It's important in most photographs that you avoid to sharpen noise unless you have a specific reason to do so. So we should try to focus on Photoshop techniques or third party plug-ins to target what's most important, which is
edges.
I can't say it enough; think twice before you apply any filter or image adjustment to a complete image. I've seen many beginners (but also more experienced users) make this mistake. The main keyword here is:selective, meaning that you only edit what has to be edited by using a selection, quite often this means using a mask. You can find several examples of how to edit in a selective way in two of my other tutorials:
So what does that mean when we want to sharpen an image? In the case of portraits it's important that the eyes are sharp, because that's the main focal point in a face, because unconsciously we always look at the eyes first. On some occasions one might even consider to only sharpen the eyes, again, to make the eyes stand out, to increase the focus on the eyes. It's very simple; sharp eyes are more important than sharpening skin which increased noise.
There are several ways to sharpen an image and although I prefer a professional plug-in like
FocalBlade, I'm quite often also happy with the result of the
High Pass Sharpening technique, which focuses mostly on the edges of an image.
Before I explain this technique, let's first add a layer that contains a merged copy of the image that we want to sharpen and we do this by adding a new layer first on top of all the other layers by clicking on the
Create a new Layer icon

in the layers palette. Rename this layer to
Merged Image.
Now for the magic trick; hold down Ctrl + Alt + Shift + E (Command + Option + Shift + E on the Mac) to merge all visible layers on the active layer (Remember this shortcut, it's a very useful one) or in other words; the layer Merged Image will contain the image that was visible in the document window (the result of all these layers) when you used this shortcut.
Duplicate this layer by clicking on the layer's thumbnail, holding down the mouse button, dragging the mouse cursor to the
Create a new Layer icon

and releasing the mouse button:
This new layer will automatically be the active layer and be named Merged Image copy.
Go to the menu and select Filter / Other / High Pass... Select a value of 1.5 pixels and click OK. The next step is to set the blending mode of this layer to Soft Light:
Click on the
Add Layer Mask icon

to add a mask to this same layer. Press
D on your keyboard to make the fore- and white and the background color black and press
X to make switch both colors; the foreground color should now be black, the background color white.
You can now paint with a soft brush

inside your document window to mask those areas that you don't want to be sharpened and in most cases these will be the areas that contain noise, like skin for example.
Alternative tools for sharpening are of course Photoshop's Unsharp Mask or in CS2: Smart Sharpen. There are however many different sharpening techniques and some of which don't even make use of any sharpening tools. The High Pass Sharpening technique is such an example.
Like I said earlier, FocalBlade (Note: I'm not affiliated with its manufacturer) delivers very good results, especially when it comes to avoiding halos or sharpening noise. Some FocalBlade reviews that confirm the quality of this product:
And here's our final result.
Important: Give your browser enough time to download the "after" image or you won't see any difference
We've reached the end of this tutorial. It has been a long trip but hopefully a useful one. Unlike some other things we do with Photoshop, retouching is quite often
not just a matter of adding 1+1=2, since most corrections have to be done by hand , almost as if we're controlling a brush and this will always
deliver slightly different results. Also the combination of several techniques or tools, for example when we clone something difficult like hair, can lead to an unpredictable outcome. The steps as mentioned in my introduction on page #1 can help you to get more control over retouching, but the main priorities should be; practice and experiment.
Hopefully this tutorial has also taught you the importance of non-destructive editing. Not only have you created an image that is highly organized, but you're also able to make some final adjustments at a later stage. Do understand that non-destructive editing is not the key to everything and there are some pitfalls you will come across.