Digital photo editing beginners often misunderstand what the Sharpening tool can do for a photo.
The first thing to remember about Sharpening is this. It doesn't matter how good your photo editing program is, you cannot fix what wasn't already there. No amount of sharpening is going to fix a bad, fuzzy picture.
If you can't fix a bad picture, then what's the point of sharpening at all? The answer to that question lies in how a digital camera or scanner actually takes a picture.
The human eye can see an almost infinite number of shades. Unfortunately, a digital camera can't. It has to reduce the incredible variety of shades it sees into a collection of dots of solid color. You can't have a pixel that's navy blue on one side and sky blue on the other. The camera has to analyze where two colors touch, and then it has to "guess" at what color the dot in between them is really supposed to be. Most of the time, it's going to be some average shade between the two colors. This fools the human eye--because we see that averaging as fuzziness. Raw digital photos often look just a little bit out of focus.
Sharpening the picture is meant to correct for the guesswork that the camera had to do. The photo-editing program analyzes the borders between colors, and makes them stand out again. Nearly every picture that comes out of a digital camera would benefit with a little bit of sharpening.
You have to be careful not to over-sharpen, however. If you zoom in very close, you can see where the sharpening program puts a lighter bit of color between the two shades, to make the border stand out. If you sharpen too much, these light lines will become obvious and distracting "halos" in your picture.
