Photoshop's a powerful tool, and while it can do lots of clever stuff, it's not going to be able to rescue out-of-focus or slightly soft images. What it can do though is add clarity and improve how detail is perceived in the image.
While the obvious choice is to use the Sharpening filter in Photoshop, or Auto Sharpen in Elements, you don't get any control over the strength of the sharpening that's applied to your image. Therefore, for more control and better results, your best bet is to use the rather confusingly named Unsharp Mask filter.
The name is a throwback to a traditional film technique, but in essence, the process increases contrast at the edges (typically light and dark areas of the image) in a photograph to improve the impression of sharpness.
Because it requires you to make some decisions about the strength of the sharpening via three slider controls, knowing how much sharpening to give an image is very important. Sharpen too much, and the image will suffer from too much contrast, look unnatural and the edges of the photo will have a halo effect in parts.
To find out how to sharpen the image correctly, and what each slider of the Unsharp Mask filter does to the image, follow our step-by-step guide below.
Sharpening should be the last thing to do before you go to print - so apply all your other image-editing adjustments first. Now go to Filter > Sharpen > Unsharp Mask (Enhance > Unsharp Mask if you're using Elements).
This will bring up a dialogue box, with three sliders: Amount, Radius and Threshold. Let's start off with the Amount slider - this sets the level of contrast between pixels and for high-resolution printing, set to 100%.
Moving on to the Radius, which determines the number of pixels to sharpen around the edges. The higher the number, the greater the amount of pixels affected. This is where over-sharpening can happen - it's recommended not to increase the Radius above 2.
Finally the Threshold. This determines what is an edge pixel - a value of 0 sharpens all pixels in the image, but to avoid over-sharpening in smooth areas in skin tones and clear skies for instance, increase the Threshold to between 2 and 20.