The formula in "Specular BSDF" page of the Blender Manual does not match its examples #80849

New Issue

Zijun Zhou · 2020-09-16T18:15:59+02:00

Zijun Zhou commented

2020-09-16 18:15:59 +02:00

System Information
Operating system: Windows-10-10.0.18362-SP0 64 Bits
Graphics card: GeForce MX130/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 452.06

Blender Version
Broken: version: 2.91.0 Alpha, branch: master, commit date: 2020-09-16 05:28, hash: blender/blender@7e8cba98b6
Worked: (newest version of Blender that worked as expected)

Short description of error
Don't know if I can report problems in the manual as a bug but, here is the screenshot:

"specular=((ior-1)/(ior+1))^2" this formula does not match examples like the "water: ior = 1.33, specular = 0.25".
I guess the examples are just simply copied and pasted from the "Principled BSDF" page? The specular formula for the Principled BSDF has a " / 0.08" at the end, which makes the examples valid. But this one does not make sense.

Exact steps for others to reproduce the error
Open this page and you can see it:
https://docs.blender.org/manual/en/latest/render/shader_nodes/shader/specular_bsdf.html

**System Information** Operating system: Windows-10-10.0.18362-SP0 64 Bits Graphics card: GeForce MX130/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 452.06 **Blender Version** Broken: version: 2.91.0 Alpha, branch: master, commit date: 2020-09-16 05:28, hash: `blender/blender@7e8cba98b6` Worked: (newest version of Blender that worked as expected) **Short description of error** Don't know if I can report problems in the manual as a bug but, here is the screenshot: ![image.png](https://archive.blender.org/developer/F8889648/image.png) "specular=((ior-1)/(ior+1))^2" this formula does not match examples like the "water: ior = 1.33, specular = 0.25". I guess the examples are just simply copied and pasted from the "Principled BSDF" page? The specular formula for the Principled BSDF has a " / 0.08" at the end, which makes the examples valid. But this one does not make sense. **Exact steps for others to reproduce the error** Open this page and you can see it: https://docs.blender.org/manual/en/latest/render/shader_nodes/shader/specular_bsdf.html

Zijun Zhou commented

2020-09-16 18:15:59 +02:00

Added subscriber: @Eary

Zijun Zhou commented

2020-09-16 18:22:22 +02:00

Also this specular value is calculated also from the ior? This specular can turn things into metal when the value is high, and it also has colors, I believe it should not be the same as the specular in Principled BSDF, since the one in Principled BSDF cannot turn things into metal and is only a grey scale value input.

Robert Guetzkow commented

2020-09-16 20:53:27 +02:00

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

Aaron Carlisle commented

2020-10-01 22:24:49 +02:00

Added subscribers: @fclem, @Blendify

Aaron Carlisle commented

2020-10-01 22:24:49 +02:00

@fclem Can you give some insight here? is the equation wrong or are the values wrong?

Clément Foucault commented

2020-10-07 16:46:50 +02:00

The formula is true, and is the same as the fresnel node when the normal and the incident vector are equal.

The issue is the examples values:

Water should be 0.02.
Glass should be 0.04.
Daimond should be 0.17.

The formula is true, and is the same as the fresnel node when the normal and the incident vector are equal. The issue is the examples values: - Water should be 0.02. - Glass should be 0.04. - Daimond should be 0.17.

blender-admin commented

2020-10-12 02:21:07 +02:00

This issue was referenced by 7217

Aaron Carlisle commented

2020-10-12 02:21:19 +02:00

Changed status from 'Confirmed' to: 'Resolved'

Aaron Carlisle closed this issue

2020-10-12 02:21:19 +02:00

Aaron Carlisle self-assigned this 2020-10-12 02:21:19 +02:00

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The formula in "Specular BSDF" page of the Blender Manual does not match its examples #80849