Hierarchical Back Projection Network for Image Super-Resolution

Deep learning based single image super-resolution methods use a large number of training datasets and have recently achieved great quality progress both quantitatively and qualitatively. Most deep networks focus on nonlinear mapping from low-resolution inputs to high-resolution outputs via residual learning without exploring the feature abstraction and analysis. We propose a Hierarchical Back Projection Network (HBPN), that cascades multiple HourGlass (HG) modules to bottom-up and top-down process features across all scales to capture various spatial correlations and then consolidates the best representation for reconstruction. We adopt the back projection blocks in our proposed network to provide the error correlated up-and down-sampling process to replace simple deconvolution and pooling process for better estimation. A new Softmax based Weighted Reconstruction (WR) process is used to combine the outputs of HG modules to further improve super-resolution. Experimental results on various datasets (including the validation dataset, NTIRE2019, of the Real Image Super-resolution Challenge) show that our proposed approach can achieve and improve the performance of the state-of-the-art methods for different scaling factors.

1. Introduction

Single Image Super-Resolution (SISR) attracts a lot of attention in the research community in the past few years. It is a fundamental low-level vision problem where the aim is to form a high-resolution (HR) image from a low-resolution (LR) image . Usually, SISR is described as an ill-posed problem , where is a downsampling operator, is additive white Gaussian noise with standard deviation .