabh Varshney
Abstract	This is to kick-off the Graphics Lunch at Maryland. We will be discussing the general overview and spirit of this series of lunches as well as talk about other issues of relevance to GVIL such as the state of ongoing projects and equipment acquisition. We will also plan out the shared software testbed for the lab.