Shadow (Catcher) Bug: Black dots #98113

New Issue

Michael Klein · 2022-05-14T11:04:26+02:00

Michael Klein commented

2022-05-14 11:04:26 +02:00

System Information
Operating system: Windows-10-10.0.22000-SP0 64 Bits
Graphics card: NVIDIA GeForce RTX 3080 Laptop GPU/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 512.59

Blender Version
Broken: version: 3.0.1 - 3.2.0 Beta, branch: master, commit date: 2022-05-12 16:38, hash: 018acc5688
Worked: Can't test with former versions (scene can't be loaded)

Short description of error
The shadow and shadow catcher pass show black dots in my example scene. Even the denoiser can't fix them.

Hi-Res Render:

50% Render:

Exact steps for others to reproduce the error

Load the attached Cycles_Shadow_Catcher_Pass_Bug.blend file
Enable the Viewport Shanding "Rendered" (Shadow Catcher Pass must already be set)

Cycles_Shadow_Catcher_Pass_Bug.blend

Original File:
220514_Blender_Cycles_Shadow_Bug.zip

**System Information** Operating system: Windows-10-10.0.22000-SP0 64 Bits Graphics card: NVIDIA GeForce RTX 3080 Laptop GPU/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 512.59 **Blender Version** Broken: version: 3.0.1 - 3.2.0 Beta, branch: master, commit date: 2022-05-12 16:38, hash: `018acc5688` Worked: Can't test with former versions (scene can't be loaded) **Short description of error** The shadow and shadow catcher pass show black dots in my example scene. Even the denoiser can't fix them. Hi-Res Render: ![220514_Blender_Cycles_Shadow_Bug_v003_Screenshot_01.jpg](https://archive.blender.org/developer/F13073701/220514_Blender_Cycles_Shadow_Bug_v003_Screenshot_01.jpg) 50% Render: ![220514_Blender_Cycles_Shadow_Bug_v003_Screenshot_02.jpg](https://archive.blender.org/developer/F13073703/220514_Blender_Cycles_Shadow_Bug_v003_Screenshot_02.jpg) **Exact steps for others to reproduce the error** - Load the attached `Cycles_Shadow_Catcher_Pass_Bug.blend` file - Enable the Viewport Shanding "Rendered" (Shadow Catcher Pass must already be set) [Cycles_Shadow_Catcher_Pass_Bug.blend](https://archive.blender.org/developer/F13082587/Cycles_Shadow_Catcher_Pass_Bug.blend) --- Original File: [220514_Blender_Cycles_Shadow_Bug.zip](https://archive.blender.org/developer/F13073634/220514_Blender_Cycles_Shadow_Bug.zip)

Michael Klein commented

2022-05-14 11:04:26 +02:00

Added subscriber: @Renderbicks

Germano Cavalcante commented

2022-05-17 23:29:38 +02:00

Added subscriber: @mano-wii

Germano Cavalcante commented

2022-05-17 23:29:38 +02:00

Testing the file, the problem seems to be related to .exr HDRIs with a well-delimited lighting source.

I tested it with other HDRIs and the black dots were more pronounced on some.

Note that the steps to reproduce the bug from scratch are not clear and the sample file is not simplified enough. So I'll edit the description before confirming...

Testing the file, the problem seems to be related to .exr HDRIs with a well-delimited lighting source. I tested it with other HDRIs and the black dots were more pronounced on some. Note that the steps to reproduce the bug from scratch are not clear and the sample file is not simplified enough. So I'll edit the description before confirming...

Germano Cavalcante commented

2022-05-17 23:39:16 +02:00

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

Michael Klein commented

2022-05-18 06:48:51 +02:00

Here's a simplified scene:

220517_Blender_Cycles_Shadow_Bug_v004_Simplified.zip

Here's a simplified scene: [220517_Blender_Cycles_Shadow_Bug_v004_Simplified.zip](https://archive.blender.org/developer/F13086174/220517_Blender_Cycles_Shadow_Bug_v004_Simplified.zip) ![220517_Blender_Cycles_Shadow_Bug_v004_Simplified_Screenshot.jpg](https://archive.blender.org/developer/F13086172/220517_Blender_Cycles_Shadow_Bug_v004_Simplified_Screenshot.jpg)

Steffen Dünner commented

2022-05-19 16:45:57 +02:00

Added subscriber: @SteffenD

Lukas Stockner commented

2022-07-24 20:56:13 +02:00

Added subscriber: @LukasStockner

Lukas Stockner commented

2022-07-24 20:56:13 +02:00

Changed status from 'Confirmed' to: 'Archived'

Lukas Stockner closed this issue

2022-07-24 20:56:13 +02:00

Lukas Stockner commented

2022-07-24 20:56:13 +02:00

From what I can tell, this isn't a bug, but an artifact of how the shadow catcher works.
Basically, these black dots are reverse fireflies. Note how the beauty pass with the cube has (bright) fireflies on its top face as well. Due to how the shadow catcher works, these turn into black dots.

There's two ways to avoid the problem in this scene:

Switch World sampling from "Manual" to "Auto". The HDR is 4K, but the manual resolution is set to 512, causing the fireflies. Switching to Auto resolves both the bright fireflies on the cube and the black dots in the shadow.
Instead of feeding the shadow pass into the denoiser node as-is, connect it to a Separate Color node, connect the Alpha channel to the Image input of the denoiser, then connect its output to the Alpha channel of a Combine Color node. Connect R, G and B directly from the Separate to the Combine node. Effectively, this tricks the Denoise node into denoising the Alpha channel, which it is not designed to do. The result is a completely noise-free shadow pass.

From what I can tell, this isn't a bug, but an artifact of how the shadow catcher works. Basically, these black dots are reverse fireflies. Note how the beauty pass with the cube has (bright) fireflies on its top face as well. Due to how the shadow catcher works, these turn into black dots. There's two ways to avoid the problem in this scene: 1. Switch World sampling from "Manual" to "Auto". The HDR is 4K, but the manual resolution is set to 512, causing the fireflies. Switching to Auto resolves both the bright fireflies on the cube and the black dots in the shadow. 2. Instead of feeding the shadow pass into the denoiser node as-is, connect it to a Separate Color node, connect the Alpha channel to the Image input of the denoiser, then connect its output to the Alpha channel of a Combine Color node. Connect R, G and B directly from the Separate to the Combine node. Effectively, this tricks the Denoise node into denoising the Alpha channel, which it is not designed to do. The result is a completely noise-free shadow pass.

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Shadow (Catcher) Bug: Black dots #98113