It's equivalent to the OpenImageDenoise prefiltering option in Cycles. See D12043. Prefilter modes: - None: No prefiltering, use when guiding passes are noise-free. - Fast: Denoise image and guiding passes together. Improves quality when guiding passes are noisy using least amount of extra processing time. - Accurate: Prefilter noisy guiding passes before denoising image. Improves quality when guiding passes are noisy using extra processing time. Reviewed By: #compositing, jbakker, sergey Differential Revision: https://developer.blender.org/D12342