Wave-optical phenomena, such as diffraction, significantly impact the visual appearance of surfaces. Despite their importance, wave-optical reflection models are rare and computationally expensive. Recently, we presented a real-time model that accounts for diffraction-induced color shifts and speckle. Given that diffraction phenomena are highly dependent on illumination and viewing directions, as well as stereoscopic vision, we developed a VR demo to evaluate the new model. This demo shows the substantial impact of diffraction on the appearance of rough surfaces, particularly in stereoscopic viewing.

Simulating light–matter interaction is a fundamental problem in computer graphics. A particular challenge is the simulation of light interaction with rough surfaces due to diffraction and multiple scattering phenomena. To properly model these phenomena, wave-optics have to be considered. Nevertheless, the most accurate BRDF models, including wave-optics, are computationally expensive, and the resulting renderings have not been systematically compared to real-world measurements. This work sheds more light on reflectance variations due to surface roughness. More specifically, we look at wavelength shifts that lead to reddish and blueish appearances. These wavelength shifts have been scarcely reported in the literature, and, in this paper, we provide the first thorough analysis from precise measured data. We measured the spectral in-plane BRDF of aluminium samples with varying roughness and further acquired the surface topography with a confocal microscope. The measurements show that the rough samples have, on average, a reddish and blueish appearance in the forward and back-scattering, respectively. Our investigations conclude that this is a diffraction-based effect that dominates the overall appearance of the samples. Simulations using a virtual gonioreflectometer further confirm our claims. We propose a linear model that can closely fit such phenomena, where the slope of the wavelength shifts depends on the incident and reflection direction. Based on these insights, we developed a simple BRDF model based on the Cook–Torrance model that considers such wavelength shifts.