Article Dans Une Revue Computer Graphics Forum Année : 2019

Glint Rendering based on a Multiple‐Scattering Patch BRDF

Résumé

Multiple-scattering glint integrator Chermain et al. [CCM18] Yan et al. [YHMR16] Figure 1: Glittery orb illuminated by an environment map using 1,024 spp. The micro-surface is modeled by a specular normal map with high RMS roughness (σ = 1). Previous methods based on classic normal mapping and single-scattering BRDF evaluations darken the appearance and create black holes (insets and white furnace tests). Importance sampling is suboptimal and causes fireflies. Our new multiple-scattering glint integrator tackles these issues. It produces renderings with no artifacts, and almost passes the white furnace test, for an extra 36% rendering time for this scene. Abstract Rendering materials such as metallic paints, scratched metals and rough plastics requires glint integrators that can capture all micro-specular highlights falling into a pixel footprint, faithfully replicating surface appearance. Specular normal maps can be used to represent a wide range of arbitrary micro-structures. The use of normal maps comes with important drawbacks though: the appearance is dark overall due to back-facing normals and importance sampling is suboptimal, especially when the micro-surface is very rough. We propose a new glint integrator relying on a multiple-scattering patch-based BRDF addressing these issues. To do so, our method uses a modified version of microfacet-based normal mapping [SHHD17] designed for glint rendering, leveraging symmetric microfacets. To model multiple-scattering, we reintroduce the lost energy caused by a perfectly specular, single-scattering formulation instead of using expensive random walks. This reflectance model is the basis of our patch-based BRDF, enabling robust sampling and artifact-free rendering with a natural appearance. Additional calculation costs amount to about 40% in the worst cases compared to previous methods [YHMR16, CCM18].

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hal-02364885 , version 1 (15-11-2019)

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Xavier Chermain, Frédéric Claux, Stephane Merillou. Glint Rendering based on a Multiple‐Scattering Patch BRDF. Computer Graphics Forum, 2019, 38 (4), pp.27-37. ⟨10.1111/cgf.13767⟩. ⟨hal-02364885⟩
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