Practical Acquisition and Rendering of Diffraction Effects in Surface Reflectance

Abstract

We propose two novel contributions for measurement based rendering of diffraction effects in surface reflectance of planar homogeneous diffractive materials. As a general solution for commonly manufactured materials, we propose a practical data-driven rendering technique and a measurement approach to efficiently render complex diffraction effects in real-time. Our measurement step simply involves photographing a planar diffractive sample illuminated with an LED flash. Here, we directly record the resultant diffraction pattern on the sample surface due to a narrow band point source illumination. Furthermore, we propose an efficient rendering method that exploits the measurement in conjunction with the Huygens-Fresnel principle to fit relevant diffraction parameters based on a first order approximation. Our proposed data-driven rendering method requires the precomputation of a single diffraction look up table for accurate spectral rendering of complex diffraction effects. Secondly, for sharp specular samples, we propose a novel method for practical measurement of the underlying diffraction grating using out-of-focus "bokeh" photography of the specular highlight. We demonstrate how the measured bokeh can be employed as a height field to drive a diffraction shader based on a first order approximation for efficient real-time rendering. Finally, we also drive analytic solutions for a few special cases of diffraction from our measurements and demonstrate realistic rendering results under complex light sources and environments.

Real-time rendering of realistic surface diffraction with low rank factorisation

“…Besides they do not present any rendering in arbitrary environments. In this work the CD is rendered using the lookup table formulation of Toisoul & Ghosh [19] and not Sun et al [18] model. In 2002, Agu [1] proposed an approach to render diffraction produced by a multislit diffraction grating (grating made of periodic rectangles).…”

“…In this work the rendering of diffraction is calculated using the lookup table formulation proposed by Toisoul & Ghosh [19] assuming a first order approximation of Stam's BRDF. The diffractive component of the BRDF in their model is given by equation 1 where F is the Fresnel term and G is Stam's geometric term [17].…”

“…Recently, Toisoul & Ghosh [19] have proposed a measurement method to render diffraction effects in surface reflectance based a first order approximation of Stam's BRDF. They measure the (a) Figure 2: (a) Diffraction of light on a periodic microgeometry.…”

“…They measure the (a) Figure 2: (a) Diffraction of light on a periodic microgeometry. The reflection is wavelength-dependent with the purple colour being reflected at a smaller angle than the red colour [19]. diffraction pattern at a single wavelength with a spectral filter and then compute the diffraction pattern for any light spectrum.…”

“…As a result prefiltering the environment map by the diffraction lobes requires a bigger convolution kernel which makes computations more expensive. Besides, due to the anisotropy the prefiltering step only works for a single orientation of the object [19]. In this work we present a factorisation approach to approximate a 2D diffraction lookup table with an outter product of two low rank matrices.…”