RED-UCATION: A Novel CNN Architecture Based on Denoising Nonlinearities

Image denoising is the most fundamental image enhancement task, and many algorithms have been proposed over the years for its solution. Interestingly, such an image denoising “engine” can be used to solve general inverse problems. Indeed, in our recent work we have presented the Regularization by Denoising (RED) framework: using a denoising engine in defining the regularization of any inverse problem. We have shown how this scheme leads to well-founded iterative algorithms in which the denoiser is applied in each iteration. In this work we describe how a learned version of RED defines a novel convolutional neural network architecture, where the commonly used point-wise nonlinearities are replaced by a denoising engine. We show how this network can be optimized end- to-end using a back - propagation that relies on guided denoising algorithms. As a case-study, we concentrate on the image deblurring problem and show the superiority of the trainable variant of RED over its analytic form.