Reflection glossiness seems off somehow

[vkiuru]

Using Alpha 5, I'm having difficulties getting glossy reflections to look glossy enough. A quick render, the wood is supposed to be almost matte:



Reflection glossiness is set to 0,05 which is  really extreme, yet the reflection behaves much like Vray glossiness at around 0,6. Any ideas?

[Ludvik Koutny]

Disable bump if you have any.

[vkiuru]

Thanks, I'll try. In the meanwhile another test. A simple scene, sofa material is Corona material,
diffuse RGB: 2,2,2
Reflection: 0,3
Refl. Gossiness: 0,001

In other renderers I've used a reflection setup like this (although glossiness value has never been this dramatic) to simulate fabric falloff like the one in velvet, yet somehow this looks strange in Corona.. it's especially visible with the blanket on the left. Am I imagining things?

[Ludvik Koutny]

There is some limit on how low can glossiness go. Vray has specific BRDF that can produce nearly diffuse glossiness, but may look less realistic in different scenarios.

As for velvet. it usually has a lot higher IOR, somewhere between 3-5, and lot lower reflection level. So tweaking just glossiness itself won't do it.

[vkiuru]

There is some limit on how low can glossiness go. Vray has specific BRDF that can produce nearly diffuse glossiness, but may look less realistic in different scenarios.

As for velvet. it usually has a lot higher IOR, somewhere between 3-5, and lot lower reflection level. So tweaking just glossiness itself won't do it.

Thanks. Are there plans to further refine the glossy behaviour? as it it now, the limit you mentioned seems pretty high. I might need to do some comparative tests with other engines though, there's a chance I'm falsely nostalgic over the effect I've gotten out of Vray, Maxwell and the like in the past.

[Ludvik Koutny]

There is some limit on how low can glossiness go. Vray has specific BRDF that can produce nearly diffuse glossiness, but may look less realistic in different scenarios.

As for velvet. it usually has a lot higher IOR, somewhere between 3-5, and lot lower reflection level. So tweaking just glossiness itself won't do it.

Thanks. Are there plans to further refine the glossy behaviour? as it it now, the limit you mentioned seems pretty high. I might need to do some comparative tests with other engines though, there's a chance I'm falsely nostalgic over the effect I've gotten out of Vray, Maxwell and the like in the past.

I do not think this will change. For example mental ray has glossiness threshold even higher and yet it sufficed in production for many years on many movies.

As i said, try to tweak ratio of reflection level (not glossiness) and reflection IOR to achieve something closer to velvet. Reflection glossiness of 0.1 should suffice for that. I may try to do some examples, but i am currently at work ;)

[vkiuru]

Ok, understood :) Yeah I'll start experimenting with the IOR values and such once I get the time.

[Ondra]

ok, not really a bug

[vkiuru]

Yeah not a bug, then.

Anyway, I'm trying to get a sofa to look right (again) and this still confuses me. How should I go about replicating a fabric? Is a falloff diffuse really the only way to get anything like the low glossiness reflection effect, because it's nineties as hell. Overall I don't think the glossiness curve Corona has right now is quite natural. Am I doing something wrong here or do others have the same problem?

[Juraj]

Yeah not a bug, then.

Anyway, I'm trying to get a sofa to look right (again) and this still confuses me. How should I go about replicating a fabric? Is a falloff diffuse really the only way to get anything like the low glossiness reflection effect, because it's nineties as hell. Overall I don't think the glossiness curve Corona has right now is quite natural. Am I doing something wrong here or do others have the same problem?

Yes, diffuse only. I do agree the curve is bit odd. In best practice , low glossies, even at full specular reflection (ideally, there is no reason to lower it) should produce identical look to fully lambertian shader.
In most renderers (with exception of Maxwell) this doesn't happen (and instead, often leave artificial 'sheen' )...and imho complicates life, because you have to tweak it with wrong stuff (lowering actual specularity, ior/curve,etc...) to achieve your needs.

[it works excellently in Disney's modeled PBR, like in Unreal4, :- ) ..]

[Javadevil]

There is some limit on how low can glossiness go. Vray has specific BRDF that can produce nearly diffuse glossiness, but may look less realistic in different scenarios.

As for velvet. it usually has a lot higher IOR, somewhere between 3-5, and lot lower reflection level. So tweaking just glossiness itself won't do it.

Thanks. Are there plans to further refine the glossy behaviour? as it it now, the limit you mentioned seems pretty high. I might need to do some comparative tests with other engines though, there's a chance I'm falsely nostalgic over the effect I've gotten out of Vray, Maxwell and the like in the past.

I do not think this will change. For example mental ray has glossiness threshold even higher and yet it sufficed in production for many years on many movies.

As i said, try to tweak ratio of reflection level (not glossiness) and reflection IOR to achieve something closer to velvet. Reflection glossiness of 0.1 should suffice for that. I may try to do some examples, but i am currently at work ;)

  For velvet doesn't it use an inverse curve ? you need to control the 0-90 reflection so 0 no reflection and at 90 degrees has reflection.  Corona can fake it with the falloff map in the diffuse.