Frequency Separation is a tool that creates two layers separating the tones in your images from the textures, creating a very powerful method for retouching. By separating the tones from the textures, we can repair places of discolouration and lighting without effecting the textures. We can also remove textures without effecting the tones in the image.
Although this tool is most popular in Portrait photography, it can be used with any type of photography where you want to effect textures and tones in an image separately.
The video below will cover how the Frequency Separation section of the panel works.