Blend material additive mode and energy conservation

[sharktacos]

When using the BlendMtl in additive mode, energy conservation can be broken making the material physically incorrect because the values of the spec total more than 1. I know there has been some talk about addressing this internally in the material (either by adding a second spec to the VrayMtl or by creating a new GlossMtl which uses a Fresnel mask.

In the meantime, I'm wondering if there is perhaps a way -- using the various nodes in the Maya Hypershade -- to normalize the result of the base and coat layers of the blendMtl in addtive mode so it is energy conserving? Anyone know a clever way to do this?

[dgruwier]

Isn't that what not ticking additive does?

[sharktacos]

Nope. With additive selected it acts like a plus node in Nuke. Unchecked it acts like an over node.

[Morbid Angel]

I could be wrong but you answered your own question there If you plug multiple materials into blend and use vray fresnel texture as a blend mask, in its own way this is producing the blending with proper energy conservation.

[sharktacos]

I believe doing that (i.e. a blend material with a VrayMtl with no spec (thus a Lambert ) in the base, then another VrayMtl with only spec and Fresnel off in coat1, using a FresnelTex as a mask, and a third VrayMtl with only spec and Fresnel off in coat2, again with a FresnelTex as a mask) would be less physically correct than simply combing two spec lobes with additive (i.e. a blend material in additive with a VrayMtl with spec and glossy Fresnel in the base, and another VrayMtl with only spec with glossy Fresnel in the coat1). I think the reason the later is more physically correct is that the FresnelTex is simply doing view-dependant Fresnel, while glossy Fresnel is done inside the BRDF and thus more complex on a microfacet level, resulting in darkening on the edges with lower glossiness values.

But perhaps I'm not understanding correctly what you are proposing? Happy to learn!

[vlado]

In the meantime, I'm wondering if there is perhaps a way -- using the various nodes in the Maya Hypershade -- to normalize the result of the base and coat layers of the blendMtl in addtive mode so it is energy conserving?

To normalize the weights, you need to divide each weight by the sum of all weight textures plus a white color for the base. It is doable but may be tedious to set up.

Best regards,
Vlado