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How can i have a softer Skin using BRDF

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Hi,

i implemented physically based shading, using the Cook Torrance BRDF Equation, with Trowbridge Reitz GGX for Normal Distribution, the Smith Schlick GGX for Geometric Shadowing, Schlick Approximation for Fresnel and for diffuse, Lambert.

All is working in Linear Space with pow(2.33) on Input and pow(0.4545) on output, and it looks good.

But the problem i have is for skin :

[attachment=22294:Skin harsh.jpg]

The falloff is too harsh, good for general objects, but the skin should look softer.

And it looks like cell shading...

So how can i make it softer like this :

crysis3-2013-01-22-10-57-22-06.jpg

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@Promit Yes, the falloff is very harsh, and without specular too (it stay the same). Do you know another diffuse equation i can use to have something softer ?

@kauna It's because Unity Free have his inputs in Gamma Space, so i had to manually correct the gamma in shaders.

 

I will try Sub Surface Scaterring, but i cant' use a method in Screen Space or anything which needs a rendertexture : in free version, rendertexture are very expensive.

So i'll try the Pre-Integrated Skin Shading but i have some questions :

if i understood well, i need my usual textures :

- Albedo, Normal map, Specular Map, Gloss Map

and

- Curvature Map (Baked from the mesh) and BRDF look up

So this method only affect diffuse calculations right ?

I can keep my Cook Torrance Specular, i just have to modify classic Diffuse Lambert to add SSS ?

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Will sub-surface scattering necessarily help the falloff though? You can however get good skin results with nice ambient occlusion, SSS, a subtle texture map, and a decent normal map.

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@Promit Yes, the falloff is very harsh, and without specular too (it stay the same). Do you know another diffuse equation i can use to have something softer ?
At risk of revealing my mountain man situation of being trapped on mobile ... I just like gamma space half lambert, as described in the HL2 slides.
	float ndotl = dot(N, L1);
	//compute half lambert term
	ndotl = (ndotl * 0.5) + 0.5;
	ndotl *= ndotl;
	ndotl = clamp(ndotl, 0.0, 1.0);

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I tested your half lambert, but the problem is the lighting looks flat : the falloff is very large, so it looks incorrect, especially with shadows.

I tried to downscale the normal map, and the result is a little softer, but it's still very harsh.

[attachment=22313:Image based Lighting Woman Harsh 2.jpg]

I'll try pre integrated sss too.

Someone knows where i can download the head scan all people use ? The Infinite site is down :(

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So this method only affect diffuse calculations right ?

 

 

Yes. Current sub-surface scattering techniques only address diffuse reflectance, so you can leave specular alone.

 

 

 

Will sub-surface scattering necessarily help the falloff though?


Absolutely. Take a look at this image from Eric Penner's slides:

 

[attachment=22314:SSS.PNG]

 

Notice how the falloff becomes much softer as curvature increases.

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