Physical Metals

[indexofrefraction]

Hi there ...

Not sure ofc, but i can't find a way to make truly physical metals...
I mean by using reflection curves/data per color chanel...
(for example by using data from https://refractiveindex.info)
instead of just using a yellow reflection color for gold.

can this be achieved by a standard c4d shader in the ref color slot?
or is there a possibility within in corona?
or if not... is it planned?

best index

[Eddoron]

Completely accurate materials are currently not possible in the C4D version. You can build a shader tree in the reflection channel with the fresnel shader(as a part) as a substitute for the extinction coefficient. Maybe even make use of the thin-film shader for the µm values inside the shader tree.(Really not sure about that)
It would, however, be more eye-balling the right result than creating something scientifically accurate.

Something like Siger Complex Fresnel Shader for the Max version would be helpful.



I think it should be added in future releases as many renderers now provide such an option and if the goal is to create a production-ready renderer, I see no way around it. Though I'm pretty sure it will be added sometime.

[indexofrefraction]

thanks...
i also think there must be an option for this, maybe as a corona shader.

but i also found this solution in the forum:
https://forum.corona-renderer.com/index.php?topic=13034.0
but i suspect this setup is not 100% correct
-

[Studio Heisenberg]

Here is a really nice solution

[indexofrefraction]

tx, i know this one...
doing it this way is most likely more correct than the metals in the thread mentioned above
it is downloadable here: http://graphos.xyz/Products/

to use it with corona i think you must
add a fresnel shader in the reflection color slot
there you paste in the gradient from the plugin (see video)
then you must invert the gradient, so that the white part is to the left

...

still, i hope corona does a complex ior shader to be put in the reflection color slot
allowing manual values and presets for the common metals :)

[burnin]

disregard

[indexofrefraction]

watch the video & observe closely
color correction (with curves) shader is needed (VRay has it), then values/curves are driven using this IOR tag

i dont think so..
the tag generates a color gradient out of the three curves
with this you dont need the curves anymore.
just put the reversed gradient in a fresnel shader in the ref color

(the r,g,b curves just define the color at a certain viewing angle)

[burnin]

true, my bad

edit:
But is not interactively driven?
meaning, the tag generating gradient doesn't drive the shader... it has to be done manually, correct?

edit2:
It also doesn't feel like real Physical Metal.
Need to make some comparative studies.

[indexofrefraction]

you set the values or choose a preset in the tag.
this will give you a gradient
copy the gradient to a fresnel shader in the materials relection color
then invert the gradient (white should be on the left)
set the ior to something like 22
the diffuse color should be black or dark gray

[Studio Heisenberg]

I use this just by adding filter in reflection color and than check gradiation curves on, after that I connect espresso with set drive set driven for each r g and b with the one to plugin and it drives my reflection color to correct values... I think it is more than good?

[Nejc Kilar]

I use this just by adding filter in reflection color and than check gradiation curves on, after that I connect espresso with set drive set driven for each r g and b with the one to plugin and it drives my reflection color to correct values... I think it is more than good?

If I understand you correctly and you are doing what I think you are doing then you are missing one important step - the falloff map.

The idea is that these curves don't just define the color of the metal reflection but also the reflection angles. So basically you need to plug it into a falloff map instead of using regular fresnel.

Regular fresnel gives you reflections according to the fresnel "curve" which ultimately depends on that number you put in (1.52 etc...). With the falloff map and these curves in there you are actually creating your own "fresnel curve" (its not fresnel anymore but just a reflection curve thats really specific and customized).

To simplify, with the falloff curves you are basically defining exactly how much that metal is reflective (and with what color) when viewed under different angles.

I feel like I've overcomplicated this. Like a lot :) Hope it helps though...

[indexofrefraction]

as you all see we need a proper shader from corona
there are too many possibilities to screw it up :)

[Studio Heisenberg]

Well these are all true things, but as I have wrote about this few months ago to developers, and we will not have these functions in near future cause it needs to be reworked in core of corona :) until than we will need to use these half-solution, but I think with pbr materials introduced in last versions we can get pretty decent results (despite all these mentioned above).