Is there a problem with the Specular material ? Tweet

[itsallgoode9]

I've recently ran across this issue that makes it seem as if there are issues in the specular material's lighting model. Basically, it seems the Reflectivity setting is directly affecting the amount of light getting through the glass. This is causing the glass to darken and reduce the amount of caustics seen. Renders are done in PMC with 100 spec bounces and 16 diffuse; the scene is lit with an HDRI. When testing, I set every render setting to both extremes and a middle value but nothing fixed the problem. The fresnel material is just using a falloff in the reflectivity setting with values of .04 and 99 and only a rough approximation of a full fresnel Falloff (note that this darkening issues still happens exactly the sameif i'm not using the falloff node).

Notice the lack of caustics as the reflectivity value gets lower. Notice that the base of the glass only looks correct in the 90% reflection render but this leaves the rest of the glass lacking in detail/contrast. The fresnel glass looks correct mostly but the interior of the glass at the base is going way too dark and the caustics are being reduced.:


This issue may not seem like a huge deal in the above image but seen in more complicated renders, it really starts to cause issues Notice the base of the bottle being way too dark in the fresnel render and the darkening in the neck glass outside the cork:


Could somebody from Octane chime in about this? Is this actually an issue or is it something to do with my scene/settings? I make my living rendering bottles so this issue is pretty major for me, and hopefully we c an git this figured out or resolved.

***i'm not meaning to step on anybody's toes bringing this issue up. I tried to do test in every way possible to make sure it wasn't just and issue I was causing myself. Tonight I will be doing a test in Maxwell render to see how glass with low reflectivity looks in there and I'll post updates

[prodviz]

I'm sure it's not this; but just to rule out, is your transmission on white for all shaders?

[itsallgoode9]

I'm sure it's not this; but just to rule out, is your transmission on white for all shaders?

yeah, i just double checked and it is. although you're right, it does just look like transmission is low. i wonder if i can use a float texture and put a value greater than one to offset that darkening issue. I'll give that a try tonight.


update: nope, that doesn't do anything

[abstrax]

Check your normals.

[itsallgoode9]

Check your normals.

hey Abstrax, I just checked them, all are facing outward. I just tried it with a brand new cylinder with no settings chagned, to make sure it wasn't my model and it still happens. I've had this problem in my other scenes well.

Here is a Maxwell render test showing comparable images to the glasses above. notice that reflectivity amount is not affecting the light absorption/refractions of the glass. This is the result i'd expect/hope to see in Octane:

[whersmy]

did you check the rayepsilon? scene scale is fine?
and do ground and glass have a 0.1mm offset space between them?

[itsallgoode9]

did you check the rayepsilon? scene scale is fine?
and do ground and glass have a 0.1mm offset space between them?

yep. Scene units in maya is in CM and the scene scale in octane settings is .01 to account for that.
tried various ray epsilon settings and pretty much ever setting except default just makes things worse. .0001, .0005, .001, .01, 1, 2 and more. I figured that covered wide enough range of settings.

Tried with floor both on and off, and on but moved away from the glass' by 1mm. no change

[abstrax]

did you check the rayepsilon? scene scale is fine?
and do ground and glass have a 0.1mm offset space between them?

yep. Scene units in maya is in CM and the scene scale in octane settings is .01 to account for that.
tried various ray epsilon settings and pretty much ever setting except default just makes things worse. .0001, .0005, .001, .01, 1, 2 and more. I figured that covered wide enough range of settings.

Tried with floor both on and off, and on but moved away from the glass' by 1mm. no change

I see your problem now. It seems that the amount of light that is refracted is independent of the amount of light that is reflected. The refraction part always assumes that the amount of light that is reflected is like a 100% fresnel reflection. We will have a look at it.

[itsallgoode9]

Awesome, thanks SO much Abstrax, this issue has ben the death of me for some time now!

[itsallgoode9]

any chance this would be fixed in the next update? i've got a couple pretty big projects starting soon and this would make life so much easier to not have to work around this.