So help me out here. I'd consider myself an advanced Photoshop user (take lots of NAPP classes, etc.). But that sharpening filter doesn't have many options ..... nothing that allows you to control which tones you want it to apply to. So how do you do that? I mean, I could do it with masks, etc. But is there a straight-forward way?
To add some info to Jeremy's post above:
1. Duplicate your background layer.
2. Do your sharpening on the duplicated layer. Set the sharpening for the important areas. Ignore the areas with shadows and highlights, etc…
3. Double-click on your duplicated layer in the layer palette. This brings up a dialog with many options (first screenshot).
4. Now, play with the two thumbs (see second screenshot) to blend both layers together.
In the example (second screenshot), the duplicated (top) layer will replace the bottom (background) layer from 30 to 86 (it'll be gradual between these two values) and from 87 to 177 (100% replacement), then gradually from 177 to 226. From 227 to 255, the top (duplicated) layer with have no effect.
Use the Option key (or Alt key on a PC) to drag the thumbs and get the gradual effect.
You could also use a layer mask either as a replacement for the above technique or in conjunction with it.
Well, it's harder to describe it with words than to do it…