HPRN: Holistic Prior-embedded Relation Network for Spectral Super-Resolution

Spectral super-resolution (SSR) refers to the hyperspectral image (HSI) recovery from an RGB counterpart. Due to the one-to-many nature of the SSR problem, a single RGB image can be reprojected to many HSIs. The key to tackle this illposed problem is to plug into multi-source prior information such as the natural RGB spatial context-prior, deep feature-prior or inherent HSI statistical-prior, etc., so as to improve the confidence and fidelity of reconstructed spectra. However, most current approaches only consider the general and limited priors in their designing the customized convolutional neural networks (CNNs), which leads to the inability to effectively alleviate the degree of ill-posedness. To address the problematic issues, we propose a novel holistic prior-embedded relation network (HPRN) for SSR. Basically, the core framework is delicately assembled by several multi-residual relation blocks (MRBs) that fully facilitate the transmission and utilization of the low-frequency content prior of RGB signals. Innovatively, the semantic prior of RGB input is introduced to identify category attributes and a semantic-driven spatial relation module (SSRM) is put forward to perform the feature aggregation among the clustered similar characteristics using a semantic-embedded relation matrix. Additionally, we develop a transformer-based channel relation module (TCRM), which breaks the habit of employing scalars as the descriptors of channel-wise relations in the previous deep feature-prior and replaces them with certain vectors, together with Transformerstyle feature interactions, supporting the representations to be more discriminative. In order to maintain the mathematical correlation and spectral consistency between hyperspectral bands, the second-order prior constraints (SOPC) are incorporated into the loss function to guide the HSI reconstruction process.