Focus

Focus corrector works quite differently from Unsharp Mask. Whereas Unsharp Mask (or Sharpen) filters increase the contrast at the edges of the image, Focus corrector reverses the out-of-focus formula through which the image got blurred. This allows the details to be recovered, whereas with Unsharp Mask it is not possible.

When the image gets out of focus, a point source of light (a small shiny object) becomes a circle of light. The user must specify circle of light radius via corresponding slider (radius).

Smooth slider allows to reduce amount of unwanted artifacts. However it reduces sharpness.

Noise factor slider helps the user to reduce noise effect on the target image, though it reduces sharpness too.

Small preview window helps to adjust this values.

Choose Image > Restoration > Focus Corrector