Frequency Separation with HDR

For a few years frequency separation has been a great way to air brush portraits. I am not a big portrait photographer, I prefer working with landscape and still life more, but as an avid learner of Photoshop I did read up on how this technique works and was happy with its outcome. Recently however I have been using frequency separation for my landscape and architectural work, especially with merged (HDR) images.

Frequency separation allows you to “clean” an image without creating the patchiness or the smudged look you get from using the clone and heal tools. Frequency separation works by separating the low frequency (Colours and light tones) details from High frequency (textures and fine details) details, allowing you to edit them separately. In portraiture this allows you to remove wrinkles without effecting the skin tones and remove blemishes without smudging the skin’s texture.

It is not uncommon in landscape images for there to a be a strange patch of colour, lens flare and with HDR images especially, strange textures appearing in the sky and clouds from too much micro contrast. Recently I was editing a shot that I took in a church in Uniejow that had some issues and I used frequency separation to rescue it.
The picture is a 32bit blended image that was edited in Lightroom. On the front two pews on the right there was a strange chromatic aberration hot spot really killing the image. I tried a few things to remove it and nothing was working. I thought why not whip out the frequency separation workflow and see if it will help. I thought it should work because I would be able to remove the colour cast and then separately remove the edges or the artefact.

I opened the image in Photoshop and duplicated the layer twice. On the second layer (the first duplication layer) I applied a Gaussian Blur of 5 pixels and named the layer blur. This layer is where I will edit the low frequency part of the image.

I clicked on the top layer and named it texture, then went Image-Apply Image; I set the layer to the blur layer, blending to subtract, scale to 2 and offset to 128. Usually when I have finished this step I would change the blending of the layer to Linear light but this was too strong so I switched to Overlay.

This has created frequency separation, if you were to delete the background layer it would make no difference as all the information is now in these two new layers. I added a new layer above blur, with the clone tool I selected a soft brush and set sample to Current and Below. I cloned away the problem areas using the colour at the bottom of the pews.

With the high frequency layer (which I called texture) I duplicated this layer and worked on a copy once again using the clone tool, this time I setting the sample to current layer. The reason I don’t clone on a new layer as I did with the Blur layer, is because it doesn’t work in the same way and just multiplies the intensity of the texture.
As I worked I did switch between them and zoom out to make sure everything looked natural and then zoomed back in.
Click on the before and after images below to see the difference.

After

Before

Once finished, I sharpened the image as the process had softened it slightly (because I used overlay instead of linear light). I also selectively cooled down the pews so that they would fit with the overall tone of the image.  It took about 45mins to clean this area, but if I had used just clone and heal tools or even content aware I feel that the area would look obviously edited whereas here it is hard to notice. I am planning for a future ”before and after forum” post to show this workflow off with portraits as there are some different steps in editing that you can take.

Let me know in the comments what you think of this process, is it something useful for you, is it something you want to give a go?

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