Denoiser will blur sharp reflections #52275

New Issue

Michael Klein · 2017-08-06T13:12:30+02:00

Michael Klein commented

2017-08-06 13:12:30 +02:00

System Information
Win 10 (latest) 64bit
Alienware 17 GTX 880M

Blender Version
Broken: 2.78.0 702e9c5
Worked: not available

Short description of error
The Denoiser will blur sharp reflections at a special direction. The issue will be described in the attached renderings and scene. Higher sample rates will not fix the issue. It looks like there's a bug in the collected scene data for the Denoiser.

Exact steps for others to reproduce the error
Use the attached .blend file and compare the renderings (with and without Denoising with 128 samples).
Same result of GPU and CPU rendering.
You will notice the white LEGO bricks are blurred in the red bricks while the floor reflection in the black bricks is correct.
For all materials the Roughness is set to 0.

170806_Denoiser_Issue_with_Reflection.zip

**System Information** Win 10 (latest) 64bit Alienware 17 GTX 880M **Blender Version** Broken: 2.78.0 702e9c5 Worked: not available **Short description of error** The Denoiser will blur sharp reflections at a special direction. The issue will be described in the attached renderings and scene. Higher sample rates will not fix the issue. It looks like there's a bug in the collected scene data for the Denoiser. **Exact steps for others to reproduce the error** Use the attached .blend file and compare the renderings (with and without Denoising with 128 samples). Same result of GPU and CPU rendering. You will notice the white LEGO bricks are blurred in the red bricks while the floor reflection in the black bricks is correct. For all materials the Roughness is set to 0. [170806_Denoiser_Issue_with_Reflection.zip](https://archive.blender.org/developer/F696347/170806_Denoiser_Issue_with_Reflection.zip)

Michael Klein commented

2017-08-06 13:12:30 +02:00

Changed status to: 'Open'

Michael Klein commented

2017-08-06 13:12:30 +02:00

Added subscriber: @Renderbicks

Brecht Van Lommel commented

2017-08-07 18:50:33 +02:00

Added subscribers: @LukasStockner, @brecht

Brecht Van Lommel commented

2017-08-07 18:50:33 +02:00

Please let us assign the priority, Needs Triage is there to indicate that a developer needs to evaluate the report.

I'll leave it to @LukasStockner to decide if this is a bug, not sure if this is a case we expect to be able to handle. Note there's also various denoising parameters that can be tweaked. In general the denoiser is always an approximation and there will be various cases where it can't detect sharp edges. There's a lot of ongoing research in this area and even the state of the art algorithms fail in some cases, we can't always consider those bugs.

The environment map is missing in this file, but I think with a flat background color the problem is visible too. As far as I can tell the reflection does become sharper with high samples, but not as quickly as it should ideally.

Please let us assign the priority, Needs Triage is there to indicate that a developer needs to evaluate the report. I'll leave it to @LukasStockner to decide if this is a bug, not sure if this is a case we expect to be able to handle. Note there's also various denoising parameters that can be tweaked. In general the denoiser is always an approximation and there will be various cases where it can't detect sharp edges. There's a lot of ongoing research in this area and even the state of the art algorithms fail in some cases, we can't always consider those bugs. The environment map is missing in this file, but I think with a flat background color the problem is visible too. As far as I can tell the reflection does become sharper with high samples, but not as quickly as it should ideally.

Michael Klein commented

2017-08-07 19:34:01 +02:00

Thanks for your detailed answer. I rated this as a bug because the floor reflection is correctly sharp while the wall reflection is sharp in the render progress and will be blurred extremely by the denoising what will falsify the result.

Lukas Stockner commented

2017-08-09 00:42:55 +02:00

Changed status from 'Open' to: 'Archived'

Lukas Stockner closed this issue

2017-08-09 00:42:55 +02:00

Lukas Stockner self-assigned this 2017-08-09 00:42:55 +02:00

Lukas Stockner commented

2017-08-09 00:42:55 +02:00

The problem here is the diffuse-specular-heuristic. The floor is classified as specular, so the feature passes are written based on the secondary bounce and therefore preserve reflections.
The brick on the other hand is considered diffuse, so the normal/albedo/depth passes contain no information about the white object.

Therefore, there's no simple way to solve this - tweaking the thresholds to make this scene sharper would introduce additional noise in other scenes. Two compromises would be exposing the specularity threshold as a user-tweakable parameter or allowing users to override the selection per-material. Both would be fine with me - of course automatic handling is generally better, but there's no single perfect way to map general BSDFs to a binary choice.

So, I'm going to close this since it's not really a bug, just a case where the heuristic fails. Improving the heuristic definitely is a ToDo for me, though, so this will hopefully improve in the future.

The problem here is the diffuse-specular-heuristic. The floor is classified as specular, so the feature passes are written based on the secondary bounce and therefore preserve reflections. The brick on the other hand is considered diffuse, so the normal/albedo/depth passes contain no information about the white object. Therefore, there's no simple way to solve this - tweaking the thresholds to make this scene sharper would introduce additional noise in other scenes. Two compromises would be exposing the specularity threshold as a user-tweakable parameter or allowing users to override the selection per-material. Both would be fine with me - of course automatic handling is generally better, but there's no single perfect way to map general BSDFs to a binary choice. So, I'm going to close this since it's not really a bug, just a case where the heuristic fails. Improving the heuristic definitely is a ToDo for me, though, so this will hopefully improve in the future.

Michael Klein commented

2017-08-09 13:49:11 +02:00

Hello Lukas,

thanks for the explanation.

Additonal info: SSS is affecting the blur extremely. When I set SSS to 0 the reflection is a bit blurred but more as expected.

Hello Lukas, thanks for the explanation. Additonal info: SSS is affecting the blur extremely. When I set SSS to 0 the reflection is a bit blurred but more as expected.

Michael Klein commented

2017-08-09 13:56:57 +02:00

Metallic and black color (no diffuse) is working fine. Specular and SSS with more diffuse will cause a blurred result.

I am looking forward to improvemts in the future. You guys do all an impressive job on this Autodesk killer. :-)

Metallic and black color (no diffuse) is working fine. Specular and SSS with more diffuse will cause a blurred result. I am looking forward to improvemts in the future. You guys do all an impressive job on this Autodesk killer. :-)

Michael Klein commented

2017-08-09 19:09:41 +02:00

I found an interim solution by using Branched Path Tracing. This looks much better. I could also set just Glossy higher and turn Indirect off in the Denoiser. But just using Branched works good actually.

Looking forward to your improvements in the future. Keep up the fantastic Autodesk killer work. ;-)

I found an interim solution by using Branched Path Tracing. This looks much better. I could also set just Glossy higher and turn Indirect off in the Denoiser. But just using Branched works good actually. Looking forward to your improvements in the future. Keep up the fantastic Autodesk killer work. ;-)![170806_Denoiser_Issue_Branched_Path_Tracing.jpg](https://archive.blender.org/developer/F702589/170806_Denoiser_Issue_Branched_Path_Tracing.jpg) ![170806_Denoiser_Issue_Path_Tracing.jpg](https://archive.blender.org/developer/F702588/170806_Denoiser_Issue_Path_Tracing.jpg)

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Denoiser will blur sharp reflections #52275