Fast temporal reprojection without motion vectors

Johannes Hanika, Lorenzo Tessari and Carsten Dachsbacher

Journal of Computer Graphics Techniques, September 2021 (official version).


Rendering realistic graphics often depends on random sampling, increasingly so even for real-time settings. When rendering animations, there is often a surprising amount of information that can be reused between frames. This is exploited in numerous rendering algorithms, offline and real-time, by relying on reprojecting samples, for denoising as a post-process or for more time-critical applications such as temporal antialiasing for interactive preview or real-time rendering. Motion vectors are widely used during reprojection to align adjacent frames’ warping based on the input geometry vectors between two time samples. Unfortunately, this is not always possible, as not every pixel may have coherent motion, such as when a glass surface moves: the highlight moves in a different direction than the surface or the object behind the surface. Estimation of true motion vectors is thus only possible for special cases. We devise a fast algorithm to compute dense correspondences in image space to generalize reprojection-based algorithms to scenarios where analytical motion vectors are unavailable and high performance is required. Our key ingredient is an efficient embedding of patch-based correspondence detection into a hierarchical algorithm. We demonstrate the effectiveness and utility of the proposed reprojection technique for three applications: temporal antialiasing, handheld burst photography, and Monte Carlo rendering of animations.