Although it may sound paradoxical, you actually can use the Blur filter to sharpen an image. Specifically, you can blur one area of your image to make the other area look sharper. In this task, you intentionally soften the background areas of an image, making the subject appear sharper in comparison. This is a good approach for images that are too soft to be remedied using the Unsharp Mask filter alone.
Open the File in Photoshop
Choose File, Open and select the file you want to modify.
Apply an Unsharp Mask
Begin by sharpening the image as much as you can. Choose Filter, Sharpen, Unsharp Mask and follow the directions in Task 5 to sharpen the image.
Select the Background
Using Photoshop's selection tools, select the area to which you want to apply the blur. For more on making selections in Photoshop, see Part 3, "Selection Techniques." In this example, I've selected the buildings on the right side of the image.
Feather the Selection
Feathering softens the edges of a selection, helping it to blend with unselected areas. Choose Select, Feather. In the Feather Selection dialog box, specify the desired pixel value. The amount of feathering you choose depends on the overall resolution of the image and the subject matter. Click OK to apply the effect.
Apply Gaussian Blur
Choose Filter, Blur, Gaussian Blur to open the Gaussian Blur dialog box. (Gauss was a mathematician; the Gaussian blur effect is based on his mathematical formulas.) Adjust the Radius slider until the proper blur amount appears in the window. Click OK.
Touch Up with the Blur Tool
After deselecting the selection (press +D or Ctrl+D), select the Blur tool from the toolbox and brush in the smaller areas to complete the blur transition.
Don't Overdo It
The blur effect works best when it is subtle and subliminal. Resist the urge to knock the background way out of focus.
Building Up the Blur Effect
In the Options bar for the Blur tool, keep the Pressure setting relatively low so that you can build the effect with multiple brushstrokes. This will give you more control and accuracy.