Light issues in the Cycles render #113291

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opened 2023-10-05 14:59:07 +02:00 by Volodymyr · 4 comments

Volodymyr commented

2023-10-05 14:59:07 +02:00

System Information
Operating system: Windows-10-10.0.19045-SP0 64 Bits
Graphics card: NVIDIA GeForce RTX 3090/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 536.40

Blender Version
Broken: Current main
Worked: (newest version of Blender that worked as expected)

Short description of error
Basically, I have described it here:
https://blender.community/c/today/2DOv/?sorting=hot&category=help&page=1
I don't know if it's a bug or if it needs to enable something to look right

Exact steps for others to reproduce the error
[Please describe the exact steps needed to reproduce the issue]
[Based on the default startup or an attached .blend file (as simple as possible)]

**System Information** Operating system: Windows-10-10.0.19045-SP0 64 Bits Graphics card: NVIDIA GeForce RTX 3090/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 536.40 **Blender Version** Broken: Current main Worked: (newest version of Blender that worked as expected) **Short description of error** Basically, I have described it here: https://blender.community/c/today/2DOv/?sorting=hot&category=help&page=1 I don't know if it's a bug or if it needs to enable something to look right **Exact steps for others to reproduce the error** [Please describe the exact steps needed to reproduce the issue] [Based on the default startup or an attached .blend file (as simple as possible)]

Screenshot 2023-10-05 154051.png

1010 KiB

Screenshot 2023-10-05 154400.png

1.0 MiB

Screenshot 2023-10-05 154244.png

1.2 MiB

Screenshot 2023-10-05 154051.png

Screenshot 2023-10-05 154400.png

Screenshot 2023-10-05 154244.png

Volodymyr added the

labels 2023-10-05 14:59:08 +02:00

Iliya Katushenock commented

2023-10-05 16:54:30 +02:00

Member

Hi @V0vi , can you add little more details to Exact steps for others to reproduce the error part? Attach example blen file?

Hi @V0vi , can you add little more details to `Exact steps for others to reproduce the error` part? Attach example blen file?

Iliya Katushenock added

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Render & Cycles

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labels 2023-10-05 16:54:41 +02:00

Volodymyr commented

2023-10-06 09:36:26 +02:00

Author

Shure, here is the file and IES for the light

Shure, here is the file and IES for the light

Light issue.blend

1.1 MiB

1.3 KiB

Iliya Katushenock added this to the 3.6 LTS milestone 2023-10-06 15:47:29 +02:00

Iliya Katushenock added

Render & Cycles

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Render & Cycles

labels 2023-10-06 15:47:50 +02:00

Volodymyr commented

2023-11-15 09:54:04 +01:00

Author

Hey! Look what I've found
Here's the difference between On and Of the Light Tree option

Hey! Look what I've found Here's the difference between On and Of the Light Tree option

Screenshot 2023-11-15 105013.png

1.0 MiB

Screenshot 2023-11-15 105028.png

1.0 MiB

Screenshot 2023-11-15 105013.png

Screenshot 2023-11-15 105028.png

Alaska commented

2024-03-01 05:43:15 +01:00

Member

There are two issues here which are related to each other.

When the light tree is enabled, some lights are getting "undersampled". When this occurs, adaptive sampling can sometimes conclude that the render is locally noise free and stop sampling, when the image is not globally noise free.

The issue with adaptive sampling is a "known issue" and I believe it is being tracked in a different report. So we won't spend too much time talking about it.

Now that light tree issue.

The light tree is used to help assist Cycles in picking which light it should sample for rendering. One of the factors it uses to help decide which light to sample is light brightness. However, once the light node setup exceeds a basic level of complexity, the light brightness just becomes an estimation, and those estimations can be wrong.

This is the primary cause for the issue in your scene. The light brightness estimations for the IES lights is too low for how bright the light actually is, resulting in it being "less important" and getting undersampled.

But you might be wondering. If this is the cause of the issue, then why does it only occur on some of the IES lights, but not others, especially since all the IES lights at the exact same?

Because the impact this estimation has on the sampling of the light is dependent on which section and level of the light tree it gets put into. And this is determined by the location, shape, and brightness of the light and the lights around it. So the automatic light tree builder is placing the lights in a "alright spot" in the light tree based on it's estimation, but some of the lights are actually in bad spots for the specific combination of how they render + what the estimate was, meaning they get undersampled. The main way to fix this is to fix the estimation so the lights actually get put in the correct spots in the light tree and get sampled more reasonably.

Anyway, I hope the explaination was helpful, even if it doesn't fix your issue.

Also, I'm closing this report. The adaptive sampling issue is already known and probably being tracked somewhere already. And the poor estimation of complex node setups (including IES textures) is a known issue and is already being tracked here: #77889

There are two issues here which are related to each other. When the light tree is enabled, some lights are getting "undersampled". When this occurs, adaptive sampling can sometimes conclude that the render is locally noise free and stop sampling, when the image is not globally noise free. The issue with adaptive sampling is a "known issue" and I believe it is being tracked in a different report. So we won't spend too much time talking about it. --- Now that light tree issue. The light tree is used to help assist Cycles in picking which light it should sample for rendering. One of the factors it uses to help decide which light to sample is light brightness. However, once the light node setup exceeds a basic level of complexity, the light brightness just becomes an estimation, and those estimations can be wrong. This is the primary cause for the issue in your scene. The light brightness estimations for the IES lights is too low for how bright the light actually is, resulting in it being "less important" and getting undersampled. But you might be wondering. If this is the cause of the issue, then why does it only occur on some of the IES lights, but not others, especially since all the IES lights at the exact same? Because the impact this estimation has on the sampling of the light is dependent on which section and level of the light tree it gets put into. And this is determined by the location, shape, and brightness of the light and the lights around it. So the automatic light tree builder is placing the lights in a "alright spot" in the light tree based on it's estimation, but some of the lights are actually in bad spots for the specific combination of how they render + what the estimate was, meaning they get undersampled. The main way to fix this is to fix the estimation so the lights actually get put in the correct spots in the light tree and get sampled more reasonably. --- Anyway, I hope the explaination was helpful, even if it doesn't fix your issue. Also, I'm closing this report. The adaptive sampling issue is already known and probably being tracked somewhere already. And the poor estimation of complex node setups (including IES textures) is a known issue and is already being tracked here: #77889

Alaska closed this issue

2024-03-01 05:43:18 +01:00

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labels 2024-03-01 05:43:20 +01:00

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