I'm working on my physically based renderer, and I've come to a sort of crossroads regarding the Fresnel factor. I'm having trouble finding the best way to represent it. I know that Schlick's fresnel approximation is based off IOR, but IORs can go up to 38.6 for a meta-material, and 4.05 for an actually natural element, Germanium (Source: https://www.quora.com/Which-medium-has-the-highest-refractive-index), which will make representing these in a 0-1 image difficult, as well as confusing. I also noticed no one really uses IOR maps.

I also read this paper on Unreal's PBR integration ( https://de45xmedrsdbp.cloudfront.net/Resources/files/2013SiggraphPresentationsNotes-26915738.pdf ), and I discovered that they initially wanted to use a F0 of 0.4 for non-metals. What would be the F0 for metals in this case, and isn a static value, 0.4, worth the limitations for that TINY bit of memory? I believe the F0 tends to the Base Color as it becomes more metallic, but I'd like confirmation.

And finally, there's reflectivity or specular, as is used in modern PBR equations. Is there a standard for this in regard to getting an F0, because it seems arbitrary (is it a float value up to that directly maps to F0?

Ultimately, I'm asking for a comparison between methods, please!

And I know this is sort of unrelated, so I'm not going to officially ask for it, but are there any real reasons NOT to combine specular color and base color, as Unreal has done? I can't think of a single real reason, even for more stylized stuff.

I'm working on a physically-based renderer, and I've come to a sort of crossroads regarding the Fresnel factor. I'm having trouble finding the best way to represent it. I know that Schlick's Fresnel approximation is based off IOR, but IORs can go up to 38.6 for a meta-material, and 4.05 for a natural element, which will make representing these in a 0-1 image difficult and confusing. I also noticed that no one really uses IOR maps.

I also read a paper on Unreal's PBR integration, and I discovered that they initially wanted to use a F0 of 0.4, for non-metals. What would be the F0 for metals, in this case, and isn't the static value of 0.4 worth the limitations for that tiny bit of memory? I believe the F0 tends to the base color, as it becomes more metallic, but I'd like confirmation.

Finally, there's reflectivity or specular, as is used in modern PBR equations. Is there a standard for this, in regard to getting an F0? It seems arbitrary; is it a float value up to that directly maps to F0?

I am not sure if there are any real reasons to not combine specular color and base color, as Unreal has done this, before. I can't think of a single real reason, even for more stylized implementations.

What is the best PBR real time Fresnel function?

So I'm working on my physically based renderer, and I've come to a sort of crossroads regarding the Fresnel factor. I'm having trouble finding the best way to represent it. I know that Schlick's fresnel approximation is based off IOR, but IORs can go up to 38.6 for a meta-material, and 4.05 for an actually natural element, Germanium (Source: https://www.quora.com/Which-medium-has-the-highest-refractive-index), which will make representing these in a 0-1 image difficult, as well as confusing. I also noticed no one really uses IOR maps.

I also read this paper on Unreal's PBR integration ( https://de45xmedrsdbp.cloudfront.net/Resources/files/2013SiggraphPresentationsNotes-26915738.pdf ), and I discovered that they initially wanted to use a F0 of 0.4 for non-metals. What would be the F0 for metals in this case, and isn a static value, 0.4, worth the limitations for that TINY bit of memory? I believe the F0 tends to the Base Color as it becomes more metallic, but I'd like confirmation.

And finally, there's reflectivity or specular, as is used in modern PBR equations. Is there a standard for this in regard to getting an F0, because it seems arbitrary (is it a float value up to that directly maps to F0?

Ultimately, I'm asking for a comparison between methods, please!

And I know this is sort of unrelated, so I'm not going to officially ask for it, but are there any real reasons NOT to combine specular color and base color, as Unreal has done? I can't think of a single real reason, even for more stylized stuff.

Thank you, guys!

I'm working on my physically based renderer, and I've come to a sort of crossroads regarding the Fresnel factor. I'm having trouble finding the best way to represent it. I know that Schlick's fresnel approximation is based off IOR, but IORs can go up to 38.6 for a meta-material, and 4.05 for an actually natural element, Germanium (Source: https://www.quora.com/Which-medium-has-the-highest-refractive-index), which will make representing these in a 0-1 image difficult, as well as confusing. I also noticed no one really uses IOR maps.

I also read this paper on Unreal's PBR integration ( https://de45xmedrsdbp.cloudfront.net/Resources/files/2013SiggraphPresentationsNotes-26915738.pdf ), and I discovered that they initially wanted to use a F0 of 0.4 for non-metals. What would be the F0 for metals in this case, and isn a static value, 0.4, worth the limitations for that TINY bit of memory? I believe the F0 tends to the Base Color as it becomes more metallic, but I'd like confirmation.

And finally, there's reflectivity or specular, as is used in modern PBR equations. Is there a standard for this in regard to getting an F0, because it seems arbitrary (is it a float value up to that directly maps to F0?

Ultimately, I'm asking for a comparison between methods, please!

And I know this is sort of unrelated, so I'm not going to officially ask for it, but are there any real reasons NOT to combine specular color and base color, as Unreal has done? I can't think of a single real reason, even for more stylized stuff.