Selected Publications

Abstract: Shadow computation in dynamic scenes under complex illumination is a challenging problem. Methods based on precomputation provide accurate, real-time solutions, but are hard to extend to dynamic scenes. Specialized approaches for soft shadows can deal with dynamic objects but are not fast enough to handle more than one light source. In this paper, we present a technique for rendering dynamic objects under arbitrary environment illumination, which does not require any precomputation. The key ingredient is a fast, approximate technique for computing soft shadows, which achieves several hundred frames per second for a single light source. This allows for approximating environment illumination with a sparse collection of area light sources and yields real-time frame rates.

BibTex:

@article{annen-siggraph2008,
    author = {Annen, Thomas and Dong, Zhao and Mertens, Tom and Bekaert,
              Philippe and Seidel, Hans-Peter and Kautz, Jan},
    title = {Real-Time, All-Frequency Shadows in Dynamic Scenes},
    journal = {ACM Trans. Graph.},
    volume = {27},
    number = {3},
    year = {2008},
    issn = {0730-0301},
    pages = {1--8},
    doi = {http://doi.acm.org/10.1145/1360612.1360633},
    publisher = {ACM},
    address = {New York, NY, USA},
}

Abstract:

Rendering high-quality shadows in real-time is a challenging problem. Shadow mapping has proved to be an efficient solution, as it scales well for complex scenes. However, it suffers from aliasing problems. Filtering the shadow map alleviates aliasing, but unfortunately, native hardware-accelerated filtering cannot be applied, as the shadow test has to take place beforehand. We introduce a simple approach to shadow map filtering, by approximating the shadow test using an exponential function. This enables us to pre-filter the shadow map, which in turn allows for high quality hardware-accelerated filtering. Compared to previous filtering techniques, our technique is faster, consumes less memory and produces less artifacts.

BibTex:

@inproceedings{annen-gi2008-esm,
     author = {Annen, Thomas and Mertens, Tom and Seidel, Hans-Peter 
               and Flerackers, Eddy and Kautz, Jan},
     title = {Exponential Shadow Maps},
     booktitle = {GI '08: Proceedings of graphics interface 2008},
     year = {2008},
     isbn = {978-1-56881-423-0},
     pages = {155--161},
     location = {Windsor, Ontario, Canada},
     publisher = {Canadian Information Processing Society},
     address = {Toronto, Ont., Canada},
}

Abstract:

We describe an approach to define contours of 3D vector fields and employ them as an interactive flow visualization tool. Although contours are well-defined and commonly used for surfaces and 3D scalar fields, they have no straightforward extension in vector fields. Our approach is to extract and visualize specific stream lines which show the most similar behavior to contours on surfaces. This way, the vector field contours are a particular set of isolated stream line segments that depend on the view direction and few additional parameters. We present an analysis of the usefulness of vector field contours by demonstrating their application to linear vector fields. In order to achieve interactive visualization, we develop an efficient GPU-based implementation for real-time extraction and rendering of vector field contours. We show the potential of our approach by applying it to a number of example data sets.

BibTex:

@inproceedings{annen-gi2008-vfc,
     author = {Annen, T. and Theisel, H. and R\"{o}ssl, C. and
               Ziegler, G. and Seidel, H.-P.},
     title = {Vector Field Contours},
     booktitle = {GI '08: Proceedings of graphics interface 2008},
     year = {2008},
     isbn = {978-1-56881-423-0},
     pages = {97--105},
     location = {Windsor, Ontario, Canada},
     publisher = {Canadian Information Processing Society},
     address = {Toronto, Ont., Canada},
}

Abstract:

We present Convolution Shadow Maps, a novel shadow representation that affords efficient arbitrary linear filtering of shadows. Traditional shadow mapping is inherently non-linear w.r.t. the stored depth values, due to the binary shadow test. We linearize the problem by approximating shadow test as a weighted summation of basis terms. We demonstrate the usefulness of this representation, and show that hardware-accelerated anti-aliasing techniques, such as tri-linear filtering, can be applied naturally to Convolution Shadow Maps. Our approach can be implemented very efficiently in current generation graphics hardware, and offers real-time frame rates.

BibTex:

@inproceedings{annen-egsr2007,
    author = {Thomas Annen and Tom Mertens and Philippe Bekaert 
              and Hans-Peter Seidel and Jan Kautz},
    title = {Convolution Shadow Maps},
    booktitle = {Rendering Techniques 2007: Eurographics Symposium on Rendering},
    year = {2007},
    isbn = {978-3-905673-52-4},
    pages = {51--60},
    publisher = {Eurographics},
    address = {Grenoble, France},
}

Abstract:

3D display technology holds great promise for the future of television, virtual reality, entertainment, and visualization. Multiview parallax displays deliver stereoscopic views without glasses to arbitrary positions within the viewing zone. These systems must include a high-performance and scalable 3D rendering subsystem in order to generate multiple views at real-time frame rates. This paper describes a distributed rendering system for large-scale multiview parallax displays built with a network of PCs, commodity graphics accelerators, multiple projectors, and multiview screens. The main challenge is to render various perspective views of the scene and assign rendering tasks effectively. In this paper we investigate two different approaches: Optical multiplexing for lenticular screens and software multiplexing for parallax-barrier displays. We describe the construction of largescale multi-projector 3D display systems using lenticular and parallax-barrier technology. We have developed different distributed rendering algorithms using the Chromium stream-processing framework and evaluate the trade-offs and performance bottlenecks. Our results show that Chromium is well suited for interactive rendering on multiview parallax displays.

BibTex:

@inproceedings{annen-ei2006,
     author = {Annen, Thomas and Matusik, Wojciech and Zwicker, Matthias 
               and Pfister, Hanspeter and Seidel, Hans-Peter},
     title = {Distributed Rendering for Multiview Parallax Displays},
     booktitle = {Proceedings of Stereoscopic Displays and 
                  Virtual Reality Systems XIII},
     year = {2006},
     pages = {231--240},
     location = {San Jose, USA},
     publisher = {SPIE Press},
     address = {San Jose, USA},
}

Abstract:

Global illumination dramatically improves realistic appearance of rendered scenes, but usually it is neglected in VR systems due to its high costs. In this work we present an efficient global illumination solution specifically tailored for those CAVE applications, which require an immediate response for dynamic light changes and allow for free motion of the observer, but involve scenes with static geometry. As an application example we choose the car interior modeling under free driving conditions. We illuminate the car using dynamically changing High Dynamic Range (HDR) environment maps and use the Precomputed Radiance Transfer (PRT) method for the global illumination computation. We leverage the PRT method to handle scenes with non-trivial topology represented by complex meshes. Also, we propose a hybrid of PRT and final gathering approach for high-quality rendering of objects with complex Bi-directional Reflectance Distribution Function (BRDF). We use this method for predictive rendering of the navigation LCD panel based on its measured BRDF. Since the global illumination computation leads to HDR images we propose a tone mapping algorithm tailored specifically for the CAVE. We employ head tracking to identify the observed screen region and derive for it proper luminance adaptation conditions, which are then used for tone mapping on all walls in the CAVE. We distribute our global illumination and tone mapping computation on all CPUs and GPUs available in the CAVE, which enables us to achieve interactive performance even for the costly final gathering approach.

BibTex:

@inproceedings{dmitriev-vrst2004,
     author = {Dmitriev, Kirill and Annen, Thomas and Krawczyk, Grzegorz and 
               Myszkowski, Karol and Seidel, Hans-Peter},
     title = {A CAVE system for interactive modeling of global 
              illumination in car interior},
     booktitle = {VRST '04: Proceedings of the ACM symposium on Virtual 
                  reality software and technology},
     year = {2004},
     isbn = {1-58113-907-1},
     pages = {137--145},
     location = {Hong Kong},
     doi = {http://doi.acm.org/10.1145/1077534.1077560},
     publisher = {ACM},
     address = {New York, NY, USA},
}

Abstract:

Spherical harmonics are often used for compact description of incident radiance in low-frequency but distant lighting environments. For interaction with nearby emitters, computing the incident radiance at the center of an object only is not sufficient. Previous techniques then require expensive sampling of the incident radiance field at many points distributed over the object. Our technique alleviates this costly requirement using a first-order Taylor expansion of the spherical-harmonic lighting coefficients around a point. We propose an interpolation scheme based on these gradients requiring far fewer samples (one is often sufficient). We show that the gradient of the incident-radiance spherical harmonics can be computed for little additional cost compared to the coefficients alone. We introduce a semi-analytical formula to calculate this gradient at run-time and describe how a simple vertex shader can interpolate the shading. The interpolated representation of the incident radiance can be used with any low-frequency light-transfer technique.

BibTex:

@inproceedings{annen-egsr2007,
    author = {Annen, Thomas and Kautz, Jan and Durand, Frédo and 
              Seidel, Hans-Peter},
    title = {Spherical Harmonic Gradients for Mid-Range Illumination},
    booktitle = {Rendering Techniques 2004: Eurographics Symposium on Rendering},
    year = {2004},
    isbn = {3-905673-12-6},
    pages = {331--336},
    publisher = {Eurographics},
    address = {Norrk{\"o}ping, Sweden},
}

Abstract:

We propose a fast, high quality tone mapping technique to display high contrast images on devices with limited dynamic range of luminance values. The method is based on logarithmic compression of luminance values, imitating the human response to light. A bias power function is introduced to adaptively vary logarithmic bases, resulting in good preservation of details and contrast. To improve contrast in dark areas, changes to the gamma correction procedure are proposed. Our adaptive logarithmic mapping technique is capable of producing perceptually tuned images with high dynamic content and works at interactive speed. We demonstrate a successful application of our tone mapping technique with a high dynamic range video player enabling to adjust optimal viewing conditions for any kind of display while taking into account user preference concerning brightness, contrast compression, and detail reproduction.

BibTex:

@inproceedings{drago-eg2003,
    author = {Drago, Frederic and Myszkowski, Karol and 
              Annen, Thomas and Chiba, Norishige},
    editor = {Brunet, Pere and Fellner, Dieter W.},
    title = {Adaptive Logarithmic Mapping For Displaying High Contrast Scenes},
    booktitle = {Proc. of EUROGRAPHICS 2003},
    publisher = {Blackwell},
    year = {2003},
    number = {3},
    volume = {22},
    pages = {419--426},
    series = {Computer Graphics Forum},
    address = {Granada, Spain},
}

Abstract:

In this paper we propose several methods that can greatly improve image quality when using the shadow mapping algorithm. Shadow artifacts introduced by shadow mapping are mainly due to low resolution shadow maps and/or the limited numerical precision used when performing the shadow test. These problems especially arise when the light source’s viewing frustum, from which the shadow map is generated, is not adjusted to the actual camera view. We show how a tight fitting frustum can be computed such that the shadow mapping algorithm concentrates on the visible parts of the scene and takes advantage of nearly the full available precision. Furthermore, we recommend uniformly spaced depth values in contrast to perspectively spaced depths in order to equally sample the scene seen from the light source.

BibTex:

@article{brabec-jgt2003,
    author = {Stefan Brabec and Thomas Annen and Hans-Peter Seidel},
    title = {Practical Shadow Mapping},
    journal = {Journal of Graphics, GPU, and Game Tools},
    volume = {7},
    number = {4},
    pages = {9-18},
    year = {2002},
}

Abstract:

In this paper we present a shadow mapping technique for hemispherical and omnidirectional light sources using dual-paraboloid mapping. In contrast to the traditional perspective projection this parameterization has the benefit that only a minimal number of rendering passes is needed during generation of the shadow maps, making the method suitable for dynamic environments and real time applications. By utilizing programmable features available on state-of-the-art graphics cards we show how the algorithm can be efficiently mapped to hardware.

BibTex:

@inproceedings{Brabec2002:HemiOmni,
  author = {Brabec, Stefan and Annen, Thomas and Seidel, Hans-Peter},
  editor = {Vince, John and Earnshaw, Rae},
  title = {Shadow Mapping for Hemispherical and Omnidirectional Light Sources},
  booktitle = {Advances in Modelling, Animation and Rendering (Proceedings 
               Computer Graphics International 2002)},
  publisher = {Springer},
  year = {2002},
  pages = {397--408},
  address = {Bradford, UK},
  isbn = {1-85233-654-4},
}