owo_sfm

Tutorial: fake SSS in post (updated for 2020)

Published: October 31st 2020, 8:54:29 pm

A while back I wrote a tutorial covering how I fake subsurface scattering/skin in post for my SFM renders. The tutorial, in retrospect, absolutely sucks. After having to walk someone through the process, not only do I feel like it's very vague in places it shouldn't be, it also encourages some bad habits regarding destructive editing.

This time around, I'm going try to do the same tutorial but better with masks and smart objects. I don't know how compatible these steps are for other programs, but I use photoshop and all images in this tutorial will feature it. If you have a somewhat recent version of photoshop made in the last 6 years or so, smart objects should be there for you.

Lets start with your base render. I'll be using Marie by Wo!262 here with a very quick light setup rendered out at 1080p.

If you're editing the image with post processing or smoothing out edges, MAKE SURE YOU ARE ABSOLUTELY HAPPY WITH ANY EDITS YOU'VE MADE THUS FAR AND DO NOT NEED TO MAKE MORE. Since we're doing this with a duplicate layer, it can be hard to transfer edits over to this new SSS layer.

We'll need to create a layer dedicated solely to the skin. Using the quick select tool, try and select as much of the skin as you can, right click on your image and select Layer via Copy

Be aware that quick select can be pretty crappy at maintaining edges and very bad at keeping shadowed areas of the body, so its a good idea to isolate the layer you just copied and check your results. If you spot any patches, use something like polygon lasso on your renders layer and use Layer Via Copy again to restore them. I'm going to mainly fix up the face for the sake of this tutorial.

Merge those layers once you're done.

now comes the most boring part: you're going to need to remove the background, clothing, hair, eyes and accessories. How you do that is up to you (I use a mix of quick select and lasso). 

This is a very destructive way of doing things, so what we can also do is convert the layer to a smart object BEFORE cleanip, and then adding a mask on afterward. In the layers tab, right click your skin layer and click "Convert to smart object" and add a mask with nothing selected (white square with black circle on the bottom of your layers tab.) 

Make sure your foreground and background colors are B/W with white being font and to clear areas out. If you make a mistake, switch to black. We're going to need to convert to a smart material anyway so whether you do this before or after cleanup is up to you, but I'd highly recommend you set up a mask after converting anyway in case there's parts of the SSS you dont like once its applied.

Once cleaned up and converted to a smart material, right click the skin again on your layers tab and select Blending Options. Disable the green and blue channels. If your characters skin tone is non-human, you may want to experiment until you get a a result close to their skin tone. Sometimes though, just keeping red visible is all you need even in those cases.

Now we can add the surface blur filter:

Unhide the original render layer to see your results.

The values I used aren't the best and you can see some blue fringes on her arms and face, but luckily since we're on a smart object we can simply adjust our values at any time. Double click surface blur on the smart filters layer and adjust your settings.

And if there's an area where the effect looks bad (such as shades of blue on white highlights), you can simply use the mask on the smart object to cleanup. Do be careful if you've previously done background cleanup on this mask, isolate the layer again if need be so you don't accidently reveal it.

We now have something like this! This was done pretty quickly, but a closeup comparison shows what it changes (note the shadows!):

Thank you for reading and let me know if you use it in your own work!