Real‐time Image‐based Lighting of Microfacet BRDFs with Varying Iridescence

Abstract

Iridescence is a natural phenomenon that is perceived as gradual color changes, depending on the view and illumination direction. Prominent examples are the colors seen in oil films and soap bubbles. Unfortunately, iridescent effects are particularly difficult to recreate in real‐time computer graphics. We present a high‐quality real‐time method for rendering iridescent effects under image‐based lighting. Previous methods model dielectric thin‐films of varying thickness on top of an arbitrary micro‐facet model with a conducting or dielectric base material, and evaluate the resulting reflectance term, responsible for the iridescent effects, only for a single direction when using real‐time image‐based lighting. This leads to bright halos at grazing angles and over‐saturated colors on rough surfaces, which causes an unnatural appearance that is not observed in ground truth data. We address this problem by taking the distribution of light directions, given by the environment map and surface roughness, into account when evaluating the reflectance term. In particular, our approach prefilters the first and second moments of the light direction, which are used to evaluate a filtered version of the reflectance term. We show that the visual quality of our approach is superior to the ones previously achieved, while having only a small negative impact on performance.

A Generalized Ray Formulation For Wave-Optics Rendering

“…Amongst the first to consider wave effects in rendering are Moravec [1981]; Stam [1999]. Later work includes the rendering of iridescent and pearlescent materials [Guillén et al 2020]; diffractive scratches [Velinov et al 2018;Werner et al 2017]; diffractive surface models, with explicit microgeometry [Falster et al 2020;Yan et al 2018] or statistical surface profiles [Holzschuch and Pacanowski 2017;; and, thin-film interference at a soap bubbles [Huang et al 2020] or due to a dielectric layer over a conductor [Belcour and Barla 2017;Kneiphof et al 2019]. Synthesis of BSDFs that account for wave interference was discussed by Toisoul and Ghosh [2017].…”

A general framework for pearlescent materials

“…Several works take into account relevant wave effects including diffraction-aware BSDFs [Dong et al 2015;Falster et al 2020;Holzschuch and Pacanowski 2017;Stam 1999;Toisoul and Ghosh 2017;Werner et al 2017;Yan et al 2018], phase functions (based on Mie scattering) [Frisvad et al 2007;Sadeghi et al 2012], or goniochromatic patterns due to birefringence [Steinberg 2019]. Goniochromatic effects due to electromagnetic interference have been simulated for single-layer thin coatings [Belcour and Barla 2017;Gondek et al 1994;Granier and Heidrich 2003;Kneiphof et al 2019;Smits and Meyer 1992;Sun and Wang 2008], and multiplelayer thin coatings [Hirayama et al 2001;Sun 2006]. In our work we model the scattering in individual iridescent platelets by using multiple thin coatings; however, as opposed to the works by Sun et al and Hirayama et al, we compute the exact reflectance and transmittance at run-time, without any precomputation.…”

Iridescent Reflectance Model for Pāua Shells

“…The growth band model itself utilises a predefined brown color (RGB: [52,40,20]) as the starting point, and works as a Lambertain reflector. The output is given by (4.6).…”

“…Iridescence mainly occurs due to thin film diffraction or diffraction due to microscopic surface structures. Models for thin films [9,10,42,43,44,45], surface diffraction [46,47,48,49,50] and the combination of the two [12,11,51,52,53,54] have been developed for various applications.…”

“…However, this model was not based on rendering sea shells but intended for rendering effects created by oil leaks, soap bubbles and car paints. Later, Kneiphof et al [52] improved upon this method to make it more compatible with real-time rendering, showing that iridescent rendering can be optimised for this space.…”