Sharpening

1. Open up the desired image in Photoshop

2. Make a duplicate layer

3. Do a high-pass / hard- or soft-light procedure.

4. Select All and Copy Merged

5. Paste the results as the top layer, and hide or remove the layer 
created in step 3.

6. Set the blending mode for the top layer to Luminosity.

7. Merge the two layers