Fresnel IOR using a Falloff map

[CiroC]

When I use a Falloff map on the Fresnel IOR (999 value) slot the result is a non-reflective material, although the falloff map works fine when used on the Diffuse, Reflection and Glossiness slot. Is not working with the 2015-01-19 build. I am using 3ds Max Design 2015.

I attached a simple scene.

Many thanks

[maru]

Please tell me you are not putting falloff map into FRESNEL IOR slot.

[CiroC]

Please tell me you are not putting falloff map into FRESNEL IOR slot.

Why not? Is not that the way if you want to tweak the IOR without using the Fresnel IOR value?

[maru]

No. Put it in reflection color.

[CiroC]

No. Put it in reflection color.

Sorry. I did the same mistake twice. I should be punch on the face.

However, this "worked" on the Alpha 7.2. :s

PS: The interactive mode doesn't work using region areas, is this a known issue?

[Juraj]

No. Put it in reflection color.

However, this "worked" on the Alpha 7.2. :s

It could, but it surely didn't provide the intended effect.

All IOR does (or the Schlick approximation used in Vray/Corona) is translate the specular intensity into correct frontal (0° degree) and grazing (90° degree) intensity (on 0-1 scale).
By creating a falloff curve, you're recreating this (Schlick apprx.) manually.

Therefore as Maru correctly said, you're supposed to put it into Reflection color (or rather intensity) slot.

[CiroC]

Thanks for the reply Juraj_Talcik.

I apologise for this stupid mistake, but on my head it makes sense plug the falloff map into the Fresnel IOR since we use this setting to control the Fresnel. That is the reason why I did it.

But, in what situations can we use the Fresnel IOR slot? And using the Falloff map, into the reflection slot do I have to connect the reflection map into the "white" slot?

[maru]

But, in what situations can we use the Fresnel IOR slot? And using the Falloff map, into the reflection slot do I have to connect the reflection map into the "white" slot?

Hmm.. If you wanted a single material that varies in Fresnel IOR. :) First thought: plastic painted with metallic paint?

I don't get the "connect reflection map into white slot" part.

[CiroC]

Whoa, I never thought about that. I tried that using Solid HDR color and it really works :D

I attached an image to explain what I mean with the white slot. :)

Guys, thanks for the patience.

[Juraj]

It's almost the same thing as using simply IOR and putting that bitmap into reflection slot.

You have to visualize what you are doing, than it will be clear. Understand what that curve does. White=1, Black=0 in the fallof graph.
It's actually super simple.

[Ondra]

All IOR does (or the Schlick approximation used in Vray/Corona) is translate the specular intensity into correct frontal (0° degree) and grazing (90° degree) intensity (on 0-1 scale).

Corona is not using the approximation ;)

[CiroC]

Just curious, but what model does Corona use? :D

[Juraj]

All IOR does (or the Schlick approximation used in Vray/Corona) is translate the specular intensity into correct frontal (0° degree) and grazing (90° degree) intensity (on 0-1 scale).

Corona is not using the approximation ;)

So what does it do ? Since there is no extinction coefficient (or is that one set to =1 ?).

[Ondra]

http://en.wikipedia.org/wiki/Fresnel_equations#Power_or_intensity_equations