Vertex color node and vertex attribute shader nodes don't produce correct vertex color values #71835

New Issue

Olivier Riedo · 2019-11-24T02:02:14+01:00

Olivier Riedo commented

2019-11-24 02:02:14 +01:00

System Information
Operating system: Windows-7-6.1.7601-SP1 64 Bits
Graphics card: Quadro K2100M/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 361.91

Blender Version
Broken: version: 2.82 (sub 1), branch: master, commit date: 2019-11-22 18:14, hash: 373e936e3e
Worked: (optional)

Short description of error
The output of the vertex color node isn't the same as the value that was painted in. Specifically, it doesn't seem to be linearized. Neither is the (equivalent) output of the vertex attribute node set to the same color layer.

Exact steps for others to reproduce the error
From starting scene:

edit cube mesh, loop subdivide (ctrl-R) the vertical edges of the cube
in vertex paint, paint the four top vertices in full white (value 1), the four middle vertices in 0.5 value gray, the four bottom vertices in full black
in the shader node editor, link a "vertex color" input node set to the layer you just painted ("Col" by default) to a math node set to "greater than 0.5", link the math node to the material output node (as depicted in the screenshot)
set the viewport shading to material preview

The expected behavior would be to have the separation between the white and black areas of the resulting material align with the edge loop formed by the four middle vertices with value 0.5, instead it occurs higher. Adding a gamma node with a gamma of 1/2.2 between the vertex color node and the math node moves the separation back where it should be, suggesting an incorrect or absent linearization from what I assume are sRGB values. Of course with that inverse gamma node added interpolation of the more or less corrected vertex color values won't be linear anymore. The same behavior occurs with the color output by the vertex attribute node, when set to a color layer. Although the math node is used to easily show the problem, directly linking the vertex color node to the material output won't produce the right values either.

The same behavior was observed in the 2.81 and 2.80 releases (although that earlier one didn't have the vertex color node, only the vertex attribute node). It happens in both Eeevee and Cycles renders.

**System Information** Operating system: Windows-7-6.1.7601-SP1 64 Bits Graphics card: Quadro K2100M/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 361.91 **Blender Version** Broken: version: 2.82 (sub 1), branch: master, commit date: 2019-11-22 18:14, hash: `373e936e3e` Worked: (optional) **Short description of error** The output of the vertex color node isn't the same as the value that was painted in. Specifically, it doesn't seem to be linearized. Neither is the (equivalent) output of the vertex attribute node set to the same color layer. **Exact steps for others to reproduce the error** From starting scene: * edit cube mesh, loop subdivide (ctrl-R) the vertical edges of the cube * in vertex paint, paint the four top vertices in full white (value 1), the four middle vertices in 0.5 value gray, the four bottom vertices in full black * in the shader node editor, link a "vertex color" input node set to the layer you just painted ("Col" by default) to a math node set to "greater than 0.5", link the math node to the material output node (as depicted in the screenshot) * set the viewport shading to material preview ![vertexcolor.PNG](https://archive.blender.org/developer/F8160031/vertexcolor.PNG) The expected behavior would be to have the separation between the white and black areas of the resulting material align with the edge loop formed by the four middle vertices with value 0.5, instead it occurs higher. Adding a gamma node with a gamma of 1/2.2 between the vertex color node and the math node moves the separation back where it should be, suggesting an incorrect or absent linearization from what I assume are sRGB values. Of course with that inverse gamma node added interpolation of the more or less corrected vertex color values won't be linear anymore. The same behavior occurs with the color output by the vertex attribute node, when set to a color layer. Although the math node is used to easily show the problem, directly linking the vertex color node to the material output won't produce the right values either. The same behavior was observed in the 2.81 and 2.80 releases (although that earlier one didn't have the vertex color node, only the vertex attribute node). It happens in both Eeevee and Cycles renders.

Olivier Riedo commented

2019-11-24 02:02:14 +01:00

Added subscriber: @Olivier.Riedo

Bartosz Moniewski commented

2019-11-25 00:49:03 +01:00

Added subscriber: @BartekMoniewski

Bartosz Moniewski commented

2019-11-25 00:49:03 +01:00

Changed status from 'Open' to: 'Archived'

Bartosz Moniewski closed this issue

2019-11-25 00:49:03 +01:00

Bartosz Moniewski self-assigned this 2019-11-25 00:49:03 +01:00

Bartosz Moniewski commented

2019-11-25 00:49:03 +01:00

Vertex colors in Blender (and many other DCC apps) are 8-bit sRGB, not linear.
Similar reports pop up sometimes but they all are invalid.
Support for generic vertex attributes with linear values would be great but that's a feature request.
https://devtalk.blender.org/t/full-precision-float-vertex-colors/4706
If you need precision for technical things I advise to use UVs. Linear, not-clamped, full float precision.

Vertex colors in Blender (and many other DCC apps) are 8-bit sRGB, not linear. Similar reports pop up sometimes but they all are invalid. Support for generic vertex attributes with linear values would be great but that's a feature request. https://devtalk.blender.org/t/full-precision-float-vertex-colors/4706 If you need precision for technical things I advise to use UVs. Linear, not-clamped, full float precision.

Bartosz Moniewski removed their assignment 2019-11-25 00:54:29 +01:00

Olivier Riedo commented

2019-11-25 03:18:25 +01:00

This comment was removed by @Olivier.Riedo

*This comment was removed by @Olivier.Riedo*

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Vertex color node and vertex attribute shader nodes don't produce correct vertex color values #71835