Global Illumination in computer graphics is a complex problem concerning the simulation of light traveling through a scene, traditionally approximated with Monte-Carlo methods such as ray- and path-tracing. Monte-Carlo methods typically require a large amount of samples to converge toward the solution, which implies long rendering times that are either uncomfortable, in offline rendering, or unacceptable, in real-time rendering where several frames must be computed per second. Reducing the amount of samples results in noisy images, and the random nature of Monte-Carlo methods means the resulting image is highly sensitive to differences in rendering parameters such as camera- and geometry positions and light sources. In real-time applications such as video games and 3D editing software, approximations that are computationally cheaper must be used to fit within frame-time budgets. This thesis compares two interpolation schemes for screen-space Radiance Cascades with world-space intervals, a novel method of approximating the irradiance at surfaces illuminated by an arbitrary amount of arbitrarily sized light sources, with a fixed set of samples to avoid temporal noise, published research of which is previously limited to 2D. The interpolation schemes are referred to as Bilateral and Min+Max, and were implemented in a DirectX12 based real-time rendering framework, then evaluated in terms of computation time and how image similarity measures compare when using a ray-traced reference image. Bilateral is determined to be marginally faster in all test cases. Image similarity to the reference images is consistently better with Min+Max, though not to the same degree that computation time with Min+Max is longer than with Bilateral. Min-Max also avoids a large class of artifacts exhibited in Bilateral renders that significantly limit the applicability of Bilateral. It is concluded that more development is required to bring screen-space radiance cascades with world-space intervals to a real-time-ready state, and to improve image quality to match contemporary methods. Min+Max may be slower, but the artifacts present when using Bilateral make building upon it infeasible.
David Kaméus (Wed,) studied this question.