Photographs taken with less-than-ideal exposure settings often display poor
visual quality. Since the correction procedures vary significantly, it is
difficult for a single neural network to handle all exposure problems.
Moreover, the inherent limitations of convolutions, hinder the models ability
to restore faithful color or details on extremely over-/under- exposed regions.
To overcome these limitations, we propose a Macro-Micro-Hierarchical
transformer, which consists of a macro attention to capture long-range
dependencies, a micro attention to extract local features, and a hierarchical
structure for coarse-to-fine correction. In specific, the complementary
macro-micro attention designs enhance locality while allowing global
interactions. The hierarchical structure enables the network to correct
exposure errors of different scales layer by layer. Furthermore, we propose a
contrast constraint and couple it seamlessly in the loss function, where the
corrected image is pulled towards the positive sample and pushed away from the
dynamically generated negative samples. Thus the remaining color distortion and
loss of detail can be removed. We also extend our method as an image enhancer
for low-light face recognition and low-light semantic segmentation. Experiments
demonstrate that our approach obtains more attractive results than
state-of-the-art methods quantitatively and qualitatively.Comment: Accepted by ACM MM 202