energy conserving shellac mode for V-Ray Blend Mat

[BEIGE]

I think this is on a lot of people's list. If you have 3 layers with additive mode on, you can reflect up to 3 times the amount of light that hits the material.

[vlado]

So what should the material do instead? Give each material 1/3rd of the total reflectance?

Best regards,
Vlado

[BEIGE]

correct me if I'm wrong but the Maxwell Layered shader is still energy conserving in Additive mode.

[vlado]

I haven't used Maxwell, so I wouldn't know if it is or isn't energy conserving. I'm simply trying to refine what you want the V-Ray material to do. If you have three materials, and you want to add them together with equal weight, then each material would only contribute one third to the result, right?

Best regards,
Vlado

[BEIGE]

well I'm not a physicist, so I'm not clear on the math. But if light hits a shellac floor, it's only reflecting a normalized mix of the shiny surface and the Lambertian wood, am I right?

[vlado]

Yes, define "normalized mix" and we are good to go

Best regards,
Vlado

[johng_JK]

I'm guessing he's referring to something along these lines:
http://mentalraytips.blogspot.com/20...mentalray.html

"The trick is to understand that the 3ds Max Blend doesn't just *add* two materials (that's what the Shellac does), but it interpolates between them. This is generally better, because you do not break any energy conservation laws!"

[vlado]

I don't think so, as this is already what the VRayBlendMtl material does anyway.

Best regards,
Vlado

[Koshi]

I usually prefer setting the material to "additive" when doing multiple reflections layer and carefully control the amount of each layer with the blend amount to not break the energy conservation law.

[Metzger]

Thing about additive mode is what if you wanted a nice top layer of dried up smeared dirt to cover your additive glossy coats and then still match beauty with render elements?

[simmsimaging]

I'm not clear on why you would need additive mode to layer reflections? It's certainly possible to get multi-layered reflections without the hassle of having to correct for the blow-out you often get with additive model. What would you need it for exactly, as there may be other workarounds?

b

[Koshi]

there is no need for that, just tried to give an alternative because the one who opened this thread asked for a way to do it with additive. if you have two layer with 100 percent reflectivity at a 90 degree angle and set both blend colors to 50% grey your fine.

[BEIGE]

ok - maybe I'm misunderstanding how shaders are handled with ADD vs. normal blending. If you want an accurate clear-coat that is energy conserving in V-Ray, what's the best method? I would have guessed that a Blend mat with 50/50 and no ADD is just an arbitrary mix without really getting something that's physically plausible. Maybe you use a Fresnel as well?

[simmsimaging]

I am aware of a couple of ways, but the simplest is to create the coat material using 100% white in the Reflect slot, and turn *off* fresnel, so that it's perfectly reflective. Then to control the reflections you can use a Falloff map (set to fresnel if you want) in the Blend Amount map slot of the VrayBlendMaterial. You can adjust reflection glossiness (and map it if you like) in the coat material, but use any spec maps that are controlling reflection *amount* inside the Blend Amount slot of the VrayBlendMtl, not in the material itself. This way wherever there is no reflection the coat material fades to the base material, and does not contribute any diffuse component. This makes it effectively like the additive mode, but with more accurate reflection behaviour and without compromising energy conservation.

b

[BEIGE]

Thanks, Brett. I'll give that a try. Recognize your name from the Maxwell forum. Cheers