The Gaussian sharpen filter has the effect of sharpening an image. It is a convolution that uses a Gaussian kernel to sharpen the image pixels.
You can specify the kernel size (the height and width of the array of pixels to consider) and the Sigma (the standard deviation for the Gaussian function used the calculate the kernel).
Gaussian sharpening can have a dramatic effect on the apparent clarity of the resulting image. However, it can also introduce artifacts that are readily apparent at high levels of magnification. Sharpening cannot correct blurry or out of focus images.