DehazeNet: An End-to-End System for Single Image Haze Removal
Bolun CaiXiangmin XuKui JiaChunmei QingDacheng Tao
Proposes DehazeNet, an end-to-end convolutional neural network architecture that integrates domain-specific dehazing priors with Maxout units and a Bilateral Rectified Linear Unit activation function to accurately estimate medium transmission maps for single-image restoration.
DehazeNet is a convolutional neural network designed to estimate the medium transmission map directly from a single hazy input image, after which the haze-free output is recovered through the standard atmospheric scattering model. The work addresses the long-standing difficulty of single-image dehazing, an ill-posed inverse problem in which haze thickness depends on unknown and spatially varying scene depth; conventional methods rely on hand-crafted priors that often produce oversaturated skies, fail on dense haze, or require heavy post-processing.
The authors built a four-stage CNN whose layers explicitly mirror established dehazing assumptions: a Maxout feature-extraction stage that can reproduce dark-channel, contrast, color-attenuation and hue-disparity cues; a multi-scale convolutional mapping; a local-extremum pooling layer that enforces spatial constancy of transmission; and a final regression layer using a newly proposed Bilateral Rectified Linear Unit (BReLU) that constrains outputs to the physically valid interval [0,1]. The network was trained end-to-end on 100,000 synthetic 16×16 patches generated from Internet-collected haze-free images by applying the scattering model with random transmission values; it contains only 8,240 parameters and runs at roughly 1.5 seconds per 640×480 image on a standard CPU.
On held-out synthetic patches DehazeNet reduced mean-squared transmission error to 1.19×10^{-2}, outperforming the next-best learning method (Random Forests) by 0.07×10^{-2} and classical priors by larger margins. Across complete synthetic images it recorded the lowest MSE, highest SSIM, PSNR and weighted SNR under varied haze densities, atmospheric colors, image scales and additive noise. On five challenging real-world photographs containing large sky or white regions, the method avoided the oversaturation and color distortion typical of prior-based approaches while still removing haze from foreground objects.
These gains matter because accurate, automatic dehazing improves visibility for consumer photography, surveillance, and downstream vision tasks without requiring multiple exposures, depth sensors or manual tuning. The architecture is already fast enough for practical use and generalizes across haze conditions better than earlier regression models.
Further work should integrate atmospheric-light estimation inside the same network and explore direct learning of the full scattering model so that transmission need not be recovered as an explicit intermediate. The main limitations are reliance on synthetic training data and the assumption that transmission is locally constant; both introduce possible domain-shift risk on real scenes whose statistics differ markedly from the training distribution.
- Paper: Image Super-Resolution Using Deep Convolutional Networks, Chao Dong et al. (2014). Reading SRCNN establishes the foundational approach of mapping low-to-high resolution features using early convolutional networks, which DehazeNet adapts for transmission estimation.
- Paper: Deep Residual Learning for Image Recognition, Kaiming He et al. (2016). ResNet extends DehazeNet's shallow CNN philosophy by introducing deep residual learning to resolve degradation problems across hundreds of layers.
