Optimizing spectral fresnel reflectance for displays

Abstract

Approximate equations for rendering Fresnel reflectance abound in computer graphics. We take a fresh approach and consider not only the approximation but the display device as well. The sRGB color standard is finally giving way to wide color spaces such as Adobe RGB and DCI P3 which display more color. We present a preprocessing method to use measured spectral index of refraction data and the color space specification to synthesize an RGB complex index of refraction. Metals, in particular, generally require a spectral renderer, but we created a way to sample the complex index of refraction and absorptive index that acts like the color filter built into the display. Our novel contribution uses a normal distribution centered around the ideal display red, green, and blue wavelengths derived from the CIE xy coordinates and respective white point to window sample the complex index of refraction. We created a WebGL experimental platform that uses the Schlick inspired Lazanyi and Szirmay-Kalos (LSK) multispectral Fresnel approximation coupled with modern physically based BRDFs to simulate the appearance of metal. Our application can compare five different Fresnel implementations coupled with physically based Blinn- Phong and GGX microfacet models. We demonstrate that with reasonable filter widths, we eliminate the need for a spectral renderer for real-time rendering. Additionally, we utilize publicly available measurement data to simulate a variety of metals ranging from silver, gold, and copper to silicon, lead, and zinc.