Ulf Assarsson | Chalmers University of Technology (original) (raw)
Papers by Ulf Assarsson
A K Peters/CRC Press eBooks, Jul 14, 2011
A K Peters/CRC Press eBooks, Apr 19, 2016
arXiv (Cornell University), Mar 3, 2022
We present a method for handling view-dependent information in radiance fields to help with conve... more We present a method for handling view-dependent information in radiance fields to help with convergence and quality of 3D reconstruction. Radiance fields with viewdependence suffers from the so called shape-radiance ambiguity, which can lead to incorrect geometry given a high angular resolution of view-dependent colors. We propose the addition of a difference plane in front of each camera, with the purpose of separating view-dependent and Lambertian components during training. We also propose an additional step where we train, but do not store, a low-resolution view-dependent function that helps to isolate the surface if such a separation is proven difficult. These additions have a small impact on performance and memory usage but enables reconstruction of scenes with highly specular components without any other explicit handling of view-dependence such as Spherical Harmonics.
In this tutorial, we discuss voxel DAGs and multiresolution hierarchies, which are representation... more In this tutorial, we discuss voxel DAGs and multiresolution hierarchies, which are representations that can encode large volumes of data very efficiently. Despite a significant compression ration, an advantage of these structures is that their content can be efficiently accessed in real-time. This property enables various applications. We begin the tutorial by introducing the concepts of sparsity and of coherency in voxel structures, and explain how a directed acyclic graph (DAG) can be used to represent voxel geometry in a form that exploits both aspects, while remaining usable in its compressed from for e.g. ray casting. In this context, we also discuss extensions that cover the time domain or consider an advanced encoding strategies exploiting symmetries and entropy. We then move on to voxel attributes, such as colors, and explain how to integrate such information with the voxel DAGs. We will provide implementation details and present methods for efficiently constructing the DAGs...
A K Peters/CRC Press eBooks, Jul 14, 2011
Figure 1: Scenes rendered with many lights casting shadows at 1920×1080 resolution on an NVIDIA G... more Figure 1: Scenes rendered with many lights casting shadows at 1920×1080 resolution on an NVIDIA Geforce Titan. From the left: HOUSES with 1.01M triangles and 256 lights (23ms), NECROPOLIS with 2.58M triangles and 356 lights (34ms), CRYSPONZA with 302K triangles and 65 lights (16ms).
arXiv (Cornell University), Mar 3, 2022
We present a method for handling view-dependent information in radiance fields to help with conve... more We present a method for handling view-dependent information in radiance fields to help with convergence and quality of 3D reconstruction. Radiance fields with viewdependence suffers from the so called shape-radiance ambiguity, which can lead to incorrect geometry given a high angular resolution of view-dependent colors. We propose the addition of a difference plane in front of each camera, with the purpose of separating view-dependent and Lambertian components during training. We also propose an additional step where we train, but do not store, a low-resolution view-dependent function that helps to isolate the surface if such a separation is proven difficult. These additions have a small impact on performance and memory usage but enables reconstruction of scenes with highly specular components without any other explicit handling of view-dependence such as Spherical Harmonics.
A K Peters/CRC Press eBooks, Apr 27, 2018
Eurographics, 2018
In this tutorial, we discuss voxel DAGs and multiresolution hierarchies, which are representation... more In this tutorial, we discuss voxel DAGs and multiresolution hierarchies, which are representations that can encode large volumes of data very efficiently. Despite a significant compression ration, an advantage of these structures is that their content can be efficiently accessed in real-time. This property enables various applications. We begin the tutorial by introducing the concepts of sparsity and of coherency in voxel structures, and explain how a directed acyclic graph (DAG) can be used to represent voxel geometry in a form that exploits both aspects, while remaining usable in its compressed from for e.g. ray casting. In this context, we also discuss extensions that cover the time domain or consider an advanced encoding strategies exploiting symmetries and entropy. We then move on to voxel attributes, such as colors, and explain how to integrate such information with the voxel DAGs. We will provide implementation details and present methods for efficiently constructing the DAGs and also cover how to efficiently access the data structures with e.g. GPU-based ray tracers. The course will be rounded of with a segment on applications. We highlight a few examples and show their results. Pre-computed shadows are a special application, which will be covered in detail. In this context, we also explain how some of previous ideas contribute to multi-resolution hierarchies, which gives an outlook on the potential generality of the presented solutions.
Symposium on Interactive 3D Graphics and Games
We present a user-guided system for accessible 3D reconstruction and modeling of real-world objec... more We present a user-guided system for accessible 3D reconstruction and modeling of real-world objects using multi-view stereo. The system is an interactive tool where the user models the object on top of multiple selected photographs. Our tool helps the user place quads correctly aligned to the photographs using a multi-view stereo algorithm. This algorithm in combination with user-provided information about topology, visibility, and how to separate foreground from background, creates favorable conditions in successfully reconstructing the object. The user only needs to manually specify a coarse topology which, followed by subdivision and a global optimization algorithm, creates an accurate model with the desired mesh density. This global optimization algorithm has a higher probability of converging to an accurate result than a fully automatic system. With our proposed tool, we lower the barrier of entry for creating high-quality 3D reconstructions of real-world objects with a desirable topology. Our interactive tool separates the most tedious and difficult parts of modeling to the computer, while giving the user control over the most common robustness issues in automatic 3D reconstruction. The provided workflow can be a preferable alternative to using automatic scanning techniques followed by re-topologization.
Proceedings of the ACM on Computer Graphics and Interactive Techniques
Rendering of realistic-looking hair is in general still too costly to do in real-time application... more Rendering of realistic-looking hair is in general still too costly to do in real-time applications, from simulating the physics to rendering the fine details required for it to look natural, including self-shadowing. We show how an autoencoder network, that can be evaluated in real time, can be trained to filter an image of few stochastic samples, including self-shadowing, to produce a much more detailed image that takes into account real hair thickness and transparency.
Shadow generation has been subject to serious investigation in computer graphics, and many clever... more Shadow generation has been subject to serious investigation in computer graphics, and many clever algorithms have been suggested. However, previous algorithms cannot render high quality soft shadows onto arbitrary, animated objects in real time. Pursuing this goal, we present a new soft shadow algorithm that extends the standard shadow volume algorithm by replacing each shadow quadrilateral with a new primitive, called the penumbra wedge. For each silhouette edge as seen from the light source, a penumbra wedge is created that approximately models the penumbra volume that this edge gives rise to. Together the penumbra wedges can render images that often are remarkably close to more precisely rendered soft shadows. Furthermore, our new primitive is designed so that it can be rasterized efficiently. Many real-time algorithms can only use planes as shadow receivers, while ours can handle arbitrary shadow receivers. The proposed algorithm can be of great value to, e.g., 3D computer games...
A K Peters/CRC Press eBooks, Jul 14, 2011
A K Peters/CRC Press eBooks, Apr 19, 2016
arXiv (Cornell University), Mar 3, 2022
We present a method for handling view-dependent information in radiance fields to help with conve... more We present a method for handling view-dependent information in radiance fields to help with convergence and quality of 3D reconstruction. Radiance fields with viewdependence suffers from the so called shape-radiance ambiguity, which can lead to incorrect geometry given a high angular resolution of view-dependent colors. We propose the addition of a difference plane in front of each camera, with the purpose of separating view-dependent and Lambertian components during training. We also propose an additional step where we train, but do not store, a low-resolution view-dependent function that helps to isolate the surface if such a separation is proven difficult. These additions have a small impact on performance and memory usage but enables reconstruction of scenes with highly specular components without any other explicit handling of view-dependence such as Spherical Harmonics.
In this tutorial, we discuss voxel DAGs and multiresolution hierarchies, which are representation... more In this tutorial, we discuss voxel DAGs and multiresolution hierarchies, which are representations that can encode large volumes of data very efficiently. Despite a significant compression ration, an advantage of these structures is that their content can be efficiently accessed in real-time. This property enables various applications. We begin the tutorial by introducing the concepts of sparsity and of coherency in voxel structures, and explain how a directed acyclic graph (DAG) can be used to represent voxel geometry in a form that exploits both aspects, while remaining usable in its compressed from for e.g. ray casting. In this context, we also discuss extensions that cover the time domain or consider an advanced encoding strategies exploiting symmetries and entropy. We then move on to voxel attributes, such as colors, and explain how to integrate such information with the voxel DAGs. We will provide implementation details and present methods for efficiently constructing the DAGs...
A K Peters/CRC Press eBooks, Jul 14, 2011
Figure 1: Scenes rendered with many lights casting shadows at 1920×1080 resolution on an NVIDIA G... more Figure 1: Scenes rendered with many lights casting shadows at 1920×1080 resolution on an NVIDIA Geforce Titan. From the left: HOUSES with 1.01M triangles and 256 lights (23ms), NECROPOLIS with 2.58M triangles and 356 lights (34ms), CRYSPONZA with 302K triangles and 65 lights (16ms).
arXiv (Cornell University), Mar 3, 2022
We present a method for handling view-dependent information in radiance fields to help with conve... more We present a method for handling view-dependent information in radiance fields to help with convergence and quality of 3D reconstruction. Radiance fields with viewdependence suffers from the so called shape-radiance ambiguity, which can lead to incorrect geometry given a high angular resolution of view-dependent colors. We propose the addition of a difference plane in front of each camera, with the purpose of separating view-dependent and Lambertian components during training. We also propose an additional step where we train, but do not store, a low-resolution view-dependent function that helps to isolate the surface if such a separation is proven difficult. These additions have a small impact on performance and memory usage but enables reconstruction of scenes with highly specular components without any other explicit handling of view-dependence such as Spherical Harmonics.
A K Peters/CRC Press eBooks, Apr 27, 2018
Eurographics, 2018
In this tutorial, we discuss voxel DAGs and multiresolution hierarchies, which are representation... more In this tutorial, we discuss voxel DAGs and multiresolution hierarchies, which are representations that can encode large volumes of data very efficiently. Despite a significant compression ration, an advantage of these structures is that their content can be efficiently accessed in real-time. This property enables various applications. We begin the tutorial by introducing the concepts of sparsity and of coherency in voxel structures, and explain how a directed acyclic graph (DAG) can be used to represent voxel geometry in a form that exploits both aspects, while remaining usable in its compressed from for e.g. ray casting. In this context, we also discuss extensions that cover the time domain or consider an advanced encoding strategies exploiting symmetries and entropy. We then move on to voxel attributes, such as colors, and explain how to integrate such information with the voxel DAGs. We will provide implementation details and present methods for efficiently constructing the DAGs and also cover how to efficiently access the data structures with e.g. GPU-based ray tracers. The course will be rounded of with a segment on applications. We highlight a few examples and show their results. Pre-computed shadows are a special application, which will be covered in detail. In this context, we also explain how some of previous ideas contribute to multi-resolution hierarchies, which gives an outlook on the potential generality of the presented solutions.
Symposium on Interactive 3D Graphics and Games
We present a user-guided system for accessible 3D reconstruction and modeling of real-world objec... more We present a user-guided system for accessible 3D reconstruction and modeling of real-world objects using multi-view stereo. The system is an interactive tool where the user models the object on top of multiple selected photographs. Our tool helps the user place quads correctly aligned to the photographs using a multi-view stereo algorithm. This algorithm in combination with user-provided information about topology, visibility, and how to separate foreground from background, creates favorable conditions in successfully reconstructing the object. The user only needs to manually specify a coarse topology which, followed by subdivision and a global optimization algorithm, creates an accurate model with the desired mesh density. This global optimization algorithm has a higher probability of converging to an accurate result than a fully automatic system. With our proposed tool, we lower the barrier of entry for creating high-quality 3D reconstructions of real-world objects with a desirable topology. Our interactive tool separates the most tedious and difficult parts of modeling to the computer, while giving the user control over the most common robustness issues in automatic 3D reconstruction. The provided workflow can be a preferable alternative to using automatic scanning techniques followed by re-topologization.
Proceedings of the ACM on Computer Graphics and Interactive Techniques
Rendering of realistic-looking hair is in general still too costly to do in real-time application... more Rendering of realistic-looking hair is in general still too costly to do in real-time applications, from simulating the physics to rendering the fine details required for it to look natural, including self-shadowing. We show how an autoencoder network, that can be evaluated in real time, can be trained to filter an image of few stochastic samples, including self-shadowing, to produce a much more detailed image that takes into account real hair thickness and transparency.
Shadow generation has been subject to serious investigation in computer graphics, and many clever... more Shadow generation has been subject to serious investigation in computer graphics, and many clever algorithms have been suggested. However, previous algorithms cannot render high quality soft shadows onto arbitrary, animated objects in real time. Pursuing this goal, we present a new soft shadow algorithm that extends the standard shadow volume algorithm by replacing each shadow quadrilateral with a new primitive, called the penumbra wedge. For each silhouette edge as seen from the light source, a penumbra wedge is created that approximately models the penumbra volume that this edge gives rise to. Together the penumbra wedges can render images that often are remarkably close to more precisely rendered soft shadows. Furthermore, our new primitive is designed so that it can be rasterized efficiently. Many real-time algorithms can only use planes as shadow receivers, while ours can handle arbitrary shadow receivers. The proposed algorithm can be of great value to, e.g., 3D computer games...