Applying BRDF Monotonicity for Refined Shading Normal Extraction from Multi-Light Image Collections. Eurographics Workshop on Graphics and Cultural Heritage

Multi-Light Image Collections (MLICs) are often transformed into geometric normals and BRDF normals for visual exploration under novel illumination. However, discrepancies between the chosen BRDF space and the complete optical behavior of objects, along with the possible presence of non-local lighting effects in measurements, often lead to sub-optimal visual outcomes even with the most accurate geometric normal recovery. In this paper, we introduce a modular component designed to convert the geometric normals into well-behaved shading normals, under the common and general assumption that the reflectance must be a monotonic function of the angle between the shading normal and the bisector of lighting and viewing directions. Since it does not require the coupling of shape and material estimation, the module allows seamless integration into existing reconstruction pipelines, supporting the mixing and matching of Photometric Stereo methods, BRDF models, and BRDF fitters. The performance and versatility of the approach are demonstrated through experiments.

@InProceedings{PZG24,
  author       = {Pintus, R. and Zorcolo, A. and Gobbetti, E.},
  title        = {Applying BRDF Monotonicity for Refined Shading Normal Extraction from Multi-Light Image Collections. Eurographics Workshop on Graphics and Cultural Heritage},
  booktitle    = {Eurographics Workshop on Graphics and Cultural Heritage},
  month        = {september},
  year         = {2024},
  publisher    = {Eurographics},
  keywords     = {visual computing,cultural heritage},
  doi          = {10.2312/gch20241241},
  url          = {https://publications.crs4.it/pubdocs/2024/PZG24},
}