[Micha]

Hi,

befor I start my critics on the Maxwell Metals, I make a conclusion of the other critics:

- plastic materials need a IOR parameter
- plastic materials need a blur fallof of the roughness
- diffuse materials need a rouhness parameter

My new thesis: metals need a special diffuse component. This special metal diffuse is something between diffuse and a very blur reflection. The reason for this effect is not a roughness, it are oxidation and other surface effects.

I attach two examples of real life aluminium. I miss this effect in Maxwell very much. The Maxwell metals are only fresh perfect polished Metals (with a roughness of fine sand paper if the user like). If Maxwell try to be a physical correct render engine, than it should not use so simple materials like now implemented.



Here an example of metal shader of AIR. In this selfwriten shader I have used a layer of diffuse metal. It is a modified diffuse function. The important difference between the standard diffuse and the metall diffuse is, that the metal diffuse samples a hemisphere area in reflection direction. In renderman code it looks like this:

standard ...

Code: Select all

diffuse(N)

metals ...

Code: Select all

diffuse(R)

Interesting for me was, if I change the contrast of the metal diffuse layer, than I get a car paint effect like here:



At the moment I find only one first aid for aluminium look - the plastic shader. This materials seems to use a metal fresnel function, so I can use an additional grey diffuse component. This looks not real, but better than the clean standard aluminium material.

I'm very curious on the final release. I hope to see more real materials.

[JesperW]

I've seen some renders of the 1.0 multilayer metals, they too look all shiny and new, so I wouldn't count on it. Myself I also use a plastic with "dirty" colormap and anisotropic rougness to get close to a natural aluminium.
/j

[tom]

I've seen some renders of the 1.0 multilayer metals, they too look all shiny and new.

JesperW, Are you sure you saw 1.0 metals? Strange...

Well Micha, it's nothing different than plastic material, here's a sample:

[Hervé]

I think italso depend on the bump map.... no..?

Tom, is it a Maxwell 1.0 render...
(could not resist to ask...)

[tom]

No, it's actual beta1.2.2a
I used plastics without roughness and with color.

[Micha]

Tom, this metal fake I know and use it at the moment, but it dosn't looks so good like in reality. I hope it will be only a temporary solution. I anticipate more from Maxwell.

[Mihai]

As far as I know, the biggest difference between say a shiny plastic and a shiny metal is that the specular reflection of a metal tends to be tinted towards the color of the metal. With plastics that is not the case.

If you can show other reflective differences between these two categories, it would be nice to see. I mean some scientific research showing the reflective properties of metals vs opaque plastics. This oxidation dullness could be achieved with layered materials which we'll have according to the white paper.

[tom]

Of course my suggestion is not the perfect replacement for the metal references above but I wanted to say it's not that simple saying Maxwell can only do shiny metals. Well, in 1.0 you'll have layers and they will provide you far more complexity.

As far as I know, the biggest difference between say a shiny plastic and a shiny metal is that the specular reflection of a metal tends to be tinted towards the color of the metal. With plastics that is not the case.

No, it's not about tinting but scattering falloff. If it's just about tinting, it would be possible with plastics too because you can set both spectral and specular reflections as the colors you want.

[Micha]

Mihai, the big difference is, that metals show a diffuse reflection of the environment. In Toms example, the diffuse part of the shader should more reflect the red ground at the edges. But it is a simple plastic diffuse function here, that collect rays in all directions of a hemisphere around the normal of the surface.
It is difficult to see in the reality, because the most people can not separate clear reflection from the underlayed subtle diffuse metal reflection. But if it is missed, than the material looks not real.

Aluminium is a extrem example. Very old aluminium can looks like diffuse plastic some times. But this is seldom, for example old aluminium pails or tankards.

Here a nice example of diffuse metal reflection. This can not be done with a plastic diffuse and this is not a very rough surface. This is a diffuse metal reflection.


Here a more difficult example. You can see the diffuse reflection only in the brightest parts, it looks a little bit like a glow. For me, this is a very nice metal effect. So should looks metal.


Maybe I post later more example, but I want to go in the cinema now.

[Mihai]

Mihai, the big difference is, that metals show a diffuse reflection of the environment.

Why couldn't you do a blurry reflection of the environment with a plastic? You say diffuse reflection, I prefer to call it blurry reflection, otherwise we are confusing the diffuse and specular components of these shaders.

Lets forget the very blurry objects, because it would be impossible to tell in real life a very blurry aluminium container like in your pic, from one made of blurry plastic. The interesting metals are the ones that aren't perfectly shiny, they have that glow as you say. I'd like to know what makes that glow. Is it actually a thin layer of oxidation that makes it blurry, while the metal underneath remains shiny?

[tom]

Is it actually a thin layer of oxidation that makes it blurry, while the metal underneath remains shiny?

Yes, and also micro imperfectness of the surface makes it glow. If you try it with perfect mirror, you won't be able to see it. It's about metal's microstructure, not about reflection behaviour. And these kind of microstructure may be simulated by measured scattering of the real surface or a generated model.

[Grim]

micha do you show me setting light car from first pictures?

[Mihai]

Yes, and also micro imperfectness of the surface makes it glow.

That's what I think too, and the fact that those imperfections run in random directions makes the reflection blurrier. When you polish the metal, you are "lining up" those imperfections in a dominant direction as well as diminishing the depth of those micro grooves, giving you a sharper reflection.

[tom]

Yes, and also micro imperfectness of the surface makes it glow.

That's what I think too, and the fact that those imperfections run in random directions makes the reflection blurrier. When you polish the metal, you are "lining up" those imperfections in a dominant direction as well as diminishing the depth of those micro grooves, giving you a sharper reflection.

eeeexactly!

[tom]

well, once falloff is implemented...would that help? you could do oxidization...fingerprints...swirlmarks....maybe?

No, we were talking about something quite different. Falloff is not a surface property and will never be. Instead, falloff is a result(behaviour) of surface's microstructure. Being more able to define the surface in small scales means the more control you have about characteristics of scattering. So it will result with different falloffs just like in velvet, polished metal etc.