Unsharp masking

Unsharp masking (USM) is an image sharpening technique, often available in digital image processing software.

The "unsharp" of the name derives from the fact that the technique uses a blurred, or "unsharp", negative image to create a mask of the original image. The unsharped mask is then combined with the positive (original) image, creating an image that is less blurry than the original. The resulting image, although clearer, may be a less accurate representation of the image's subject. In the context of signal processing, an unsharp mask is generally a linear or nonlinear filter that amplifies the high-frequency components of a signal.