Boosting Supervised Dehazing Methods via Bi-level Patch Reweighting

Abstract

Natural images can suffer from non-uniform haze distributions in different regions. However, this important fact is hardly considered in existing supervised dehazing methods, in which all training patches are accounted for equally in the loss design. These supervised methods may fail in making promising recoveries on some regions contaminated by heavy hazes. Therefore, for a more reasonable dehazing losses design, the varying importance of different training patches should be taken into account. Such rationale is exactly in line with the process of human learning that difficult concepts always require more practice in learning. To this end, we propose a bi-level dehazing (BILD) framework by designing an internal loop for weighted supervised dehazing and an external loop for training patch reweighting. With simple derivations, we show the gradients of BILD exhibit natural connections with policy gradient and can thus explain the BILD objective by the rewarding mechanism in reinforcement learning. The BILD is not a new dehazing method per se, it is better recognized as a flexible framework that can seamlessly work with general supervised dehazing approaches for their performance boosting.