This repository contains an implementation of the paper A Low-Dimensional Function Space for Efficient Spectral Upsampling by Wenzel Jakob and Johannes Hanika.

In comparison to the supplemental material of the original paper that optimized polynomial coefficients using Google's CEPHES solver, the code here relies on a much simpler and self-contained Levenberg–Marquardt solver. Mitsuba and PBRT use a variant of this code that is simply executed as part of the CMake build system.