P73: Optimizing Spectral Fresnel Reflectance for Displays

Metzgar,J.B., Semwal,S.K.

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 for wide color spaces such as Adobe RGB and DCI P3 which display more color. We present a method to automatically adapt to the color specification which also requires careful attention to using wavelength dependent index of refraction. Metals in particular would normally require a spectral renderer, but we created a way to resample the complex index of refraction and absorptive index that acts like the color filter built in to 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 refraciton. 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 is able to compare five different Fresnel implementations coupled with physically based Blinn-Phong and GGX microfacet models. We demonstrate that with reasonable filter widths, the need for a spectral renderer is eliminated for realtime rendering. Additionally, we utilize publicly available measurement data to simulate a variety of metals ranging from silver, gold, and copper to silicon, lead, and tungsten.