The sharpen filter has the effect of sharpening an image. It is a convolution that replaces each pixel with a weighted sum of the initial pixel value and its neighbors.
Sharpening can help enhance the edges of objects by improving the contrast of the image. The sharpen filter creates a crisp edge between light and dark parts of the image by darkening the dark pixels and lightening the light pixels. Sharpening cannot correct blurry or out of focus images.