Specular reflection vs diffuse reflection.

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daros
Posts: 47
Joined: Thu Dec 12, 2019 3:25 pm

Re: Specular reflection vs diffuse reflection.

Post by daros » Fri Nov 27, 2020 4:41 pm

tokiop wrote:
Fri Nov 27, 2020 3:40 pm
daros wrote:
Fri Nov 27, 2020 1:33 pm
The mixer test would be perfect if you would be allowed to use a fresnel function to blend the nodes. It cannot be a constant value (like it is in maxwell after version alpha) but a value which varies accordingly to the incidence angle.
It is pure non technical speculation, but as I understand :
  • IOR controls the fresnel faloff
  • mix shader normalizes reflected light between the two shaders
If this is true and I understand what you are explaining, playing with IOR and mix factor acts as a fresnel blend.

Here is a test with different IOR values for a glossy with black diffuse to see better the effect :


ClearcoatIOR.jpg


Higher the IOR and "flatter" are the reflections. However looking up for IOR references, IORs above 3 seem pretty rare, so it might not be physically sound to use it like this.
Correct, the higher ior trick is the same Maxwell users are forced to follow but it simply wrong. Things have to look realistic at real IORs.

tokiop
Posts: 33
Joined: Fri Apr 13, 2018 8:11 pm

Re: Specular reflection vs diffuse reflection.

Post by tokiop » Fri Nov 27, 2020 5:51 pm

It seems "simple/single number IOR" are only valid for dielectrics, non-dielectics materials like metals requiring "Complex/full IOR" with more complex equation and additional components/values.

Maybe the "simple" real IORs that can be found in some list, for some metals for example, don't make sense because they are only one component of their complex IOR ? Therefore they might not be a better or "more real" approximation than using the "high" IOR trick ?

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