What is Frequency Separation Technique

A lot of users out there ask me "hey what is this thing called Frequency Separation or Split Frequency, well it’s the process of creating/splitting  your image into color and texture layers. The bottom layer contains the low frequency details (its a blurred version of the image), and above is is a layer that contains the high frequency details. When done correctly they should be identical to the original.

This allows you to edit the two layers separately. I suggest cleaning up with clone/heal and fine details like pores this way it wont affect the details shadows or highlights this comes down to your workflow but that will be a separate post.

You can blur away the details afterwards on the low frequency layer its best to do this on a "blank" layer. This can be called "Band Stop" or paint layer as it removes a band of frequencies. Can be a great help when clearing up blotchy or discolored skin.

You do not have to use Gaussian Blur but its pretty common. You could use Surface Blur, Dust & Scratches, Lens Blur, or any other filter as a base for the separation(I prefer Dust & Scratches).

1. Open up your image in Photoshop.
2. Make 2 copies of the background layer Naming the bottom one "Low" and the upper one "High"
3. Select your Low layer and go to filter Noise and choose dust and scratches. (radius and/or threshold is different for each image)
4. Select your High layer and go to Image - Apply image and depending on whether you are editing a 8 bit or 16 bit image. (check examples)
5. Now set the blending mode of your High layer to Linear light.
6. Now your high and low layer should give you exactly the same as the background layer. Now you can begin to edit your high and low layer separately.
7. Place a transparent Layer in-between both the High and Low layers this will be your non-destructive paint layer.

1. 8 bit image:
2. Layer: low
3. Blending: Subtract
4. Scale: 2
5. Offset: 128

1. 16 bit image:
2. Layer: low
3. Blending: Subtract
4. Scale: 2
5. Offset: 0