Thorsten-Walther Schmidt
Doctoral Dissertation, Karlsruhe, Germany, 2017
Creating realistic images is an important goal of computer graphics, with applications, among others, in the feature film, architecture, and medical industries. Physically based rendering, which has recently seen wide adoption across fields, refers to the accurate numerical simulation of light transport along the paths prescribed by the model of geometric optics, which is sufficient to achieve photorealism for typical scenes in the aforementioned cases.
Overall, the computer-based authoring of images and animations with well-designed and theoretically sound shading is vastly simplified today. However, taking into account details such as the structure of the output device is important for practical implementations, and, for example, the subdomain of scalable physically based rendering of participating media is far from being a solved problem.
Moreover, image synthesis is only one part of a larger process: the effective communication of ideas and information between people. Be it the shape and function of a building, the medical visualization of a computed tomography scan, or the mood of a movie sequence: messages in the form of reconstructed images are ubiquitous in today’s world. Unfortunately, adoption of the simulation-centered methodology of physically based rendering has also led to a loss of intuitive, fine-grained, and local artistic control over the final image that was present in earlier, less rigorous paradigms.
The contributions of this dissertation cover several aspects of image synthesis, spanning the range from high-quality rendering of finely detailed geometry at the subpixel level, to efficient physically based rendering algorithms for participating media. The main focus of this work, however, are approaches that enable effective visual understanding and artistic manipulation of light transport, while maintaining globally consistent, plausible results. The central idea is that visualization, selection, and editing operations should be performed directly in the space encompassing all possible light paths, as opposed to state-of-the-art methods which either work in image space or are tailored to specific, isolated lighting effects, such as mirror reflections, shadows, or caustics. Testing of the proposed methods has shown them to be effective in solving real-world rendering problems.
Luca Fascione, Johannes Hanika, Marcos Fajardo, Per Christensen, Brent Burley, Brian Green, Rob Pieké, Ryusuke Villemin, Thorsten-Walther Schmidt, Christopher Kulla, Daniel Heckenberg, André Mazzone
Course Contribution, Co-presented at SIGGRAPH 2017, Los Angeles, USA, 2017
Thorsten-Walther Schmidt, Fabio Pellacini, Derek Nowrouzezahrai, Wojciech Jarosz, Carsten Dachsbacher
State of the Art Report, EUROGRAPHICS 2014, Strasbourg, France, 2014
Extended Version, Computer Graphics Forum, 2015
Mimicking the appearance of the real world is a longstanding goal of computer graphics, with several important applications in the feature-film, architecture and medical industries. Images with well-designed shading are an important tool for conveying information about the world, be it the shape and function of a CAD model, or the mood of a movie sequence. However, authoring this content is often a tedious task, even if undertaken by groups of highly-trained and experienced artists. Unsurprisingly, numerous methods to facilitate and accelerate this appearance editing task have been proposed, enabling the editing of scene objects' appearances, lighting, and materials, as well as entailing the introduction of new interaction paradigms and specialized preview rendering techniques. In this STAR we provide a comprehensive survey of artistic appearance, lighting, and material editing approaches. We organize this complex and active research area in a structure tailored to academic researchers, graduate students, and industry professionals alike. In addition to editing approaches, we discuss how user interaction paradigms and rendering backends combine to form usable systems for appearance editing. We conclude with a discussion of open problems and challenges to motivate and guide future research.
Research Article, Computer Graphics Forum, 2013
Presented at Eurographics Symposium on Rendering 2015, Darmstadt, Germany, 2015
Subpixel rendering increases the apparent display resolution by taking into account the subpixel structure of a given display. In essence, each subpixel is addressed individually, allowing the underlying signal to be sampled more densely. Unfortunately, naïve subpixel sampling introduces color aliasing, as each subpixel only displays a specific color (usually R, G, and B subpixels are used). As previous work has shown, chromatic aliasing can be reduced significantly by taking the sensitivity of the human visual system into account. In this work, we find optimal filters for subpixel rendering for a diverse set of 1D and 2D subpixel layout patterns. We demonstrate that these optimal filters can be approximated well with analytical functions. We incorporate our filters into GPU-based multisample antialiasing to yield subpixel rendering at a very low cost (1-2ms filtering time at HD resolution). We also show that texture filtering can be adapted to perform efficient subpixel rendering. Finally, we analyze the findings of a user study we performed, which underpins the increased visual fidelity that can be achieved for diverse display layouts, by using our optimal filters.
Thorsten-Walther Schmidt, Jan Novák, Johannes Meng, Anton S. Kaplanyan, Tim Reiner, Derek Nowrouzezahrai, Carsten Dachsbacher
Research Article, ACM Transactions on Graphics (Proceedings of SIGGRAPH 2013)
Presented at SIGGRAPH 2013, Anaheim, USA, 2013
Industry-quality content creation relies on tools for lighting artists to quickly prototype, iterate, and refine final renders. As industry-leading studios quickly adopt physically-based rendering (PBR) across their art generation pipelines, many existing tools have become unsuitable as they address only simple effects without considering underlying PBR concepts and constraints. We present a novel light transport manipulation technique that operates directly on path-space solutions of the rendering equation. We expose intuitive direct and indirect manipulation approaches to edit complex effects such as (multi-refracted) caustics, diffuse and glossy indirect bounces, and direct/indirect shadows. With our sketch- and object-space selection, all built atop a parameterized regular expression engine, artists can search and isolate shading effects to inspect and edit. We classify and filter paths on the fly and visualize the selected transport phenomena. We survey artists who used our tool to manipulate complex phenomena on both static and animated scenes.
Thorsten-Walther Schmidt, Anton S. Kaplanyan
Talk, Co-presented at FMX 2013, Stuttgart, Germany, 2013
Enabling lighting artists to quickly prototype, iterate and refine a rendered image is essential for industrial-grade content creation, as evidenced by the many lighting tools available. As leading studios are quickly adopting Physically-Based Rendering (PBR) across their art generation pipelines, many of these tools have become unsuitable as they only address simple shading effects without considering the underlying PBR concepts and constraints. We present a novel light manipulation technique that operates directly in a physically based renderer. We expose intuitive direct and indirect manipulation approaches for editing complex shading effects, such as (multi-refracted) caustics, diffuse and glossy indirect illumination, and direct and indirect shadows. With our sketch- and object-based selection, all built atop a parameterized classification, artists can search and isolate effects they wish to inspect and edit. We classify and filter illumination features on the fly (without precomputation) and support the user with a visualization of the selected transport phenomena.
Thomas Engelhardt, Jan Novák, Thorsten-Walther Schmidt, Carsten Dachsbacher
Research Article, Computer Graphics Forum (Proceedings of Pacific Graphics 2012)
Presented at Pacific Graphics 2012, Hong Kong, China, 2012
In this paper we present a novel method for high-quality rendering of scenes with participating media. Our technique is based on instant radiosity, which is used to approximate indirect illumination between surfaces by gathering light from a set of virtual point lights (VPLs). It has been shown that this principle can be applied to participating media as well, so that the combined single scattering contribution of VPLs within the medium yields full multiple scattering. As in the surface case, VPL methods for participating media are prone to singularities, which appear as bright “splotches” in the image. These artifacts are usually countered by clamping the VPLs’ contribution, but this leads to energy loss within the short-distance light transport. Bias compensation recovers the missing energy, but previous approaches are prohibitively costly. We investigate VPL-based methods for rendering scenes with participating media, and propose a novel and efficient approximate bias compensation technique. We evaluate our technique using various test scenes, showing it to be visually indistinguishable from ground truth.