Banding artifacts in particle hair at render time (Rounded Ribbons) #82966

New Issue

MrP · 2020-11-24T12:44:17+01:00

MrP commented

2020-11-24 12:44:17 +01:00

System Information
Operating system: OpenSUSE Linux Leap 15.2
Graphics card: NVIDIA RTX 2070
system-info.txt

Blender Version
Broken: 2.90.1, 2.91.0-6c6a5a72c297, blender-2.92.0-b0a908188377
Worked: 2.83.9 LTS (but that didnt have the Rounded Ribbons yet)
Change came with the switch to Embree 207338bb58: Cycles: port curve-ray intersection from Embree for use in Cycles GPU

With default hair render settings since 2.9, there is a visible horizontal banding produced in many instances when rendering particle hair. By default Hair is rendered as Shape "Rounded Ribbons" - visual artifact is not present when Shape is set to "3D Curve".

Under 2.83, this visual artifact was not visible with defaults (Shape: "Ribbons", Primitive: "Line Segments").

Exact steps for others to reproduce the error
Load attached blend file, and press Render.
hairbanding.zip

Artifacts will be visible as per this screenshot:

They are far more pronounced when using a darker material, eg with a principled hair shader:

Changing Render Properties > Hair > Shape to "3D Curve" and the banding does not appear anymore (at cost of render time).

This does not present an issue when rendered using 2.83 (note - will need to add a HDRI or environment shader, as sample blend file uses the 2.9 sky texture).

**System Information** Operating system: OpenSUSE Linux Leap 15.2 Graphics card: NVIDIA RTX 2070 [system-info.txt](https://archive.blender.org/developer/F9365060/system-info.txt) **Blender Version** Broken: 2.90.1, 2.91.0-6c6a5a72c297, blender-2.92.0-b0a908188377 Worked: 2.83.9 LTS (but that didnt have the Rounded Ribbons yet) Change came with the switch to Embree 207338bb58: Cycles: port curve-ray intersection from Embree for use in Cycles GPU With default hair render settings since 2.9, there is a visible horizontal banding produced in many instances when rendering particle hair. By default Hair is rendered as Shape "Rounded Ribbons" - visual artifact is not present when Shape is set to "3D Curve". Under 2.83, this visual artifact was not visible with defaults (Shape: "Ribbons", Primitive: "Line Segments"). **Exact steps for others to reproduce the error** Load attached blend file, and press Render. [hairbanding.zip](https://archive.blender.org/developer/F9365007/hairbanding.zip) Artifacts will be visible as per this screenshot:![roundedribbons-noshader.png](https://archive.blender.org/developer/F9365004/roundedribbons-noshader.png) They are far more pronounced when using a darker material, eg with a principled hair shader: ![roundedribbons.png](https://archive.blender.org/developer/F9365011/roundedribbons.png) Changing Render Properties > Hair > Shape to "3D Curve" and the banding does not appear anymore (at cost of render time). ![3dcurves.png](https://archive.blender.org/developer/F9365022/3dcurves.png) This does not present an issue when rendered using 2.83 (note - will need to add a HDRI or environment shader, as sample blend file uses the 2.9 sky texture).

MrP commented

2020-11-24 12:44:17 +01:00

Added subscriber: @thechode

Philipp Oeser commented

2020-11-24 16:17:04 +01:00

Added subscribers: @brecht, @lichtwerk

Philipp Oeser commented

2020-11-24 16:17:04 +01:00

Changed status from 'Needs Triage' to: 'Confirmed'

Philipp Oeser commented

2020-11-24 16:17:04 +01:00

Change came with the switch to Embree 207338bb58

Banding is dependend on Particle Settings > Render > Path > Steps (so the lower you go, the further apart the dark bands are)

Havent looked at code and dont know the implementation, but this somehow looks like we have the darkening happening on each of the steps.
This is just a stab in the dark, but could it be that the ribbon rounding (faking the normal) happens along the length of each segment as well? (whereas it should only happen across the hair?)

CC @brecht

Change came with the switch to Embree 207338bb58 Banding is dependend on `Particle Settings` > `Render` > `Path` > `Steps` (so the lower you go, the further apart the dark bands are) Havent looked at code and dont know the implementation, but this somehow looks like we have the darkening happening on each of the steps. This is just a stab in the dark, but could it be that the ribbon rounding (faking the normal) happens **along** the length of each segment as well? (whereas it should only happen **across** the hair?) CC @brecht

Philipp Oeser changed title from ~~Banding artifacts in particle hair at render time~~ to Banding artifacts in particle hair at render time (Rounded Ribbons)

2020-11-24 16:17:41 +01:00

blender-admin commented

2021-01-20 19:40:35 +01:00

This issue was referenced by c60c30205d

This issue was referenced by c60c30205d6d2482a1ae04acd10f9bb2c8e98ec2

Brecht Van Lommel commented

2021-01-20 20:01:32 +01:00

Changed status from 'Confirmed' to: 'Resolved'

Brecht Van Lommel closed this issue

2021-01-20 20:01:32 +01:00

Brecht Van Lommel self-assigned this 2021-01-20 20:01:32 +01:00

MrP commented

2021-01-25 04:15:05 +01:00

Thanks Brecht, I've tested in nightly 2.92.0-d3506c86daa4-linux64 which appears to have commit c60c30205d, and can confirm that the banding artifacts are no longer present.

Thanks Brecht, I've tested in nightly 2.92.0-d3506c86daa4-linux64 which appears to have commit c60c30205d6d, and can confirm that the banding artifacts are no longer present.

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Banding artifacts in particle hair at render time (Rounded Ribbons) #82966