Tweet
Fake SSS Tutorial.
Hey everyone, got some free time between the projects and decided to share some of the techniques I have developed to overcome some of the serious issues when rendering subscattering surfaces in vray.
One can ask why would you need to have fake sss in vray? since vray is fast with it and can handle pretty much any set of surfaces with sss/glossy and etc.
Answer is, that true way is always correct but sometimes not right for you purpose or shot. In my case I have come across this when rendering heavy displaced surfaces and sss. The render times were already heavy enough, and by adding sss the render times went from 2 hours per frame to 25 hours per frame.
So I was forced to come up with alternate way, which gave us satisfactory result. I have to say that fake sss is nowhere near as good as true sss, but it might just do the trick in desperate times.
So here is the effect we'r after the sss box with directional light hitting it. GI and vray light.
To achieve this we will render 2 baked versions of sss. Brighter and darker one.
The idea is to bake SSS uv's and the apply them thru a blend map. So make sure your model has layed out uv's which do not overlap since vray will render artifacted surfaces if they do. We will also need to create vray dome light, since we need the sss to illuminate all of the surface at one time for single bake. Create a dome light with no decay checked and intensity of 1. Subdvis 24, qmc sampler noise 0.002 global subdivs 4 so we get lesser noise.
Render pass 1 with birght sss settings in vray mat mainly light multiplier at 4.0 and 2nd pass with light multiplier at 3.
once the 2 passes are rendered you can create your shader:
Shader would be simple standard mat with FallOff map in shadow/light mode blending between dark sss map and bright sss map. To get a sharper fall of blend like on true sss I will make the fall of blend curve is S shaped form. Where the white value will dominate ontop and darker on the bottom.
Now we compare the true sss with gi and fake sss with gi and their light interaction.
http://www3.telus.net/public/vinnik8...S_TUT/SSS_.mov
As you can see the shader behaves similar to the true sss, where its brighter/darker in necessary areas.
Now we take step ahead and try this with displaced surface. For this to work, we will need to rebake sss maps with displacement on. Since vray displacement doesnt work too well with baking, I will use standard displacement with high tessellation.
Once the maps are baked we apply them back and do another test render.
http://www3.telus.net/public/vinnik8.../SSS_DISPL.mov
Here is when the delema comes in:
By applying baked map we gain render time segnificantly, but lose sss's true precision of scattering light in the edges of the object. However I think its a small price to pay when you are stuck and cannot use true sss at all.
Hey everyone, got some free time between the projects and decided to share some of the techniques I have developed to overcome some of the serious issues when rendering subscattering surfaces in vray.
One can ask why would you need to have fake sss in vray? since vray is fast with it and can handle pretty much any set of surfaces with sss/glossy and etc.
Answer is, that true way is always correct but sometimes not right for you purpose or shot. In my case I have come across this when rendering heavy displaced surfaces and sss. The render times were already heavy enough, and by adding sss the render times went from 2 hours per frame to 25 hours per frame.
So I was forced to come up with alternate way, which gave us satisfactory result. I have to say that fake sss is nowhere near as good as true sss, but it might just do the trick in desperate times.
So here is the effect we'r after the sss box with directional light hitting it. GI and vray light.
To achieve this we will render 2 baked versions of sss. Brighter and darker one.
The idea is to bake SSS uv's and the apply them thru a blend map. So make sure your model has layed out uv's which do not overlap since vray will render artifacted surfaces if they do. We will also need to create vray dome light, since we need the sss to illuminate all of the surface at one time for single bake. Create a dome light with no decay checked and intensity of 1. Subdvis 24, qmc sampler noise 0.002 global subdivs 4 so we get lesser noise.
Render pass 1 with birght sss settings in vray mat mainly light multiplier at 4.0 and 2nd pass with light multiplier at 3.
once the 2 passes are rendered you can create your shader:
Shader would be simple standard mat with FallOff map in shadow/light mode blending between dark sss map and bright sss map. To get a sharper fall of blend like on true sss I will make the fall of blend curve is S shaped form. Where the white value will dominate ontop and darker on the bottom.
Now we compare the true sss with gi and fake sss with gi and their light interaction.
http://www3.telus.net/public/vinnik8...S_TUT/SSS_.mov
As you can see the shader behaves similar to the true sss, where its brighter/darker in necessary areas.
Now we take step ahead and try this with displaced surface. For this to work, we will need to rebake sss maps with displacement on. Since vray displacement doesnt work too well with baking, I will use standard displacement with high tessellation.
Once the maps are baked we apply them back and do another test render.
http://www3.telus.net/public/vinnik8.../SSS_DISPL.mov
Here is when the delema comes in:
By applying baked map we gain render time segnificantly, but lose sss's true precision of scattering light in the edges of the object. However I think its a small price to pay when you are stuck and cannot use true sss at all.
another thing to add to my list of things to try
I'm always lost in the settings because you can get the same effect with 10 different combinations, but then it behaves differently under varying light conditions etc... I would like to know when I need to use lower fog, or lighter fog, or lighter refract, etc...
Comment