Cycles: improve subsurface scattering for some meshes shapes #91540

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Brecht Van Lommel · 2021-09-20T19:25:22+02:00

Brecht Van Lommel commented

2021-09-20 19:25:22 +02:00

In cycles-x, the Christensen-Burley dipole approximation was fully replaced by random walk.

However for some mesh shapes results are not as good, or could be improved regardless.

Self-intersection meshes give dark borders. Counting back/front facing intersections could help determine inside/outside better to avoid such artifacts.
Sharp corners "glow", which may be physically correct but is not necessarily desired. It may be possible to add user control with an option somehow, using some minimum throughput

If these can't be solved, we may consider adding back the dipole approximation, but since path splitting and the memory usage is a difficult fit for the new kernels we'd really like to avoid it.

In cycles-x, the Christensen-Burley dipole approximation was fully replaced by random walk. However for some mesh shapes results are not as good, or could be improved regardless. * Self-intersection meshes give dark borders. Counting back/front facing intersections could help determine inside/outside better to avoid such artifacts. * Sharp corners "glow", which may be physically correct but is not necessarily desired. It may be possible to add user control with an option somehow, using some minimum throughput If these can't be solved, we may consider adding back the dipole approximation, but since path splitting and the memory usage is a difficult fit for the new kernels we'd really like to avoid it.

Brecht Van Lommel commented

2021-09-20 19:25:22 +02:00

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

Brecht Van Lommel commented

2021-09-20 19:25:22 +02:00

Added subscriber: @brecht

Paul Larson commented

2021-09-21 02:47:46 +02:00

Added subscriber: @GeorgiaPacific

David Kozma commented

2021-09-22 12:26:53 +02:00

Added subscriber: @DavidKozma

David Kozma commented

2021-09-22 12:26:53 +02:00

Hi Brecht,
I'd like to add my 2cents for this. I recently created a tutorial where I specifically talk about this problem in the current Cycles.
My method was to create an illusion of continuous meshes with shrinkwrap and normal transfer modifiers. With SSS this creates various artifacts I present below.

Could you please weight in on how much of this specific problem could be possibly elevated with the improvements of this task?

I added the images from the tutorial and a link to blend file containing the skull mesh.

When I tested the file for this post I realized - with Random Walk - the artifact is magnitudes stronger when the meshes are joined.
I hope this specific use of normal aligned and very close proximity meshes give you an edge case which's good for testing.

https://www.dropbox.com/s/vptgmlzulblptdv/skull.blend?dl=0

Hi Brecht, I'd like to add my 2cents for this. I recently created a tutorial where I specifically talk about this problem in the current Cycles. My method was to create an illusion of continuous meshes with shrinkwrap and normal transfer modifiers. With SSS this creates various artifacts I present below. Could you please weight in on how much of this specific problem could be possibly elevated with the improvements of this task? I added the images from the tutorial and a link to blend file containing the skull mesh. When I tested the file for this post I realized - with Random Walk - the artifact is magnitudes stronger when the meshes are joined. I hope this specific use of normal aligned and very close proximity meshes give you an edge case which's good for testing. ![image.png](https://archive.blender.org/developer/F10541092/image.png) ![image.png](https://archive.blender.org/developer/F10541108/image.png) https://www.dropbox.com/s/vptgmlzulblptdv/skull.blend?dl=0

Brecht Van Lommel commented

2021-09-22 13:30:59 +02:00

Objects that together form a single volume must be joined for SSS to work. There is no intent to remove that requirement.

Emi Martinez commented

2021-10-29 00:12:24 +02:00

Added subscriber: @Emi_Martinez

Sam Green commented

2022-01-09 21:21:43 +01:00

Added subscriber: @SamGreen

Brecht Van Lommel added this to the Render & Cycles project 2023-02-07 19:08:06 +01:00

Philipp Oeser removed the

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Cycles: improve subsurface scattering for some meshes shapes #91540