Digital photo editing beginners many times misunderstand what the Sharpening tool can do for a photo.
The first thing to remember about sharpening is that it does not concern how good your photo editing program is, you cannot fix what wasn’t already there. There is no amount of sharpening that can fix a bad, fuzzy picture.
If you are unable to fix a bad picture, then what is the point of sharpening at all? The answer to that question lies in how a digital camera or scanner actually captures a picture.
The human eye can see roughly infinite number of shades. Unfortunately, a digital camera cannot. It has to decrease 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 side. The camera has to analyze where two colors touch, and then it has to “guess” at what color the dot in between them is actually supposed to be. Most of the time, it is going to be some average shade between the two colors. This fools the human eye since we see that averaging as fuzziness. Raw digital photos generally look just a little bit out of focus.
Sharpening the picture has a purpose to correct for the guesswork that the camera had to do. The photo-editing program examines the borders between colors, and makes them stand out again. Roughly every picture that comes out of a digital camera would benefit with a little bit of sharpening.
You have to be cautious not to over-sharpen, however. If you zoom in very close, you can see where the sharpening program has put 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 image.