I am toning a senior portrait right now and am wondering what the best skin smoothing technique is. Think glamor. I know how to take care of blemishes, but I'm looking to enhance that silky skin look.
Whatever method you chose, try and blend as much of the original skin in as possible! I usually try and clean up the original first, by removing as many blemishes as possible with the spot removal tool or similar, and lighting any shadows by dodging and burning.
Then I mask the important areas like the nose, eyes, mouth so they are not affected, and using a duplicate of the original face layer apply a combination of median (to remove the worst imperfections while retaining detail) and gaussian blur (to finish off and hide the subtle edges that median leaves) giving a perfectly smooth result.
Then I add a small amount of monochromatic noise to replicate skin pores and then, importantly, set the opacity of the perfectly smooth layer to no higher than 50%. This ensures that the image does not take on a scary plastic look and retains most of the original character, moles etc. but at a reduced level, in order to get a polished but still very human look.
edit here some examples I've managed to dig out, these are crops of larger images. The first panel is the original, the second is the smoothed layer and the final image is the original plus smoothed layer at 40-45% opacity, I've also included a screenshot showing the mask for the first portrait:
An alternative to post-processing, you could look into either a soft focus lens, which are portrait lenses designed to produce smoother, softer shots when photographing people. If you don't wish to invest in another lens, there are also soft-focus filters from Lee, Cokin, and the like. They are a variety of mesh and net filters, or sometimes special glass and polyester, often with a small port where the key facial features (nose, mouth) can be centered without a lot of softening.
From my own perspective, doctoring skin post-process always seems to produce skin that is too surrealistic or just plain fake. The effects of a soft-focus lens or filter is quite often more pleasing and natural.
For a more automated way, you may want to look at Topaz Detail assuming you use Photoshop. I use it, it's got some nice presets, but also has lots of fine tuning options. They have a free trial for giving it a go.
Note: most of the following apply to photoshop CS.
Work on a duplicate layer
This goes without saying really, but always work on a duplicate layer. If you really overdo the effect, you may be able to simply lower the opacity to get an acceptable result. Also when applying any filters, use of a smart object layer allows you to go back at any later time and change the amount of blur.
Do not try to smooth skin until you've removed major blemishes and wrinkles using a healing brush or other technique. Otherwise you will find you are overdoing the skin softening to cover up these larger blemishes
Apply softening or blur
I find the best results in photoshop come from using Surface Blur. It takes longer but is worth it. You can also use Gaussian blur. Also Topaz Clean has a "SkinEven" filter that does a terrific job.
You'll probably want to slightly overdo the blur, as you can adjust it by lowering the layer opacity. Or better, apply the blur to a smart object layer, then you can return to the blur filter and adjust it.
Apply a Mask
You can start with a black mask and paint in the softening with a white brush, or a quick and easy way to get a good skin mask in photoshop is the following:
See below for an example of the mask
Restore some skin texture
To avoid the "plastic" look, you'll want some skin texture. Two ways to do this:
using noise (per Matt's technique above) add a new layer, fill with 50% grey, add monochromatic noise and set blending mode to overlay or soft light (suggest making this a smart layer so you can adjust noise up/down)
or blend back in some of the original skin texture
duplicate the original skin layer
Sharpen the eyes, lips
To really make the skin look soft, it helps to have everything else sharp. One tip here is to apply the sharpening only to the red channel, as skin areas will tend to be very light in the red channel and sharpening will not have much effect. This is far easier than trying to mask in/out the sharpening effect with a brush:
Here is an example of using Apply Image from the Red Channel and doing a quick levels adjustment. It requires further refinement with a brush, but is an easy way to get a quick mask to start with.
The above steps are a lot easier than it might seem, and you can make it even easier by creating an Action. Then run your action, and all that's left is to go into the masks and tidy them up, and adjust layer opacities to suit.
I may have just answered my own question, though I'm open to more suggestions.
Nice and quick, looks decent.