Path-Traced Inverse Rendering with Global Illumination in 3D Gaussian Fields

Ray tracing enables 3D Gaussian fields to serve as a representation for physically based light transport. Faithful inverse rendering requires forward rendering and backward optimization to be defined within a consistent light-transport pipeline. Existing inverse rendering methods estimate G-buffers via splatting and optimize materials in screen space, tying the recovered properties to a rasterization-based pipeline. This pipeline mismatch, together with simplified rendering equations that neglect indirect illumination, often leads to inconsistent shading, visible artifacts, and inaccurate material-lighting estimation under path-traced rendering. Therefore, we propose a splatting-free path-traced inverse rendering framework for 3D Gaussian fields, where forward light transport and backward gradient propagation are defined within a unified ray-tracing pipeline. Our key idea is to define a path-space equivalent interaction model for overlapping Gaussian primitives, under which Monte-Carlo-based path tracing is unbiased for the induced light-transport integral, while pathwise gradients are replayed over the same ray-traced interactions rather than splatting-derived screen-space buffers. The framework optimizes materials and a compact Spherical-Gaussian environment under the full rendering equation with ray-traced visibility and multi-bounce light transport. Extensive experiments demonstrate competitive material inversion and improved path-traced rendering quality, producing more plausible shadows, reflections, and relighting results under global illumination.