Banding-like effect in Cycles using OpenVDB volumes #100714

New Issue

Félix Olart · 2022-08-30T16:14:25+02:00

Félix Olart commented

2022-08-30 16:14:25 +02:00

System Information
Operating system: Linux-5.15.0-46-generic-x86_64-with-glibc2.35 64 Bits
Graphics card: Quadro RTX 6000/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 510.85.02

Blender Version
Broken: version: 3.4.0 Alpha, branch: master, commit date: 2022-08-29 23:11, hash: 5ae3fa50e2
Worked: unkown

Short description of error
I have some weird looking artifacts going on when importing custom OpenVDB files.
Let's take a look at these screenshots:

Blender 2.93.5:
Blender 3.0.1:
Blender 3.1.2:
Blender 3.2.2:
Blender 3.3.0 (beta, b814f64f4a):
Blender 3.4.0 (alpha, 5ae3fa50e2):

I am not talking about this giant black thing (but I wanted to show it too because this is also weird).
The point here is about this banding effect:
blender_weird_issue_1.webm

Hypotheses:

Wrong data manipulation in the shader node tree
My data are "corrupted" or not well defined (missing values in the volume when I generate it), so this would be an error on my side.
There is a bug in Blender

Exact steps for others to reproduce the error
#100714.blend
vdb_sample.zip

Extract VDB files and download .blend file into folder
Open .blend file

**System Information** Operating system: Linux-5.15.0-46-generic-x86_64-with-glibc2.35 64 Bits Graphics card: Quadro RTX 6000/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 510.85.02 **Blender Version** Broken: version: 3.4.0 Alpha, branch: master, commit date: 2022-08-29 23:11, hash: `5ae3fa50e2` Worked: unkown **Short description of error** I have some weird looking artifacts going on when importing custom OpenVDB files. Let's take a look at these screenshots: * Blender 2.93.5: ![blender_2.93.5.png](https://archive.blender.org/developer/F13435504/blender_2.93.5.png) * Blender 3.0.1: ![blender_3.0.1.png](https://archive.blender.org/developer/F13435511/blender_3.0.1.png) * Blender 3.1.2: ![blender_3.1.2.png](https://archive.blender.org/developer/F13435515/blender_3.1.2.png) * Blender 3.2.2: ![blender_3.2.2.png](https://archive.blender.org/developer/F13435518/blender_3.2.2.png) * Blender 3.3.0 (beta, b814f64f4ab2): ![blender_3.3.0.png](https://archive.blender.org/developer/F13435531/blender_3.3.0.png) * Blender 3.4.0 (alpha, 5ae3fa50e224): ![blender_3.4.0.png](https://archive.blender.org/developer/F13435538/blender_3.4.0.png) I am not talking about this giant black thing (but I wanted to show it too because this is also weird). The point here is about this banding effect: ![blender_2.93.5_cropped.png](https://archive.blender.org/developer/F13435559/blender_2.93.5_cropped.png) [blender_weird_issue_1.webm](https://archive.blender.org/developer/F13435622/blender_weird_issue_1.webm) Hypotheses: * Wrong data manipulation in the shader node tree * My data are "corrupted" or not well defined (missing values in the volume when I generate it), so this would be an error on my side. * There is a bug in Blender **Exact steps for others to reproduce the error** [#100714.blend](https://archive.blender.org/developer/F13442070/T100714.blend) [vdb_sample.zip](https://archive.blender.org/developer/F13435657/vdb_sample.zip) - Extract VDB files and download .blend file into folder - Open .blend file

Félix Olart commented

2022-08-30 16:14:25 +02:00

Added subscriber: @Felix-Olart

Félix Olart commented

2022-08-30 16:29:12 +02:00

I think I have the same sort of issue using another file.
Here is what it looks like:
blender_weird_issue_2.webm

Exact steps for others to reproduce the error

Open Blender 3.4.0 alpha
Delete everything
Import OpenVDB sequence (see attached files)
Open shading view
Create a new material as shown in the video above (attribute : SEDIMENT COH1)
Go frame 28 for example

vdb_sample_2.zip

I think I have the same sort of issue using another file. Here is what it looks like:![Screenshot from 2022-08-30 16-24-59.png](https://archive.blender.org/developer/F13435787/Screenshot_from_2022-08-30_16-24-59.png) [blender_weird_issue_2.webm](https://archive.blender.org/developer/F13435790/blender_weird_issue_2.webm) **Exact steps for others to reproduce the error** * Open Blender 3.4.0 alpha * Delete everything * Import OpenVDB sequence (see attached files) * Open shading view * Create a new material as shown in the video above (attribute : SEDIMENT COH1) * Go frame 28 for example [vdb_sample_2.zip](https://archive.blender.org/developer/F13435805/vdb_sample_2.zip)

Richard Antalik commented

2022-08-30 23:21:10 +02:00

Added subscriber: @iss

Richard Antalik commented

2022-08-30 23:21:10 +02:00

Looking at provided VDB, I see there is volume filling the space, which seems to be the black thing you saw in previous versions. Here it is rendered as blackbody

I am not very knowleddgable in this area and not sure how shader is supposed to blend blackbody. I would guess it should be pure emissive color if it has no density, which it does not have, but not sure really, will have to read up on this.

Looking at provided VDB, I see there is volume filling the space, which seems to be the black thing you saw in previous versions. Here it is rendered as blackbody ![Untitled.png](https://archive.blender.org/developer/F13438177/Untitled.png) I am not very knowleddgable in this area and not sure how shader is supposed to blend blackbody. I would guess it should be pure emissive color if it has no density, which it does not have, but not sure really, will have to read up on this.

Félix Olart commented

2022-08-31 09:04:07 +02:00

First, thank you very much for your answer.
Ok, so if I understand correctly, this area corresponds to volume, but does not have enough density to be rendered? Or something like that?
I tried to replicate what you have done with the second example I provided, here is the result:

Here is the result when I boost the density (multiplied by 1e9):
So I am not sure to be right seeing this, I thought I would see the whole volume turn red as the density would be > 1 for each voxel.

I tried to set the clipping value of the volume down to 0 instead of 1e-4.
Here is the result:

Thus, it seems to be solving my issue:Screencast from 31-08-2022 08:59:23.webm
I don't really understand why.

First, thank you very much for your answer. Ok, so if I understand correctly, this area corresponds to volume, but does not have enough density to be rendered? Or something like that? I tried to replicate what you have done with the second example I provided, here is the result: ![Screenshot from 2022-08-31 08-54-36.png](https://archive.blender.org/developer/F13440056/Screenshot_from_2022-08-31_08-54-36.png) Here is the result when I boost the density (multiplied by 1e9): ![Screenshot from 2022-08-31 08-53-27.png](https://archive.blender.org/developer/F13440050/Screenshot_from_2022-08-31_08-53-27.png) So I am not sure to be right seeing this, I thought I would see the whole volume turn red as the density would be > 1 for each voxel. I tried to set the clipping value of the volume down to 0 instead of 1e-4. Here is the result: ![Screenshot from 2022-08-31 08-57-40.png](https://archive.blender.org/developer/F13440062/Screenshot_from_2022-08-31_08-57-40.png) Thus, it seems to be solving my issue:[Screencast from 31-08-2022 08:59:23.webm](https://archive.blender.org/developer/F13440069/Screencast_from_31-08-2022_08_59_23.webm) I don't really understand why.

Omar Emara commented

2022-08-31 10:13:21 +02:00

Added subscriber: @OmarEmaraDev

Omar Emara commented

2022-08-31 10:13:21 +02:00

Changed status from 'Needs Triage' to: 'Needs Developer To Reproduce'

Omar Emara commented

2022-08-31 10:13:21 +02:00

If I understand correctly, lowering the clipping to zero fixes the issue. Is that correct?
This seems similar to #53472. Voxels in the volume whose value is less that the clipping value are "turned off" and are not rendered resulting in those empty spaces.
So the workaround for now is to never turn off any voxels by lowering the clipping to zero.
I am not sure why that depends on the viewing angle as you have showed though. So I will tag the module for more information.

If I understand correctly, lowering the clipping to zero fixes the issue. Is that correct? This seems similar to #53472. Voxels in the volume whose value is less that the clipping value are "turned off" and are not rendered resulting in those empty spaces. So the workaround for now is to never turn off any voxels by lowering the clipping to zero. I am not sure why that depends on the viewing angle as you have showed though. So I will tag the module for more information.

Omar Emara changed title from ~~Banding-like effect in Cycles using OpenVDB volumes~~ to Banding-like effect in Cycles using OpenVDB volumes when clipping is not zero

2022-08-31 10:13:58 +02:00

Félix Olart commented

2022-08-31 10:40:15 +02:00

Hum. I tested it on the first sample I provided and it does not give the same result.
Screencast from 31-08-2022 10:27:20.webm
I think with this video we can clearly see the "black bars" which are not visible using the first shader and then revealed using the second shader.
Thus, we can sort of deduce how this banding-like effect is affected by the viewing angle.

So to answer your question, I am not convinced that lowering the clipping value to zero fixes the issue.
About #53472, if I understand correctly, that issue is more related to camera clipping values.
Whereas I was mentioning the clipping settings in the volume properties. I don't know if it is related but I don't think so.

Hum. I tested it on the first sample I provided and it does not give the same result. [Screencast from 31-08-2022 10:27:20.webm](https://archive.blender.org/developer/F13440342/Screencast_from_31-08-2022_10_27_20.webm) I think with this video we can clearly see the "black bars" which are not visible using the first shader and then revealed using the second shader. Thus, we can sort of deduce how this banding-like effect is affected by the viewing angle. So to answer your question, I am not convinced that lowering the clipping value to zero fixes the issue. About #53472, if I understand correctly, that issue is more related to camera clipping values. Whereas I was mentioning the clipping settings in the volume properties. I don't know if it is related but I don't think so.

Omar Emara commented

2022-08-31 10:41:47 +02:00

Changed status from 'Needs Developer To Reproduce' to: 'Needs Triage'

Omar Emara commented

2022-08-31 10:43:08 +02:00

Does the scale of the volume object have any effect on the banding effect?

Félix Olart commented

2022-08-31 10:48:47 +02:00

No, it does not seem to have any effect.
Screencast from 31-08-2022 10:46:26.webm

No, it does not seem to have any effect. [Screencast from 31-08-2022 10:46:26.webm](https://archive.blender.org/developer/F13440386/Screencast_from_31-08-2022_10_46_26.webm)

Omar Emara commented

2022-08-31 11:25:51 +02:00

Just a note, looking at the attached files, it seems they include negative values, contrary to a number of OpenVDB file samples I looked at, and those negatives values seems to take the shape of those bands, so I suspect this might have something to do with the issue you are experiencing.

Félix Olart commented

2022-08-31 13:29:18 +02:00

Yes, I think you are pointing out an interesting element. I also checked the values and some of them are negative. I did not managed to see how these data are arranged but that could be something causing my issue.
Maybe this could explain why setting the clipping value to 0 was not giving any result in this video.

In #100714#1410503, @Felix-Olart wrote:
Hum. I tested it on the first sample I provided and it does not give the same result.
Screencast from 31-08-2022 10:27:20.webm

So to answer your question, I am not convinced that lowering the clipping value to zero fixes the issue.

Indeed, if the negative values are causing these artifacts, then setting the clipping value to 0 or not won't probably change anything.
That said, is it still normal that the volume is rendered like that for negative values? Because it seems to act like a powerful filter.

Yes, I think you are pointing out an interesting element. I also checked the values and some of them are negative. I did not managed to see how these data are arranged but that could be something causing my issue. Maybe this could explain why setting the clipping value to 0 was not giving any result in this video. > In #100714#1410503, @Felix-Olart wrote: > Hum. I tested it on the first sample I provided and it does not give the same result. > [Screencast from 31-08-2022 10:27:20.webm](https://archive.blender.org/developer/F13440342/Screencast_from_31-08-2022_10_27_20.webm) > > So to answer your question, I am not convinced that lowering the clipping value to zero fixes the issue. Indeed, if the negative values are causing these artifacts, then setting the clipping value to 0 or not won't probably change anything. That said, is it still normal that the volume is rendered like that for negative values? Because it seems to act like a powerful filter.

Omar Emara commented

2022-08-31 14:03:16 +02:00

I will try to ask the developers about this and get back to you.

Raimund Klink commented

2022-08-31 15:10:56 +02:00

Changed status from 'Needs Triage' to: 'Needs Developer To Reproduce'

Raimund Klink commented

2022-08-31 15:11:05 +02:00

Added subscriber: @Raimund58

Omar Emara commented

2022-08-31 16:08:35 +02:00

Changed status from 'Needs Developer To Reproduce' to: 'Confirmed'

Omar Emara changed title from ~~Banding-like effect in Cycles using OpenVDB volumes when clipping is not zero~~ to Banding-like effect in Cycles using OpenVDB volumes

2022-08-31 16:08:57 +02:00

blender-admin commented

2022-08-31 18:04:15 +02:00

This issue was referenced by b5ff47667d

This issue was referenced by b5ff47667da593860b9a207daa24fec48163ee67

blender-admin commented

2022-08-31 18:04:15 +02:00

This issue was referenced by e665f0f497

This issue was referenced by e665f0f497f6ea6a4cff36e977bbac29dd762c00

blender-admin commented

2022-08-31 20:55:56 +02:00

This issue was referenced by None@63016