in Computer Vision Image Restoration Inverse Problem ~ read.

Selection of optimal stopping time for nonlinear diffusion filtering

Mrázek, Pavel, and Mirko Navara. "Selection of optimal stopping time for nonlinear diffusion filtering." International Journal of Computer Vision 52.2-3 (2003): 189-203.

very simple idea of choosing the stop time of a filter.

let filter get
observation = image+noise

noise should be independent of the image

question: This assumption seems not ture while the noise is not AWG