The standard sharpening techniques like Sharpen, Sharpen Edges and Smart Sharpen are useless when sharpening faces. It works ok with hair, but the last thing you want to do is sharpen skin, especially women's skin. It is the fastest way you will get negative feedback on your images if you over sharpen womens faces. Why do you think there is so much makeup available, it is to soften the skin not give it a crackling effect.
We will be using Unsharp Mask in this tutorial and sharpening an inverted red channel on top of a Luminosity blend mode. Well that is the super condensed summary version. Lets start off with an image I got from Public Domain Pictures. I did not download the full sized image but you can do it yourself and get better results.
Step 1: Open the image you like to edit in RGB mode.
|Unsharpened image of a model. We want to sharpen the hair but not the skin. Image obtained from Public Domain Pictures|
Step 2: Create a duplicate layer background by pressing CTRL-J.
|Create a duplicate layer by pressing CTRL-J. The duplicate layer is visible in the Layers (F7) palette.|
Step 3: With the top layer selected, click on the Channels tab
|Click on the Channels tab and select the red channel|
|Invert the red channel by pressing CTRL-I. Note the change.|
Now don't worry, you still have the original background layer so if you mess this layer up, just delete it and start over. The red channel must still be selected, don't deselect it.
Step 5: Select from the top menu <Filter><Sharpen><Unsharp Mask>
|Apply the settings as shown in the image and press ok when done. It might look a bit radical but relax|
Step 6: Invert the image again by pressing CTRL-I.
Step 7: Select from the top menu <Filter><Sharpen><Unsharp Mask>
|With the red channel inverted AGAIN, apply Unsharp mask but this time with low Amount level and some Threshold|
Step 8: Select layers palette and change top layer blend mode to Luminosity.
|Select the layers palette and change the blend mode to luminosity. Do not deselect the red channel|
You must change the top layer to Luminosity otherwise you will see red highlights throughout the image.
Step 9: Admire your work.
|The top image is the sharpened image. Notice it has more contrast and "pop" in it. The best part is the skin, it has a little more detail and colour, but it is not oversharpened.|