Mastering Frequency Separation for Landscape Photography

Frequency separation is a technique used a lot by portrait photographers to clear blemishes from skin. However the technique is also useful for landscape photography.

I learned Frequency Separation for Landscape Photography in Adobe Photoshop and the Photoshop implementation tells you exactly why the technique is so obscure. It is complicated and requires deep technical knowledge to navigate. Affinity Photo has implemented a Frequency Separation Filter which is a whole lot easier to work with.

Video

What is Frequency Separation?

The idea behind frequency separation is that if we separate Color information from Structural (Shape and Texture) we can clone areas of color or structure, separately thus obtaining properly seamless corrections with none of the danger of repeating patterns or badly matched color that comes with using the Clone Tool on its own.

In Affinity photo, the Filter generates two new layers from a pixel layer. The two layers are High Frequency, containing the structural information and Low Frequency, containing the color information. These two layers can be grouped and applied with masks to localise the effect.

What is Frequency Separation Used For?

Portrait Photography

Removal of blemishes from skin

Landscape Photography

• Removing inconsistencies from texture (eg sand) whilst retaining the color.
• Sharpening (Using the High Frequency Layer with a mask
• Orton Effect (Again, using the High Frequency Layer)
• Lens Flare Removal (Cloning in the Low Frequency Layer)

How Frequency Separation Works

I’ve described why it works, but the practicalities of using this technique creatively are still slightly obscure.

As we know, layers in Affinity and Photoshop work from the top down. We use masks to reveal and hide the information in any one layer so if we take a simplistic view, imagine the RAW photo in the base layer. If we create a new layer and apply a Vibrance filter, that vibrance will be applied across the entire layer. We’re still using the base layer to provide the raw information but the color is enhanced in places by the updated information in the new layer.

If we then create a mask on the new layer and paint it black, it conceals all of the information in that new layer and we look straight through to the base layer. If we then apply a white brush to the mask we can selectively “paint in” the areas of the vibrance filter we want to highlight.

Now consider the two layers created by the Frequency Separation Filter. One is texture, the other is color. We can apply corrections to either the texture or the color, independently of one another. This is way better than simply cloning because it avoids the risk of introducing repetitive patterns (structure) into a correction intended to address color. Let’s consider Lens Flare as an example.

Lens Flare Removal

What causes lens flare, is certain frequencies of light bouncing around inside the lens. We see this usually when we shoot into the sun and the lens hood is unable to shield the lens sufficiently. In the photograph it manifests as circular patches of light which looks as though a red, blue or green filter has been applied.

Removing lens flare can sometimes be done with the clone tool but sometimes that is too blunt an instrument. Consider the case of lens flare occurring on the trunk of a tree for example or on a sculpture made from a highly textured material. In both of these cases we more seamlessly retain the patterns in the material, by cloning only the color information from elsewhere in the tree or sculpture.

More complex cases where the flare overlaps several elements of the photography can be treated with a curves tool, using the RGB curves to suppress the color of the flare. This is much more time consuming but sometimes works better than frequency separation.

You can follow this process step by step in the video on this page.