This page describes the Noise Level render channel and its uses.
Overview
The Noise Level Render Channel shows the level of noise in the scene. Noise Level is available as a separate render element for situations where it would be useful on its own outside of the V-Ray Denoiser, such as for manual denoising or debugging purposes.
In this render element, black areas indicate no noise, white pixels indicate a great deal of noise in that area, and grey pixels indicate a moderate level of noise.
UI Path
||Node Editor|| > Add > Render Channels > Color Channel > Type > Noise Level