Regression: Blender 3.5: Hair: Cycles render passes GlossDir, GlossInd, GlossCol, TransDir, TransInd, and TransCol #104586

New Issue

David Black · 2023-02-10T19:07:39+01:00

David Black commented

2023-02-10 19:07:39 +01:00

System Information
Linux Mint 21.1 Cinnamon kernel 5.19.0-28
3400G

Blender Version
Broken:
From: blender-3.5.0-alpha+master.789e549dbae8-linux.x86_64-release.tar.xz
To: blender-3.5.0-alpha+main.7e0e07657c7e-linux.x86_64-release.tar.xz

Worked:
blender-3.5.0-alpha+master.27e2b32a0619-linux.x86_64-release.tar.xz
blender-3.4.1-linux-x64.tar.xz

Short description of error
Hair: Render passes producing blue glowing halos during compositing.

Exact steps for others to reproduce the error

open 'Hair - render passes issue.blend' and press F12.
close the render window.
in the Compositing window compare render passes.

Notes:
First appeared in blender-3.5.0-alpha+master.789e549dbae8-linux.x86_64-release.tar.xz

Only passes shown seem affected, others appear okay.

**System Information** Linux Mint 21.1 Cinnamon kernel 5.19.0-28 3400G **Blender Version** Broken: From: blender-3.5.0-alpha+master.789e549dbae8-linux.x86_64-release.tar.xz To: blender-3.5.0-alpha+main.7e0e07657c7e-linux.x86_64-release.tar.xz Worked: blender-3.5.0-alpha+master.27e2b32a0619-linux.x86_64-release.tar.xz blender-3.4.1-linux-x64.tar.xz **Short description of error** Hair: Render passes producing blue glowing halos during compositing. ![Hair - render passes issue.png](/attachments/ce09d379-1886-441a-8f95-057dee133158) ![Production render compare.png](/attachments/aea8fd0b-b124-4ed8-8c69-35769a1c3130) **Exact steps for others to reproduce the error** 1. open 'Hair - render passes issue.blend' and press F12. 2. close the render window. 3. in the Compositing window compare render passes. Notes: First appeared in blender-3.5.0-alpha+master.789e549dbae8-linux.x86_64-release.tar.xz Only passes shown seem affected, others appear okay.

Hair - render passes issue.blend

114 KiB

Production render compare.png

161 KiB

Hair - render passes issue.png

242 KiB

David Black added the

labels 2023-02-10 19:07:40 +01:00

Jesse Yurkovich added

and removed

labels 2023-02-12 01:26:14 +01:00

Jesse Yurkovich commented

2023-02-12 01:27:20 +01:00

@LukasStockner This seems to have been caused by 73000c792d

@LukasStockner This seems to have been caused by 73000c792d4

Lukas Stockner commented

2023-02-12 04:31:00 +01:00

Hm, this is a tricky one.

The problem here is that previously, the Principled Hair BSDF didn't write its color into the color passes at all, so there was no issue.
Since that commit, the albedo of the hair is used for the shader. However, apparently the computed albedo is not a very good indicator for very dark hairs - for the given example scene, there are hairs which have a slight reflection on them, but the predicted albedo is so low (0.0000001) that after the division the resulting value becomes way too high.

I guess one way of "fixing" this would be to clamp the albedo to a minimum of 0.01, for this scene that brings the direct/indirect passes into a reasonable range.

It's worth noting that I did find some issues in the current code for the albedo, but fixing them didn't address the underlying problem. I'll post those changes later as a PR.

Hm, this is a tricky one. The problem here is that previously, the Principled Hair BSDF didn't write its color into the color passes at all, so there was no issue. Since that commit, the albedo of the hair is used for the shader. However, apparently the computed albedo is not a very good indicator for very dark hairs - for the given example scene, there are hairs which have a slight reflection on them, but the predicted albedo is so low (0.0000001) that after the division the resulting value becomes way too high. I guess one way of "fixing" this would be to clamp the albedo to a minimum of 0.01, for this scene that brings the direct/indirect passes into a reasonable range. It's worth noting that I did find some issues in the current code for the albedo, but fixing them didn't address the underlying problem. I'll post those changes later as a PR.

Lukas Stockner self-assigned this 2023-02-12 04:31:07 +01:00

Lukas Stockner referenced a pull request that will close this issue

2023-02-12 22:11:00 +01:00

Cycles: Clean up the Principled Hair BSDF implementation #104669

Lukas Stockner referenced this issue from a commit

2023-02-13 22:49:12 +01:00

Cycles: Clean up the Principled Hair BSDF implementation

Lukas Stockner closed this issue

2023-02-13 22:49:13 +01:00

Blender Bot added

and removed

labels 2023-02-13 22:49:14 +01:00

Lukas Stockner referenced this issue

2023-02-13 23:35:37 +01:00

Cycles: Clean up the Principled Hair BSDF implementation #104669

Lukas Stockner referenced this issue

2023-02-13 23:50:35 +01:00

Cycles: Temporary fix for Principled Hair albedo #104723

Lukas Stockner referenced this issue from a commit

2023-02-14 12:18:23 +01:00

Cycles: Temporary fix for Principled Hair albedo

David Black commented

2023-02-15 12:09:40 +01:00

Thank you Lukas,

Temporary fix works well. Plus today's BuildBot build dcc80748d3 also provides finer hair details compared with the last working version 27e2b32a06, is this due to new GlossCol and TransCol albedo information?

In closing, would also like to thank you for your great Blender developments, and interesting Principled v2 Blender conference talk.

Thank you Lukas, Temporary fix works well. Plus today's BuildBot build dcc80748d327 also provides finer hair details compared with the last working version 27e2b32a0619, is this due to new GlossCol and TransCol albedo information? ![Production render compare 2.png](/attachments/407aeea9-9099-4687-b392-1e286389e450) In closing, would also like to thank you for your great Blender developments, and interesting Principled v2 Blender conference talk.

Production render compare 2.png

146 KiB

🎉 1

Sign in to join this conversation.

No Label

Download

What's New

Blender Studio

Manual

Developers Blog

Documentation

Benchmark

Blender Conference

Development Fund

One-time Donations

Regression: Blender 3.5: Hair: Cycles render passes GlossDir, GlossInd, GlossCol, TransDir, TransInd, and TransCol #104586