Flash Cache: Reducing Bias in Radiance Cache Based Inverse Rendering

TL;DR

This paper introduces a bias-free, efficient radiance caching method for inverse rendering that improves accuracy and handles complex light effects better than previous biased approaches.

Contribution

It proposes a novel unbiased radiance cache technique using importance sampling and a control variate architecture, enhancing inverse rendering quality and generality.

Findings

Reduces bias in radiance caching for inverse rendering.

Improves rendering quality with complex light transport effects.

Maintains computational efficiency comparable to biased methods.

Abstract

State-of-the-art techniques for 3D reconstruction are largely based on volumetric scene representations, which require sampling multiple points to compute the color arriving along a ray. Using these representations for more general inverse rendering -- reconstructing geometry, materials, and lighting from observed images -- is challenging because recursively path-tracing such volumetric representations is expensive. Recent works alleviate this issue through the use of radiance caches: data structures that store the steady-state, infinite-bounce radiance arriving at any point from any direction. However, these solutions rely on approximations that introduce bias into the renderings and, more importantly, into the gradients used for optimization. We present a method that avoids these approximations while remaining computationally efficient. In particular, we leverage two techniques to reduce variance for unbiased estimators of the rendering equation: (1) an occlusion-aware importance sampler for incoming illumination and (2) a fast cache architecture that can be used as a control variate for the radiance from a high-quality, but more expensive, volumetric cache. We show that by removing these biases our approach improves the generality of radiance cache based inverse rendering, as well as increasing quality in the presence of challenging light transport effects such as specular reflections.