Frequency separation allows you to retouch images by editing one aspect without affecting others. For example, it will allow you to soften the skin while maintaining its texture. Here's a 21-minute video by PiXimperfect on how to use this advanced technique to improve your retouching skills.
Michael Woloszynowicz of Vibrant Shot is back with another share-worthy and thorough tutorial, and this time he's showing you how to fix some of the hair and skin issues that tend to crop up in portraiture.
Here's a great introductory retouching tutorial by photographer Sara Kiesling, who writes,
Basic skin retouching using frequency separation and dodging & burning. I use this process on every photo that I do, and I usually spend about 4-5 minutes on headshots like this (and less time on full body shots when there is obviously less detail in the face). This is not intended to be a high-end retouching tutorial, but techniques that can help people who want to do natural-looking retouching while maintaining most of the natural skin texture!
Frequency separation is a technique that allows you to give skin a smooth-yet-sharp look.