Imperfect shadow maps for efficient computation of indirect illumination

Abstract

We present a method for interactive computation of indirect illumination in large and fully dynamic scenes based on approximate visibility queries. While the high-frequency nature of direct lighting requires accurate visibility, indirect illumination mostly consists of smooth gradations, which tend to mask errors due to incorrect visibility. We exploit this by approximating visibility for indirect illumination with imperfect shadow maps ---low-resolution shadow maps rendered from a crude point-based representation of the scene. These are used in conjunction with a global illumination algorithm based on virtual point lights enabling indirect illumination of dynamic scenes at real-time frame rates. We demonstrate that imperfect shadow maps are a valid approximation to visibility, which makes the simulation of global illumination an order of magnitude faster than using accurate visibility.

Modified filtered importance sampling for virtual spherical Gaussian lights

“…To generate shadow maps for so many lights, Ritschel et al [14] proposed imperfect shadow maps. In their follow-up paper [7], a bidirectional reflective shadow mapping method was introduced to estimate a viewdependent importance for the image-based PDF. This method roughly computes the contribution of light paths from the eye to each reflective shadow map texel, and thus generates dynamic and highfrequency PDFs.…”

“…However, while this approach is simpler and faster than k-means-based VPL clustering [5,6], it does induce flickering structured artifacts due to the previously mentioned overlaps and gaps. This problem is noticeable when a bidirectional reflective shadow mapping method [7] is used to build the PDF. This is because the bidirectional reflective shadow mapping method produces a dynamic and high-frequency PDF.…”

Reciprocal shading for mixed reality

“…However, moving objects cannot influence indirect visibility calculation. In 2008, Ritschel et al [19] introduced the concept of imperfect shadow maps (ISMs). The idea is to represent the scene as a sparse point cloud and use this point cloud to generate a shadow map for every VPL.…”

“…Since VPLs can be placed on real and on virtual objects, we always need two imperfect shadow maps [19].…”

Interactive Volume-Based Indirect Illumination of Dynamic Scenes

“…An extension of this method by the same authors [4] reorganizes the computation of the indirect light to achieve better performance, but it still ignores occlusion for the indirect lighting. Imperfect shadow maps [14] use a point based representation of the scene to efficiently render extremely rough approximations of the shadow maps for all the VPLs in one pass. They achieve interactive frame rates but indirect shadows are smoothed out considerably by the imperfections and the low resolution of the shadow maps.…”