You cannot choose what part of the image is in focus with a point-and-shoot camera.

The approach improves the definition of the edges of an image. They come from a digital camera or a scanner, most images can benefit from the focus operation. The degree of focus required requires the quality function of the digital camera or scanner. Note that the focus cannot correct a very out of focus image.

Tips to improve the approach:

Focus the image in a separate capacity so that you can focus again later if you are going to use a different output medium.

If you focus the image on a separate layer, set the layer's blending mode to Brightness to avoid color variations at the edges.

The focus increases the contrast of the images. If the highlights or shadows appear cropped after focusing, use the layer blending controls (if a separate ability is focused) to avoid focusing on highlights and shadows. See Specifying a tonal range for layer blending.

Reduce the image noise before focusing it, otherwise it will increase the noise level.

Focus the image several times in small quantities. The first time, focus it to correct the blur detected by capturing the image (scanning or taking it with a digital camera). After making color and size corrections, focus the image again (or a copy of it) to add the appropriate amount of focus for the output medium you are going to use.

If possible, use the final output medium to determine the amount of focus needed, as this will affect one output medium to another.