Author Topic: New Corona Physical Material and Metals  (Read 532 times)

2021-02-21, 21:13:22

SharpEars

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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?





2021-02-21, 22:57:15
Reply #1

burnin

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

2021-02-22, 10:45:58
Reply #2

mmarcotic

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Hello,

thank you for the feedback.
The Physical material is not at all in its final stage and there will be more improvements down the line. The developers are looking into adding more control over the metal reflection (Fresnel) before V7 release (don't quote me on this), the approach to its implementation is however not set in stone yet, so there is no real ETA.

Thank you again,
Jan

2021-02-22, 23:11:37
Reply #3

SharpEars

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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.

2021-03-02, 22:12:04
Reply #4

lllab

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overall the metalness has more realworld than the old methods with "specular reflection" and ior. the reflection color of metals is always 255 i the glancing angles,which is only fully possibe with the metalness method, which puts the "color" in diffuse", and keeps the reflection white. Vlado explained this well in the past:

https://www.chaosgroup.com/blog/understanding-metalness

that said i am also amazed that the ior is greyed out inc orona. even though it makes only a slight difference for metal ness workflows usualy there are ior values used close to 1. here a table from vray 5 which is more or les the identicalmaterials as system as v7 it seems:

https://docs.chaosgroup.com/display/VMAX/Metal+Shaders+IOR

in vray 5 wich has all same settings, they kept the ior ungreyed and have even given a lost on usual ior values and colors, for metals with metalness workflow.
i hope the ior can be opened also in corona v7 to be set freely in metalness mode?