Unsharp masking is an effective enhancement tool to improve the visual quality of fine details in images. However, it also amplifies noisy and over-enhances steep edges. To address this problem, this paper proposes a parametric rational unsharp masking. It utilizes the horizontal and vertical gain factors to enhance image details in two directions independently. Experiments and comparisons are provided to demonstrate its excellent enhancement performance. © 2014 SPIE-IS&T.