Light artifacts in reflection using V-Ray GPU 5, hotfix 2

[lightwriter]

Good afternoon,

I noticed artifacts in some lights (but not all) reflected in a mirror. These artifacts appear when using Engine type CUDA with only the graphics card (RTX 2070 Super) or the CPU+GPU.
Those same artifacts don't appear when I render using V-Ray 5, hotfix 2 (only CPU).

The settings are the same (or as close to the same as they can be), as is visible in the title of every image. VRayLanczosFilter was used in both examples. I have the latest Nvidia Studio driver, released 2021-01-26.

Is there something I can do to solve this?

Software: 3ds max 2021.3, v-ray 5 hotfix 2

[GregCooper]

I can't see the artifacts in those images cos they're coming up super tiny for me, But I'm getting some artifacting in my reflections using CUDA as well. Strange square areas that are lighter than they should be. They seem to be only appearing using light cache however, switching to Brute Force for GI and there's no artifacts.

Maya 2020.4, Vray 5 hotfix 2

[GregCooper]

You guys want a scene to analyse?

[lightwriter]

I can't see the artifacts in those images cos they're coming up super tiny for me, But I'm getting some artifacting in my reflections using CUDA as well. Strange square areas that are lighter than they should be. They seem to be only appearing using light cache however, switching to Brute Force for GI and there's no artifacts.

Maya 2020.4, Vray 5 hotfix 2

Sorry for the delay. Here are some higher resolution samples with arrows pointing to the problematic areas. The first one was rendered with V-ray 5 hotfix 2, and the second one was rendered with V-ray GPU 5, hybrid mode.
No denoiser was used in both renders.

[GregCooper]

Ah yep, I think we might have different issues. Yours looks like a sampling issue, I sometimes get that with hot reflections that are out of focus, needs a lot of samples to resolve and sometimes it still just doesn't get there. Whatever method is being used on GPU to resolve out of focus areas often seems less effective than CPU

[GregCooper]

Not to confuse the thread but I've attached an image of the issue I'm having. I've managed to resolve it either by switching to Brute Force for GI or changing the light evaluation from Adaptive to Full Evaluation, both solutions which seem to increase my render time a lot. There's definitely some issue going on here. That's a glass plane and a simple backplate with a vray mtl and an image connected. You can see the strange discoloured rectangular regions in the top half of the window pane.

[lightwriter]

Ah yep, I think we might have different issues. Yours looks like a sampling issue, I sometimes get that with hot reflections that are out of focus, needs a lot of samples to resolve and sometimes it still just doesn't get there. Whatever method is being used on GPU to resolve out of focus areas often seems less effective than CPU

Vray 5 is simplified now; how do I increase the number of samples?

[lightwriter]

Not to confuse the thread but I've attached an image of the issue I'm having. I've managed to resolve it either by switching to Brute Force for GI or changing the light evaluation from Adaptive to Full Evaluation, both solutions which seem to increase my render time a lot. There's definitely some issue going on here. That's a glass plane and a simple backplate with a vray mtl and an image connected. You can see the strange discoloured rectangular regions in the top half of the window pane.

I might have the same problem as you. When I render an animation,every object behind two panes of glass (didn't try yet with one pane of glass only) gains square artifacts; very annoying in animation, especially because the squares are always moving.

I will make a new post demonstrating this issue, hoping someone can help me (and you).

[GregCooper]

I might have the same problem as you. When I render an animation,every object behind two panes of glass (didn't try yet with one pane of glass only) gains square artifacts; very annoying in animation, especially because the squares are always moving.

I will make a new post demonstrating this issue, hoping someone can help me (and you).

Yeah it’s broken. I’ve had to roll back to Vray Next just to finish my render without the square artifacts in reflections (possibly refractions) and also to lose random black pixels I’m getting, like negative fireflies. Have logged with support.

Vray GPU needs some serious work

[GregCooper]

Vray 5 is simplified now; how do I increase the number of samples?

You can’t change sample values on specific materials but it’s a global setting under render settings. Min/max subdivs. Try min 1, max 100

[piotrus3333]

this is good old adaptive dome producing these bucket shaped artefacts (bf for secondary gi and full light evaluation are turning this function off)
I'm in the process of going cpu>>>gpu and what solves it for me is "render hidden lights" option off.
even if there is no hidden lights it works for me (in my case usually hidden portals since I've never trusted adaptive dome in production on cpu).
let me know if that helped.

[GregCooper]

this is good old adaptive dome producing these bucket shaped artefacts (bf for secondary gi and full light evaluation are turning this function off)
I'm in the process of going cpu>>>gpu and what solves it for me is "render hidden lights" option off.
even if there is no hidden lights it works for me (in my case usually hidden portals since I've never trusted adaptive dome in production on cpu).
let me know if that helped.

Right, okay. Yeah I never would have even considered trying turning "render hidden lights" off. Will give that a go today, thanks for this.
Now searching adaptive dome light artefacts it looks like this issue has been around since 2018, you'd think it would have been ironed out by now

[piotrus3333]

on cpu side there was a lot of little things confusing adaptive dome algorithm. I guess it's all good for quite a while now. I gave up on that quickly since portals were never a problem for me.
I haven't rendered on gpu for like 3 years so no idea how thing are here.

I missed something before though - hidden dome light. this was most likely the culprit. but keeping "render hidden lights" off should be considered good practice imo. just confusing being on by default and I missed it this time.

but your issue might be actually caused by view behind the window being done through VRayLightMtl on geo that is excluded from some light calculation like casting shadows.