DLML: Deep linear mappings learning for face super-resolution with nonlocal-patch

Abstract

Learning-based face super-resolution approaches rely on representative dictionary as self-similarity prior from training samples to estimate the relationship between the low-resolution (LR) and high-resolution (HR) image patches. The most popular approaches, learn mapping function directly from LR patches to HR ones but neglects the multi-layered nature of image degradation process (resolution down-sampling) which means observed LR images are gradually formed from HR version to lower resolution ones. In this paper, we present a novel deep linear mappings learning framework for face super-resolution to learn the complex relationship between LR features and HR ones by alternately updating multi-layered embedding dictionaries and linear mapping matrices instead of directly mapping. Furthermore, in contrast to existing position based studies that only use local patch for self-similarity prior, we develop a feature-induced nonlocal dictionary pair embedding method to support hierarchical multiple linear mappings learning. With coarse-to-fine nature of deep learning architecture, cascaded incremental linear mappings matrices can be used to exploit the complex relationship between LR and HR images. Experimental results demonstrate that such framework outperforms state-of-the-art (including both general super-resolution approaches and face super-resolution approaches) on FEI face database.