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Archive republication: This article was originally published on 14 January 2021. It has been translated into English and lightly updated for clarity while preserving the original reporting and context.
This article originally appeared in Digital Production 02 : 2017.
The word “photoshopping” has already entered common parlance, and beauty corrections are also becoming increasingly commonplace in the field of video post-production. When beautifying the skin, there is a central problem: the skin should be smoothed out, but to ensure that the result does not look like a polished wax figure, the fine skin structure should be preserved at the same time. The After Effects script “Skin Retouch” helps with this.
I provide this free of charge at com/skin-re aescripts. – touch free of charge.
No 1-click solution
There are now plenty of beauty retouch plug-ins for After Effects. With “BCC Beauty Studio” from Boris FX, the “Beauty” effect from GenArts Sapphire Collection, “Beauty Box” from Digital Anarchy and “Magic Bullet Cosmo” from Red Giant, pretty much all the major plug-in manufacturers have a corresponding product in their repertoire.
All of these plug-ins offer comprehensive solutions that deliver a finished result in as few clicks as possible. From isolating the skin areas with automated keying or tracking processes to blurring the skin and preserving details, everything is combined in one compact effect.
Skin Retouch splits the image into two layers using Frequency Separation: The high frequencies represent the fine skin structure and similar details, while the low frequencies contain all the remaining image information and look like a blurred version of the original image. These can now be blurred separately or modified in other ways before being recombined for the final result
Skin Retouch takes a different approach here. It is only dedicated to a single, central aspect of digital beauty correction. It splits the image into two layers: one layer containing the details of the fine skin structure and a second containing the remaining image information. The clever thing about this is that both layers together produce the original image again when combined with the appropriate fill method. This means that both parts of the image can be corrected independently of each other and then combined again to produce the final result. In particular, the remaining image can be smoothed without removing the fine structures typical of the skin, so that no details are lost.
The theory: Frequency Separation
Technically speaking, Skin Retouch performs a frequency separation. To explain this in more detail, I need to go into a little more detail. In compositing, it is common to split an image into its individual colour components and apply certain corrections only to the red-green or blue channel of the image.
The basic principle here is that the overall image can be composed from different individual images – one greyscale image for each of the three colours. Frequency Separation breaks down the image in the same way, except that it is not broken down into individual colours, but into individual frequency ranges.
High frequencies mean rapid changes in brightness or colour from one pixel to the next, while low frequencies indicate slow, continuous changes in colour and brightness. Skin Retouch therefore does not divide the image into individual colour channels, but into detail channels: One channel with the fine details (the high frequencies) and another channel with the coarse colour and brightness gradients of the image.
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In this example, I first smoothed out the skin and then used the copy stamp to remove the wrinkles on the forehead. As I only applied the copy stamp to the high frequency part of the image, the skin tone and the shading on the forehead remain unchanged, so that the natural facial expression is retained
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It is also advantageous to remove wrinkles around the eyes with the copy stamp only in the partial image with the high frequencies (shown on the right) so that the natural shading around the eyes is retained.How does such a decomposition work? Mathematically speaking, it is surprisingly simple. An image without the details, i.e. an image with only the low frequencies, can be created with a Gaussian blur. The image with the high frequencies can be created by subtracting the blurred image from the original image.
Flexible corrections
The strength of Skin Retouch lies in the fact that it does not specify a fixed workflow for the corrections. Once the image has been split into high and low frequencies, both parts can be manipulated as required. Blurring the low frequencies to smooth the skin is usually the most important step here, but splitting the image into two partial images can also be very helpful for further subsequent corrections.
An example of this is working with the After Effects copy stamp tool. Spots or other problem areas, for example, are mainly visible in the high frequencies and have already disappeared in the low frequencies after the first simple smoothing. In such cases, it is therefore perfectly sufficient to work with the copy stamp only on the image with the high frequencies and not on the entire original image. This makes working with the copy stamp considerably easier, as the brightness and colour tone of the areas to be corrected are automatically retained. This is because these are not contained in the image with the high frequencies, but are contributed by the image with the low frequencies. For example, structures can be copied from shaded skin areas to brighter areas because they automatically adjust their brightness and colour.
Generally speaking, the strength of Skin Retouch lies in the fact that not all aspects always have to be taken into account at the same time during correction. If a problem is only in one of the two frequency ranges, then only this range needs to be corrected. How exactly the problem is then corrected is left to the user: Skin Retouch only takes care of splitting the image into the different frequencies and reassembling it appropriately after applying all corrections.
Tracking
Unlike in Photoshop, the movement of the image content is an additional factor for beauty corrections in After Effects. While other beauty plug-ins have their own tools on board for this, which can recognise and isolate the skin areas using keying or tracking techniques, Skin Retouch leaves this task entirely to the user. This again shows that Skin Retouch is not a complete solution, but merely simplifies one aspect of beauty correction. When working with Skin Retouch, rotoscoping with Mocha AE can be used to isolate the skin areas.
With my MochaImport tool, the copy stamp can also be moved along with a Mocha track, for example. If you don’t like working with Mocha, you can also use the Face Tracker from After Effects as an alternative, even if it offers significantly fewer features.
Tutorials
I have explained various workflows with Skin Retouch in a five-part, free tutorial series, which is available at mamoworld.com/ after-effects-beautyretouch-tutorials. The first part focuses on the core function of Skin Retouch. The other parts cover various additional aspects of digital beauty correction, such as the above-mentioned work with the copy stamp, but also digital make-up and various tracking methods.
Availability
With the release of Skin Retouch, the Mamoworld team would like to thank all After Effects users. That is why we are making Skin Retouch available free of charge. It can be downloaded at aescripts.com/skin-retouch.
Conclusion
Skin Retouch is not a one-click solution, but these are already available as commercial plug-ins like sand by the sea. In my opinion, Skin Retouch is particularly interesting for two target groups: Occasional users who are looking for a simple beauty retouch workflow without having to invest money in additional plug-ins, and power users for whom the fully automated workflows of other plug-ins do not offer enough flexibility in some situations. Here, Skin Retouch can also be used after the application of other beauty retouch plug-ins to correct any remaining problem areas.
Links
Skin Retouch
aescripts.com/skin-retouch
Skin Retouch Tutorials
https://mamoworld.com/after-effectsbeauty-retouch-tutorials
MochaImport
https://aescripts.com/mochaimport/
