reflectivity on a black material covered with a clear one

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lighting_freak
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reflectivity on a black material covered with a clear one

Post by lighting_freak » Sun May 10, 2020 8:20 pm

Hi all,

just a quick question. How does luxcorerender handle the refelctivity of a fresnel glossy black material that is covered with a clear one?
This *.blend file should show the principle:
Intermediate.blend
(723.95 KiB) Downloaded 18 times
Usually it should be like this for light inicidence normal to the surface:
For the clear IOR = 1.492 vs. air IOR = 1 it's around 4%.
For the black glossy IOR =1.584 vs. air IOR = 1 it's around 5%.
For the intermediate black glossy vs. clear it's around 0.1%.

Does luxcorerender treat this situation like that?
Thanks in advance.

BR
OS - Windows 7 X64
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lighting_freak
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Re: reflectivity on a black material covered with a clear one

Post by lighting_freak » Thu May 14, 2020 7:12 am

Hello,

I could really use some help here.
Thanks in advance.

BR
OS - Windows 7 X64
CPU - Intel CORE i7
GPU1 - Variants of notebook card from nVidia
GPU2 - Variants of notebook onboard card from Intel
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lighting_freak
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Re: reflectivity on a black material covered with a clear one

Post by lighting_freak » Thu May 28, 2020 7:27 pm

Hi everyone,

... obviously my of asking is not very suitable.
Let me try it in a different manner.

If I set my geometry up like in the *.blend file above, how many light will be reflected from the inner black face?

Thank you for your help.
OS - Windows 7 X64
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juangea
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Re: reflectivity on a black material covered with a clear one

Post by juangea » Thu May 28, 2020 8:09 pm

I don’t fully understand your question.

Can you explain it with some pictures, even if they are from other render engine, and what’s the shader nodes tree you have in mind?

(Can’t open Blender right now)

lighting_freak
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Re: reflectivity on a black material covered with a clear one

Post by lighting_freak » Fri May 29, 2020 10:19 am

Hello
juangea wrote:
Thu May 28, 2020 8:09 pm
Can you explain it with some pictures
YES, and thanks!

This is a simple setup.
A block that is made from two materials - one is a black one and the other one is clear. Both are with almost perfect polished surface qualities.
setup.jpg
this is the material for all faces black to air:
black-part.jpg
this is the material for all faces clear to air:
clear-part.jpg
this is the material for the face that both materials share:
face-in-between.jpg
Does the luxcorerender algo takes into account the little remaining difference in IOR of black and clear component?

BR
Attachments
clear-volume.jpg
OS - Windows 7 X64
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Dade
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Re: reflectivity on a black material covered with a clear one

Post by Dade » Fri May 29, 2020 11:09 am

The glossy IOR has nothing to do with volumes and it doesn't affect them in any way. The Glossy IOR affects the specular component of the glossy material like if there was an air/material interface, it just a different way to specify the amount of specular component: https://wiki.luxcorerender.org/LuxCoreR ... or_and_IOR
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juangea
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Re: reflectivity on a black material covered with a clear one

Post by juangea » Fri May 29, 2020 12:36 pm

I still don't understand what are you trying to achieve, sorry for that.

let's put an actual example, for example, a table top made out of Black Acrylic with a Clear Glass on top of it?

That's what you want?

Because what I don't understand is why are you using volumes at all, unless you want the glass to not be clear, but rather to have some volumetric absortion.

ALso I don't understand the material that you say that is for the faces that both materials share.

In the end if you have two surfaces you just have that, to surfaces, each one with it's material, and the "mix" will be done by the engine, like in the reality.

Please confirm if my example with the table top is what you are trying to achieve, and why do you want to use volumes, I actually don't understand why would you want to use volumes here.

Sorry for asking so many explanations, just trying to help here :)

lighting_freak
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Re: reflectivity on a black material covered with a clear one

Post by lighting_freak » Fri May 29, 2020 2:36 pm

Hello,

That is more or less the answer I was looking for.
Dade wrote:
Fri May 29, 2020 11:09 am
The glossy IOR has nothing to do with volumes
Lets modify your example. I have a black table top covered with water (really no air gap between).
The touching surface is shared by the water medium and by the table top.
juangea wrote:
Fri May 29, 2020 12:36 pm
In the end if you have two surfaces you just have that, to surfaces, each one with it's material, and the "mix" will be done by the engine, like in the reality.
As Dade mentioned it won't be handled by the engine - at least not in a right way!
lighting_freak wrote:
Sun May 10, 2020 8:20 pm
For the clear IOR = 1.492 vs. air IOR = 1 it's around 4%.
For the black glossy IOR =1.584 vs. air IOR = 1 it's around 5%.
For the intermediate black glossy vs. clear it's around 0.1%.
Instead of having just 0,1% refelctivity its still 5% - and therefore I'd like to ask to change that!

In my real work I will deal with lot of those interfaces with different coloured materials. That's why I'm dealing with volumes.

BR
OS - Windows 7 X64
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lighting_freak
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Re: reflectivity on a black material covered with a clear one

Post by lighting_freak » Fri May 29, 2020 5:22 pm

Hello,

The more I think about this, the more it pops up that really don't know what should happen in real world on such an intermediate surface...

For sure the amount of direct/specular reflected light is reduced but by how much and what are the physics behind?

What happens to the diffuse scattered light. I mean white acrylic remains white even if its covered with another acrylic...

Does anyone know about that?

BR
OS - Windows 7 X64
CPU - Intel CORE i7
GPU1 - Variants of notebook card from nVidia
GPU2 - Variants of notebook onboard card from Intel
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lacilaci
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Re: reflectivity on a black material covered with a clear one

Post by lacilaci » Fri May 29, 2020 5:36 pm

I'm so confused by this thread. What is your expected outcome, or some reference.. Maybe that would help.
I was rendering some concept devices(mobile phones) that have glass backs and fronts that are layered on top of each other and never once i cared how the interaction between the surfaces works. Obviously, if there would be an artifacting cause of overlaps it would need some tweaks in pushing meshes into each other or creating a gap instead of infinitely airtight gap but that's all.

If you need some help best way is provide reference (photo for example) and a render of what you get using your approach.

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