Environment Map Emitter

Jiayi Sun

Updated Files

• include/nori/emitter.h
• src/envmap.cpp
• src/direct_mis.cpp
• src/direct_mats.cpp
• src/path_mis.cpp
• src/path_mats.cpp
• src/vol_path_mis.cpp

Implementation

The environment map emitter simulates infinite area lighting using HDR images. It loads the HDR image, precomputes luminance-based importance sampling distributions, and supports transformations for flexible orientation in the scene. For a given direction, the emitter evaluates radiance by mapping the direction to the HDR image and sampling the corresponding pixel. Importance sampling ensures brighter regions of the map contribute more to the lighting, reducing noise in Monte Carlo integration. The implementation is based on PBRT 12.5 Infinite Area Lights.

Validation

We compare out result with Mitsuba3 on an outdoor scene with two spheres with different materials, from left to right: dielectric, diffuse in red albedo and full mirror. The scene is only lit by the environment map emitter.

Compared to Mitsuba3, our implementation shows slightly more noise, though the difference is not significant. Mitsuba uses a Hierarchical2D structure for sampling environment light directions, which combines hierarchical importance sampling to improve sampling efficiency effectively.