Sharpen effect

Sharpen filter effect is opposite to Blur filter effect. Still, you cannot return initial sharpness to the image blurred with the help of Blur effect, as algorithms of these functions are different.

Anyway, Sharpen filter does what it is designed to do. It sharpens images and improves their contrast.

Try applying this filter to slightly blurred images. This will clearly show how Sharpen function should be applied.