Cycles fully transparent shader is brighter when a Clear Coat shader is behind it #99087

New Issue

baoyu · 2022-06-22T12:51:43+02:00

baoyu commented

2022-06-22 12:51:43 +02:00

System Information
Operating system: Windows-10-10.0.22000-SP0 64 Bits
Graphics card: NVIDIA GeForce RTX 2080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 471.68

Blender Version
Broken: version: 3.3.0 Alpha, branch: master, commit date: 2022-06-05 19:05, hash: 8589f60546
Worked: Never Worked

Short description of error
When doing Decals, we often use alpha channel to define transparent area. However, I found when the Object's base color is above hsl(h,s,0.01), who's under the Decal, then the decal's transparent area will affect the underneath object's shading.
My test configuration is that 2048 viewport samples alongwith light bounces param all been set to 64.
The BUG is easier to notice when the background object is light grey, and the light is quite dimmed(or just turn down the exposure in colormangement to observe.)

Please open the attached Blend file to test.
Transparent shading BUG.blend

**System Information** Operating system: Windows-10-10.0.22000-SP0 64 Bits Graphics card: NVIDIA GeForce RTX 2080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 471.68 **Blender Version** Broken: version: 3.3.0 Alpha, branch: master, commit date: 2022-06-05 19:05, hash: `8589f60546` Worked: Never Worked **Short description of error** When doing Decals, we often use alpha channel to define transparent area. However, I found when the Object's base color is above hsl(h,s,0.01), who's under the Decal, then the decal's transparent area will affect the underneath object's shading. My test configuration is that 2048 viewport samples alongwith light bounces param all been set to 64. The BUG is easier to notice when the background object is light grey, and the light is quite dimmed(or just turn down the exposure in colormangement to observe.) ![image.png](https://archive.blender.org/developer/F13216472/image.png) ![image.png](https://archive.blender.org/developer/F13216481/image.png) Please open the attached Blend file to test. [Transparent shading BUG.blend](https://archive.blender.org/developer/F13216477/Transparent_shading_BUG.blend)

baoyu commented

2022-06-22 12:51:43 +02:00

Added subscriber: @baoyu

Omar Emara commented

2022-06-22 14:41:18 +02:00

Added subscriber: @OmarEmaraDev

Omar Emara commented

2022-06-22 14:41:18 +02:00

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

Omar Emara commented

2022-06-22 14:41:18 +02:00

The issue seems to be with Clear Coat in Principled BSDF in this case. A simpler example is to have two planes, the lower one has a default Principled BSDF with Clear Coat set to 1, while the upper plane has a completely transparent shader. A lamp is positioned away from them along the x axis.

One would expect no different since the upper plane is transparent, but it seems to be less noisy and brighter.

cyclesTransparentClearCoat.blend

The issue seems to be with Clear Coat in Principled BSDF in this case. A simpler example is to have two planes, the lower one has a default Principled BSDF with Clear Coat set to 1, while the upper plane has a completely transparent shader. A lamp is positioned away from them along the x axis. One would expect no different since the upper plane is transparent, but it seems to be less noisy and brighter. ![20220622-143611.png](https://archive.blender.org/developer/F13216840/20220622-143611.png) [cyclesTransparentClearCoat.blend](https://archive.blender.org/developer/F13216843/cyclesTransparentClearCoat.blend)

Omar Emara changed title from ~~Cycles Transparent shading BUG~~ to Cycles fully transparent shader is brighter when a Clear Coat shader is behind it

2022-06-22 14:42:23 +02:00

baoyu commented

2022-06-22 15:00:58 +02:00

This comment was removed by @baoyu

*This comment was removed by @baoyu*

baoyu commented

2022-06-22 15:04:14 +02:00

In #99087#1378537, @OmarEmaraDev wrote:
The issue seems to be with Clear Coat in Principled BSDF in this case. A simpler example is to have two planes, the lower one has a default Principled BSDF with Clear Coat set to 1, while the upper plane has a completely transparent shader. A lamp is positioned away from them along the x axis.

One would expect no different since the upper plane is transparent, but it seems to be less noisy and brighter.

cyclesTransparentClearCoat.blend

Indeed, you got the fundamental cause of the problem.

> In #99087#1378537, @OmarEmaraDev wrote: > The issue seems to be with Clear Coat in Principled BSDF in this case. A simpler example is to have two planes, the lower one has a default Principled BSDF with Clear Coat set to 1, while the upper plane has a completely transparent shader. A lamp is positioned away from them along the x axis. > > One would expect no different since the upper plane is transparent, but it seems to be less noisy and brighter. > > ![20220622-143611.png](https://archive.blender.org/developer/F13216840/20220622-143611.png) > > [cyclesTransparentClearCoat.blend](https://archive.blender.org/developer/F13216843/cyclesTransparentClearCoat.blend) Indeed, you got the fundamental cause of the problem.

baoyu commented

2022-11-23 02:58:32 +01:00

I can confirm that this BUG still exists in the Principled BSDF v2 branch, yet not been fixed.

System Information
Operating system: Windows-10-10.0.22621-SP0 64 Bits
Graphics card: NVIDIA GeForce RTX 2080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 526.47

Blender Version
Broken: version: 3.4.0 Alpha, branch: principled-v2, commit date: 2022-10-30 15:33, hash: 45cd4c9c82
Worked: never

Exact steps for others to reproduce the error
Open the demo blend files provided in the previous posts.

While this time when the clearcoat roughness been set to 0, the problem's gone.

I can confirm that this BUG still exists in the Principled BSDF v2 branch, yet not been fixed. **System Information** Operating system: Windows-10-10.0.22621-SP0 64 Bits Graphics card: NVIDIA GeForce RTX 2080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 526.47 **Blender Version** Broken: version: 3.4.0 Alpha, branch: principled-v2, commit date: 2022-10-30 15:33, hash: `45cd4c9c82` Worked: never **Exact steps for others to reproduce the error** Open the demo blend files provided in the previous posts. ![image.png](https://archive.blender.org/developer/F13962199/image.png) While this time when the clearcoat roughness been set to 0, the problem's gone. ![image.png](https://archive.blender.org/developer/F13962203/image.png)

Philipp Oeser removed the

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Cycles fully transparent shader is brighter when a Clear Coat shader is behind it #99087