Frequency Space Environment Map Rendering
We present a new method for real-time rendering of objects with complex isotropic BRDFs under distant natural illumination, as specified by an environment map. Our approach is based on spherical frequency space analysis and includes three main contributions. Firstly, we are able to theoretically analyze required sampling rates and resolutions, which have traditionally been determined in an ad-hoc manner. We also introduce a new compact representation, which we call a spherical harmonic reflection map (SHRM) , for efficient representation and rendering. Finally, we show how to rapidly prefilter the environment map to compute the SHRM ---our frequency domain prefiltering algorithm is generally orders of magnitude faster than previous angular (spatial) domain approaches.
Ravi Ramamoorthi and Pat Hanrahan. "Frequency Space Environment Map Rendering". ACM Transactions on Graphics (Proceedings of SIGGRAPH 2002), 21(3):517 – 526, 2002.