Chaos Corona for Cinema 4D > [C4D] Daily Builds

New Corona Physical Mat (separating reflections from refractions)

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There appears to be no way, that I have been able to figure out, to adjust the brightness and blur of reflections of a transparent surface, without changing the transparency as well. I am not talking about breaking “Energy Conservation” here, quite the opposite actually.

I would just like the ability to _decrease_ the brightness and increase the roughness of reflections without completely screwing up the refraction/absorption settings in the process.

With the “old” material, you could adjust the reflection settings independently (both color and glossiness), making it as rough and dim as you want dependent on the lighting and other scene objects.

With the new physically based material, when creating a fully transparent material (or even mostly transparent with little roughness) with maybe slight amount of absorption, reflections, especially of bright lights, tend to be super bright and razor sharp, dominating the material’s appearance and not giving the refractive properties a chance to show.

Perhaps what I am asking for is “bias” and the new material is supposed to move in the unbiased direction, but consider a good camera lens. It is coated with an anti-glare material that actually makes more light go through the lens, while reducing reflections from the lens elements’ surfaces. Clearly this is possible in the physical world! With Corona’s new material, sure there is a coating feature, but it sits on top of the horrid unchangeable reflections already present in a transparent material and can only add to “obscure” things further.

I haven’t found any way to tone reflections down (as in less bright via say a gray color instead of pure white) or blur them, while maintaining a good clean sharp transparency for a material.

Any tips short of masking/compositing?

BTW, node material doesn’t help here, because reflections get pulled in from the Directly Visible slot and do not get overridden by the reflection settings of the material connected to the Reflection socket. I don’t know if this is a bug or not, but in any case the material itself should allow for reflection adjustments (in terms of both color/brightness and roughness/glossiness) for refractive materials.

I have created a sample scene (latest daily build of Corona from Feb. 2021 was used) demonstrating the issue (attached). It may be obvious to most, but the spheres in the image are hollow (with proper normal orientations).

The situation is much worse than I thought. There seems to be no way with the new physical material to create a completely opaque black diffuse (non-metallic) material that has a real world IOR (e.g., 1.4-1.6) value.

Try it!

Forget about refraction, turn it off completely. Just create a basic Physical non-metal material with Base layer color set to black and a real world IOR of 1.4-1.6. You don't want it to be reflective, so set Glossiness to 0.0% (or Roughness to 100.0%). This should result in a simple black diffuse material, but it is gray and there is no way to get rid of that gray without using a fake low unrealistic IOR value closer to 1.0.

That's just wrong in the real world!

On top of that, what about glossiness? Turn it up to 100% and you get a harsh white reflection from a completely 100% black colored object! What the??? I am not talking Fresnel effects at glancing angles, here - that would be fine. I am talking direct front facing bright white reflections from an object that is solid 100% black in color.

All of this stems from the fact that there is no way to set the color, glossiness/roughness, and IOR values of the reflection itself in a physical material and to do so completely independent of (i.e., without affecting) any other properties of the material. Of course, energy conservation should continue to be in effect - that's expected.

Don't get me wrong. I love all of the features added by the new physical material. But, without having direct independent control over the color, intensity (i.e., brightness), and blurriness of its reflection property, it is pretty much useless as an accurate representation of a vast amount of real word materials that do not subscribe to the "Reflection reigns supreme over all other material properties!" philosophy.

Lower IOR.

& Learn about Color Science ("Pixar in a box" from Khan Academy)

ahh the old forum code...

You don't even need roughness if you fudge the IOR like that. That's my point - not physical reality, at all.
Do you know what dialectrics (i.e., non-metals) in this world have an IOR value close to 1.13? Liquid methane, with an IOR of 1.15! Air is 1.0. Water is 1.33 and most dielectric solids have IORs that fall squarely between 1.4 and 1.6.

The black Shader Ball in your scene, as great as it looks in a biased sort of way, it's made out of liquid methane, right? Because it looks more like black rubber to me (thanks to the roughness applied), which by the way has a real world IOR of 1.52 or approx. the value used for the gray Shader Ball on the right, proving my point, exactly (i.e., blacks appear gray under reasonable lighting conditions).

If the new Physical Material is supposed to be closer to the real world, it should behave like it. Your example of the black Shader Ball solved the "blackness" problem for rough materials, but it's a workaround (and it is a workaround, mind you) that can only be applied to opaque materials.

There is still no solution to the transparency/translucency issue I described in my original post which suffers from a similar IOR issue, even with a hack and even with layered materials. But, I would love if someone can find a workaround for that (i.e., getting transparency to be independent of reflection or at least figuring out a way to tone down and blur those reflections without obliterating clear transparency), because the new material does have some great features that unfortunately are blocked by this reflective "elephant in the room!" And, I am talking a material based workaround that doesn't resort to compositing/post-processing, render masks and render elements, or other non-material based solutions.


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