Photography: Diffuse photo techniques ...

David Nightengale on Chromasia posts a useful tip:

In Scott Kelby’s The Photoshop CS Book for Digital Photographers for adding a slightly diffuse effect to an image (used to smooth the skin and hair in this shot).

1) Make two duplicate layers of the main image.
2) Set the blend mode of the first to Darken and Gaussian blur it by 40px.
3) Set the blend mode of the second to Lighten and Gaussian blur it by 60px.
4) Create a blank layer above these two layers, make sure all other layers other than this layer and the two layers you just created are hidden, then merge these three layers (Merge Visible).
5) Set the opacity of this layer to around 30% and unhide your other layers.
6) With a soft brush erase any of the areas of the images you want to be sharp, or use a Layer Mask (with a portrait this would be the eyes, teeth, and so on).

I’ve found this really useful for softening the skin tones in portraits without affecting either the contrast or the colour balance.