  Currently, to further improve visual enjoyment, Ultra-High-Definition (UHD)
images are catching wide attention. Here, UHD images are usually referred to as
having a resolution greater than or equal to $3840 \times 2160$. However, since
the imaging equipment is subject to environmental noise or equipment jitter,
UHD images are prone to contrast degradation, blurring, low dynamic range, etc.
To address these issues, a large number of algorithms for UHD image enhancement
have been proposed. In this paper, we introduce the current state of UHD image
enhancement from two perspectives, one is the application field and the other
is the technology. In addition, we briefly explore its trends.
