Visualization and Editing of Light Transport

Computer graphics nowadays is able to produce stunning photorealistic renderings of complex scenes. Looking closely at an image, we quickly gain insight into the scene’s geometry, and may become aware of the materials used. Many settings of lighting are evident, especially for viewers familiar with computer graphics, yet we are often lacking “the big picture”: why is there a vague shadow or strong caustic? Generally speaking: in what way is light traveling within this scene?

Inspection tools developed for versatile analysis of light transport in virtual scenes. From left to right: (a) false-color rendering, (b) spherical plots, (c) light path inspector, (d) volumetric inspector, (e) particle flow visualization.

Extracting and conveying this information in a meaningful visual way can be of great help for architects, engineers, lighting designers, and maybe even for graphics researchers when working on global illumination methods. Recent work on artistic light manipulation demonstrates that manipulation can only be intuitive when the user easily grasps the phenomena which are modified.

A prototypal manipulation tool for bending caustics generated by a glass bust. The caustics are visualized with our volumetric inspection tool.

Inspection and Manipulation
To this end, we developed tools for a versatile local inspection of light transport in virtual scenes (Fig. 1) as a first step. All these tools were discussed with domain experts, and tested during comprehensive user study. As a consequence, several improvements were added as well as every tool was assessed for suitability for different problems. Besides that, basic light manipulation tools (Fig. 2) were developed to foster the development of more intricate manipulations in the next phase. All tools were implemented as extended objects in Autodesk Maya, which makes it possible using them along with the full infrastructure of a professional Digital Content Creation package.

Efficient Global Illumination
One important, yet expected, feedback about the light inspection tools was that interactivity is of utmost importance. This poses challenging requirements for the computation of light transport which serves as input for the visual inspection and produces the phenomena to be manipulated interactively. Here, we pursue a multi-track strategy: the Maya plug-in builds on photon mapping (also often used in production rendering), where we strive to develop novel progressive density estimation techniques to improve the otherwise low-quality preview rendering.

At the same time, we worked on novel many-lights methods combining implicit and explicit visibility computation for scalable global illumination. And lastly, one focus of our research in this area is the discrete ordinate method (DOM), which discretizes light transport spatially and directionally and thus maps well to modern parallel hardware. We demonstrated that plausible images can be computed in milliseconds, and our next goal is to reduce the problems inherently arising from the discretization, such as memory consumption and inferior accuracy – and ultimately achieve a practical, fast, and high-quality global illumination method for rendering, inspection and manipulation.

 

Project team

Principal Investigator
Prof. Dr.-Ing. Carsten Dachsbacher

Researchers
Anton Kaplanyan
Tim-Christopher Reiner
Stephan Bergmann
Thorsten-Walter Schmidt