Single image super-resolution via hybrid resolution NSST prediction

Abstract Convolutional neural networks (CNNs) have achieved great success in single image super-resolution (SR). However, most previous methods predict high-resolution (HR) images in the spatial domain, producing over-smoothed outputs while losing texture details. To address this problem, in this paper we propose to predict nonsubsampled shearlet transform (NSST) coefficients, which better represent the global topology information and local texture details of HR images. On the other hand, we propose a deep hybrid resolution network by a residual-in-residual style, which aggregates features of multiple resolutions so as to gather rich context information in compact representations. When evaluated on a newly released RealSR dataset and traditional simulated datasets, our method, namely hybrid resolution NSST prediction (HRNP), achieves more appealing results, w.r.t. PSNR and SSIM, than the state-of-the-art methods. Moreover, we find our HRNP is more capable of preserving complex edges and curves than other methods.