Texture painting - Erase alpha creates dark halo around alpha #80745

New Issue

Daniel Bystedt · 2020-09-13T15:26:38+02:00

Daniel Bystedt commented

2020-09-13 15:26:38 +02:00

System Information
Operating system: Windows-10-10.0.18362-SP0 64 Bits
Graphics card: GeForce GTX 1080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 442.59

Blender Version
Broken: version: 2.91.0 Alpha, branch: master, commit date: 2020-09-11 09:14, hash: 1b6dd42803
Worked: 2.91.0 Alpha, Hash 4ccd5bf5c6, date 2020-09-09 10:38

Likely caused by D8234: Use DrawManager for Image/UV Editor

Short description of error
When painting texture in the image editor and then erasing alpha, there is a dark halo around the pixels where alpha was erased.

Exact steps for others to reproduce the error

Create a new image in the image editor
enter paint mode
paint colors in the image
Change [brush settings > blend] to [erase alpha]
Erase alpha on the image with the brush
Start sampling the pixel values. The sampled colors appear "correct", but the pixel values on the displayed pixels look incorrect (i.e. too dark)

texture painting and alpha sample line.mp4

debug_D8234_texture_paint_erase_alpha_v001.blend

**System Information** Operating system: Windows-10-10.0.18362-SP0 64 Bits Graphics card: GeForce GTX 1080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 442.59 **Blender Version** Broken: version: 2.91.0 Alpha, branch: master, commit date: 2020-09-11 09:14, hash: `1b6dd42803` Worked: 2.91.0 Alpha, Hash 4ccd5bf5c658, date 2020-09-09 10:38 Likely caused by [D8234: Use DrawManager for Image/UV Editor](https://archive.blender.org/developer/D8234) **Short description of error** When painting texture in the image editor and then erasing alpha, there is a dark halo around the pixels where alpha was erased. **Exact steps for others to reproduce the error** 1. Create a new image in the image editor 2. enter paint mode 3. paint colors in the image 4. Change [brush settings > blend] to [erase alpha] 5. Erase alpha on the image with the brush 6. Start sampling the pixel values. The sampled colors appear "correct", but the pixel values on the displayed pixels look incorrect (i.e. too dark) ![image.png](https://archive.blender.org/developer/F8872533/image.png) [texture painting and alpha sample line.mp4](https://archive.blender.org/developer/F8872536/texture_painting_and_alpha_sample_line.mp4) [debug_D8234_texture_paint_erase_alpha_v001.blend](https://archive.blender.org/developer/F8872532/debug_D8234_texture_paint_erase_alpha_v001.blend)

Daniel Bystedt commented

2020-09-13 15:26:38 +02:00

Added subscriber: @DanielBystedt

Daniel Bystedt commented

2020-09-13 15:32:10 +02:00

Added subscribers: @fclem, @Jeroen-Bakker

Daniel Bystedt commented

2020-09-13 15:32:10 +02:00

Jeroen Bakker messaged me on blender.chat and asked me to test the new submit D8234: Use DrawManager for Image/UV Editor, so I'm pinging @Jeroen-Bakker and @fclem to this bug report

Jeroen Bakker messaged me on blender.chat and asked me to test the new submit [D8234: Use DrawManager for Image/UV Editor](https://archive.blender.org/developer/D8234), so I'm pinging @Jeroen-Bakker and @fclem to this bug report

Jeroen Bakker commented

2020-09-14 08:25:41 +02:00

Added subscriber: @brecht

Jeroen Bakker commented

2020-09-14 08:25:41 +02:00

Hmm this seems to be a functional change. Blender 2.91 properly display pure emissive colors by default, these are colors where the RGB values are set, and Alpha is set to 0.0. But users might not expect this and have no way to control it.

Solutions

Add an option (image flag) to display pure emissive colors in the UV/image editor. By default this is off, as tools expect this.
Add addition channel modes to the UV/Image editor. But that seems to be cluttering the interface
Color (emissive) Color + Alpha (emissive)
** Per channel (emmisive)
A combination of the two solutions where the emissive channel modes are only there when the image flag is set to pure emissive.
Add a space property to display pure emissive colors.
Remove the support of pure emissive colors until ....

Personally I would suggest option 4 to be the best short term solution. The problem with the first solution is that when working on multi layer files (oir render results) the option would still be different based on the layer. On user perspective they might need to switch between the modes, but at least they have full control to what they want to see.

In order to support pure emissive colors from the ground up would need additional brush parameters and be sure that the compositors doesn't add artifacts.

@brecht do you have any suggestion?

Hmm this seems to be a functional change. Blender 2.91 properly display pure emissive colors by default, these are colors where the RGB values are set, and Alpha is set to 0.0. But users might not expect this and have no way to control it. **Solutions** 1. Add an option (image flag) to display pure emissive colors in the UV/image editor. By default this is off, as tools expect this. 2. Add addition channel modes to the UV/Image editor. But that seems to be cluttering the interface **Color (emissive)** Color + Alpha (emissive) ** Per channel (emmisive) 3. A combination of the two solutions where the emissive channel modes are only there when the image flag is set to pure emissive. 4. Add a space property to display pure emissive colors. 5. Remove the support of pure emissive colors until .... Personally I would suggest option 4 to be the best short term solution. The problem with the first solution is that when working on multi layer files (oir render results) the option would still be different based on the layer. On user perspective they might need to switch between the modes, but at least they have full control to what they want to see. In order to support pure emissive colors from the ground up would need additional brush parameters and be sure that the compositors doesn't add artifacts. @brecht do you have any suggestion?

Jeroen Bakker self-assigned this 2020-09-14 08:38:17 +02:00

blender-admin commented

2020-09-15 12:28:58 +02:00

This issue was referenced by f492c8d488

This issue was referenced by f492c8d488b7eb2166ca894e10a8128a1678a885

Brecht Van Lommel commented

2020-09-15 14:23:16 +02:00

The image in the example .blend has byte colors. By convention, in Blender such images are always unpremultiplied and can not contain pure emissive colors. Only float images can, which use the premultiplied alpha convention.

So, to me it seems the image editor is not correctly drawing the image based on its alpha convention.

We should not add an option, especially not an option that is disabled by default. We really should be showing renders correct by default.

The image in the example .blend has byte colors. By convention, in Blender such images are always unpremultiplied and can not contain pure emissive colors. Only float images can, which use the premultiplied alpha convention. So, to me it seems the image editor is not correctly drawing the image based on its alpha convention. We should not add an option, especially not an option that is disabled by default. We really should be showing renders correct by default.

Jeroen Bakker commented

2020-09-15 14:34:36 +02:00

The fox for #80746 also fixed this one. In the end it was an error in the shader logic. I reverted the option.

Jeroen Bakker commented

2020-09-15 14:34:53 +02:00

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

Jeroen Bakker closed this issue

2020-09-15 14:34:53 +02:00

Thomas Dinges added this to the 2.91 milestone 2023-02-08 16:20:31 +01:00

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Texture painting - Erase alpha creates dark halo around alpha #80745