DehazeFlow: Multi-scale Conditional Flow Network for Single Image Dehazing

Single image dehazing is a crucial and preliminary task for many computer vision applications, making progress with deep learning. The dehazing task is an ill-posed problem since the haze in the image leads to the loss of information. Thus, there are multiple feasible solutions for image restoration of a hazy image. Most existing methods learn a deterministic one-to-one mapping between a hazy image and its ground-truth, which ignores the ill-posedness of the dehazing task. To solve this problem, we propose DehazeFlow, a novel single image dehazing framework based on conditional normalizing flow. Our method learns the conditional distribution of haze-free images given a hazy image, enabling the model to sample multiple dehazed results. Furthermore, we propose an attention-based coupling layer to enhance the expression ability of a single flow step, which converts natural images into latent space and fuses features of paired data. These designs enable our model to achieve state-of-the-art performance while considering the ill-posedness of the task. We carry out sufficient experiments on both synthetic datasets and real-world hazy images to illustrate the effectiveness of our method. The extensive experiments indicate that DehazeFlow surpasses the state-of-the-art methods in terms of PSNR, SSIM, LPIPS, and subjective visual effects.