Using Pixel Value and Position Data

Sharpening

Sharpening is really a misnamed feature because it doesn't actually increase the image's sharpness. Rather, it increases the accutance, which is the rate of change from a dark area to a bright area. Basically, the software looks at pixels that are close to each other and increases the difference between them if they are within a specified range.

There are a variety of different mathematical algorithms used to achieve this kind of effect, but they all increase the abruptness of a change from light to dark or from one color to another.

In effect, edges are enhanced, potentially bringing back some of the definition lost in scanning.

There are many different sharpening algorithms, using a variety of mathematical techniques and yielding slightly different results. Your image editing software will have information about the algorithms it can use.