Issue: Glass and Transparency, it does not look like glass

[Uhlhorn]

Hi,

if I compare the renderings of my glass bowl, rendered in Modo 902 and rendered in V-Ray, the edges does not look like glass (refer to the images). Is it possible to get an better result?

Rendered in V-Ray:


Rendered in Modo 902:

[Lupaz]

I'd check that "max depth" is high enough and that you add some greenish color to the fog of the material. Also enable reflections on both sides.

[Uhlhorn]

The modo material does not have fog or reflections on both sides. I have to make a new material in V-Ray.

[vladimir.nedev]

Are you using MODO's Advanced material with V-Ray ? I have a bug when handling these materials when they don't have "Double Sided" enabled.
Check "Double Sided" and see if this fixes the problem.

It will be best to send me the scene, so I can confirm the problem, and later the fix for it.

Greetings,
Vladimir Nedev

[Uhlhorn]

It will be best to send me the scene, so I can confirm the problem, and later the fix for it.

I have made the scene file public: Choco_Drops_3D_0015_V-Ray_v3_bundled.zip

[Lupaz]

I'm curious if you got this to work in the end.
Thanks.

[vladimir.nedev]

In the latest nightly builds, the absorption distance of MODO's material will be respected by V-Ray.
That's where the slight blue tint on the glass in MODO's renderer comes from.

Also, by mistake I had applied the "transparent amount" twice on each refraction, when the MODO material is in "Physically based" mode.
That's why it looks much darker in the V-Ray version. That's also fixed in the nightly builds.

Still, I haven't solved all the problems, the glass in the V-Ray version is still somewhat darker. And the fix created problems when "dissolve" is used.
So I need to redo my solution and then I will report back with the results, and hopefully renders.

I also found an internal precision bug that affects both the MODO material's "absorption distance" and V-Ray fog color/multiplier.
Internally both of these implement what is known as "Beer's law", so they are really the same physical effect.
The bug happens only in V-Ray for MODO because of the scene units that MODO uses - meters, whereas
Max/Maya usually use centimeters/inches, where the precision is enough. This bug is not fixed yet.

Edit: In V-Ray for 3ds Max the precision bug is not present even if the scene units are meters.

Greetings,
Vladimir Nedev

[Lupaz]

Thanks.

I don't have Modo so I couldn't try this scene in Max (I know, this is the Modo forum). However I created my own scene using Uhlhorn's HDR.
The result with RT is pretty good (not as good as ulhorn's modo scene though).
The result with Vray production is horrible. I'm probably missing something stupid, but I still don't understand why the difference between RT and Production "out of the box".
GI is BF and LC, default.

The result with Corona was good on both production and interactive.

My questions are, is it possible to get with Vray for Max the same result as Modo's renderer? And, why does the result with vray production look like this?

VrayRT:



Vray 3.2:


Corona Interactive:


Corona Production:



Should I post this in a different forum? Just let me know.

I can upload the scene, but I don't know how to. The forum allows to upload only images.

Thanks.

[vladimir.nedev]

You can zip the scene and then you might be able to upload it. Or use "wetransfer.com" or something similar and post the link.

Out of the box, I think V-Ray RT uses a different default ray depth, but it is lower (to facilitate faster preview), so it seems the result should be the opposite of what you have.

Also, V-Ray RT CPU doesn't use the light cache, so that's a possible source of the difference.

Which V-Ray for 3ds Max version are you using ?

Greetings,
Vladimir Nedev

[Lupaz]

Here's the scene:
http://we.tl/YQUb3CKZd5

I used vray 3.2

Thank you.

Edit: in vray production, checking "abbe number" does the trick.

[vladimir.nedev]

Are you sure about the "abbe number" ? I don't think it can have that effect.

It looks like there is a bug in the production mode of V-Ray for 3ds Max.
If refraction depth of the material is larger then the reflection depth of the material, you get this black shadow inside the glass.
Try setting both to the same value (64-64, 300-300, whatever).
The bug might be present in V-Ray for MODO as well, need to check.

In RT mode, there is a separate depth which is 5 by default. See image. That's why it is working there. I am not sure, but probably it overrides the reflection/refraction depth of the material completely.



Greetings,
Vladimir Nedev

[vladimir.nedev]

Yep, same thing happens in V-Ray for MODO.
Basically, because the reflection depth is lower than the refraction depth, it gets reached first, and the reflection exit color (which is black) gets used. So that's where the black edge comes from.
Not sure if that was always the behavior, but it seems we should do something about it, as it is a pretty serious caveat.

Greetings,
Vladimir Nedev