VRay IOR and reflection color dependence?

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  08 August 2013
VRay IOR and reflection color dependence?

Hello.
If IOR (in fresnel equation) defines how quickly reflection changes (from 4% -for glass at normal angle to almost 100% (almost means 99,999%) at 90deg or from 40-60 for example for metals an normal angle to near 100% at 90degrees) AND ALL materials have fresnel reflectance: brick, paper, walls have fresnel - with various VISIBLE reflectance intensity (due to MICROFACETS, "little irregularities" in surface we cannot see "mirror" reflections, rather very glossy for bricks, paper etc & very low IOR: 2-4 = low reflectance) MY QUESION: What is dependence between IOR graph and reflection color slot??? (we know already, that for all materials refl at 90deg =100 (white) - fresnel, of course). REFLECTION COLOR SLOT in Vray mat IS FOR.....???? How gray values in refl color slot changes IOR GRAPH??
Piotr
 
  08 August 2013
1,Metal has no fresnel effect
2, refl color slot NOT changes IOR graph, the color MUTIPLY with IOR graph. In physical, refl color slot should be PURE WHITE for clean surface.
 
  08 August 2013
1. metal has no fresnel???? EXPLAIN, please
2. If values in IOR graph are multiplied by refl. color slot values, then graph is changed by this operation. Could you, please, tell me what Refl value at normal angle has IOR 4 MULTIPLIED by refl color slot = 0,5 (RGB=127), or MULTIPLIED by pure white?
 
  08 August 2013
1. It does, surface reflection of metals can be approximated using the full Frensel equation. However that has two input parameters (n, k) instead of the one (n) used for non-metals. This is because k is practically zero for non-metals/dielectrics.

Note that the full equation uses complex numbers which takes a bit longer to compute and set up. I'm guessing that's the reason why you hardly see it implemented anywhere, though I hardly see any difference in render times.


2. Other than that no realistic material would have an IOR (= n) of 4.0 without a k component, the reflection value would just be whatever value an IOR of 4.0 at normal angle would give you, multiplied with the value in the reflection colour slot.

This is helpful because just Fresnel and glossiness (surface roughness) don't always come close to describing the surface of a material. For instance rubber always looks better if you lower the reflection colour by at least a factor of 10.
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  08 August 2013
Originally Posted by Rens: 1. It does, surface reflection of metals can be approximated using the full Frensel equation. However that has two input parameters (n, k) instead of the one (n) used for non-metals. This is because k is practically zero for non-metals/dielectrics.

Note that the full equation uses complex numbers which takes a bit longer to compute and set up. I'm guessing that's the reason why you hardly see it implemented anywhere, though I hardly see any difference in render times.


2. Other than that no realistic material would have an IOR (= n) of 4.0 without a k component, the reflection value would just be whatever value an IOR of 4.0 at normal angle would give you, multiplied with the value in the reflection colour slot.

This is helpful because just Fresnel and glossiness (surface roughness) don't always come close to describing the surface of a material. For instance rubber always looks better if you lower the reflection colour by at least a factor of 10.


Than You for answer
01. Of course im using n=n+ik (ex. coeff. is everywhere but for high transmittance materials is soooo low like 1.33e-7) Metals have fresnell, You can retrieve it from Reflectance at (0) (but you cannot retrieve simple n and orginal k from R(O)--> complex n will be high)
02. I agree 100% with You. But If im lowering refl color slot to 10% (rgb=25) my IOR values (at (0) or everywhere on IOR graph) are multiplied by refl color values (this 10%). in other words. I had 30% reflectance at normal angle, now this value is 3% (is multiplied by 0,1) and IOR value for 3% is different than for 30% (R(0) = 30% for IOR 3,5, R(0) = 3% for IOR 1,42). IOR 3,5 and IOR 1,42 are not the same. My question: Should I rise IOR value to match orginal reflectance (30%) (couple of times org ior for ex)?

Next question. Do you have extionction coefficients for non - transparent materials other than metals? For wood or opaque plastic?? Could you share it?

And last question. If i use color in refl color slot other than white, should i "degamma" it. (Use values rgb multiplied by 255*((x/255)^2.2, where x = rgb values

???

What do you think?

Piotr
 
  08 August 2013
Also, the reason you can select a color for the reflections is for metals. Most other materials have white reflections.
 
  08 August 2013
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