Chapter 7:
Exploiting Temporal Coherence in Final Gathering

Abstract

In high quality animation rendering, computationally expensive final gathering technique is commonly used. We extend this technique to the temporal domain by exploiting coherence between the subsequent frames. We store previously computed incoming radiance samples and refresh them evenly in space and time using some aging criteria. The approach is based upon a two-pass photon mapping algorithm with irradiance cache, but it can be also applied in other gathering methods. The algorithm significantly reduces the cost of expensive indirect lighting computation and suppresses temporal aliasing with respect to the state of the art frame-by-frame rendering techniques.

Animations

Scene: BOX

	Full Global Illumination	Only Indirect Illumination
Reference	(ref-movie-1.mpg)	(ref-movie-1-i.mpg)
Our Method	(movie-1.mpg)	(movie-1-i.mpg)

Scene: LIGHT

	Full Global Illumination	Only Indirect Illumination
Reference	(ref-movie-2.mpg)	(ref-movie-2-i.mpg)
Our Method	(movie-2.mpg)	(movie-2-i.mpg)

Scene: ROOM

Reference (ref-movie-3.mpg)
Our Method (movie-3.mpg)
Our Method (The camera is moving) (movie-3-cam.mpg)

Note our method has less flickering in indirect illumination because of exploiting of temporal coherence.

Incoming Radiance Samples

Reference	Our Method
(E-ref.mpg)	(E-age.mpg)

Reference: the frame-by-frame computation
Our Method: 10% of samples is refreshed for each frame according to the aging criterion

Note although our method less frequently resamples directions, incoming radiances used to irradiance evaluation keep similarity with the reference method at each frame.