Frequency separation retouching is an amazing technique for separating two main tasks of retouching in general: editing the fine details in your image and editing the tones, shadows and colors. In many cases, it can be hard to get both right at the same time if you are using conventional retouching techniques. If you are using the frequency separation technique in Photoshop, however, you can divide your image into two layers: one that only holds the fine details and one that only contains the tones and colors. Those can then be edited separately and independently of each other.
In this featured video, Aaron Nace from Phlearn.com shows you how to use frequency separation on a portrait in Photoshop.
In a Nutshell
To separate the frequencies in his photo, Aaron does the following:
First, he creates two copies of his image layer. Then he blurs the copy 1 until the fine details disappear from it.
Next, he uses the Apply Image tool (Image > Apply Image) on copy 2 to subtract copy 1 (the blurred layer) from it. This leaves you with only the details because copy 1 does not have any details (blur).
Finally, to create the original look of the image again, he uses the Linear Light blending mode to blend the details layer with the tones and color layer.
In the rest of the video, Aaron shows you how to work with those layers to separate the editing of the fine details from the work on the tones and colors in this very example.