Use Split Frequency Healing to Retouch a Photo in Photoshop
Split Frequency Healing is a technique that you can use in Photoshop that will allow you retouch photos without affecting the photo's respective tone or texture. In this tutorial, commercial retoucher, Daniel Meadows, who has worked for clients such as Harper's Bazaar, Elle, Marie Claire, Chanel, and L'Oreal Paris, will explain this technique and how it can be used in your workflow. Let's get started!
Special thanks to Dubai Photographer, Sherif Mokbel for providing the photography for this tutorial.
The following assets were used during the production of this tutorial.
Before You Begin
Let's take a look at the image that we'll be using for this tutorial. Below you'll see a typical example of markup you might receive from a client. It might be a jpeg like this, a scan of a pen-annotated print or simply a set of instructions or suggestions, but ultimately you'll be expected to deliver on a set brief.
We have instructions to clean up the image, a little liquify for a more pleasing curve to the back and waist, and to remove the purple-blue tone from the model's legs. I'll cover the techniques you'll need to complete the shot over the course of several tutorials. Remember not to deviate too far from what your client is asking for, run it by them first. If you think a background color change is really going to make the subject pop, try discussing your ideas, especially if it's for a portfolio project. If it's a commercial or editorial job however and the art director wants neutral white, he or she of course, gets white.
There are quite a few ways to achieve a similar result in Photoshop, and I'll be going through a number of them, often focusing on one in particular and giving a couple of alternatives you might want to try.
The first step we're going to follow in completing this shot is the healing, the 'basic cleanup.' For this we're going to be mostly using the clone stamp (S), but we'll do it a little differently to the way the software intended. Be sure to start off using the key commands for your tools, you'll save yourself a lot of time in the long run. When you're trying to meet an unreasonable deadline and your left hand is bringing up every tool and command without giving it a thought you'll thank me for it. Take a look at the look at the shot we have to work with:
The lighting's a blessing, the well defined shadows and highlights give us a great guide to follow when we come to carving, but we'll get to that. The skin is very good, with just enough marks and texture variance to give us a good run at the exercise. Remember that with high end commercial retouching you're going to be getting professional models with great skin, great lighting, make up, wardrobe etc. It isn't about changing the shot, or the model, it's about perfecting it. Here's a close up of the kind of texture variations I mentioned:
It might be instinctive to head straight for the clone stamp or healing tools, but the clone stamp will carry luminosity and tone with it, causing problems in light to shadow or vice versa. The healing tools carry the texture and then attempt to approximate the tone and luminosity with an algorithm. What if there was a way of cloning nothing but the texture, ignoring the luminosity and tone, and simply replacing a piece of texture elsewhere? Well we've got one, and it's called frequency separation.
Split Frequency Healing
Now we're going to split the image into its low and high frequencies. To get a better idea of what that means, take a look at this blog post regarding the reason for the famous 'Mona Lisa Smile.'
It was very clear to me that when I looked at her mouth, she wasn't smiling as much as when I looked at her eyes.
Da Vinci's Mona Lisa smiles in the blurry low frequency, but not in the high frequency texture. Look directly at the lips in the full image on the left, and then at the shadow that suggests a more pronounced smile in the blurred image to the right:
To split an RGB image into it's low and high frequencies do the following. Create two copies of your background layer (when we've finished the following steps, one will be low, one high, and the original background image is kept for reference).
You'll notice I've renamed them to 'LF' and 'HF.' As you might expect, to achieve the low frequency image, we use a blur. Gaussian Blur the LF layer at a radius of around 15.
The interesting bit is how we turn the HF layer into one that contains only the high frequency data, so we can view it together with the low frequency layer as one composite image. For an 8bit image, select the HF layer, head to Image > Apply Image, and use the following settings:
For 16bit images use the settings in this box:
Hit ok and you'll have an image that looks like this:
In that layer is all the sharp, high frequency texture detail we've been hoping to isolate, against a neutral grey. To tell Photoshop to ignore the unhelpful grey, set the Layer Mode to Linear Light:
Our image should now look like the image below which is indistinguishable from the original (the eagle-eyed amongst you might notice a barely perceptible difference if you look very closely).
If you switch off the Background layer for a moment and toggle the visibility between just the LF and just the HF layers, you'll notice that the image we now have is a true composite, one layer without the other doesn't work.
But together we get the full image. The benefit we have now is that we can clone and heal on just the HF, or 'texture' layer without affecting the tones, and we also have the opportunity to fix tones and luminosity on the LF layer without ever affecting the texture.
Grab your Clone Stamp (S), making sure it is set to 'Current Layer' (we don't want to carry any of the low frequency information onto the texture layer):
And begin to remove any blemishes by Alt (Mac: Opt)-clicking an area of good texture and painting over the areas of poor texture:
As you can see, the overall tone and lighting has remained, with only the texture affected. It's not something we can usually do with the Clone Stamp, and the Healing Brush can fall short.
You may notice that this method fails when dealing with hard edges, and areas where there is a dominant tone beneath the texture, such as the rather extreme example below:
For this reason, it's necessary to start a new layer above your frequency layers, and clone over any problem areas this way. Don't forget to set the Clone Stamp's Sample back to Current & Below.
And here's a close up of the skin after nothing but some careful cloning, 95% of which was done on the high frequency layer:
At this point, we've improved the condition of the model's skin so we don't have to worry about print size, we know the blemishes are gone and for many purposes this is far enough. Not for us of course, in the next tutorial we're going to head into dodging and burning, locally adjusting luminosity to even out tones. Please share and post your comments, and I'll see you soon!