Using a Sub Surface Scattering Plugin for a compositing layer in Lightwave
Many newbies and casual 3d artists have a habit of rendering things in one go. This can be one of the reasons that their 3d works seem kind of flat or just lack that edge they look for. Compositing is a skill which anyone 3d artists can learn and should consider when making their 3d art. It's not difficult and can give you alot of control of your final image.
I'm not going to go in depth into compositing but I can give you a simple tip in regards to compositing your sub-surface scattering layer.
There are plugins in many 3d programs these days which allows for Sub-Surface Scattering (SSS) for things like skin and other natural elements. In some cases, it involves a plugin of some kind and no option to render a separate pass for SSS. This can be frustrating if you want to composite your image in post.
In this tutorial, I'm going to show you a quick and cheesy way of doing this. While I will be using Lightwave (and a free plugin called TB Fake skin), it is not too difficult to transfer the technique to another program.
1) In modeller, load up your model which will be getting the SSS treatment. It is most likely that you already have it textured and everything. Make a copy of this model and make all the surfaces into the one surface as it will be easier for your rendering.
Save it out under a different name, preferably under an easy to remember name. EG if your original model name is "head.lwo", name your single surface model "head_alpha.lwo"
2) Make your scene as you usually would with your normal model then make a copy of that scene and save it out under a new name. EG if your original scene name is "head_scene.lwo", name your new scene "head_scene_alpha.lwo"
3) Even though you have your new scene you still have your original model in it (well, duh!). The first change we do is to replace your original model with the single surface version EG use Replace Item on "head.lwo" for "head_alpha.lwo"
4) Once you have your replaced model in your scene, change the surface settings to this:
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Color - RGB = 0,0,0
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5) Click on the Shaders tab and 'add shader'. Scroll down until you find 'TB_fakeskin' (you can get the shader from http://home.att.ne.jp/omega/tabo/3dlabo/p_lwp.html). Double click on the shader text to open the settings for the shader.
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Change the settings to this: Sheen Color - RGB = 255,255,255 Diffuse roughness - 100% |
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Later on, you may want to crank up Ksub and Ksheen to 200% for an alternate SSS alpha which has whiter whites for more control when you composite with it.
6) The other things you need to change are your lights, background and render settings.
The lights should be kept at the settings you want except keep them white. If you want, you can later do separate renders for each light so that you can control the amount of SSS for each light. But, for now, we will stick with the one light set-up, just to keep things simple.
Your background should be changed to completely black with no other things on like HDRI and radiosity. If you can, remove all other objects in the scene that doesn't contain SSS.
Your render settings should be basic like shadows on, Antialiasing to low or medium, etc... Don't change the position or zoom of your camera because it has to match you normal render.
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7) Once you are done, do a render and save the image out. Now, save out your scene and load up the original scene with the original model.
Go to Windows > Backdrop Options and click on the Processing options. Click on 'Add image filter' and select the 'Photoshop PSD export' plugin. Double-click the plugin text to open its settings and click on the layers you want to export. Because this scene is simple, these are the layers I am rendering out:
Raw Color
Alpha
Shadows and Shading
Radiosity
Select where you want the PSD saved and render out your scene.
You could manually render out each layer if you know what you are doing instead of the Photoshop export plugin as you will have better control of your renders, though. For a beginner, I suggest you use the plugin.
8) Now that you have all you components, open up Photoshop and load up the PSD file you jusr rendered. You will need to rearrange the layers because the plugin sets things its own way and it is not always suitable for others.
I like to create a new PSD file and copy and paste all the separate layers in my own way. This is how the layers and opacities are set up for this image (from top to bottom):
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9) Now that your layers are arranged, make a copy of your Raw Color layer, place it above you Raw Color layer and use hue/saturation to give you your SSS shading (or you can have an additional raw colour render with a different texture map. It's what they did for The Hulk. The texture had all veins and sub skin stuff).
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10) Open up your SSS render (the grayscale one you rendered first) and attach it to your new SSS color layer as a layer mask. You may need to invert the mask, though.
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11) You may want to move your SSS colour layer and change its opacity to suit your needs but, basically, that's all there is to it.
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| Before SSS Layer | After SSS Layer |
With this technique you can adjust the contrast or levels of your SSS layer mask to control the level of your SSS. You also have more control of the colour of your SSS for the surface which is better than fiddling with the settings in Lightwave.
You may not immediately notice the effect of the sub surface scattering but it is there. Just switch the SSS layer in Photoshop and you will notice. There is a much more warmer feel to the skin and it will improve your renders.
Anyway, good luck with your 3d art and I hope this tutorial has given you a technique to improve your work.
I hope you enjoyed this tutorial and found it helpful.
Regards,
Mix Mash
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