Professional Skin Retouching in GIMP
In this tutorial I will show you how to use the ‘Frequency Separation’ method for professional skin retouching in GIMP. GIMP is free to download and use on Windows, Mac & Linux systems, and is a good alternative to Photoshop. Download it here.
Let me preface this tutorial by saying that this is not a technique I use in my everyday editing. Fine lines, pores, freckles, skin pigmentation – they are natural, and I do not consider them to be unsightly ‘blemishes’, but rather signs of being human. That said, I am providing this tutorial as there are times when skin retouching is necessary. For example, in wedding photography a bride may have heat rash on her face and neck from nerves leading up to the ceremony; a client may have severe acne scarring that they are self conscious about and would prefer not to have feature in their portrait photographs; you may have recently been on holiday to somewhere hot and humid and succumbed to more than your fair share of mosquito bites (this happened to me recently – I counted more than 50 bites on my legs alone!); or perhaps your subject was simply tired and has dark circles under his or her eyes. There are many reasons for choosing to retouch skin in post, and it is a matter of personal preference whether you as a photographer choose to retouch skin or go for a more minimal and natural approach to post-processing. This tutorial provides the ‘how to’, so that you have the tools at your disposal to retouch skin as and when needed.
There are many tutorials for this technique using the more popular ‘Photoshop’ software, but it is possible to achieve the same results for free using open-source software such as GIMP. I’m a big fan of GIMP. It’s a bit clunky at times but it’s incredibly powerful and brilliant for beginners who don’t want to shell out for a premium subscription to Photoshop.
I have chosen to use a bare faced self-portrait for this tutorial, not out of a love for seeing my own face at 100% magnification, but rather to spare friends and family the ordeal! The process is a little up close and personal, after all.
In order for this tutorial to be effective, I suggest using the largest version of your image that you have at your disposal. I exported my image from Lightroom after post-processing of exposure / tones at 4000px on the long side and then expanded the frame in GIMP (tutorial coming soon). To open an image in GIMP go to ‘File’ and scroll down to ‘Open’.
Zoom in to 100% to see what you will be working on. To do this navigate to ‘View’ – ‘Zoom’ – ‘100%’. In this example, I am working on removing my freckles as a proof of concept.
The Frequency Separation Method of skin retouching involves separating your image into two layers. One of these layers holds the information concerning colour and exposure – for example skin tones, freckles, heat rash, the skin discolouration of insect bites. The second layers holds the ‘texture’ information. For example hair, pores, dry skin, skin texture. By separating the original image into two layers, it is then possible to work on each of these layers separately. This means that you can change the colour of the skin without removing pores and fine lines and vice versa. As a result, your final image will look much more natural. If you have ever seen a portrait image which looks a bit plastic, it is likely the result of skin retouching which has over smoothed the texture layer, removing details such as pores, fine lines and skin texture.
To begin Frequency Separation, duplicate your original image. To duplicate your original image, right click on it in your layers panel (Ctrl + L will bring up your layers panel if it is missing) and navigate to ‘Duplicate Layer’.
This duplicate layer will be your ‘skin’ layer. Many people call the skin layer the ‘low frequency’ layer, as this is the layer that contains colour detail but no texture detail. Rename your layer to something meaningful to you. I have chosen ‘Skin’. Right click on your duplicate layer (called something like Original.jpg copy), and navigate to ‘Edit Layer Attributes’ where you can insert a new name.
Now that we have renamed our low frequency / skin layer, we need to isolate the colour information from the texture information. To do this, we will use the ‘Gaussian Blur’ tool. Please be careful to make sure that you have your skin layer selected in your layers panel (rather than your original layer), and then navigate to ‘Filters’ – ‘Blur’ – ‘Gaussian Blur’.
Make sure that you have the little key chain connected. This means that the Horizontal and Vertical settings are linked and that if you change one setting the other will change too. Select a blur radius of approximately 8px. You can see a preview in the dialogue panel. You don’t want to over blur the skin at this point, as doing so will reduce the information you have available in your ‘texture’ layer.
Now we separate the layers. Select your ‘skin’ layer and navigate in your layers panel to the ‘Mode’ drop down. Select ‘Grain Extract’.
Right click on your ‘skin layer’ and navigate to ‘New from Visible’. This will create a new layer based upon your skin layer.
Change the mode of this new layer to ‘Grain Merge’ in the same way as you did to your skin layer in Step 7. Now reselect your skin layer, and change the blend mode back to ‘Normal’.
Rename your top layer, the layer you created ‘from visible’ to something more meaningful. This is your ‘high frequency’ layer but you may find it more helpful to call it something like ‘Texture’. Follow the instructions in Step 4 to rename your layer.
If you have followed Step 1 – 10, you should now have separated your original image into two layers. To double check, toggle the little eyes in your layers panel. If you deselect them all you will have a blank canvas. You should find that your ‘skin’ layer is blurred and that your ‘texture’ layer is grey with a very crunchy looking outline of your face, pores, wrinkles, hair etc. The bottom layer is your original image. When combined, your skin and texture layer should look identical to your original image. Now we can begin retouching.
In this tutorial I am retouching the ‘skin’ layer and leaving the ‘texture’ layer untouched. There are several tools I will demonstrate in this tutorial that you can use to retouch skin. Feel free to pick and choose the tools which you feel are most appropriate for the areas of skin you need to work on.
The Ellipse Tool Method
Having first made sure that you have selected the ‘skin’ layer in your layers panel, navigate to the Ellipse Select Tool in your tool box (See image 11). This is a good tool to use on the forehead. In ‘Tool Options’ (image 12) make sure that you tick ‘feather edges’ so that you have a soft transition between the blur selection and the rest of your image. You may wish to select a larger blur than you did when creating your ‘skin’ layer in Steps 5 & 6. I opted for a 16px blur but adapt this setting as needed. Again, you can see a preview in the options box.
The Free Select Tool Method
For smaller, irregular areas of the skin it is easier to use the ‘Free Select’ tool than the ‘Ellipse Select’ tool. Again, tick ‘feather edges’ in the Tool Options box. You can select smaller areas of skin this way, and tackle areas such as the nose and under the eyes in small sections.
Rather than going back through the menus each time you need to apply a blur, navigate to ‘Filters’ – ‘Repeat Gaussian Blur’ to quickly repeat your previous blur settings on a new section.
The Clone Tool Method
For individual freckles, blemishes or details, it may be better to use the clone or heal tools. The difference between these two tools is the subtlety with which they are applied. The ‘Clone’ tool will take a perfect sample (of colours on the skin layer and texture on the texture layer) from anywhere on your image and apply it to the location you prescribe. The ‘Heal’ tool will take a sample, and ‘repair’ an area, blending the sample you have selected with the existing colour tones of the prescribed area. In order to apply these tools with an even lighter hand, it is possible to select a softer brush or lower the opacity in the ‘Tool Options’ panel as above (image 15).
To sample skin, press and hold down ‘Ctrl’ on your keyboard (Windows, or the equivalent key on a Mac) and select an area of skin which is a similar shade to the colour you wish to change your patch of skin to. Once you have selected your sample, you may apply it by clicking on the skin where you wish to apply your sample.
The Healing Tool Method
The ‘Healing’ tool is applied in exactly the same way as the ‘Clone’ tool, as set out in the previous two steps. Look for the yellow bandages symbol in your toolbox to find the healing tool.
With all of these tools, it is best to work in small patches. You can change the brush shape, size, opacity in Tool Options at any time whilst you are working. If you make a mistake, simply navigate to ‘Edit’ – ‘Undo’.
A before and after to demonstrate skin retouching of a lightly freckled face.
Once you have finished retouching, you need to flatten your image ready for export. Navigate to ‘Image’ – ‘Flatten Image’.
To export, navigate to ‘File’ and then ‘Export’. Note, if you select ‘Save’ you will save the image as a GIMP file and not a jpeg.