GGX material problem

[nokia_usa]

Hi,

I'm having an issue with the GGX material. The scene just has one rectangular panel light straight in front, the object is just a cylinder.
I created a metal type of material so normally you would only see one light reflection in the center of the cylinder. But if I leave the default value of the GTR tail falloff to the default number 2 (ref image : Material_02_result), then you start seeing light reflection on each sides like there is 2 extra lights on the left and right of the cylinder. When I bring the GTR tail falloff number to 3 (ref image : Material_01_result) then you get a more realistic look with only one centered light reflection.

How is this possible to get light relfection on each side? this is not realistic so I'm trying to understand how those parameters are influencing the light reflections to "create" 2 new lights.

But also if I look at the reflection map generated, it looks like fine with only the light reflection centered on both results.

[M.Max]

Does "Glossy Fresnal" checkbox have any effects with this?
Also I see that Fesnal is turned off and you are using a map for reflection, what is this map and does using the default create the same issue?

[nokia_usa]

Yes I have a map reflection that I created with a fall off. I tried a bunch of things and don't remember trying what you said. Let me try and come back to you tonight.
The thing is that I created a new material from scratch again to try to find ou where this problem come from and the only parameters that created those 2 "fakes" light was the GTR tail falloff number.

[nokia_usa]

M.Max you were right on the reflection map. I turned off my falloff map to just use the color from the default and I only get on light in the middle
. Fresnel didn't change anything (with my reflection map), just made it darker
But I attached a sceenshot of my falloff map curve and preview, I'm not sure why I get those reflection on the sides, my guess is that the 2 left points should be to 0, so when the light hit the surface parallel to it, it will be dark.
But my question now is, if this is a typical behavior of a metal type of material to have the light reflecting on specific angles of the surface, then why this does not appear in the reflection map pass?
Let me know your thought on that.

[M.Max]

That's interesting.
I wouldn't except that result even with this falloff map.
Unfortunately I can't test this now as I'm away from my computer for few days, but I would start by opening a ticket support and provide the scene so the support team can take a look at it.
Btw are you on the latest update? It might worth giving a shot to see if that already "fixed"

[nokia_usa]

Yes, I could work my way around this problem but I want to know the science behind it and why this happening. Especially if this is supposed to be photorealism rendering when there is nothing realistic about those reflection.
I'm currently using 3Ds Max 2018 with Vray adv 3.60.05.
I will open a tickets with Chaos and let you know if there is any result.

[hermit.crab]

Check if you have the 'Glossy Fresnel' (Options>Glossy Fresnel) checkbox in the material disabled. Also, try switching the black and white colors of the falloff map.
Otherwise, send the scene to support@chaosgroup.com so we can take a look. Mention this thread in the e-mail as well.

[nokia_usa]

FIY submitted a ticket to Chaos couple days ago but still no answer, probably because coronavirus and people working from home

[Muhammed_Hamed]

Using your settings, I'm not getting this behvior in Vray Next
And Metalness is a much better/physcially accurate workflow for metals than using a falloff map in the reflection color slot

[Muhammed_Hamed]

But my question now is, if this is a typical behavior of a metal type of material to have the light reflecting on specific angles of the surface, then why this does not appear in the reflection map pass?

the highlights of light sources will be in your specular pass, not reflection pass
Reflection pass is the result of Reflection filter x Raw reflection

[nokia_usa]

Using your settings, I'm not getting this behavior in Vray Next
And Metalness is a much better/physcially accurate workflow for metals than using a falloff map in the reflection color slot

Muhammed_Hamed So this could be coming from my outdated version of Vray.
Also I'm using a falloff curve for the reflection that would mimicking the science datas of each metal I'm trying to recreate. In my opinion this is more accurate for the type of work I do as each metals as its own relfection curves and vray use a general metal rules (unless I'm mistaking). This gives me different curves for the RGB.
You can find those values here.
https://refractiveindex.info/

[^Lele^]

Also I'm using a falloff curve for the reflection that would mimicking the science datas of each metal I'm trying to recreate. In my opinion this is more accurate for the type of work I do as each metals as its own relfection curves and vray use a general metal rules (unless I'm mistaking). This gives me different curves for the RGB.
You can find those values here.
https://refractiveindex.info/

You'd be probably much better off using this, or better still the same but in C++, as shown in the picture (although now i ain't sure the pluginTex node exists for 3.x).
The OSL page will explain how to use it.

You should however *really* upgrade to Next if you could, as the new metalness workflow is much more accurate, and straightforward.

[Muhammed_Hamed]

Also I'm using a falloff curve for the reflection that would mimicking the science datas of each metal I'm trying to recreate. In my opinion this is more accurate for the type of work I do

Ya that is what I used to do before Vray Next, I'm familiar with this workflow and the complex fresnel plugin
Like what Lele said, metalness is just easier to setup and more physically accurate
At the end of this post, Vlado posted the papers he based the metalness implementation on, and it shows how more accurate it is compared to the old workflows
https://www.chaosgroup.com/blog/understanding-metalness

+1 for upgrading to Vray next
Best,
Muhammed