​​​​​​​Confusion how falloff works to control IOR

[dcode]

Hi Andrey,

Hope you can help, my ultimate goal is to use a custom output curve in the falloff map to control material IOR.
I have two reasons for wanting to do this, number one to dial in true physically accurate IOR curves for different materials and secondly to create unique effects (say for example weld discoloration).

My question is how do I turn off the falloff map preset so that the output curve takes over and does not just multiply over the presets. I tried setting falloff IOR to 0 to flatten the curve but this did not work in my tests.
I believe in Vray and Corona by activating the output curve map in the falloff map it deactivates the falloff preset by default??
With both those two engines you are also required to dial in 999 (or something along those lines) in the IOR to deactivate material base IOR before putting a map in.

I also noticed that a falloff map with IOR 1.5 assigned to the IOR map does not create the same IOR as a material with 1.5 IOR in the material settings.
I have attached images to explain, I did try to dial IOR up to 999 to deactivate the material setting as with Corona but to no success.

Many thanks!!

[Karba]

if you want to do proper comparison, you have to set ior in material (not in falloff texture) to 1000 in order to disable fresnel effect and put falloff texture to reflection slot.

[dcode]

Hi Andrey,

Doh......yep many thanks! Indeed that makes perfect sense I was plugging the falloff map into the wrong slot.
Tried again with the 1000 IOR cutoff and correct slot and although still not a perfect match they were close enough.

As for second observation there is still not an apparent way I can figure out to use the newly added output curve to produce a physically accurate custom fresnel.
Currently it appears to additively effect the falloff setting already in place rather than deactivate it and use the custom curve independently. Is this a feature that needs to be added or is there another method to achieve this?

Thanks again!

[Karba]

"physically accurate custom fresnel"
It sounds silly already.
default falloff settings gives you cosine of ray angle as initial input. It is up to you how to use it.

[dcode]

No not at all. Custom, ie. the user can create their 'own' curve instead of a default setting. Physically accurate because it is from scientific data ie. https://refractiveindex.info/.
The Grant Warwick Vray method to reproduce metals from data using this method, I thought, was the most realistic I had seen.
That is only one aspect of how to use a custom curve another is for more artistic purposes, velvet, heat coloration etc. Sorry I thought is was a reasonable question/request.

[Karba]

Try to use this type of falloff settings

[dcode]

Cheers Andrey! That helps enormously, using your approach I have also tried to tweak the index curve to be as straight as possible, assuming this to be the closer to correct output.
I have tried some tests for gold and plastic using data from https://refractiveindex.info/ (method stolen from Grant Warwick) and tried a more artistic approach for a heat treated aluminium manifold (which is far from correct but a good initial experiment). Thanks again!

[dcode]

Gold setup

[dcode]

Plastic setup using Polycarbonate data.

[dcode]

Heat Treated Manifold experiment

[GeorgeK]

Gold setup



[ATTACH=CONFIG]n11274[/ATTACH] [ATTACH=CONFIG]n11275[/ATTACH]

Hi, Dcode , would you be so kind to share the details of that lovely gold material above? Im very new with fstorm and rendering in general and mine does not turn out like yours on that ring picture.
Thanks!

[dcode]

Hi George,

If you are new to rendering it is probably better to get some basics in first.
A good HDRI will help you to get going, I recommend one of Maxime Roz's free interior ones, :-

http://www.maximeroz.com/hdri/

One of those should get the reflection details in and have good EV range for realism.

I could just give you the material but that teaches you nothing.

For a Gold material, start with a dark grey diffuse colour. Technically it should be black but generally no real world metal will have an immaculate surface so metals look more true to life with a very dark grey diffuse, some people make the dark grey warm or cool depending on the metal type.

Now you have two routes for reflection, basic and complex.

A basic gold will have a default IOR of around 15+ and a coloured reflection texture with a very slightly rough surface (glossiness 0.95) so it is not too perfect.
CGMood offer a very good choice of free gold materials, they put a falloff of gold/yellow to white in the reflection colour which is very effective as it adds a deeper gold into the shaded parts of a model and a near white on extremities. You can download here:-

https://cgmood.com/search?search=gold

Now I was attempting to replicate a method for a complex fresnel which uses real world data and was developed by Grant Warwick and one of his colleagues.
If you are familiar with Vray or Corona it offers essentially the same results as Siger's free complex fresnel plugin.
If you can find it online, the method is described in his second video of the Mastering Vray series, I can not remember if it was a free vid or not, I was a subscriber so I don't know.
At current in Fstorm you can not duplicate exactly the method as it does not offer the same linear falloff option that the standard 3DS max falloff does, so I have tried to approximate a straight line response as best as I could using the method Andrey suggested. (hey, this is all to the best of my own knowledge and would love to be corrected). Using the output curve you can then change the response of the linear falloff to match real world data, my setting are all in the jpeg attached with the ring image.

As for the rest of the material they were just artistic, a gentle fine bump map using Fstorm scratches to replicate wear and a mix material with a simple dark brown matt material that is mixed in using Fstorm dirt on a very small setting just to get a small amount of dirt into crevices.

You can also put scratch, dirt and grunge maps into the reflection glossiness slot for more interesting effects, hope this helps.

[Iskánder ivp87]

Hey decode, your heat curves are sick, how did you came out with that!??

[Iskánder ivp87]

another method, more simplified, you could use a mix map with white in color one and the other color in the other slot, and then using the falloff in the mask slot, nevertheless karba would have to tell us if it's more inefficient or slower, but is a lot more easy to setup, that's sure
that way you can control the exacts colors you want and the exact mix curve separately, very useful to matching certain rose-gold tones or anodized surfaces shades
but it's unable to do anything like your heat treated manifold!

[dcode]

Hey decode, your heat curves are sick, how did you came out with that!??

Thanks Iskander, when I used to use Corona and Vray I experimented a lot with custom fresnels.
Although not as accurate with Fstorm I am getting close to same results. It is fun to play with, I'll probably add more experiments in the future.