Used Aluminium or wish for a new illumination model

[Micha_cg]

Hallo,

one year befor I have try to get a metal that looks like used aluminium. After a long time of observation and shader coding tests I have found a simple solution. It is not full physical correct, because I'm not a programmer.

What I have needed was a metal with two layers - a full reflective layer and a special metal diffuse layer. Here two examples of the real world.



In my first shader code test I have used a combination of a very blury reflection plus a clear reflection. The problem was, the extrem blury layer need much samples and a long time for calculation. I never have got a clean smooth strong blury layer.

surface color = blury reflection + clear reflection;

I have thought, the standard diffuse function take samples from the whole hemisphere around the shading point and do the approx. the same like a blury reflection but without a long rendertime. The big difference is, the diffuse based on the surface normal N and reflection use the reflection direction R. My new shader code was:

surface color = diffuse(R) + reflection(R);

I was happy, the diffuse(R) give me a diffuse metalic look in a very short calculation time. Now I ask me, how could I concentrate the new metalic diffuse look so that I can simulate different grad of patina? Here I have not find a solution how I can modify the illumination model and so I have start to build in a fake. I have changed the gamma value of the metal diffuse component.

Here an example of my old shader.


How could we get this effect in Vray in a physical correct way? I think, we need a flag option that change the sample direction from standard diffuse (N) (surface normal dir) to metalic diffuse(R) (reflection dir) and we need a parameter for the diffuse component that gradually change the illumination model from lampert to phong/blinn.

For example I have the feeling the left real world example image is more phong and the right example more lambert (the metalic glow effect in the reflections looks more like standard diffuse).

Starting point for me at my biased renderer was, that for speculars are used different illumination models. But this models was working with point/distant/spot lights only. With GI lights this models are not used, only diffuse and reflection are enable. I'm not sure how Vray works. Maybe it can handle a metal with two reflection layers - one very blury and one clear - without the modified diffuse function.

I hope my ideas are not to confusing.

[joe_b]

Used Aluminium or wish for a new illumination model

We have been discussing the ability to create multiple reflection layers. VRay is more than capable of it.

[edit]
The VRay for Rhino material is just a layered brdf material. For simplicity sake right now we limit one of each layer. Diffuse and reflection layers are the only ones that make sense to have multiple instances of in the VRay BRDF model. There are some bugs to work out, but I think we may be able to get the extra reflection layer in by our final 1.0 release

[Micha_cg]

Used Aluminium or wish for a new illumination model

Sounds good. Implement it. Metals without this effect looks to clean and death.

[flipside]

Used Aluminium or wish for a new illumination model

I think it is perfectly possible with 1 layer. You just need good mapping, so you can make maps for reflection, glossiness, bump etc... The worn out effect on your pics comes from bumps, scratches and oxidation.

Your left example is alu+rain, the sharp reflections come from the water...

[Micha_cg]

Used Aluminium or wish for a new illumination model

Wouter, I'm curious to see a Vray rendering with the same effect like in my render test above - a steel sphere with a little bit patina. Are you sure you will get it? And don't forget how much work it is?
My suggested material could be very simple to use - for example 40% "metal diffuse" instead the standard diffuse and 60% reflection could be steel. And 70% "metal diffuse" + 30% reflection could be aluminium.

Here a few examples done per AIR and my shader. I hope you feel the diffuse metal effect in the reflections. It is not easy to see, but I love this effect. It bring life in the reflections.







If I remember me right, I have used a light metal diffuse effect for the stone too. It give the stone more depth.


Also I remember me on a test from me with a wood texture on a diffuse metal with plastic coat - I have got an effect like tiger eye stone. Today I have try it again, here the result. Not perfect, but I think a beginning.



I have started the diffuse metal shader as I have needed a metalic car paint in a GI environment. Here an old example with the diffuse metal effect in combination with a fresnel layer.

[flipside]

Used Aluminium or wish for a new illumination model

I think I see what you mean now, kinda like the falloff map in max.

[Micha_cg]

Used Aluminium or wish for a new illumination model

I think I see what you mean now, kinda like the falloff map in max.

I'm not sure what a fallof map is, but I have the feeling it is a big fake. Is it dependent from the angle of the surface in direction to the camera? What I need is not a fake. If you look at my renderings and if you look at the metalic car paint of the cars on the street in the real world than you will see, the brightest area of the metailc diffuse glow are around the area of the brightest clear reflection. The metalic diffuse effect based on the reflection, and not on fallof or the surface normal (like the diffuse component). What is the big difference between a blur reflection and a diffuse illumination? The reflection is view dependent and the diffuse not.

If the render engine has no problem to render a strong blury reflection than we could simple combine a clear reflection layer to a blur reflection layer (maxwell can do it). If Vray need much more time to render a blury reflection as a diffuse surface (for example AIR does) , than it should be better to modify the diffuse function.

[vlado]

Used Aluminium or wish for a new illumination model

The V-Ray engine itself has no problem rendering multiple reflection layers, as shown in the image below which was rendered with the standalone version - the teapot has two glossy layers and a diffuse layer:



However, at present, there is no UI to allow the setting up of such materials. I am not sure if this will be possible with v. 1.0 of V-Ray for rhino, but I suppose we will wait and see.

Best regards,
Vlado

[Micha_cg]

Used Aluminium or wish for a new illumination model

Ohhhh, I love this effect.
If you see a way to implement it, than try to do it please.

Maybe, you could implement a second sublayer at the reflection options. You could implement a simple compact control with only one line:

[blur layer active]    [reflection color]   [Glossiness] [subdivs]
    flag                  color              value        value

The sublayer glossiness could be a single option that control highlight and reflection together.

I'm curious for the future of Vray.

[joe_b]

Used Aluminium or wish for a new illumination model

Maybe, you could implement a second sublayer at the reflection options. You could implement a simple compact control with only one line:

[blur layer active]    [reflection color]   [Glossiness] [subdivs]
    flag                  color              value        value

The sublayer glossiness could be a single option that control highlight and reflection together.

I'm curious for the future of Vray.

We want to make unlimited layers a possibility to allow any combination of layers the user sees fit. Like I previously said, the layering stuff is not an issue of VRay, it has the capability already. But I need to hook up our UI to properly create the layered materials.

We are working on some other things right now, but materials will become our main focus again sometime early in next week.

[Micha_cg]

Used Aluminium or wish for a new illumination model

[Micha_cg]

Used Aluminium or wish for a new illumination model

... and as first aid up to the layer stuff works it helps to manual render the passes.