Unsharp Masking can be used for enhancing images by improving their sharpness. The effect is also called "Local Contrast Enhancement." Here's how the syntax goes:
Technically, we did not introduce a separate operation for Unsharp Masking. Instead, we added the :amount parameter to the blur transformation. Negative :amount combined with reasonably high blur :strength provides the Unsharp Masking behavior.
See how improving local contrast looks like in our docs or read more about Unsharp Masking in this Wikipedia article.