  Since the proposal of big data analysis and Graphic Processing Unit (GPU),
the deep learning technology has received a great deal of attention and has
been widely applied in the field of imaging processing. In this paper, we have
an aim to completely review and summarize the deep learning technologies for
image denoising proposed in recent years. Morever, we systematically analyze
the conventional machine learning methods for image denoising. Finally, we
point out some research directions for the deep learning technologies in image
denoising.
