  As an integral component of blind image deblurring, non-blind deconvolution
removes image blur with a given blur kernel, which is essential but difficult
due to the ill-posed nature of the inverse problem. The predominant approach is
based on optimization subject to regularization functions that are either
manually designed, or learned from examples. Existing learning based methods
have shown superior restoration quality but are not practical enough due to
their restricted and static model design. They solely focus on learning a prior
and require to know the noise level for deconvolution. We address the gap
between the optimization-based and learning-based approaches by learning a
universal gradient descent optimizer. We propose a Recurrent Gradient Descent
Network (RGDN) by systematically incorporating deep neural networks into a
fully parameterized gradient descent scheme. A hyper-parameter-free update unit
shared across steps is used to generate updates from the current estimates,
based on a convolutional neural network. By training on diverse examples, the
Recurrent Gradient Descent Network learns an implicit image prior and a
universal update rule through recursive supervision. The learned optimizer can
be repeatedly used to improve the quality of diverse degenerated observations.
The proposed method possesses strong interpretability and high generalization.
Extensive experiments on synthetic benchmarks and challenging real-world images
demonstrate that the proposed deep optimization method is effective and robust
to produce favorable results as well as practical for real-world image
deblurring applications.
