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Messages - SharpEars

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1
General CG Discussion / Re: Midjourney V5
« on: 2023-05-17, 17:18:30 »
I've been searching for a good rock veining texture forever. The starting images in this post still look somewhat artificial.

I am hoping to find a method that can randomly generate fairly realistic real-world natural mineral deposits like the following, preferrably with a tweakable control over veining percentage (as a function of volume, or something along those lines - i.e., not a hard-set baked-in amount):








2
Towards the end of the article at:

https://support.chaos.com/hc/en-us/articles/11905001704977-New-Volume-Resolving-in-Corona-1

..., under limitations, it says:

If a light is placed inside a medium, the caustics solver (Max | C4D) will ignore the absorption of the medium for caustics generated outside of it. Observe how the blue glass ball is casting non-blue caustics when the light is inside it.

and provides an example:


Is this something you guys are working to address in time for the release of Corona 10? It seems like a pretty large shortcoming.


3
Please Devs, dont release this shader without thinking about it more. It is not ready to replace the Corona material.
We are also not sold on the quality in any image you have shared so far. That blog post did not do it justice.

Hi! In order for us to make any changes, you'd need to be more specific. Let us know the things you think it needs in order to be ready, what you think it is missing, or does less well, and so on. On image quality, we've done hardly any "beauty" shots, other than say the robot in the blog post - the rest of the blog post (and other images) are simply tutorial images to show what the parameters are/do to help people understand and get used to it.

More specific:

- Metals: Re-enable IOR control
- Dielectrics: Control of the following for the reflections shader/group of a material that is independent of the same settings for the refraction shader/group:
  o Color
  o Roughness/glossiness
  o IOR


4
Yes, as Mike says.

Corona Legacy material is here to stay, if you prefer Legacy in some scenarios and Physical in other, feel free to do so!

Thanks for the feedback, we are closely monitoring it for future tweaks and updates.
Jan

So for the record, does the Corona team _not_ want to allow for control of reflection {color,glossiness/roughness,IOR} independently of that of refractions in the Physical Material?

5
I kinda understand why you're saying this but your examples are really not showing anything.
Studio glass photography is a hack from start to end, always. Plus some (or a lot of) retouching. Also, your example shows nicely what studio lighting is about - creating soft gradients and sharp contrasts with creative lighting. The material has no blurriness here, it's a matter of how the studio is set up.
I'm pretty sure the second example is all about retouching. The original photo probably didn't have any tinting in it, it's all post production.

With that said - have you tried to recreate the examples you are talking about with PBR mats within a Layer material? I think that in some cases it'll be the only way to achieve a few effects like tinted reflections etc with the new PBR material.

I've played some time with it and yes, some things are harder to produce and may require the use of Layer material. Working with reflection maps got harder now since we're mapping IOR and the current behavior is not the most convenient. On the other hand, the material produces really great results.

I don't want to be in the developers' position right now - creating a material that allows for the same functionality while not breaking physical rules is probably impossible, and to make the UI nice, logical and convenient at the same time... that's really hard, and maybe impossible without sacrifices in other places.

I hear what you are saying. Unfortunately, I do not see any way to use Layer material to “lessen, blur, or re-color” the harsh reflections of an almost perfectly smooth refractive material. I need something that basically subtracts from the material (at least for the case of re-color and dim/lessen, when it comes to reflection), not adds on top of (re: layer material), for which clear coating can suffice. If I diminish a refractive material in any way via the layered material, I will affect its refractive properties as well as its refractive (which I want to remain at full brightness and unaffected).

If you know of a way to darken, blur, or re-color _just_ the reflections of a material without resorting to masking/compositing, feel free to describe said method in greater detail. I haven’t been able to find any way to do that using materials (including Layer Material) and their properties, alone. If such a workaround already exists, and I just haven’t found it, then there will be nothing to complain about with regard to highly glossy transparent materials. I love the new physical material for most textures, it’s just this shortcoming for highly transparent materials that makes it unusable for some common real world glass/crystal/acrylic highly transparent objects, when hard lighting is present and visible in their reflections (and cannot be toned down/blurred without touching the lighting itself, which of course cascades to other properties of the material and other objects and their materials, that are illuminated directly/indirectly by the same light).


6
[C4D] Daily Builds / Re: New material
« on: 2021-03-24, 16:27:28 »
...
Stay tuned for future daily builds if you'd like to get your hands on materials sooner than the release...

Little advice, change the name from daily to monthly builds :D

Hahaha, true dat! Max just got a fresh new build.

Where is the Cinema 4D version with all those added features, especially with regard to the new Physical Material?

7
And on this very topic:

Note: While you can use Clearcoat to increase reflection intensity over a lower IOR Base material as above, you cannot reduce the reflection intensity of a high IOR Base material. This is an example of a constraint introduced by physical realism.

Quoted from: https://blog.corona-renderer.com/behind-the-scenes-the-physical-material/

Well, I beg to differ (see attachment 1). Plenty of blurriness (and darkness) in the reflections, in a completely transparent (i.e., nearly 0% roughness/100% glossiness) material with a reasonably high IOR of at least 1.53 or higher.

And with regard to coatings, see attachment 2, or did you guys completely forget that there are anti-reflective coatings that can reduce, dull, and convert (to transparency) the original material's reflective properties?? Which by the way would necessitate separate color, glossiness/roughness, and IOR controls for reflection (at least at glancing angles, due to Fresnel affect), while making the reflection of the original uncoated material get converted into refraction (well transmission, to be physically correct) when the object is viewed head on (i.e., directly along its normal vector).


8
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.


9
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.



10
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).

11
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.

12
Check "Physical Metals" thread, if it can be of any help.

Unfortunately most of that thread is old combined with "not presently possible in Corona." I was hoping that with the new physical material, some progress could be made on getting metals to looks somewhat realistic.

13
[C4D] Daily Builds / New Corona Physical Material and Metals
« on: 2021-02-21, 21:13:22 »
So in trying to use the new Physical Material to form metal surfaces, I've noticed the following limitations (either in the material itself or my understanding of how it works). Everything discussed below is with the Metalness Mode set to Metal

#1.
In Metal mode, our ability to control IOR gets disabled. Now, my understanding is that IOR is now controlled indirectly via Base Layer color and Roughness/Glossiness.

But, different metals have different Fresnel curves for reflection. For example, compare the Fresnel curve for Bronze with the Fresnel curve for Copper. This can be easily done in the Corona Node Material Editor:

Steps:

1. Create two Fresnel Shaders (New Shader/Fresnel)
2. Turn on Physical in the properties for both and set the Preset for one to Copper and for the other to Bronze.

Compare the resulting gradients.

Attached is an image showing four such gradients for Copper, Bronze, Iron, and Nickel.

Although it is true that their colors are different, the Fresnel curves for the four metals are vastly different. Compare for example the Iron curve with the Nickel curve.

So, my point is that with the inability to supply a proper Fresnel curve for our metal, we have no control over the type of metal we are trying to represent.

#2.

Taking this a step farther, it would be nice to enter the Red, Green, and Blue n/k value separately, since they are not necessarily the same for metals.

For example, SigerShaders has a nice free Complex Fresnel plugin for 3ds max that takes the Normal Incidence (n) and Extinction (k) values for each of the three primary colors to come up with a Complex Fresnel curve, that they have created based on Vlado's Complex Fresnel OSL shader code at: https://docs.chaosgroup.com/display/OSLShaders/Complex+Fresnel+shader (See the second attached image for its UI).

Can something like this be done for Corona for Cinema 4D, to make metals render more realistic?





14
I used your formula for the glass, but used the Diamond preset for the bubbles, otherwise, they disappear if the refraction is the same.

The bubbles disappear probably if you don't make their normals "inside-out" . That is their "blue" sides should be towards the outside and their "yellow/orange" polygon sides should be towards their respective centers.

Here is a picture of something like what I am trying to achieve (from an item being sold on eBay). Notice the translucency and blurriness of the white swirls inside the marble:


15
PS what I describe with 2 spheres is for those "swirls of color inside the marble" - it wouldn't work for cracks or bubbles, because those need refraction and reflection, and volume materials don't have refraction or reflection.

And a PPS, turning on absorption etc. in a normal material only gives a homogenous result, that is, color etc. is taken to be the same all the way through the material, so it can account for depth of the material (how much of the material light is passing through) but the material is assumed to be the same all the way through and not varying in 3D space. Heterogeneous volumes that change in 3D space require the dedicated Corona Volume shader.

THIS, THIS is the problem. I would use a volume material for the whole thing, but as you pointed out:

Volume materials don't have reflection or refraction (or an IOR!!) making them only useful for non-solid translucent visual effects like smoke, fire, etc., and not for solid objects like glass or other transparent/translucent solids with actual textured structure inside of them.

This is why I tried to get things to work with a Physical Material and discovered that I can only texture its surface and not its inside volume.

Since modeling Cinema 4D 3d noise would be very painful, I will try your approach of putting a volumetric material inside of a physical material and see where that takes me.

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