The V-Ray Denoiser takes an existing render and applies a denoising operation to it after the image has been completely rendered out via normal means. The denoising operation detects areas where noise is present and smooths them out. Images can also be denoised using the Standalone Denoise Tool included with the installation of V-Ray for Nuke. For more information on the way the Denoiser works, please see the V-Ray Denoiser page.
