Frequency Separation

Frequency separation is a 'go to' technique used by many photographers for retouching photos, especially portraits.   The technique relies upon the separation of colour or 'tone' from 'detail', allowing each to be edited independently.

Step 1 - Set up
Copy image twice to create two new layers above the original in the Layer Stack 
•Label one immediately above as “Tone” 
•Label top one as “Detail”
•On the Tone layer select Apply Filter  then Gaussian Blur, 15 pixels
•On the Detail layer select Image then Apply Image,

This will open the dialogue box, right.  Enter the following details
 -Layer should be the new Tone layer 
 -Blending should be set to Subtract
 -Scale 2%, Offset 128.

This produces a grey scale copy with just the texture detail

I usually prefer to work on the detail layer first.


Step 2 - Edit the detail 

Select the detail layer

To completely replace any detail, for example removing blemishes, you can use your preferred tool(s); clone, healing, patch, tools etc ensuring your sample area is set to Current layer, to replace the un-wanted detail with detail from the sampled area.

To reduce or completely remove all detail (for example if you specifically want a smooth porcelain skin, devoid of any texture) you can simply paint directly on the layer with a 50% grey brush.

As with the above, any changes made are destructive / baked into the image.

If I want to soften the detail uniformly across the whole image, you simply reduce the opacity of the whole detail layer. I rarely do this unless I specifically want a soft image.

However, if instead of editing the detail layer directly, you apply a layer mask, you can control the amount of softening and where it applies, by paining on the mask with a black brush with low opacity. The darker the mask, the less the detail show. For example if you only paint the skin but not lips, eyes, etc, you can restrict the softening to those areas needing it.

Remember, you can also alter the impact of the mask by changing the opacity of the mask as well as the density of the black painted areas.

Tip: Using a mask is a great way to reduce the prominence of any moles etc, without removing them.

To make the changes to the detail layer visible, change the Blend Mode for that layer to Linear Light.


Step 3 - Edit the tone 

Select the Tone Layer (blurred layer)

This is where you can fix blotchy skin, reduce the prominence of or soften birthmarks, etc or touch up the makeup colour and even completely change it!

To remove blotches, you can use the clone, heal or patch tools ensuring the sample area is set to Current layer. These make changes directly onto the Tone layer and as such are destructive.

An alternate method of reducing blotches is to select an area using a feathered lasso then apply Gaussian Blur to that area. You can repeat to smoothen the colour. This averages out the tones, reducing shadows and bumps giving the skin the appearance of a smoother surface (photoshop Botox).

Care: don’t blur across boundaries of tone changes as this will cause one area to bleed into the other.

To change the colour or tone, non destructively, place another layer above the Tone layer and below the Detail layer. It is important that the blend model for this new layer is set to either Colour or Hue (depending upon the image, one may work better than the other – so I usually try both) then paint on this layer with your chosen colour. I usually do this with a brush at 100% opacity and control the extent of the colour change by altering the opacity of the new layer or using a mask to control its impact. This will change the tone where you paint without changing the contrast or luminosity (which will still be controlled by the underlying tone layer).

Painting over the lip area in blue will for example change the lipstick accordingly. Less extreme examples of use would the to fill gaps in make-up, particularly useful for body painting.

In the same was as you can add layers in between to paint different colours in different areas, you can also apply adjustment layers in between to make global changes to tone, as you would normally.

Finally, if you kept the original image below the added tone and detail layers, using a layer mask on the tone allows you to hide that blurred layer, allowing increasing contrast and apparent detail. I something use to enhance eyelashes / eyebrows.


Step 4 – Optional

Its good housekeeping to place the detail, tone and any added layers in between, together as a group.


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