Vray fresnel reflection problem

[Bigguns]

Hi Vlado,

As I was doing test on the skin shader for the fresnel reflection, I discovered that it's impossible in the Vray mtl to get nice fesnel effect, like it should be.

I tried in Mental ray with the architectural mtl and design to do a fresnel effect, and it's quite simple and easy, I just played with the curve and I get a nice effect. I tried to reproduce this effect in Vray but was unable, and also notice where the light hit the surface and generate a high light how much better the one in mr look.

I tried to join an image but it do not work.. I don't know why..

Here is some doc about fresnel reflection in Mr maybe it can give you ideas http://books.google.ca/books?id=feVF...resnel&f=false

I think something like a vray fresnel map or something like that that you can add and have lots of control would be really cool addition! Or something into the Mtl already integrate like in the arch and design

[joconnell]

I think most people end up using the falloff map in max to get more control whereas in maya and maybe softimage there's a vray fresnel map?

[grantwarwick]

I think most people end up using the falloff map in max to get more control whereas in maya and maybe softimage there's a vray fresnel map?

Exactly...
Use a falloff map and set it to fresel. Problem solved

But I do remember Vlado saying the SSS2's reflection was different from the standard vray material...hmmm maybe I'm wrong here, I'll try and find the thread.

[Bigguns]

Yes your wrong. Thats what i do using à fallof iu do not get the same result as in Mr and in the sss2, there is just something not working well in the reflection right now. Cant wait to have an option to get it right.

[Svetlozar Draganov]

Would it be possible to show some examples (screen-shots /scenes) between MR and Vray and explain us what is not possible to be created with Vray ?
Thank you very much in advance.

[joconnell]

Yep - could you pop out some render buffers of the affect you'd like to see from mental ray? Maybe a black object with one or two area lights from the side so we can see exactly what the reflections look like?

[joconnell]

Is this what you're looking for?



For what it's worth, I reckon the mental ray glass in that book is wrong, the spec highlight is changing but the actual environment reflection is not being affected in the same way.

[Bigguns]

Here's an exemple, ( i tried to upload it , it was not working had to do it with the basic uploader version..) so you see, the one top left is the one in mr, you noticed a nice fresnel edge effect, all the other are Vray test, I tried with fallof custom curve, with the vray mtl fresnel checked and with the arch and design .. and I could not get the same result.. I have the same problem for my skin shader trying to do a custom fresnel, the one in the sss2 shader seems to wrok well but is not exposed and cannot be used in any other mtl on tweaked etc. So I would like it to be exposed, I kn ow vlado told me it should be exposed soon, hope it's not just exposed in the sss2 shader but also as a map fresnel or something so we can use it in other mtl, like the vray mtl, etc.

[joconnell]

Hmm - what is the MR one reflecting? It's got a nice fresnel edge alright but is it reflecting brighter than the environment it's seeing? As in is it breaking energy laws for the sake of looking nice? Is it the white rim at the edge that you're liking in the mr render?

[vlado]

joconnell is right, there is nothing in the scene (nothing that is visible from that angle, at any rate) to cause the bright edge in the mr rendering if the shader is physically accurate. Can you post that scene?

Best regards,
Vlado

[Bigguns]

I guess it's reflecting the plane, wich is grey. I do not have the scene, but I just rebuilted it now, and I put the plane pink and the environnement white, work well to me.. Yes I like the fresnel effect around, I cannot get it right in Vray, it's like if it's never as sharp and there is energy loss at some angle compared to mr. That's also why I was not able to match the fresnel of the sss2. BTW the fresnel effect was strong because I putted it to the roof, just for show cas.. you can lower if you want, you will see in the exemple and in the scene that I will post.

I cannot link the files or images from work, so I'll do it when I'm home, in about 1h.

[Bigguns]

Finally I got home late..
But here are 2 types of fresnell in mr

I cannot send it here the file.. so I sended it on your email Vlado, plus some other things

[samuel_bubat]

You can get the same effect with a Vray Blend Material. Create a VrayBlendMaterial. In the Base material slot you put a VrayMaterial with your intended diffuse color.
In the first Coat Materials slot also put a Vray material with a black diffuse, reflections and fresnel as desired. Activate the "Additive shellac mode" and turn the blend amount color
to white.

[joconnell]

He's using that for some things already as with this rather nice tutorial!

http://www.youtube.com/watch?v=AANYPdBZM5Y

[Bigguns]

Yeah I already know all that stuff Samuel for years now... the point is that I can't get an accurate fresnel effect in Vray, Vlado is supposed to exposed the fresnel in the sss2 so it should be good after since the fresnel in the sss2 look quite good, but we need to be able to adjust it, like the glossiness,etc and be able to add maps to control the effect better.