Blurry Reflections And Refractions In Denoised Image When GPU Rendering

[cmascari]

Hello. When using the denoiser in V-Ray Next I get blurry reflections and refractions. This happens specifically when GPU rendering. If I render the same scene on CPU with the same setting the reflections and refractions in the denoised image looks crisp. Is this a limitation of rendering on the GPU or is there something I can do to solve this problem?

I have noticed that the Render Elements look different when CPU and GPU rendering. For example, my rendering is looking at a mirror. The Material ID Color of the mirror when GPU rendering is a single color, the Material ID Color of the mirror when CPU rendering has multiple colors showing objects in the reflection of the mirror. I assume this has something to do with this issue.

Any help is much appreciated.

Chris

[hermit.crab]

Could you give an example of the difference between CPU and GPU for an image where the noise threshold is the quality controlling parameter so we can take a look?
Regarding the render elements - this is a known current limitation of the 'Affect All Channels' functionality of reflective/refractive materials on the GPU.

[cmascari]

Hello Aleksandar,

Thanks for the answer about the Render Elements. Regarding an example scene, please see the attached images showing the difference between the denoised image from CPU vs GPU vs RGB_Color(No Denoiser). Not sure if I know what you mean by "noise threshold is the quality controlling parameter". I took that to mean up the max subdivisions to like 100. These are rendered with Min Sub.= 1 / Max Sub. = 100 and noise threshold of 0.05. Easiest place to notice the difference is on the reflected wood door and shelves reflected in the mirror, but you can also see the bluriness of the stone through the glass in the shower on the left. Let me know if you need anything else. Thanks.

[Micha]

Same problem I have seen at V-Ray for Rhino. I didn't know that that more details are available per CPU. I hope the GPU output can be brought at the CPU level.

[hermit.crab]

What I meant was to use render results, which have reached the set noise threshold rather than some maximum amount of samples, in order to determine if the issue is due to the difference in image quality or the denoiser itself. From what I tested on a simple scene with such a setup, I was able to produce similarly denoised images in both CPU and GPU. You may try using a 'Custom' denoising preset and reduce its effectiveness and afterward update without re-rendering.

[cmascari]

Did the settings I mentioned achieve what you are talking about? Im not sure what settings you are asking me to setup in the scene, could you offer any specific settings I should change? It is not scene specific, I have noticed this same behavior in all my scenes.

Regarding the "custom" denoiser options, I have messed around with them but they do not help. I really think this has something to do with the lack of render elements 'affect all channels' when GPU rendering. Because in V-Ray 3.6 for Rhino I was getting this same exact blurry problem (when CPU rendering) and then I learned about the 'affect all channels' reflections and refractions and setting the denoiser type to "Denoise render elements separately"and that immediately solved the problem. I recently posted this issue in the V-Ray For Rhino General forum section (was posted before I learned how to use render elements in V-Ray Next).

Thanks.

[hermit.crab]

The denoiser is the same for CPU and GPU, so the difference in the output possibly stems from a difference in the Reflection pass of the two engines (which may very well be due to the 'affect all channels' option). My colleague has requested the scene for investigation in the Rhino forum thread, so I suggest you send it so we can take a look.

[cmascari]

Thanks. Will do.

Regarding your comment from above:

"Regarding the render elements - this is a known current limitation of the 'Affect All Channels' functionality of reflective/refractive materials on the GPU"

Is this a feature/functionality we will see on GPU rendering in the future?

[hermit.crab]

Yes, it is something on our developers' to-do lists.

[cmascari]

Just upgraded to VRay 5 for Rhino. I was hoping the above requested improvement might have been added to the GPU renderer but unfortunately that seems to not be the case. I thought the denoiser plus GPU would be a game changer for me, but this limitation makes the workflow very difficult. Any idea when GPU rendering will output the correct Material_ID_Color for reflections so that it can correctly denoise reflections?

[Micha]

.... and setting the denoiser type to "Denoise render elements separately"and that immediately solved the problem.

This options isn't available at VfR5.

Also I'm disappointed to see that the denoising of reflections/refractions is still not working at VfR5. Here an example, the region area is rendered per GPU, the area around per CPU.

[cmascari]

Thanks Micha, Im glad Im not the only one! I am literally in the middle of making a very similar test scene to show this exact same problem(Ive already posted about this issue in the past, I just want to keep it on their radar). Very frustrating...I decided to spend more on GPU than CPU for my latest build and Im really regretting my purchase because of this exact problem. Scenes render way faster on my GPU , but without being able to use the denoiser its still not that fast compared to CPU (lower settings) + denoiser which works perfectly. I will still post my test scene tomorrow even though its just like yours. There is really no other feature I would like to see included more.

[Micha]

A problem is - also if you set a high quality for the GPU rendering, for example per 100 subdivs and noise 0,005, so that no noise is at your scene, the denoiser kills details at reflections/refractions. So, there is no way to get 100% quality in GPU mode like seen in CPU mode. (Is it a problem of VfR only or is it the same at 3ds max?)

[nikoleta.garkova]

Hi guys,

I've replied on the other forum thread here.

[cmascari]

Thanks for the update, glad to hear yall are aware of the issue and working on a solution.