Modular Radiance Transfer (MRT) is a recent technique for computing approximate direct-to-indirect transport. Scenes are dynamically constructed by warping and connecting simple shapes, and compact transport operators are only precomputed on these simple shapes. MRT ignores fine-scale transport from “clutter” objects inside the scene and computes light transport with reduced dimensional operators, which allows extremely high performance but can lead to significant approximation error. We present several techniques to alleviate this limitation, allowing the light transport from clutter in a scene to be accounted for. We derive additional low-rank delta operators to compensate for these missing light transport paths by modeling indirect shadows and interreflections from, and onto, clutter objects in the scene. We retain MRT’s scene-independent precomputation and augment its scene-dependent initialization with clutter transport generation, resulting in increased accuracy without a performance penalty. Our implementation is simple, requiring a few small matrix-vector multiplications that generate a delta lightmap added to MRT’s output, and does not adversely affect the performance benefits of the overall algorithm.
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