A common misunderstanding about image sharpening is that it can save a blurry or out-of-focus image. It can’t. Sharpening tools can do a lot to enhance your pictures, but don’t try to use it to fix an out-of-focus original.
That said, all images shot digitally, regardless of how well you capture them, usually require some sharpening to match what the lens saw. This is because as light passes through the lens to the sensor and data is converted from analog to digital, some softening occurs. If you’re shooting in JPEG format, sharpening can take place in the camera’s internal-processing software, but additional global and selective sharpening is usually needed, too. If you shoot RAW files, you’ll definitely need to do some sharpening in postprocessing.
What Sharpening Does
Sharpening increases the contrast between light and dark pixels at the edges of objects in your image. In sharp photos, the transition from light to dark happens quickly, over a small area. In soft images,the transition is blurred across a larger area. So by enhancing the difference in tone at the edges of objects in a scene, the image appears sharper.
Keep in mind that you don’t have to sharpen the entire image uniformly. In fact, it’s often better to make this adjustment selectively.
The most practical way to sharpen is simply by adjusting the sharply focused parts of a photo and leaving the rest alone. Depending on the scene, each image requires a different degree of sharpening.
For example, a landscape with fine details will handle more sharpening than a portrait where you want to keep skin tones smooth. So sharpening selectively is often the way to go. If your image has areas that are out of focus, overall sharpening can cause problems because it affects tonal details, and blurry areas tend to look best when left unaltered.
A popular sharpening tool is Unsharp Mask in Photoshop because it allows a great degree of control. It’s found in the Filter menu (Filter > Sharpen > Unsharp Mask). This tool has three sliders. Amount is the top slider, which determines the intensity of the effect and ranges from 1% to 500%. Image resolution influences this setting, with higher-resolution cameras allowing for values as high as 200% or more.