Computer Graphics Techniques for Time-Dependent Lighting
Julie Dorsey
Department of Architecture
MIT
One of the central aspects of the lighting design process is the time- dependent component. New computer graphics techniques that facilitate the interactive design of complex, time-dependent lighting in scenes with fixed geometry will be described. Fast interaction is achieved regardless of scene and lighting complexity, even when used in conjunction with costly rendering techniques such as radiosity and ray tracing.
Techniques will be presented for two application areas: theatrical lighting design and architectural daylighting design. For both areas, time-variant lighting is simulated using linear combinations of static images, each depicting the scene under different lighting conditions.
For theatrical lighting design, multiple levels of accuracy facilitate interactive design by trading image quality for speed in a controlled way. Coarse approximations are used in the preliminary design stage to allow for instantaneous feedback, then the sequence is progressively refined by computing basis solutions in order of increasing overall contribution. When changes to the design are required, existing global solutions are re-used to the greatest extent possible.
For daylighting simulation, the theory of steerable functions provides the machinery to derive a set of basis images that can be combined to generate an image of the scene with the illumination function at any orientation. This enables the fast preview of the interaction of sunlight with architectural scenes over the duration of a typical day.