Problem with GI shadows

[VISUALMAN_TOKYO]

Hi noticed that when using 3d motion blur and override environment (only reflection and refraction) I get very weak GI shadows. I am rendering a fast moving car and without motion blur the character inside the vehicle is quite dark, but when using motion blur it gets very bright, same happens with the shadow area on the tires.
Is there anything that can fix this issue? Using maya 2016 on windows with vray3.1

[VISUALMAN_TOKYO]

Actually the problem happens even just using a dome light with an hdr, without using override environment. Is it a known bug or else?

[yolov]

Can you share a simple scene that shows the problem? I couldn't quite get the same result on my end.
Thanks in advance.

[VISUALMAN_TOKYO]

I tried to reproduce it on a simple scene but I don't see the problem either. In my scene either rendering locally or mayabatch I have the same problem.

[yolov]

Can you send us that scene ?

[VISUALMAN_TOKYO]

I will try to send it to you after the project is done, now I am not allowed to send the data, as for the issue I will fix it in compositing.

[yolov]

OK. Until then, if you think you can just replace some scene objects so it's safe to send them to us, please let us know. We'd like to see if there's a bug somewhere or not, but we couldn't reproduce it here.

[VISUALMAN_TOKYO]

Hi Alex, I sent an email to support with link to the scene. The same scene also causes the problem described in "Vray multipass render - Nuke rRgG channels" thread.

[yolov]

I just got the scene and I noticed a few things:

1. You have disabled refractive caustics, which basically means that vray will not trace GI behind refractive objects. Try enabling it and see if it helps, it is always enabled by default (render settings > GI > refractive caustics).
http://docs.chaosgroup.com/pages/vie...activeCaustics

Note: the reflective caustics are always disabled by default, because they usually slow down the render significantly

2. You have enabled motion blur both in your physical camera and in the global settings (render settings > vray > camera)
http://docs.chaosgroup.com/display/V...CameraOverview

These global settings are ignored for the physical camera, so you can disable them if you're not using standard cameras in your scene too. However the prepass samples and geometry samples always affect the scene for all cameras.

[VISUALMAN_TOKYO]

I know that global settings motion blur is ignored when using physical cam motion blur that is why I never turned it off, however the problem still persists even if I turn off physical camera. I don't think it is a problem of casting caustics behind refractive material either, because the car tires are not behind glass and they have the same issue. Even enabling refractive caustics nothing changes. I suggest you to try to render twice the same frame (try around frame 36) with and without motion blur and you will notice the difference in brightness in the shadow areas (I am not talking about small difference, it looks like there are no shadows at all). without motion blur everything looks correct.

[yolov]

You are correct, there is in fact something wrong there. I've narrowed it down to the geometry samples for motion blur. If they are set above 2, things get a bit strange. I've logged this to our system and I'll update you when we have some news on this.

[VISUALMAN_TOKYO]

Thanks, look forward to find a solution, I got this issue on another project, though it was less visible. By the way when I am using VrayRT for lights setup, it renders correctly even with motion blur.

[VISUALMAN_TOKYO]

Hi, is this issue been fixed with the latest 3.3?

[Svetlozar Draganov]

It is not fixed yet, we'll let you know when it is.