Generating physically-based sky light probes for photorealistic rendering

Abstract

Image-based lighting (IBL) has become a very popular technique in computer graphics. IBL is a rendering technique that captures lighting information from the real-world and converts it into omni-directional, high-dynamic range images (HDRI) called light probes that are used to illuminate virtual environments. However, the technique requires a high dynamic range (HDR) camera with a specialised setup and is extremely time consuming. This study aims to address cost and time concerns related to IBL by synthetically generating physically-correct light probes. A model for generating the light probes was devised, and simulates the Sun, Moon and stars in terms of their positions, illumination and appearance. The atmosphere is simulated for both the day and night skies and includes scattering by aerosols and molecules, as well as ozone layer contribution. Furthermore, the accuracy of the generated probes was evaluated by comparison to photographs of the real-world. The photographs were captured on the same date, time and geographic location of the light probes and then visually compared to investigate whether they yield similar results. The results showed overall accuracy in the generated probes, both in terms of celestial positions and radiance values. The celestial positions in the light probes were identical to their positions in the real world and the radiance values comparisons matched closely to photographs, except for some minor discrepancies. However, the model can be potentially improved in future work to cater for simulations of more specialised conditions.