Unsupervised Contrastive Masking for Visual Haze Classification

Abstract

Haze classification has gained much attention recently as a cost-effective solution for air quality monitoring. Different from conventional image classification tasks, it requires the classifier to capture the haze patterns of different severity degrees. Existing efforts typically focus on the extraction of effective haze features, such as the dark channel and deep features. However, it is observed that the light-haze images are often mis-classified due to the presence of diverse background scenes. To address this issue, this paper presents an unsupervised contrastive masking (UCM) algorithm to segment the haze regions without any supervision, and develops a dual-channel model-agnostic framework, termed magnifier neural network (MagNet), to effectively use the segmented haze regions to enhance the learning of haze features by conventional deep learning models. Specifically, MagNet employs the haze regions to provide the pixel- and feature-level visual information via three strategies, including Input Augmentation, Network Constraint, and Feature Enhancement, which work as a soft-attention regularizer to alleviates the trade-off between capturing the global scene information and the local information in the haze regions. Experiments were conducted on two datasets in terms of performance comparison, parameter estimation, ablation studies, and case studies, and the results verified that UCM can accurately and rapidly segment the haze regions, and the proposed three strategies of MagNet consistently improve the performance of the state-of-the-art deep learning backbones.