Dark buckets - Rendered on single workstation - linked to HDRI in Vray Domelight

[rjohnson33]

Hello,

I'm having problems with darker buckets rendering here and there on a scene. I know there are lots of 'dark bucket' threads on the forum but they all seem to relate to distributed rendering. I'm just rendering on a single workstation.

The issue seems to be linked to a Vray Domelight with HDRI. The darker buckets show up only in the vrayglobalillumination and vraylighting elements as far as I can tell.
I have tried different HDRI's, different texture resolutions and different subdivs in the HDRI. I've also tried recreating the light from scratch - none fix the problem.

Vray version is 3.00.03
3ds Max 2012 x64
GI is BF + LC

I have been working with this scene for quite some time and doing test renders but I only started to notice this happening yesterday.
I don't know if it could be of any relevance but I did use the RebusFarm plugin for the first time to export to the render farm yesterday also.
It didn't work first time around so I merged the entire scene into a new 3ds max file. I think that this started occurring around then but can't pinpoint it.

I've attached an example. The darker buckets are most obvious on the floor and the wall/ceiling to the left.

Any ideas why this might be happening please?

[rjohnson33]

I've just gone back to a version of the scene before I merged into a new scene and uploaded using the RebusFarm plugin and the error still exists so there is no relationship to that event.

[tashko.zashev]

Hi,

Is it possible to send us all files required to reproduce the bucket differences?
We have a similar report in the past with different buckets when very high dome light subdivisions are used, but I'm not sure if this is the same case.
It will be best to check the scene.

[rjohnson33]

Hi,

Is it possible to send us all files required to reproduce the bucket differences?
We have a similar report in the past with different buckets when very high dome light subdivisions are used, but I'm not sure if this is the same case.
It will be best to check the scene.

I will do, thanks. It's quite a heavy scene but I'll see if I can strip it down to the basics and still reproduce the same error with the buckets. Where should I send the scene to please?

[rjohnson33]

I've been running some tests on this using a simplified version of the scene and have found that the darker buckets can be eliminated if I raise the bucket size - originally I had it set at 8x8.
The smaller I make the size the more frequent the dark buckets are. I seem to lose them altogether at values above 16x16.

Also raising the subdivs in the domelight is solving the problem. I didn't think it was initially (setup is universal - 1 to 100 AA and min shading rate 5) but if I go up to 512 in the light I can use 8x8 buckets.

So the strange thing is that with 512 domelight subdivs & 8x8 buckets there is no issue but with 512 domelight subdivs & 4x4 buckets the dark buckets are back.
Why should the bucket size even have an effect?

[vlado]

So the strange thing is that with 512 domelight subdivs & 8x8 buckets there is no issue but with 512 domelight subdivs & 4x4 buckets the dark buckets are back. Why should the bucket size even have an effect?

If the bucket size is too small, it may happen that none of the initial shadow rays make any contribution and V-Ray will assume that the entire bucket is black. Increasing the bucket size increases the chances that an actual light contribution is detected, which will cause the bucket to be sampled appropriately.

Best regards,
Vlado

[rjohnson33]

Ah, I see, that makes sense now thank you. I hadn't previously thought that all of the pixels in a bucket shared sampling info in that way.