Learning Cross-scale Correspondence and Patch-based Synthesis for Reference-based Super-Resolution

In this paper, we explore the Reference-based Super-Resolution (RefSR) problem, which aims to super-resolve a low definition (LR) input to a high definition (HR) output, given another HR reference image that shares similar viewpoint or capture time with the LR input. We solve this problem by proposing a learning-based scheme, denoted as RefSR-Net. Specifically, we first design a Cross-scale Correspondence Network (CCNet) to indicate the cross-scale patch matching between reference and LR image. The CC-Net is formulated as a classification problem which predicts the correct matches from the candidate patches within the search range. Using dilated convolution, the training and feature map generation are efficiently implemented. Given the reference patch selected via CC-Net, we further propose a Super-resolution image Synthesis Network (SS-Net) for the synthesis of the HR output, by fusing the LR patch and the reference patch at multiple scales. Experiments on MPI Sintel Dataset and Light-Field (LF) video dataset demonstrate our learned correspondence features outperform existing features, and our proposed RefSR-Net substantially outperforms conventional single image SR and exemplar-based SR approaches.