Sharpening using the High Pass Filter has less chance of creating the unwanted contrast halo often associated with unsharp mask (or similar).
Here's how to do it:
1. Open the original in Photoshop – in this particular case CS3.
2. Duplicate the layer to be sharpened.
3. With the 'Copy' layer selected, go to – Menu Bar>Filter>Other>High Pass.
4. In the High Pass Filter dialog select a radius of between 1.0 to 3.5 – general rule of thumb, the larger the image, the larger the number before ‘distortion’ - then click 'OK'
5. Ensure the 'Copy' layer is highlighted (it should be) and go to Menu Bar>Layer>Layer Style> select Blending Options.
6. In the dialog box General Blending (top) section select Hard Light for the Blend Mode. This will immediately display the resulting image underneath.
7. If the effect is too great it can be reduced using the opacity scale just under Hard Light – or 'Cancel' and return to section 3 (return to the appropriate position in the History palette) and try again.
8. When satisfied go to Menu Bar>Layer>Merge Down (or Flatten Image if there are just the two layers.)
9. The History and Layers palettes should look something like this when finished from the point you started the process.
That is the end of the process. I should recommend creating a series of Actions at High Pass Filter .5 radius intervals, then the process can be fully automated – just select which you think maybe the appropriate level to use.
Words by David Kidd (CaptainTweaky).