Time coherence in computer animation by ray tracing

Abstract

Raytracing is a powerful, but relatively time consuming technique for realistic image synthesis in computer graphics. Two algorithms are presented accelerating raytracing of animations by considering coherence over time. The look-ahead algorithm avoids repeatingly tracing the same ray for several frames. More precisely, if a ray remains constant over l frames, the look-ahead algorithm does not need more than O(log l) queries into the scene, compared to l queries for the frame-by-frame approach. This type of coherence particularily occurs for a fixed camera, and scenes only partly changing over time. The preprocessing time is increased by a factor 2 compared to the frame-by-frame approach, while space requirements grow by a factor of log f, f the number of frames to be calculated. The frame interpolation algorithm is based on image interpolation using knowledge about the scene. The central algorithmic task is the comparison of two transformed pixel grids which is solved by a modified version of the plane sweep algorithm for line segment intersection reporting. The frame interpolation algorithm is not restricted to fixed cameras, but may lose information against the frame-by-frame approach.

Work was partially supported by DFG (Mu744/1-1).