Frequency separation (FS) is still one of the most important, powerful techniques for retouching currently available to photographers. The basic concept is to split high and low detail elements to more easily address things like blemishes and discoloration. In the September issue of Photoshop Proving Ground I add another layer of control.
Traditional FS stops at the detail level, but we can further split the low frequency elements into color and luminosity domains. The steps are a little different, but fortunately very easy to incorporate into current workflows, including automation through actions and panels. By separating color from luminosity, we have better control over each.
The dress on the right is a great demonstration of the power involved.